X Chromosome Inactivation

advertisement
X Chromosome Inactivation
Peters et al. Nature Genetics 30, 77 – 80 (2002)
X Chromosome Inactivation
• X chromosome inactivation occurs early
during development – around 24 cell
• Thus, females embryos have two active X
chromosomes until one is inactivated
X Chromosome Inactivation
Probe: anti-4x-methylH3-K9
What is this males karyotype?
What Determines X-chromosome
Inactivation?
X Chromosome Inactivation
• Mechanism of X Chromosome inactivation
• XIC – X chromosome Inactivation Center
• XIC controls expression of the XIST gene
• XIST: X-inactive-specific transcript
• XIST produces a non-coding 17 kb RNA molecule
• “Coats” the entire local X-chromosome – cisacting
EMBO Rep. 2007 January; 8(1): 34–39.
doi: 10.1038/sj.embor.7400871.
X Chromosome Inactivation
• X chromosome inactivation
requires:
• Initial XIST RNA expression and
coating
• Association of chromatin
modifying proteins
• DNA methylation 5’ of Xchromosome genes
• Modification of histones by
methyltransferases (HMTase)
• Other chromatin modifying
proteins
X Chromosome Inactivation
• Approaches for examining XIST biology
1) Knock it out!
Nature, January 1996
XIST knockout in mouse ES cells
ES cell
Dffr
or
ES cell
Dffr
100/0
50/50
X Chromosome Inactivation
• Approaches for examining XIST biology
2) Knock it in!
Tet Repressor Model
XIST inactivation is Reversible
up to 48 hours
XIST
X
XIST
No Choice after 48 hrs
XIST
X
XIST
No inactivation after 48 hours
XIST
XIST acts Early During
Development and is Irreversible
What Controls XIST Expression?
TSIX is the Anti-Sense Strand of
the XIST gene
TSIX is the Anti-Sense Stand of the
XIST gene
Knock-down of TSIX Causes Skewed
X-Chromosome Inactivation
X
TSIX Asymmetry Governs Choice
• TSIX must be downregulated for XIST
expression on the (future) inactivated X
Chromosome
• TSIX expression must remain for XIST
downregulation on the (future) activated X
Chromosome
Human Pathology
• Without XIST, Human X Chromosome
aneuploidy is Severe
Molecular cytogenetic characterisation of a small ring X chromosome in a Turner
patient and in a male patient with congenital abnormalities: role of X inactivation.
Callen DF, Eyre HJ, Dolman G, Garry-Battersby MB, McCreanor JR, Valeba A, McGill JJ.
J Med Genet. 1995 Feb;32(2):113-6.
Ubiquitin – Amino Acid
Conservation
*
*
Ubiquitin – Nucleotide
Conservation
* * * * * * * * * * * * * * * *
*
*
Amino Acid Conservation in Critical
Domains
11_03.jpg
Errors in Protein Function
• Eg. Cystic Fibrosis
• Mutation causes loss-of-function
• High occurrence of error may be a result of a
heterozygote advantage
Nature 393, 79 - 82 (07 May 1998)
Salmonella typhi uses CFTR to enter intestinal epithelial cells
GERALD B. PIER*, MARTHA GROUT*, TANWEER ZAIDI*, GLORIA MELULENI*,
SIMONE S. MUESCHENBORN*, GEORGE BANTING†, ROSEMARY RATCLIFF‡,
MARTIN J. EVANS§ & WILLIAM H. COLLEDGE‡
11_07.jpg
11_09.jpg
11_10.jpg
11_10_2.jpg
11_10_3.jpg
11_16.jpg
11_16_2.jpg
11_11.jpg
11_11_2.jpg
11_12.jpg
11_13.jpg
11_05.jpg
11_05_2.jpg
Huntington’s Disease
• CAG repeat codes for glutamine (Q)
• polyQ located near the N-terminus of
Huntingtin protein
• Expansion in the coding region of the gene
(unlike, for eg. FMR1 – Fragile X
syndrome - expansion is in 5’ UTR )
Huntington’s Disease
MATLEKLMKA
QPLLPQPQPP
PEFQKLLGIA
APRSLRAALW
FGNFANDNEI
LVPVEDEHST
ELTLHHTQHQ
SIVELIAGGG
AASSGVSTPG
FESLKSFQQQ QQQQQQQQQQ
PPPPPPPPGP AVAEEPLHRP
MELFLLCSDD AESDVRMVAD
RFAELAHLVR PQKCRPYLVN
KVLLKAFIAN LKSSSPTIRR
LLILGVLLTL RYLVPLLQQQ
DHNVVTGALE LLQQLFRTPP
SSCSPVLSRK QKGKVLLGEE
SAGHDIITE………
QQQQQQQQQQ
KKELSATKKD
ECLNKVIKAL
LLPCLTRTSK
TAAGSAVSIC
VKDTSLKGSF
PELLQTLTAV
EALEDDSESR
PPPPPPPPPP
RVNHCLTICE
MDSNLPRLQL
RPEESVQETL
QHSRRTQYFY
GVTRKEMEVS
GGIGQLTAAK
SDVSSSALTA
PQLPQPPPQA
NIVAQSVRNS
ELYKEIKKNG
AAAVPKIMAS
SWLLNVLLGL
PSAEQLVQVY
EESGGRSRSG
SVKDEISGEL
MATLEKLMKA
QQQQQQQQQQ
AVAEEPLHRP
AESDVRMVAD
PQKCRPYLVN
LKSSSPTIRR
RYLVPLLQQQ
LLQQLFRTPP
QKGKVLLGEE
FESLKSFQQQ
QQQQQQQQQQ
KKELSATKKD
ECLNKVIKAL
LLPCLTRTSK
TAAGSAVSIC
VKDTSLKGSF
PELLQTLTAV
EALEDDSESR
QQQQQQQQQQ
PQLPQPPPQA
NIVAQSVRNS
ELYKEIKKNG
AAAVPKIMAS
SWLLNVLLGL
PSAEQLVQVY
EESGGRSRSG
SVKDEISGEL
QQQQQQQQQQ
QPLLPQPQPP
PEFQKLLGIA
APRSLRAALW
FGNFANDNEI
LVPVEDEHST
ELTLHHTQHQ
SIVELIAGGG
AASSGVSTPG
QQQQQQQQQQ
PPPPPPPPGP
MELFLLCSDD
RFAELAHLVR
KVLLKAFIAN
LLILGVLLTL
DHNVVTGALE
SSCSPVLSRK
SAGHDIITE…
QQQQQQQQQQ
PPPPPPPPPP
RVNHCLTICE
MDSNLPRLQL
RPEESVQETL
QHSRRTQYFY
GVTRKEMEVS
GGIGQLTAAK
SDVSSSALTA
Huntington CAG Repeat
P.Sudbery, Human Molecular Genetics 2nd ed, Prentice Hall.
PCR analysis of CAG repeat length in family with
Huntington’s disease
Huntington’s Disease
GFP-Huntingtin
GFP-polyQ138-Huntingtin
Xia et al., Human Molecular Genetics, 2003, Vol. 12, No. 12 1393-1403
Heterozygous knockouts are normal!
Transgenic Mouse
Trinucleotide Repeat
Polymorphism
Disease
Gene
Location
Repeat
Sequence
Normal
Repeat
Mutant
Repeat
Huntington 4p16.3
CAG
9-36
37-150
SCA1
CAG
19-36
43-81
CTG
5-36
50-4000
6p23
Myotonic 19q13
Dystrophy
Download
Related flashcards

Mitochondrial diseases

16 cards

Epigenetics

15 cards

Genes

38 cards

Medical genetics

20 cards

Genes

37 cards

Create Flashcards