MOSAIC VARIEGATED ANEUPLOIDY: A
CILIOPATHY WITH A PREDISPOSITION TO
PREMATURE-AGEING PHENOTYPES?
Bas de Wolf - 3220435
Molecular and Cellular Life Sciences
Prof. Dr. Geert Kops Lab
Department of Medical Oncology
University Utrecht
Department of Molecular Cancer Research
January 15th 2013
University Medical Center Utrecht
0
Contents
1. Abstract ........................................................................................................................................... 2
2. Abbreviations .................................................................................................................................. 3
3. Mosaic variegated aneuploidy ........................................................................................................ 4
4. BUBR1 .............................................................................................................................................. 5
4.1 Mitotic functions ....................................................................................................................... 5
4.2 Interphase functions.................................................................................................................. 6
5. CEP57 ............................................................................................................................................... 7
6. Comparison of functions and phenotypes of BUBR1 and CEP57 .................................................... 8
7. Aneuploidy....................................................................................................................................... 9
8. Cellular senescence and premature ageing .................................................................................. 10
9. Ciliary defects ................................................................................................................................ 11
10. Concluding remarks ..................................................................................................................... 14
11. References ................................................................................................................................... 15
12. Supplementary Table 1: Clinical and cytogenetic findings MVA patients ................................... 21
12. Supplementary Table 2: Other clinical findings MVA patients.................................................... 23
1
1. Abstract
Mosaic variegated aneuploidy (MVA) is a rare autosomal recessive disorder characterized by constitutional mosaic aneuploidies of multiple chromosomes and tissues. MVA is associated with a broad range
of symptoms and genetic and clinical heterogeneity among its patients, which has complicated the
identification of a molecular basis underlying this disease. So far, mutations in two proteins have been
implicated in causing MVA: BUBR1, an essential component of the spindle assembly checkpoint; and
CEP57, a centrosome protein important for microtubule and centriole stability. Although both proteins
are required for faithful chromosome segregation, they also play roles in other processes: BUBR1 counters ageing and affects cilia formation, a process that requires centrosomes and thus likely also involves
CEP57. In this article I review the theories of aneuploidy, ageing and defective cilia as causes for MVA,
and describe a potential link between cilia and ageing that could explain the molecular origin of MVA
and its broad and heterogeneous phenotype.
2
2. Abbreviations
APC/C, anaphase promoting complex/cyclosome
BUB1, budding uninhibited by benzimidazoles 1
BUB1, mitotic checkpoint serine/threonine-protein kinase BUB1
BUB3, mitotic checkpoint protein BUB3
BUBR1, budding uninhibited by benzimidazole-related 1
CDC20, cell-division cycle protein 20
CDH1, Cadherin-1
CEP57, centrosomal protein 57kDa
CEP57R, CEP57-related protein
CNS, central nervous system
DVL, dishevelled
FGF-2, fibroblast growth factor 2
G phase, gap phase
K-MT, kinetochore-microtubule
KNL1, kinetochore-null protein 1
MAD1, mitotic arrest deficient 1
MAD2, mitotic arrest deficient 2
MCC, mitotic checkpoint complex
MIS12, centromere protein mis12
MPS1, monopolar spindle 1
MVA, mosaic variegated aneuploidy
NDC80, kinetochore protein NDC80 homolog
p16, p16Ink4A, cyclin-dependent kinase inhibitor 2A
P21, cyclin-dependent kinase inhibitor 1
PCM, pericentriolar matrix
PCS, premature chromatid separation
PLK1, serine/threonine-protein kinase PLK1
PP2A, protein phosphatase 2A
RAE1, mRNA export factor
SAC, spindle assembly checkpoint
SASP, senescence-associated secretory phenotype
xCEP57, Xenopus CEP57
3
3. Mosaic variegated aneuploidy
Mosaic variegated aneuploidy (MVA; OMIM 257300) is a rare autosomal recessive disorder
characterized by constitutional mosaic aneuploidies of multiple chromosomes and tissues. The first
known case of MVA was a 29-year-old woman described by Scheres et al. in 1986 [1], who suffered
from mental retardation and microcephaly. Cell culture studies showed various aneuploidies in 15% of
her lymphocytes and premature chromatid separation in 60% of the analyzed metaphases. To date 46
cases of MVA have been described (Supplementary Table 1). Variegated aneuploidies, mainly trisomies and monosomies, are usually seen in different tissues of the patients. Several authors report predominant gains and losses of chromosomes 8, 18, and X in lymphocytes and 2, 7, 12, and 20 in fibroblasts, suggesting the existence of tissue-specific differences [2][3]. Others, on the other hand, observed a random distribution of aneuploidies in the tissues of their patients [4][5]. Common MVA phenotypes include microcephaly, intrauterine growth retardation, facial dysmorphism, mental retardation, central nervous system (CNS) anomalies, seizures, polycystic kidneys, child obesity and cataracts
and other eye abnormalities. Additionally, MVA is associated with a high risk of developing malignancies, mostly rhabdomyosarcoma, Wilms’ tumor, and myeloid leukemia [6]– [11]. In about 2/3 of the
cases, MVA is associated with premature chromatid separation (PCS; OMIM 176430), an autosomal
dominant trait that can be found in asymptomatic parents of patients with MVA [8][11].
MVA-associated PCS was proposed to be the result of a defect in the mitotic spindle assembly checkpoint (SAC) by Matsuura et al. [12], who predicted mutations in any of the proteins involved (MAD1,
MAD2, MPS1, BUB1, BUBR1, and other proteins). The SAC is a control mechanism that monitors the
fidelity of mitosis by ensuring correct attachment of all chromosomes to the mitotic spindle before
allowing the cell to proceed to anaphase. Until this is realized, CDC20 is prevented from activating the
E3 ubiquitin ligase, anaphase-promoting complex/cyclosome (APC/C), resulting in persistent high levels of cyclin B and securin. As such, the metaphase–anaphase transition is delayed [13]. In 2004 and
2006, Hanks et al. [7] and Matsuura et al. [9] confirmed this idea by identifying mutations in BUB1B.
BUB1B encodes budding uninhibited by benzimidazole-related 1 (BUBR1), a key component of the SAC
that directly inhibits CDC20 [14]. Hanks et al. found biallelic mutations of the BUB1B gene in five of
eight analyzed MVA families (Supplementary Table 1, patients 9, 11, 12, 24, 38, 39 and 41). Each affected individual carried an allele that led to premature truncation of the protein or an absent transcript in combination with a missense mutation. Matsuura et al. initially found monoallelic mutations
in seven Japanese families (Supplementary Table 1, patients 15, 17, 18, 19, 20, 22, 28, 29), but later
identified a second mutation in the opposite allele of these patients 44 kb upstream of the BUB1B
transcription start site [15]. In 2011, Snape et al. identified biallelic mutations in a second gene, which
encodes centrosomal protein 57kDa (CEP57), in four out of 18 BUB1B-negative MVA patients [4] (Supplementary Table 1, patients 7, 8, 10 and 23). CEP57 has not been implicated in SAC signaling, but is
important for mitosis by stabilizing microtubules and is involved in intracellular trafficking.
Although it is currently unclear what molecular pathogenesis is responsible for causing MVA,
three distinct theories have been proposed. Initially, Tolmie et al. [16] speculated that MVA might be
caused by impaired tissue growth as a result of aneuploidy. Later, a second theory originated from
work done by Baker et al. who proposed that BUBR1 is a key regulator of normal aging, suggesting that
MVA might be a premature ageing disorder [17]. The third theory was only recently proposed by Miyamoto et al. who discovered that cells of two BUB1B mutated MVA patients exhibited impaired ciliogenesis and therefore suggested that MVA might be a novel ciliopathy, a disease characterized by dysfunctional cilia. In this article, I summarize recent findings regarding MVA and its associated proteins.
4
In addition, I review the theories of aneuploidy, ageing and defective cilia, and describe a potential link
between cilia and ageing that could explain the molecular origin of MVA and its broad and heterogeneous phenotype.
4. BUBR1
BUBR1 is a multidomain protein implicated in many different processes including SAC signaling, kinetochore-microtubule (K-MT) attachments, centrosome amplification, ciliogenesis and several
other mitotic and interphase processes [18][19].
4.1 Mitotic functions
BUBR1 was initially identified as a component of the SAC. To ensure the fidelity of cell division,
the SAC delays mitosis until all chromosomes are correctly attached to the mitotic spindle. During mitosis, checkpoint proteins (including MAD1, MAD2, MPS1, BUB1 and BUBR1) assemble on the centromere of a chromosome, forming a structure to which microtubules can attach known as the kinetochore. Until the kinetochore is correctly attached to the spindle, it catalyzes the production of the
mitotic checkpoint complex (MCC; Figure 1). The MCC inhibits the APC/C by repressing its activator
CDC20. Inhibition of APC/C subsequently prevents the ubiquitination and degradation of both cyclin B
and securin, which is required for the metaphase-anaphase transition. Once all chromosomes are
properly attached, the APC/C is activated and cyclin B and securin are degraded, signaling the transition to anaphase. Together, the loss of cyclin B and activation of separase initiate the events required
for the segregation of the chromatids to the daughter cells [13][20]. BUBR1 is a key subunit of the MCC,
which further consists of BUB3 and MAD2 (Figure 1). In vitro, BUBR1 bound to CDC20 is sufficient to
inhibit the APC/C and mutations that abolish this interaction lead to elimination of the checkpoint
[21][22].
Figure 1: The spindle assembly checkpoint. An unattached kinetochore catalyzes the production of the mitotic checkpoint
complex (MCC), which consists of BUBR1 (BR1), BUB3 (B3) and MAD2 (M2). The MCC binds CDC20 (C20) and prevents the
ubiquitination (Ub) of Cyclin B1 (CB) and Securin, thereby delaying transition to anaphase. The additional players BUB1 (B1)
and MAD1 are shown as well. Figure adopted from Saskia Suijkerbuijk [73].
In addition to its role in the SAC, BUBR1 plays a role in promoting stable K-MT attachments and
chromosome alignment. Microtubules attach to the kinetochore by binding NDC80 or KNL1 on the
KMN (KNL1/MIS12 complex/NDC80 complex) network. To promote sister chromatid bi-orientation,
aurora B phosphorylates NDC80 and KNL1 in case of improper K-MT attachment, reducing their microtubule-binding affinity and breaking the attachment. BUBR1 is thought to be responsible for recruiting
the B56 family of protein phosphatase 2A (PP2A) to unattached kinetochores to counteract this destabilizing activity of aurora B, thereby promoting stable attachments. BUBR1 interacts with PP2A-B56
through its KARD domain; blocking this interaction abolishes chromosome alignment and delays cells
in mitosis [23][24].
5
4.2 Interphase functions
During mitosis, the formation of a bipolar spindle is essential for faithful chromosome segregation. Therefore, it is important that a cell contains two centrosomes at the start of mitosis (these
give rise to the spindle poles; Figure 2). The presence of supernumerary spindle poles results in the
formation of a multipolar spindle, which, most likely, leads to chromosome segregation errors. In interphase, BUBR1 is thought to prevent inappropriate centrosome amplification by negatively regulating the centrosome activity of PLK1 [25]. PLK1 localizes to centrosomes in interphase where it, upon
activation, promotes the maturation of procentrioles. These mature procentrioles then disengage
from mother centrioles and ultimately duplicate, giving rise to new centrosomes. Izumi et al. demonstrated that overexpression of PLK1 in HeLa cells induced centrosome amplification and multipolar
mitosis in 40% of transfected cells. They also observed centrosome amplification and subsequent multipolar mitoses in cells derived from BUB1B mutated MVA patients [25].
Figure 2: The centrosome cycle in the cell cycle. The centrosome consists of mother and daughter centrioles (green) that are
embedded in the pericentriolar material (grey). The mother centriole can be distinguished by the presence of appendages
(black lines). (a) During G1, centrioles lose their perpendicular arrangement (b) As in G1/S, a procentriole (blue) forms perpendicular to each centriole (c) During S phase, the new centrioles elongate (d) At G2, the two newly formed centriole pairs
disconnect, and (e) by G2/M, the PCM is also divided between the pairs of centrioles (f) At the end of the cycle, the daughter
centrioles acquire appendages and behave as a mother centriole during the next cycle. Adopted from Crasta et al. [74].
Recently, Miyamoto et al. proposed that BUBR1 is also involved ciliogenesis. In G0 phase,
BUBR1 maintains APC/CCDH1 activity by suppression of CDC20. APC/CCDH1 activity is required for ciliogenesis through ubiquitin-mediated proteolysis of dishevelled (DVL) [26]. Cells derived from BUB1B
mutated MVA patients and BUB1B siRNA-transfected control cells demonstrated increased levels of
DVL and did not generate primary cilia, a phenotype that was rescued by transfection with the chromosome containing BUB1B and knockdown of DVL respectively [27].
BUB1B mutations have been identified in 18 of 46 MVA patients (Supplementary Table 1).
These mutations are associated with elevated rates of PCS and an increased risk of developing malignancies. MVA-associated BUB1B mutations fall in two classes: missense or frameshift mutations that
result in truncated protein products, and missense mutations that cause single amino acid substitutions; the latter predominantly in the kinase domain (Figure 3). Suijkerbuijk et al. [28] demonstrated
6
that substitution mutations in the kinase domain of BUBR1, which was later proposed to lack kinase
activity [18], negatively affect protein stability and abundance. Additionally, they demonstrated that
also the majority of the truncation mutations were responsible for significantly lower BUBR1 levels in
cells derived from MVA patients. Furthermore, forced overexpression of unstable BUBR1 substitution
mutants rescued SAC defects and CIN in BUBR1 depleted cells. Therefore, they proposed that CIN in
MVA patients carrying BUB1B mutations is a result of low BUBR1 protein abundance.
Figure 3: Schematic representation of BUB1B demonstrating the relative exon sizes and positions of known mutations.
Truncating mutations are depicted above the figure, with missense mutations below. Biallelic mutations are represented by
colored lines, with mutations in the same individual in matching colors. Monoallelic mutations are represented by black lines
and font. Source: http://atlasgeneticsoncology.org/. Note: the kinase domain spans the last 300 residues of BUBR1.
5. CEP57
CEP57, also named translokin, is a relatively understudied protein. CEP57 was initially thought
to be involved in intracellular trafficking of fibroblast growth factor 2 (FGF-2) [29] and later identified
as a centrosome component [30]. It is a multidomain protein with an unconventional N-terminal centrosome-localization domain and a C- terminal microtubule-binding domain. CEP57 also binds and stabilizes microtubules and is required for centriole stability in interphase [31]. There are two CEP57 family members in vertebrate cells, CEP57 and CEP57-related protein (CEP57R) [32]. Even less is known
about the functions of CEP57R. Xenopus CEP57, its homolog, localizes to the kinetochore and centrosome and is required for stable K-MT attachments and centrosome-microtubule anchorage in oocyte
extracts [33].
FGF-2 is a mitogenic fibroblast growth factor that internalizes into the cytoplasm with fibroblast growth factor receptors and subsequently translocates into the nucleus during G1 phase. Although the precise function of nuclear FGF-2 is unclear, its nuclear localization was found to be required
for its mitogenic activity. CEP57 is essential for the intracellular transport of FGF-2 [34]. Cuevas et al.
[31] later reported that FGF-2 and CEP57 are both involved in centriole duplication and demonstrated
that CEP57 is necessary for normal centriole duplication by stabilizing daughter centrioles (Figure 2).
7
Wu et al. [35] likewise observed that CEP57 is required for centriole stability and report that
CEP57 is a pericentriolar material (PCM) component. Depletion of CEP57 in siRNA-treated cells resulted
in unaligned chromosomes and multipolar spindles due to PCM fragmentation. They proposed that it
is a spindle pole- and microtubule-stabilizing factor for establishing robust spindle architecture.
To date, bi-allelic loss of function mutations in CEP57 have been found in five MVA patients
(Supplementary Table 1, patients 7, 8, 10, 23 and 37; Figure 4). All five of these patients exhibited
random gains and losses of chromosomes and were diagnosed with mild growth retardation. There
was no gross dysmorphology and their development was normal or mildly delayed. So far none of
these patients have been diagnosed with cancer, although none have reached adulthood.
Figure 4: Schematic representation of CEP57 demonstrating the relative exon sizes and positions of known mutations.
Biallelic mutations are represented by colored lines, with mutations in the same individual in matching colors. Source:
http://atlasgeneticsoncology.org/
6. Comparison of functions and phenotypes of BUBR1 and CEP57
It is likely that both BUBR1 and CEP57 are involved in the same process that is ultimately responsible for causing MVA. Comparison of both proteins and their respective functions reveals that
both are required for the fidelity of mitosis: BUBR1 through its functions in SAC signaling, stabilizing KMT attachments and prevention of centriole overduplication; and CEP57 for maintaining a bipolar spindle by stabilizing centrioles. This suggest that perhaps MVA is caused by defects in mitosis, leading to
CIN and aneuploidy, a theory that is supported by the fact that aneuploidy is observed in all MVA
patients. By changing the dosage of many genes, aneuploidy can lead to dramatic consequences [36].
A second process both proteins might be involved in is ciliogenesis. Miyamoto et al. [15] recently proposed that BUBR1 is required for the formation of primary cilia. CEP57, on the other hand, is not directly implicated in ciliogenesis. It is, however, linked to cilia through being a centrosome protein and
its role in stabilizing centrioles. Centrosomes contain centrioles and later give rise to basal bodies that
nucleate cilia (see chapter 9). Therefore, it might be possible that mutations in BUBR1 and CEP57 both
result in impaired ciliogenesis. Alternatively, the mechanism underlying MVA may be one of which the
involvement of one of the two proteins is not yet established. Work done by Baker et al. has implicated
BUBR1 deficiency in premature-ageing. Although CEP57 has not been linked to ageing, it is a relatively
understudied protein and it is possible that CEP57 has functions that are currently not known.
When comparing the BUB1B and CEP57 phenotypes two striking differences become apparent.
Firstly, BUB1B mutations are strongly associated with the development of cancer, while no malignancies have so far been diagnosed in CEP57 mutated patients. Garcia-Castilló et al. observed that nine of
the 13 BUB1B mutated MVA patients they analyzed were previously diagnosed with Wilm’s tumor,
rhabdomyosarcoma, and/or leukemia [2]. Although none of the patients with CEP57 mutations and
MVA have reached adulthood, many of those with BUB1B mutations developed cancer under the age
of three and not seldom even in utero [2]. Secondly, while PCS is observed in virtually all BUB1B mutated patients, it was found in only one patient with CEP57 mutations and at a relatively low rate compared to PCS of BUB1B mutated patients (Supplementary Table 1, patient 8). PCS is thought to be the
8
result of SAC dysfunction [37]. Therefore, the fact that BUBR1 is a major component of SAC signaling
could explain the high incidence of PCS in BUB1B mutated patients. It is unclear though, whether PCS
is responsible for the aneuploidy observed in BUB1B mutated MVA patients. There seems to be no
correlation between the levels of PCS and aneuploidy. Furthermore, centrosome amplification and
multipolar mitoses were observed in a BUB1B mutated individual described by Frio et al. [38] that
demonstrated mosaic aneuploidies, but no PCS, and in two BUB1B mutated MVA patients described
by Matsuura et al. [9]. Interestingly, CEP57 depletion has also been shown to induce the formation of
a multipolar spindle. Therefore, it is likely that multipolar mitoses contribute to CIN and aneuploidy in
both BUB1B and CEP57 mutated patients [35]. PCS could additionally contribute to CIN in BUB1B mutated patients, but since it is hardly observed in CEP57 mutated patients it may merely be a side-effect
of BUBR1 deficiency rather than an important characteristic of the MVA phenotype.
In short, mosaic variegated aneuploidy is a rare disorder with a broad and heterogeneous clinical spectrum that ranges from a severe and even lethal course (some BUB1B mutated patients) to a
mild phenotype sometimes without microcephaly or mental retardation and a low risk of cancer
(CEP57 mutated patients) [2]. It is currently unclear what the molecular mechanism is underlying MVA.
The three theories of aneuploidy, ageing and defective cilia are discussed in the following chapters.
7. Aneuploidy
Aneuploidy is the single feature of MVA that is found in all known MVA patients, therefore,
the cause of MVA was initially attributed to a defect in mitosis leading to aneuploidy and impaired
tissue growth [16]. If this were true, one would expect to find recurring aneuploidies in the tissues of
different patients, such as is the case in Down’s syndrome patients (tisomy 21) [39]. However, there
seems to be no correlation between the clinical phenotype and predominant aneuploidies. It should
be noted though, that in these studies brain tissue was not examined and therefore the possibility that
a specific aneuploidy in the brain is responsible for causing MVA cannot be excluded. However, recent
studies have demonstrated that aneuploid cells are present at a high frequency in the healthy human
brain argue against this [39][40][41]. In the fetal brain, it has been estimated that 30–35% of neurons
are aneuploid [36]. Furthermore, mosaic aneuploidies were found in several individuals with biallelic
BUB1, BUB3 or BUB1B mutations that did not exhibit any other MVA-associated symptoms [38][42].
This suggests that perhaps aneuploidy is not the main factor responsible for causing MVA. Several
observations do, however, implicate aneuploidy in the development of certain malignancies associated
with MVA. Genomic instability, commonly manifested by structural aberrations or aneuploidy, is one
of the hallmarks of cancer [43]. Structural genomic aberrations leading to activation of oncogenes or
elimination of tumor suppression genes have been studied extensively, however, little is known about
the oncogenic role of aneuploidy, which is the most common in cancer [44]. In several MVA patients
non-random aneuploidies were found that, strikingly, resembled non-MVA related cases of cancer. For
example, the association of monosomy 7 (35%, Supplementary Table 1, patient 14) in bone marrow
with acute lymphoblastic leukemia in one MVA patient [3] recalls the relationship between monosomy
7 and myelodysplasic syndrome that evolved into sporadic acute lymphoblastic leukemia in several
non-MVA patients [45]. Likewise, the gain of chromosome 8 found in two rhabdomyosarcomas in MVA
patients [46] (Supplementary Table 1), is consistent with trisomy 8 observed in rhabdomyosarcoma
tissues analyzed by Dietrich et al. and Afify et al. [2][47]. Predominant trisomy 8 was found in most of
the 21 MVA patients analyzed by Garcia et al. [3][2] and has further been linked to Wilms’ tumor [48]
9
and myeloid leukemia [49]. Interestingly, these malignancies are observed in BUB1B mutated individuals only. This, combined with the observed elevated levels of PCS in these patients, suggests that
perhaps CIN caused by BUB1B mutations predisposes MVA patients to the development of cancer. This
would suggest that cancer is not necessarily associated with MVA but may be a bystander effect of
BUB1B mutations. Several mouse models support this theory. Although transgenic mice with reduced
expression of the mitotic checkpoint proteins BUB3 [50], RAE1 [51] and BUBR1 [17] do not demonstrate a significant increase in the development of spontaneous tumors, they do exhibit moderate to
severe levels of aneuploidy and increased susceptibility to externally induced tumorigenesis. Taken
together, these observations suggest that although aneuploidy may not be sufficient to cause MVA, it
might contribute to the development of several malignancies associated with MVA.
8. Cellular senescence and premature ageing
With aneuploidy unlikely being the cause of MVA, the theories of ageing and defective cilia
remain as probable alternatives. The former theory was derived from work done by Baker et al. who
implicated BUBR1 in the process of ageing in certain mouse tissues. CEP57, on the other hand, has not
been linked to ageing, but, as said, it is a relatively understudied protein.
In 2004, Baker et al. [17] studied the physiological role of BUBR1 by producing a series of mice
in which the expression of BUBR1 was reduced in a graded fashion from normal levels to zero. They
observed that with lower expression of BUBR1 the levels of aneuploidy and cellular senescence increased. This was accompanied by the development of a variety of progeroid features including short
lifespan, cachectic dwarfism, lordokyphosis, cataracts, loss of subcutaneous fat and impaired wound
healing. Later, Wijshake et al. [52] demonstrated that mice expressing BUBR1 with a MVA mutation
exhibited similar symptoms. In addition to the premature-ageing phenotype, Baker et al. [17] discovered that BUBR1 levels gradually decreased in several tissues as wild-type mice aged. Therefore, they
proposed that BUBR1 may be a key regulator of normal ageing, which led to the idea that perhaps
MVA is an early-ageing syndrome. This theory is supported by the resemblance of the MVA phenotype
to that of a progeroid syndrome, which is commonly associated with a short lifespan, growth retardation, facial dysmorphisms, and cataract formation (Table 1) [52].
Senescent cells are cells characterized by a permanent state of cell-cycle arrest mediated predominantly by the cyclin dependent kinase inhibitors p21 and/or p16Ink4a (p16), both negative regulators of cell cycle progression [53]. Importantly, senescent cells acquire a unique secretory profile referred to as SASP (senescence-associated secretory phenotype). This SASP is hypothesized to contribute to ageing and age-related disorders through altering the tissue microenvironment. Baker et al. [54]
observed that MEFs from BUB1B hypomorphic mice accumulated high levels of p21 and p16 and therefore suggested that the onset of early ageing in these mice is probably linked to cellular senescence.
P16 is a an effector of cellular senescence of which the expression has been shown to increase
with age in different mouse and human tissues [55][56][57]. Baker et al. observed that the tissues that
demonstrated early-ageing related phenotypes in BUB1B hypomorphic mice, such as skeletal muscles
and fat and eye tissue, exhibited significantly elevated expression levels of p16 and an increase in the
accumulation of senescent cells. Knockdown of p16 significantly delayed the development of ageingrelated symptoms and cellular senescence in these tissues. Conversely, tissues that were not subjected
to premature ageing, including lung, pancreas, colon and liver, maintained low expression of p16.
Therefore, Baker et al. proposed that upregulation of p16 and a subsequent induction of cellular senescence in response to BUBR1 deficiency is responsible for premature ageing in different mouse tissues [58]. This was later supported by the finding that clearance of p16-positive senescent cells from
10
BUBR1 deficient mice significantly delayed the development of progeroid symptoms. Moreover, overexpression of BUBR1 in wild-type mice extended lifespan and delayed age-related deterioration. This
was accompanied by lower expression of p16 in several tissues including muscle, kidney, eye and heart.
On the other hand, development of osteoporosis and cataractogenesis, two age-related disorders, was
not delayed [59].
In the experiments done by Baker et al. aneuploidy levels tightly correlated with increased
cellular senescence and premature ageing in response to BUB1B hypomorphism, as well as the delayed
development of progeroid features in response to BUBR1 overexpression. This, together with the fact
that BUBR1 plays an important role in SAC signaling, suggests that perhaps BUBR1 influences ageing
through affecting chromosomal stability. However, while BUB3/RAE1 double haploinsufficient mice
also exhibit mild premature ageing phenotypes, several other aneuploidy mouse models do not [54].
Therefore, Baker et al. speculate that aneuploidy might be required, but not sufficient for the induction
of age-related pathologies [60]. They suggest that perhaps aneuploidy may contribute to the induction
of age-related pathologies only in the presence of other age-associated damage, such as DNA double
stranded breaks, which were increased in the kidneys of BUB1B hypomorphic mice. However, apart
from a few marker chromosomes, there have been no reports of DNA damage in MVA patients
[11][46]. Alternatively, they propose, the effects of BUBR1 could be independent of chromosome segregation. BUBR1 is normally present throughout the cell cycle and known to be implicated in roles
outside mitosis, including DNA repair and ciliogenesis [19]. Wijshake et al. speculate that perhaps impairment of its function to serve as an inhibitor of APC/CCDC20 activity in interphase leads to unscheduled degradation of APC/CCDC20 substrates, which, in turn, could lead to cellular stresses that engage
p16 and induce senescence [52].
Although the MVA phenotype includes several symptoms associated with progeroid disorders
(table), other age-related phenotypes observed in BUB1B hypomorphic mice, such as fat loss, muscle
wasting and cardiac arrhythmias, have not been found in MVA patients. Wijshake et al. attribute this
to the fact that the MVA syndrome is rare and that most patients die at a very young age [52]. On the
other hand, some MVA symptoms, such as microcephaly and polycystic kidneys, are not commonly
associated with premature-ageing. Therefore, it is likely that a different process underlies MVA.
9. Ciliary defects
Since it is unlikely that aneuploidy and premature ageing are responsible for causing MVA, the
one remaining probable alternative, based on the comparison of the functions of both BUBR1 and
CEP57, is defective ciliogenesis. Cilia are antenna-like organelles that protrude from the apical surface
of most mammalian cells. There are two types of cilia: motile and non-motile or primary cilia. Primary
cilia are important signaling centers that harbor components of multiple pathways (including Wnt,
hedgehog and notch) essential for normal development. They are found on epithelial cells of the bile
ducts, kidney tubules, the pancreas and the thyroid glands as well as on nonepithelial cells such as
chondrocytes, fibroblasts, smooth muscle cells and neurons. Motile cilia, in contrast to primary cilia,
are usually present on the cell in large numbers. These cilia are found on epithelial cells lining airways,
ependyma and choroid plexus in the brain, oviduct and epididymis of the reproductive tracts and are
involved in movement of mucus in the lung and cerebrospinal fluid in the brain, or in transport of ovum
and sperm along the reproductive tracts [61].
Primary cilia typically form during G0 or G1 phase of the cell cycle. The mother centriole, which
serves as a component of the centrosome, differentiates into a basal body to nucleate a cilium. Multi-
11
ciliated cells, on the other hand, only assemble cilia upon terminal differentiation. The extra basal bodies required for ciliogenesis are rapidly generated by overduplication and maturation of existing centrioles. The earliest stage of ciliogenesis is marked by the association of basal bodies with membrane
vesicles and the plasma membrane, after which growth of the axoneme starts. Basal bodies nucleate
outgrowth of microtubules that protrude beneath an extension of the membrane. In epithelial cells,
such as those found in the lung or kidney, the basal body docks with the plasma membrane before the
axoneme assembles (Figure 5; extracellular pathway), while in mesenchymal cells, fibroblasts, and
neuronal precursors, membrane biogenesis occurs in parallel with axoneme elongation as secondary
vesicles are recruited, and subsequently fuse, with the plasma membrane, exposing the cilium (Figure
5; intracellular pathway) [62][63].
Figure 5: Schematic representation of the Intracellular and extracellular pathways of ciliogenesis. Adopted from MollaHerman et al.[75]
Mutations that result in defective ciliary structure and function cause human disorders termed
ciliopathies [64]. Defects in cilia result in many phenotypes affecting a wide variety of organ systems,
including cystic kidneys (defects in renal cilia), retinal degeneration (defects in photoreceptor cilia),
left–right asymmetry defects (abnormal nodal cilia), infertility (defective sperm and oviduct flagella
and cilia), obesity (neuronal cilia defects), and airway abnormalities (dysfunctional tracheal motile cilia)
[65]. The fact that many of these correspond to symptoms found in MVA patients, suggests that cilia
might be defective in these individuals (Table 1).
Moreover, cells derived from two MVA patients with BUB1B mutations (Supplementary Table
1, patients 28 and 29) were shown to lack primary cilia. Miyamoto et al. [27] observed that basal bodies
in epithelial cells derived from these patients failed to dock apically to the membrane, which is required
for ciliogenesis. As much as 30% of cells from a normal individual were ciliated, but only 4% and 1% of
the cells derived from the individuals suffering of MVA. Furthermore, morpholino knockdown of
BUBR1 in medaka fish also caused ciliary dysfunction [27]. This, combined with fact that CEP57 is a
centrosome protein, links both proteins implicated in causing MVA with cilia and ciliogenesis. In contrast to BUBR1, CEP57 has not been directly linked to ciliogenesis. It is, however, required for centriole
stability and has been suggested to play a role in centriole duplication [31][35]. In multiciliated cells,
centrioles are duplicated many times to give rise to the sometimes hundreds of basal bodies of cilia
[66]. Therefore, defects in CEP57 might negatively impact the formation of supernumary cilia in multiciliated cells. It would be interesting to examine whether cells derived from CEP57 mutated patients
12
demonstrate a lack of primary cilia as observed in the two BUB1B mutated patients or that the effects,
if any, are mainly visible in multiciliated cells.
Table 1: The MVA phenotype closely resembles that of ciliopathies [39][54][67][68][69]
Ciliopathy
Progeroid Aneuploidy
Microcephaly
x
x
Growth retardation
x
x
x
Facial dysmorphism
x
x
x
Mental retardation
x
x
x
CNS anomalies
x
x
x
Seizures
x
x
x
Polycystic kidneys
x
Cataracts and other
x
x
x
eye abnormalities
Obesity
x
x
Cancer*
x
Note: Association of the symptoms with these disorders was based on whether they are commonly
found in patients. Examples of disorders: polycystic kidney disease (ciliopathy), Werner syndrome
(progeroid), Down’s syndrome (aneuploidy). *Wilm’s tumor, rhabdomyosarcoma and myeloid leukemia.
Finally, a major consequence of losing primary cilia is reduced ciliary signaling of pathways
whose components reside in primary cilia, such as hedgehog signaling [70]. Interestingly, downregulation of hedgehog signaling is associated with ageing-related diseases such as type 2 diabetes, neurodegeneration, atherosclerosis and osteoporosis [71]. Furthermore, Bishop et al. [70] recently demonstrated that hedgehog signaling suppresses the expression of p16 in cultured human epithelial cells.
This suppression was observed both in the presence and absence of primary cilia, but to a significantly
higher extent in cells with primary cilia. These observations recall the relationship of BUBR1 insufficiency with the elevated levels of p16 in BUB1BH/H mice and suggest that perhaps decreased hedgehog
signaling is responsible for the observed accumulation of p16. This idea is supported by the fact that
reduced hedgehog signaling is associated with several ageing-related phenotypes. Furthermore, the
fact that the development of cataractogenesis and osteoporosis (which were both characterized as
progeroid features based on previous observations by the same authors) was not delayed by the overexpression of BUBR1 in wild-type mice [60], could be explained by a) primary cilia and thus hedgehog
signaling already being functional and not further upregulated in response to elevated BUBR1 levels
or b) them being ciliopathy instead of ageing symptoms. This would imply that the progeroid symptoms
observed by Baker et al. in BUB1B hypomorphic mice originate from defects in cilia.
I propose that mutations associated with MVA perturb ciliogenesis, thereby both disrupting
normal functioning of certain ciliated cells and suppressing hedgehog signaling. Impaired hedgehog
signaling could lead to the overexpression of p16 and induction of cellular senescence, which could
explain the progeroid symptoms observed in BUBR1 deficient mice. This would imply that MVA is a
ciliopathy with a predisposition to premature ageing symptoms.
13
10. Concluding remarks
Mosaic variegated aneuploidy is a rare disorder with a broad range of symptoms and clinical
and genetic heterogeneity among its patients. I propose that MVA is a ciliopathy characterized by impaired ciliogenesis and defective hedgehog signaling, resulting in decreased suppression of p16. This
bridges a link to research done by Baker et al. who demonstrate that BUBR1 insufficiency induces
premature ageing phenotypes in mice through the overexpression of p16. The combination of symptoms associated with ciliary defects and premature ageing, with increased susceptibility to the development of malignancies, could explain the diverse clinical phenotypes associated with MVA.
It is unclear what the role is of aneuploidy, if any, in causing MVA. Several non-random aneuploidies have been linked to certain cancers of MVA patients, suggesting that aneuploidy might be
causally implicated in the development of these malignancies. However, the facts that these symptoms
are solely observed in BUB1B mutated patients, while CEP57 mutated patients exhibit aneuploidy levels comparable to those with BUB1B mutations, suggests that this might be the result of an impaired
function of BUBR1 instead. Further research should elucidate whether any such function is related to
PCS, the formation of (primary) cilia or to a different process altogether. Another interesting fact about
aneuploidy in MVA patients is that some patients seem to exhibit random aneuploidies, while others
have a predisposition to gain or lose specific chromosomes. It will be interesting to investigate whether
this is related to any of the functions of the proteins involved or to a selection process present in cultured cells or in vivo (most predominant aneuploidies are found in cultured cells). The fact that aneuploidy is found in all MVA patients suggests that aneuploidy might be necessary for – and thus contributes to – the MVA phenotype. It is possible, though, that aneuploidy is simply a byproduct of the mutations that cause MVA. This is an interesting thought that would imply that MVA is actually a collection
of different ciliopathies and/or premature ageing disorders caused by mutations that additionally predispose to aneuploidy. In this case, it may be possible to find patients with similar clinical phenotypes,
but without variegated mosaic aneuploidies.
To validate whether MVA indeed is a ciliopathy, it will be crucial to investigate whether cells
derived from CEP57 and BUB1B mutated MVA patients exhibit defective ciliogenesis. Interesting questions would be whether cells with CEP57 mutations exhibit impaired ciliogenesis of primary cilia or
only of multiciliated cells (as is suggested by its role in centriole duplication). And whether defects in
ciliogenesis caused by BUBR1 deficiency, if any, are present in epithelial cells only or also in, for instance, fibroblasts. It would also be interesting to examine the effects of manipulating hedgehog signaling on p16 levels in BUBR1 deficient mice. Dashti et al. [71] report that the status of hedgehog
signaling integrity seems to continuously decline over time. Perhaps this is related to the decline in
expression of BUBR1 as mice age, which would suggest that hedgehog signaling might play an important role in normal ageing.
14
11. References
[1]
J. M. Scheres, T. W. J. Huntinx, K. Madam, J. Beltman, and D. Lindhout, “A mitotic mutant
causing non-disjunction to man,” Proc. 7th Int. Congr. Hum. Genet. Berlin. Part 1163, Mar.
1986.
[2]
H. García-Castillo, A. I. Vásquez-Velásquez, H. Rivera, and P. Barros-Núñez, “Clinical and
genetic heterogeneity in patients with mosaic variegated aneuploidy: delineation of clinical
subtypes.,” Am. J. Med. Genet. A, vol. 146A, no. 13, pp. 1687–95, Jul. 2008.
[3]
S. Jacquemont, M. Bocéno, J. M. Rival, F. Méchinaud, and A. David, “High risk of malignancy in
mosaic variegated aneuploidy syndrome.,” American journal of medical genetics, vol. 109. pp.
17–21; discussion 16, 2002.
[4]
K. Snape, S. Hanks, E. Ruark, P. Barros-Núñez, A. Elliott, A. Murray, A. H. Lane, N. Shannon, P.
Callier, D. Chitayat, J. Clayton-Smith, D. R. Fitzpatrick, D. Gisselsson, S. Jacquemont, K.
Asakura-Hay, M. a Micale, J. Tolmie, P. D. Turnpenny, M. Wright, J. Douglas, and N. Rahman,
“Mutations in CEP57 cause mosaic variegated aneuploidy syndrome.,” Nat. Genet., vol. 43,
no. 6, pp. 527–9, Jun. 2011.
[5]
L. Pinson, L. Mannini, M. Willems, F. Cucco, N. Sirvent, T. Frebourg, V. Quarantotti, C. Collet,
A. Schneider, P. Sarda, D. Geneviève, J. Puechberty, G. Lefort, and A. Musio, “CEP57 mutation
in a girl with mosaic variegated aneuploidy syndrome.,” Am. J. Med. Genet. A, pp. 1–5, Nov.
2013.
[6]
A. Plaja, T. Vendrell, D. Smeets, E. Sarret, T. Gili, V. Català, C. Mediano, and J. M. Scheres,
“Variegated aneuploidy related to premature centromere division (PCD) is expressed in vivo
and is a cancer-prone disease.,” American journal of medical genetics, vol. 98. pp. 216–223,
2001.
[7]
S. Hanks, K. Coleman, S. Reid, A. Plaja, H. Firth, D. Fitzpatrick, A. Kidd, K. Méhes, R. Nash, N.
Robin, N. Shannon, J. Tolmie, J. Swansbury, A. Irrthum, J. Douglas, and N. Rahman,
“Constitutional aneuploidy and cancer predisposition caused by biallelic mutations in
BUB1B.,” Nat. Genet., vol. 36, no. 11, pp. 1159–61, Nov. 2004.
[8]
P. Callier, L. Faivre, V. Cusin, N. Marle, C. Thauvin-Robinet, D. Sandre, T. Rousseau, P. Sagot, E.
Lacombe, V. Faber, and F. Mugneret, “Microcephaly is not mandatory for the diagnosis of
mosaic variegated aneuploidy syndrome.,” Am. J. Med. Genet. A, vol. 137, no. 2, pp. 204–7,
Aug. 2005.
[9]
S. Matsuura and Y. Matsumoto, “Monoallelic BUB1B mutations and defective mitotic-spindle
checkpoint in seven families with premature chromatid separation (PCS) syndrome,” Am. J. …,
vol. 367, pp. 358–367, 2006.
[10]
M. Micale and D. Schran, “Mosaic variegated aneuploidy without microcephaly: implications
for cytogenetic diagnosis,” Am. J. …, vol. 1893, pp. 1890–1893, 2007.
[11]
T. Kajii and T. Ikeuchi, “Premature chromatid separation (PCS) vs. premature centromere
division (PCD).,” Am. J. Med. Genet. A, vol. 126A, no. 4, pp. 433–4, May 2004.
15
[12]
S. Matsuura, E. Ito, H. Tauchi, K. Komatsu, T. Ikeuchi, and T. Kajii, “Chromosomal instability
syndrome of total premature chromatid separation with mosaic variegated aneuploidy is
defective in mitotic-spindle checkpoint.,” Am. J. Hum. Genet., vol. 67, no. 2, pp. 483–6, Aug.
2000.
[13]
G. J. P. L. Kops, B. A. A. Weaver, and D. W. Cleveland, “On the road to cancer: aneuploidy and
the mitotic checkpoint.,” Nat. Rev. Cancer, vol. 5, pp. 773–785, 2005.
[14]
A. R. Tipton, K. Wang, L. Link, J. J. Bellizzi, H. Huang, T. Yen, and S.-T. Liu, “BUBR1 and closed
MAD2 (C-MAD2) interact directly to assemble a functional mitotic checkpoint complex.,” J.
Biol. Chem., vol. 286, pp. 21173–21179, 2011.
[15]
H. Ochiai, T. Miyamoto, A. Kanai, K. Hosoba, T. Sakuma, Y. Kudo, K. Asami, A. Ogawa, A.
Watanabe, T. Kajii, T. Yamamoto, and S. Matsuura, “TALEN-mediated single-base-pair editing
identification of an intergenic mutation upstream of BUB1B as causative of PCS (MVA)
syndrome.,” Proc. Natl. Acad. Sci. U. S. A., Dec. 2013.
[16]
J. L. Tolmie, E. Boyd, P. Batstone, M. E. Ferguson-Smith, L. al Roomi, and J. M. Connor,
“Siblings with chromosome mosaicism, microcephaly, and growth retardation: the phenotypic
expression of a human mitotic mutant?,” Human genetics, vol. 80. pp. 197–200, 1988.
[17]
D. J. Baker, K. B. Jeganathan, J. D. Cameron, M. Thompson, S. Juneja, A. Kopecka, R. Kumar, R.
B. Jenkins, P. C. de Groen, P. Roche, and J. M. van Deursen, “BubR1 insufficiency causes early
onset of aging-associated phenotypes and infertility in mice.,” Nat. Genet., vol. 36, no. 7, pp.
744–9, Jul. 2004.
[18]
S. J. E. Suijkerbuijk, T. J. P. van Dam, G. E. Karagöz, E. von Castelmur, N. C. Hubner, A. M. S.
Duarte, M. Vleugel, A. Perrakis, S. G. D. Rüdiger, B. Snel, and G. J. P. L. Kops, “The vertebrate
mitotic checkpoint protein BUBR1 is an unusual pseudokinase.,” Dev. Cell, vol. 22, no. 6, pp.
1321–9, Jun. 2012.
[19]
R. Karess, K. Wassmann, and Z. Rahmani, “New Insights into the Role of BubR1 in Mitosis and
Beyond.,” Int. Rev. cell …, vol. 306, pp. 223–73, Jan. 2012.
[20]
G. J. P. L. Kops and J. V. Shah, “Connecting up and clearing out: how kinetochore attachment
silences the spindle assembly checkpoint,” Chromosoma, vol. 121. pp. 509–525, 2012.
[21]
P. Lara-Gonzalez, F. G. Westhorpe, and S. S. Taylor, “The spindle assembly checkpoint.,” Curr.
Biol., vol. 22, pp. R966–80, 2012.
[22]
S. Elowe, K. Dulla, A. Uldschmid, X. Li, Z. Dou, and E. A. Nigg, “Uncoupling of the spindlecheckpoint and chromosome-congression functions of BubR1.,” J. Cell Sci., vol. 123, pp. 84–
94, 2010.
[23]
T. Kruse, G. Zhang, M. S. Y. Larsen, T. Lischetti, W. Streicher, T. Kragh Nielsen, S. P. Bjørn, and
J. Nilsson, “Direct binding between BubR1 and B56-PP2A phosphatase complexes regulate
mitotic progression.,” J. Cell Sci., vol. 126, no. Pt 5, pp. 1086–92, Mar. 2013.
[24]
S. J. E. Suijkerbuijk, M. Vleugel, A. Teixeira, and G. J. P. L. Kops, “Integration of kinase and
phosphatase activities by BUBR1 ensures formation of stable kinetochore-microtubule
attachments.,” Dev. Cell, vol. 23, no. 4, pp. 745–55, Oct. 2012.
16
[25]
H. Izumi, Y. Matsumoto, T. Ikeuchi, H. Saya, T. Kajii, and S. Matsuura, “BubR1 localizes to
centrosomes and suppresses centrosome amplification via regulating Plk1 activity in
interphase cells.,” Oncogene, vol. 28, no. 31, pp. 2806–20, Aug. 2009.
[26]
A. Ganner, S. Lienkamp, T. Schäfer, D. Romaker, T. Wegierski, T. J. Park, S. Spreitzer, M.
Simons, J. Gloy, E. Kim, J. B. Wallingford, and G. Walz, “Regulation of ciliary polarity by the
APC/C.,” Proc. Natl. Acad. Sci. U. S. A., vol. 106, pp. 17799–17804, 2009.
[27]
T. Miyamoto, S. Porazinski, H. Wang, A. Borovina, B. Ciruna, A. Shimizu, T. Kajii, A. Kikuchi, M.
Furutani-Seiki, and S. Matsuura, “Insufficiency of BUBR1, a mitotic spindle checkpoint
regulator, causes impaired ciliogenesis in vertebrates.,” Hum. Mol. Genet., vol. 20, no. 10, pp.
2058–70, May 2011.
[28]
S. J. E. Suijkerbuijk, M. H. J. van Osch, F. L. Bos, S. Hanks, N. Rahman, and G. J. P. L. Kops,
“Molecular causes for BUBR1 dysfunction in the human cancer predisposition syndrome
mosaic variegated aneuploidy.,” Cancer Res., vol. 70, no. 12, pp. 4891–900, Jun. 2010.
[29]
C. Bossard, H. Laurell, L. Van den Berghe, S. Meunier, C. Zanibellato, and H. Prats, “Translokin
is an intracellular mediator of FGF-2 trafficking.,” Nat. Cell Biol., vol. 5, pp. 433–439, 2003.
[30]
J. S. Andersen, C. J. Wilkinson, T. Mayor, P. Mortensen, E. A. Nigg, and M. Mann, “Proteomic
characterization of the human centrosome by protein correlation profiling.,” Nature, vol. 426,
pp. 570–574, 2003.
[31]
R. Cuevas, N. Korzeniewski, Y. Tolstov, M. Hohenfellner, and S. Duensing, “FGF-2 disrupts
mitotic stability in prostate cancer through the intracellular trafficking protein CEP57.,” Cancer
Res., vol. 73, no. 4, pp. 1400–10, Feb. 2013.
[32]
K. Momotani, A. S. Khromov, T. Miyake, P. T. Stukenberg, and A. V Somlyo, “Cep57, a
multidomain protein with unique microtubule and centrosomal localization domains.,”
Biochem. J., vol. 412, no. 2, pp. 265–73, Jun. 2008.
[33]
M. J. Emanuele and P. T. Stukenberg, “Xenopus Cep57 is a novel kinetochore component
involved in microtubule attachment.,” Cell, vol. 130, pp. 893–905, 2007.
[34]
S. Meunier, M. G.-J. Navarro, C. Bossard, H. Laurell, C. Touriol, E. Lacazette, and H. Prats,
“Pivotal role of translokin/CEP57 in the unconventional secretion versus nuclear translocation
of FGF2.,” Traffic, vol. 10, pp. 1765–1772, 2009.
[35]
Q. Wu, R. He, H. Zhou, A. C. H. Yu, B. Zhang, J. Teng, and J. Chen, “Cep57, a NEDD1-binding
pericentriolar material component, is essential for spindle pole integrity.,” Cell Res., vol. 22,
no. 9, pp. 1390–401, Sep. 2012.
[36]
G. Chen, B. Rubinstein, and R. Li, “Whole chromosome aneuploidy: big mutations drive
adaptation by phenotypic leap.,” Bioessays, vol. 34, no. 10, pp. 893–900, Oct. 2012.
[37]
D. Perera, V. Tilston, J. A. Hopwood, M. Barchi, R. P. Boot-Handford, and S. S. Taylor, “Bub1
maintains centromeric cohesion by activation of the spindle checkpoint.,” Dev. Cell, vol. 13,
pp. 566–579, 2007.
17
[38]
T. R. Frio, J. Lavoie, and N. Hamel, “Homozygous BUB1B mutation and susceptibility to
gastrointestinal neoplasia,” … Engl. J. …, 2010.
[39]
M. a Kingsbury, Y. C. Yung, S. E. Peterson, J. W. Westra, and J. Chun, “Aneuploidy in the
normal and diseased brain.,” Cell. Mol. Life Sci., vol. 63, no. 22, pp. 2626–41, Nov. 2006.
[40]
D. M. Bushman and J. Chun, “The genomically mosaic brain: aneuploidy and more in neural
diversity and disease.,” Semin. Cell Dev. Biol., vol. 24, no. 4, pp. 357–69, Apr. 2013.
[41]
A. W. Duncan, “Aneuploidy, polyploidy and ploidy reversal in the liver.,” Semin. Cell Dev. Biol.,
vol. 24, pp. 347–56, 2013.
[42]
R. M. de Voer, A. Geurts van Kessel, R. D. a Weren, M. J. L. Ligtenberg, D. Smeets, L. Fu, L.
Vreede, E. J. Kamping, E. T. P. Verwiel, M.-M. Hahn, M. Ariaans, L. Spruijt, T. van Essen, G.
Houge, H. K. Schackert, J. Q. Sheng, H. Venselaar, C. M. a van Ravenswaaij-Arts, J. H. J. M. van
Krieken, N. Hoogerbrugge, and R. P. Kuiper, “Germline mutations in the spindle assembly
checkpoint genes BUB1 and BUB3 are risk factors for colorectal cancer.,” Gastroenterology,
vol. 145, no. 3, pp. 544–7, Sep. 2013.
[43]
R. A. Weinberg and D. Hanahan, “The Hallmarks of Cancer,” Cell, vol. 100. pp. 57–70, 2000.
[44]
M. R. Teixeira and S. Heim, “Multiple numerical chromosome aberrations in cancer: what are
their causes and what are their consequences?,” Semin. Cancer Biol., vol. 15, pp. 3–12, 2005.
[45]
D. Aktas and E. Tuncbilek, “Myelodysplastic syndrome associated with monosomy 7 in
childhood: a retrospective study.,” Cancer Genet. Cytogenet., vol. 171, pp. 72–75, 2006.
[46]
C. Limwongse, S. Schwartz, M. Bocian, and N. H. Robin, “Child with mosaic variegated
aneuploidy and embryonal rhabdomyosarcoma.,” American journal of medical genetics, vol.
82. pp. 20–24, 1999.
[47]
a Afify and H. F. Mark, “Trisomy 8 in embryonal rhabdomyosarcoma detected by fluorescence
in situ hybridization.,” Cancer Genet. Cytogenet., vol. 108, no. 2, pp. 127–32, Jan. 1999.
[48]
E. M. Sloand, J. J. Melenhorst, Z. C. G. Tucker, L. Pfannes, J. M. Brenchley, A. Yong, V. Visconte,
C. Wu, E. Gostick, P. Scheinberg, M. J. Olnes, D. C. Douek, D. A. Price, A. J. Barrett, and N. S.
Young, “T-cell immune responses to Wilms tumor 1 protein in myelodysplasia responsive to
immunosuppressive therapy.,” Blood, vol. 117, pp. 2691–2699, 2011.
[49]
C. Hahm, Y. C. Mun, C. M. Seong, S.-H. Han, W. S. Chung, and J. Huh, “Single Nucleotide
Polymorphism Array-Based Karyotyping in Acute Myeloid Leukemia or Myelodysplastic
Syndrome with Trisomy 8 as the Sole Chromosomal Abnormality.,” Acta Haematol., vol. 129,
pp. 154–158, 2012.
[50]
P. Kalitsis, K. J. Fowler, B. Griffiths, E. Earle, C. W. Chow, K. Jamsen, and K. H. A. Choo,
“Increased chromosome instability but not cancer predisposition in haploinsufficient Bub3
mice.,” Genes. Chromosomes Cancer, vol. 44, pp. 29–36, 2005.
[51]
J. R. Babu, K. B. Jeganathan, D. J. Baker, X. Wu, N. Kang-Decker, and J. M. van Deursen, “Rae1
is an essential mitotic checkpoint regulator that cooperates with Bub3 to prevent
chromosome missegregation.,” J. Cell Biol., vol. 160, pp. 341–353, 2003.
18
[52]
T. Wijshake, L. a Malureanu, D. J. Baker, K. B. Jeganathan, B. van de Sluis, and J. M. van
Deursen, “Reduced life- and healthspan in mice carrying a mono-allelic BubR1 MVA
mutation.,” PLoS Genet., vol. 8, no. 12, p. e1003138, Jan. 2012.
[53]
J. Campisi and F. d’Adda di Fagagna, “Cellular senescence: when bad things happen to good
cells.,” Nat. Rev. Mol. Cell Biol., vol. 8, pp. 729–740, 2007.
[54]
D. J. Baker, K. B. Jeganathan, L. Malureanu, C. Perez-Terzic, A. Terzic, and J. M. a van Deursen,
“Early aging-associated phenotypes in Bub3/Rae1 haploinsufficient mice.,” J. Cell Biol., vol.
172, no. 4, pp. 529–40, Feb. 2006.
[55]
J. Krishnamurthy, C. Torrice, M. R. Ramsey, G. I. Kovalev, K. Al-Regaiey, L. Su, and N. E.
Sharpless, “Ink4a/Arf expression is a biomarker of aging.,” J. Clin. Invest., vol. 114, pp. 1299–
1307, 2004.
[56]
F. Zindy, D. E. Quelle, M. F. Roussel, and C. J. Sherr, “Expression of the p16INK4a tumor
suppressor versus other INK4 family members during mouse development and aging.,”
Oncogene, vol. 15, pp. 203–211, 1997.
[57]
Y. Liu, H. K. Sanoff, H. Cho, C. E. Burd, C. Torrice, J. G. Ibrahim, N. E. Thomas, and N. E.
Sharpless, “Expression of p16(INK4a) in peripheral blood T-cells is a biomarker of human
aging.,” Aging Cell, vol. 8, pp. 439–448, 2009.
[58]
D. J. Baker, C. Perez-Terzic, F. Jin, K. Pitel, N. J. Niederländer, K. Jeganathan, S. Yamada, S.
Reyes, L. Rowe, H. J. Hiddinga, N. L. Eberhardt, A. Terzic, and J. M. van Deursen, “Opposing
roles for p16Ink4a and p19Arf in senescence and ageing caused by BubR1 insufficiency,” Nat.
Cell Biol., vol. 10, no. 7, pp. 825–836, May 2008.
[59]
D. J. Baker, T. Wijshake, T. Tchkonia, N. K. LeBrasseur, B. G. Childs, B. van de Sluis, J. L.
Kirkland, and J. M. van Deursen, “Clearance of p16Ink4a-positive senescent cells delays
ageing-associated disorders.,” Nature, vol. 479, no. 7372, pp. 232–6, Nov. 2011.
[60]
D. J. Baker, M. M. Dawlaty, T. Wijshake, K. B. Jeganathan, L. Malureanu, J. H. van Ree, R.
Crespo-Diaz, S. Reyes, L. Seaburg, V. Shapiro, A. Behfar, A. Terzic, B. van de Sluis, and J. M. van
Deursen, “Increased expression of BubR1 protects against aneuploidy and cancer and extends
healthy lifespan.,” Nat. Cell Biol., vol. 15, no. 1, pp. 96–102, Jan. 2013.
[61]
N. F. Larusso and T. V Masyuk, “The role of cilia in the regulation of bile flow.,” Dig. Dis., vol.
29, pp. 6–12, 2011.
[62]
S. Kim and B. D. Dynlacht, “Assembling a primary cilium.,” Curr. Opin. Cell Biol., vol. 25, no. 4,
pp. 506–11, Aug. 2013.
[63]
H. Ishikawa and W. F. Marshall, “Ciliogenesis: building the cell’s antenna.,” Nat. Rev. Mol. Cell
Biol., vol. 12, pp. 222–234, 2011.
[64]
C. Bergmann, “Educational paper: ciliopathies.,” Eur. J. Pediatr., vol. 171, no. 9, pp. 1285–300,
Sep. 2012.
[65]
P. Avasthi and W. F. Marshall, “Stages of ciliogenesis and regulation of ciliary length.,”
Differentiation., vol. 83, no. 2, pp. S30–42, Feb. 2012.
19
[66]
E. a Nigg and J. W. Raff, “Centrioles, centrosomes, and cilia in health and disease.,” Cell, vol.
139, no. 4, pp. 663–78, Nov. 2009.
[67]
R. Shaheen, E. Faqeih, H. E. Shamseldin, R. R. Noche, A. Sunker, M. J. Alshammari, T. AlSheddi, N. Adly, M. S. Al-Dosari, S. G. Megason, M. Al-Husain, F. Al-Mohanna, and F. S.
Alkuraya, “POC1A Truncation Mutation Causes a Ciliopathy in Humans Characterized by
Primordial Dwarfism,” The American Journal of Human Genetics, vol. 91. pp. 330–336, 2012.
[68]
D. J. Baker, R. L. Weaver, and J. M. van Deursen, “p21 both attenuates and drives senescence
and aging in BubR1 progeroid mice.,” Cell Rep., vol. 3, no. 4, pp. 1164–74, Apr. 2013.
[69]
R. S. Møller, S. Kübart, M. Hoeltzenbein, B. Heye, I. Vogel, C. P. Hansen, C. Menzel, R. Ullmann,
N. Tommerup, H.-H. Ropers, Z. Tümer, and V. M. Kalscheuer, “Truncation of the Down
syndrome candidate gene DYRK1A in two unrelated patients with microcephaly.,” Am. J. Hum.
Genet., vol. 82, pp. 1165–1170, 2008.
[70]
C. L. Bishop, A.-M. H. Bergin, D. Fessart, V. Borgdorff, E. Hatzimasoura, J. C. Garbe, M. R.
Stampfer, J. Koh, and D. H. Beach, “Primary cilium-dependent and -independent Hedgehog
signaling inhibits p16(INK4A).,” Mol. Cell, vol. 40, no. 4, pp. 533–47, Nov. 2010.
[71]
M. Dashti, M. P. Peppelenbosch, and F. Rezaee, “Hedgehog signalling as an antagonist of
ageing and its associated diseases.,” Bioessays, vol. 34, no. 10, pp. 849–56, Oct. 2012.
[72]
C.-P. Chen, C.-C. Lee, W.-L. Chen, W. Wang, and C.-Y. Tzen, “Prenatal diagnosis of premature
centromere division-related mosaic variegated aneuploidy.,” Prenat. Diagn., vol. 24, no. 1, pp.
19–25, Jan. 2004.
[73]
S. Suijkerbuijk, The role of BUBR1 in the maintenance of chromosomal stability. Ph.D. Thesis.
University Utrecht. Netherlands, 2012.
[74]
K. Crasta and U. Surana, “Disjunction of conjoined twins: Cdk1, Cdh1 and separation of
centrosomes.,” Cell Div., vol. 1, p. 12, 2006.
[75]
A. Molla-Herman, R. Ghossoub, T. Blisnick, A. Meunier, C. Serres, F. Silbermann, C. Emmerson,
K. Romeo, P. Bourdoncle, A. Schmitt, S. Saunier, N. Spassky, P. Bastin, and A. Benmerah, “The
ciliary pocket: an endocytic membrane domain at the base of primary and motile cilia.,” J. Cell
Sci., vol. 123, pp. 1785–1795, 2010.
20
12. Supplementary Table 1: Clinical and cytogenetic findings MVA patients
Gender
Age at death
Aneuploidy
Predominant
aneuploidy
PCS
Cancer
MC
GR
MR
Callier et al. [2005]
M
3-54% a/b
19, 8, 18
-
-
-
+
+
Chen et al. [2004] [a]
F
7.7% a
ND
47.4%
-
+
+
-
-
+
+
-
#
Reference
1
2
Mutations BUB1B
Mutations CEP57
45% b
33.3%
3
Chen et al. [2004] [b]
Prenatal
44% c
Multiple
+
4
D’Agostino et al. [2000]
M 8 months
40% a
ND
<25%
+
-
+
+
-
5
Flejter et al. [1998] [a]
F
8% a
8, 18,13
-
-
+
+
-
6
Flejter et al. [1998] [b]
F
19% a
8, 18,14
-
-
+
+
-
7
Garciá-Castillo et al.
M
53% a
None
-
-
-
+
-
F
48% a
None
14%
-
-
+
-
ND
30% a
8, 22
ND
-
+
+
ND
M
17% a
Ya
-
-
+
+
+
6% b
-
[2008] [a]
8
Garciá-Castillo et al.
c.520_521delGA
c.915_925dup11
-
[2008] [b]
c.520_521delGA
c.915_925dup11
9
Hanks et al. [2004] [a]
2211-2insGTTA
10
Hanks et al. [2004] [b]
-
11
Hanks et al. [2004] [c]
2211−2insGTTA
2441G > A
c.241C>T; p.R81X
c.241C>T; p.R81X
18% b
Yb
ND
ND
ND
ND
-
+
+
-
ND
ND
ND
ND
ND
ND
ND
ND
ND
-
+
+
-
M
8-10% a/b
8, 5, 7, 21
ND
+
+
+
+
F 1.5 years
20% a
None
67–86%
+
+
+
+
92% b
7, 15, 20
87%
+
+
+
+
+
+
+
+
3035T>C
12
Hanks et al. [2004] [d]
IVS10−1G T
1649G A
13
Hanks et al. [2004] [e]
14
Jacquemont et al. [2002]
15
Kajii et al. [1998] [a]
-
1833delT
3, 5, 7, 8, 15,
16
Kajii et al. [1998] [b]
M 18 months
10% a
18, 22, X, and Y
17
Kajii et al. [2001] [a]
IVS10-5A > G
M 5 months
9% a
None
48%
35% b
7, 18
73%
18
Kajii et al. [2001] [b]
107G>A
F
25% a
6, 7
68-83%
+
+
+
+
19
Kajii et al. [2001] [c]
1833delT
M 1.1 years
18% a
None
36%
+
+
+
+
20
Kajii et al. [2001] [d]
1833delT
M 7 months
32% a
8
+
+
+
+
+
21
Kajii et al. [2001] [e]
F 16 months
20% a
ND
10,50%
+
+
+
+
22
Kawame et al. [1999]
M 1.6 years
17% a
8
82%
+
+
+
+
23
Lane et al. [2002]
24
Limwongse et al.
580C > T
[1999] [a]
2530C > T
1833delT
c.915_925dup11
24% b
None
M
24% a
Multiple
-
-
+
+
+
M
22-33% a
None
+
+
+
+
-
None b
ND
ND
ND
ND
ND
-
+
+
-
ND
ND
ND
ND
-
+
+
-
M 5 months
+a
ND
48.5%
+
+
+
-
+b
ND
48%
c.915_925dup11
2763G > C
25
26
27
Limwongse et al.
2211−2insGTTA
[1999] [b]
2441G A
Limwongse et al.
2211−2insGTTA
[1999] [c]
3035T C
Matsuura et al. [2000]
21
Matsuura et al.
28
670C>T
F
12% a
ND
17%
-
-
+
ND
1833delT
F
10% a
ND
66%
+
+
+
+
-
F
9% a
8, 9, 18, 19
-
-
-
+
-
None b
None
39–51%
-
+
+
+
8
ND
+
+
ND
ND
8
-
-
+
+
ND
-
+
+
ND
[2006] [a]
Matsuura et al.
29
[2006] [b]
30
Micale et al. [2007]
8,2, others
31
Miller et al. [1990]
M
78% a
None a,b
32
Nakamura [1985]
F 16 months
33
Nash et al. [1997]
34
Newman et al. [2003]
35
Papi et al. [1989] [a]
M
36
Papi et al. [1989] [b]
F
37
Pinson et al. [2013]
2211-2insGTTA
F 4 months
3035T > C
16%
83% a
ND b
-
M 3 months
8
14% a
None a
-
3% b
ND
-
15-20% a/b
8,18,7
-
-
+
+
+
15-20% a/b
8,18,7
-
-
+
+
+
+
ND
-
-
-
+
+
F
12% a
8, 18
47%
+
+
+
+
F
28% a
91%
-
+
+
+
F 42 years
15% a
44-51%
+
+
+
+
-b
80%
c.915_925dup11
c.915_925dup11
38
Plaja et al. [2001] [a]
IVS10-1G > T
1649G > A
39
Plaja et al. [2001] [b]
40
Plaja et al. [2001] [c]
41
Plaja et al. [2003]
2726T > C
IVS10-1G > T
19
Prenatal
51% c
7, 15
43%
ND
ND
ND
ND
M
ND
Multiple
ND
ND
ND
ND
ND
X,8,18
60%
-
+
+
+
-
-
+
+
+
-
+
+
+
-
+
+
+
1649G > A
42
Rosensaft et al. [1999]
43
Scheres et al. [1986]
F
15% a
44
Tolmie et al. [1988] [a]
-
F 2.2 years
35-84% a
45
Tolmie et al. [1988] [b]
-
M 3 days
28% b
46
Warburton et al. [1991]
F
18
2, 21
4-30% a
18
-
7% b
ND
-
6–20% a
8,18,2,12,X a/b
ND
4–42.4% b
ND
a, lymphocytes; b, fibroblasts; c, amniocytes
MC, microcephaly; GR, growth retardation; MR, mental retardation
Sources: [2]–[5], [7], [8], [72]
22
12. Supplementary Table 2: Other clinical findings MVA patients
#
Reference
Mutations BUB1B
1
Callier et al. [2005]
Dysmorphic face
2
Chen et al. [2004] [a]
Hypertelorism, thin upper lip, low-set ears, broad and flat nasal bridge, overriding toes
3
Chen et al. [2004] [b]
Oligohydramnios
4
D’Agostino et al. [2000]
Escavated chest, hypospadia, cryptorchidism, hepatosplenomegaly
5
Flejter et al. [1998] [a]
Café au lait spots
6
Flejter et al. [1998] [b]
Ccafé au lait spots
7
Garciá-Castillo et al. [2008] [a]
-
Mutations CEP57
c.520_521delGA
Other clinical findings
Occipital prominence, frontal bossing triangular face, micrognathia
c.915_925dup11
8
Garciá-Castillo et al. [2008] [b]
-
c.520_521delGA
Occipital prominence, frontal bossing triangular face, micrognathia
c.915_925dup11
9
Hanks et al. [2004] [a]
2211-2insGTTA
10
Hanks et al. [2004] [b]
-
11
Hanks et al. [2004] [c]
2211−2insGTTA
Eye abnormality, multicystic kidney, lissencephaly, bilateral hip dysplasia, clinodactyly
2441G > A
c.241C>T; p.R81X
Mild facial dysmorphism, seizures
c.241C>T; p.R81X
Atrial septal defec, pulmonary stenosis, hypothyroidism, anemia
3035T>C
12
Hanks et al. [2004] [d]
IVS10−1G T
ND
1649G A
13
Hanks et al. [2004] [e]
14
Jacquemont et al. [2002]
15
Kajii et al. [1998] [a]
-
Seizures
Lymphoblastic leukemia
1833delT
16
Kajii et al. [1998] [b]
17
Kajii et al. [2001] [a]
IVS10-5A > G
18
Kajii et al. [2001] [b]
107G>A
19
Kajii et al. [2001] [c]
1833delT
20
Kajii et al. [2001] [d]
1833delT
21
Kajii et al. [2001] [e]
22
Kawame et al. [1999]
1833delT
23
Lane et al. [2002]
c.915_925dup11
Occipital prominence, bilateral cataract, depressed nasal bridge, midface hypoplasia,
hypertelorism, low-set ears, cleft palate, Dandy-Walker, Wilms tumor, seizures
Closed fontanel, bilateral cataract; low-set ears; micrognathia; a short neck; a short
sternum; ambiguous genitalia with a small penis with the urethral orfice at its base; a
bifid scrotum; undescended testes; Dandy-Walker cyst with hypoplasia of the cerebellar vermis; cerebral oligogyria; seizures
Partial hypoplasia of the cerebellar vermis, a prominent cisterna magna, an enlarged
posterior fossa, Wilms’ tumor at age 8 weeks, clonic seizures,
Hypoplasia of the brain, agenesis of the corpus callosum, Dandy–Walker complex type
A, Wilms’ tumor at age 10 months, bilateral cataracts, internal hydrocephalus with
brain atrophy, seizures
Dandy–Walker complex type A, hydrocephalus, hypoplasia of the brain, partial agenesis of the corpus callosum, urinary tract botryoid rhabdomyosarcoma at age 7 months,
suspected Wilms’ tumor treated with chemotherapy, seizures,
Dandy–Walker complex type B, enlarged ventricles, hypoplasia of the brain, hypoplasia of the corpus callosum, multicystic lesions in bilateral kidneys, clonic seizures,
death at age 7 months of hemorrhage into the tumor, polycystic nephroblastoma at
postmortem examination
Bilateral cataracts, right microphthalmia, hypotonia; hypoplasia of the brain, Dandy–
Walker complex, clonic seizures, Wilms’ tumor at age 7 month
Hypertelorism, exophthalmos, corneal opacities, cataracts, broad nasal bridge, upturned nasal tip, short neck, Wilms tumor, Dandy-Walker, seizures
Hearing impairment; sleep apnea
c.915_925dup11
24
Limwongse et al. [1999] [a]
580C > T
Mild malar hypoplasia, upturned nasal tip, smooth filtrum, cryptorchidism, rhabdomyosarcoma, clinodactyly
2530C > T
2763G > C
25
Limwongse et al. [1999] [b]
26
Limwongse et al. [1999] [c]
2211−2insGTTA
Multicystic kidney
2441G A
2211−2insGTTA
Atrial septal defect; pulmonary stenosis, hypothyroidism, anemia
3035T C
23
Hypodysplasia of the brain, Dandy–Walker anomaly, hypoplasia of the corpus callosum, seizures, Wilms’ tumor at age 9 weeks
27
Matsuura et al. [2000]
28
Matsuura et al. [2006] [a]
670C>T
Annular pancreas
29
Matsuura et al. [2006] [b]
1833delT
Cataracts, Dandy-Walker, Wilms tumor, rhabdomyosarcoma
30
Micale et al. [2007]
-
31
Miller et al. [1990]
32
Nakamura [1985]
33
Nash et al. [1997]
Epicanthal folds, exotropia, hypotonia, hydronephrosis, small hands/feet, tapering fingers
Combined immune deficiency, seizures ambiguous genitalia, dysmorphic facial features, clinodactyly, flat broad nasal bridge, low-set ears, horizontal nystagmus, hemangiomata simplex on the forehead
Bilateral cystic nephroblastomas, Dandy-Walker syndrome, bilateral cataracts, and
cerebellar heterotopia
Corneal opacities, glaucoma, micrognathia, pulmonary stenosis, anemia, clinodactyly,
hypothyroidism
2211-2insGTTA
3035T > C
Temporal bossing, deep set eyes, short palpebral fissures, rhizomelic shortening, clinodactyly, cardiac septal defect, aortic coarctation, duodenal atresia, abnormal lung loculation
34
Newman et al. [2003]
-
35
Papi et al. [1989] [a]
Seizures
36
Papi et al. [1989] [b]
Seizures
37
Pinson et al. [2013]
c.915_925dup11
Deep set eyes, Ears anomalies, Small mouth/micrognatia, Rhizomelic shortening, Single palmar crease/clinodactyly
c.915_925dup11
38
Plaja et al. [2001] [a]
IVS10-1G > T
Convergent strabismus, thin upper lip, square shaped ears, hemangioma, thumb adduction, rhabdomyosarcoma, cyst in posterior fossa
1649G > A
39
Plaja et al. [2001] [b]
40
Plaja et al. [2001] [c]
2726T > C
Horizontal nystagmus, vermis hypoplasia, ventriculomegaly, colpocephaly
41
Plaja et al. [2003]
42
Rosensaft et al. [1999]
43
Scheres et al. [1986]
44
Tolmie et al. [1988] [a]
-
Occipital prominence, small jaw, quadriplegia, seizures
45
Tolmie et al. [1988] [b]
-
Occipital prominence
46
Warburton et al. [1991]
ND
IVS10-1G > T
ND
1649G > A
ND
Primary amenorrhea
Flat broad nasal bridge, low-set ears, myopia, esotropia, atopic dermatitis, seizures
Sources: [2]–[5], [7], [8], [72]
24