BIO403
DEVELOPMENTAL NEUROBIOLOGY
MID-TERM TEST
FEBRUARY 15, 2003
6- 7:30 PM
There are two parts to this test
Do not separate the pages
Instructions:
Answer all questions
4 written questions
20 multiple choice questions
You may use the back of the page
You may use diagrams
PART A 25 MARKS
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PART B 20 MARKS
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TOTAL 45 MARKS
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1) You are interested in the signaling molecules that mediate dorsal-ventral polarity of the
vertebrate neural tube. You have discovered a new ligand (called Quasimodo) that you think
mediates dorsalization, but not ventralization, of the neural tube. Using approaches discussed in
class, design an experiment and describe the results that could support this point of view. [5
marks]
Possibilities:
A) dissect intermediate neural tube tissue and culture. We know exposure to Shh will cause
ventralization, that Shh + BMP will cause dorsal markers. Therefore adding shh + Quasi should
cause dorsal markers if Quasi is important for dorsalization. Dorsal markers might include pax7,
which is normally restricted to dorsal aspect of neural tube.
B) Generate a knockout mouse for Quasimodo and observe neural tube development versus
controls. Quasi -/- mice should have defects in dorsal neural tube and might have a completely
ventralized neural tube eg might expect lack of Pax7 and excess Nkx6.1
C) could try to use interfering antibodies that would disrupt interaction between Quasimodo and
its receptor. Need to observe neural tube development and observe distribution of dorsal and
ventral markers as in B
2) Discuss the idea that individual neuroblasts acquire some of their unique properties by way of
their position in the anterior / posterior axis. Use the developing Drosophila nerve cord and the
vertebrate hindbrain to provide specific examples. Short forms of gene names are acceptable. [8
marks]
Points to include:
Drosophila:
General notion of A/P axis formation – maternal, gap, pair rule, segment polarity genes ( and
hox)
Segment polarity genes divide each hemisegment into 4 rows (en, wg, gsb, hh)
Ind, vnd, and mash (homeobox genes) divided the segments into columns.
Now the hemi-segments are dived into 4x3 array and each neuroblast arising in this array will
have a unique transcription factor profile.
Vertebrate:
The vertebrate hindbrain is segmented into rhombomeres r1-r8
Members of the Hox gene families are differentially expressed in each of the rhombomeres.
Thus position along the A/P axis is important for detemining which Hox genes are found there.
Unique neural populations arise from the rhombomeres and produce distinct nerves with distinct
target.
Examples: Hox 1 paralogs are confined to r4, hox 2 are found at highest levels in r2,3,4 and 5,
hox 3 highest in r5,6,7,8 and hox 4 in r7,8
Example genetic knockout of Hox a1 leads to loss of r5 and reduction of r4, and alterion in the
nerves, loss of abducens nerve, smaller facial nerve.
3) You discover a new gene involved in neural development which you call Einstein. You have
alleles of this gene which cause loss of the protein, and excess protein. How would you
determine if this gene belongs to the family of neurogenic or proneural genes? [4 marks]
Examine alleles of Einstein for number of neurons; distinguishing between the phenotypes
allows Einstein to be classified
If Einstein is a neurogenic gene than the loss of Einstein allele should have too many neurons,
excess Einstein could potentially have too few neurons
If Einstein is a proneural gene than loss of Einstein should have fewer (no) neurons, while the
excess Einstein allele should have too many neurons.
That is, expect opposite phenotypes for neurogenic or proneural alleles.
4) Comparing ipsilateral and contralateral axon projections provides a useful model for axon
guidance studies.
A) Describe the molecular mechanisms that are thought to be important for axon guidance across
the Drosophila midline. Include both ipsi- and contralateral projection neurons. [6 marks]
B) What is a major difference in the mechanisms used in Drosophila and vertebrate contralateral
projections? [2 marks]
Netrin is attractive cue that guides axons to the midline
Slit is repulsive cue expressed by midline cells that acts through robo receptors
Presence or absence of robo helps determine whether growth cones cross midline or not
Commissureless is a protein that regulates Robo on GC surface. When comm is active Robo is
diverted from surface.
Ipsilateral projecting neurons do not have comm. Therefore robo IS present in the GC surface.
These GCs initially attracted to midline by netrin but do not cross due to robo/slit repulsion.
They take a longitudinal course.
Contralateral – initially these GCs have active Comm, therefore Robo is diverted from surface
and are insensitive to Slit. GCs attracted to midline by netrin and cross midline. However, upon
crossing the midline, the GCs regain sensitivity to slit and do not re-enter the midline area.
2)
verts do not seem to have a Comm homolog
instead in verts – Robo3 inhibits Robo 1, regulating Robo1 lower in contralateral projecting
axons.
1) Transition of the developing embryo from blastula to gastrula is characterized by what?
A. Fertilization
B. Neural plate involution
C. Meiotic nuclear divisions
D. Formation of germ layers
2) A loss of function mutation in the Drosophila dorsal gene would result in:
A. A dorsalized embryo
B. A ventralized embryo
C. Redistribution of bicoid
D. A healthy fruit fly
3) in situ hybridization is a useful technique for visualizing?
A. mRNA distribution
B. Protein distribution
C. The amount of protein expressed
D. DNA distribution
E. All of the above
4) The achaete gene functions to:
A. Establish dorsal-ventral polarity
B. Identify the neurogenic region
C. Inhibit neighbouring cells from becoming neurons
D. Specify a proneural cluster
E. None of the above
5) Establishing the neurogenic region of Drosophila requires the action of:
A. Maternal dpp
B. Inhibition of sog
C. Activation of SoxN
D. Zygotic shh
6) Dorsal-ventral patterning occurs under the action of dpp and sog because:
A. Sog inactivates dpp
B. Dpp inhibits sog translation
C. Dorsal activity is inhibited by dpp
D. Dorsal activates SoxN
7) Evidence that sog activates and dpp represses SoxN includes:
A. Loss of SoxN expression in sog loss of function mutants
B. Loss of SoxN in dpp overexpression mutants
C. Loss of SoxN expression in dpp loss of function mutants
D. A and B
E. A, B, and C
8) The lateral inhibition model of neuroblast selection suggests that:
A. Mesoderm is a dominant fate
B. Neural cells are the default fate in the neuroectoderm
C. Epidermal cells are the default fate in the neuroectoderm
D. Endoderm is important for neural cell fates
9) Proneural gene expression is regulated by:
A. SoxN
B. Homeobox transcription factors
C. Notch signaling
D. All of the above
E. None of the above
10) A key factor in the ability of Notch signaling to inhibit cells from becoming neurons is:
A. Notch is repressed in the receiving cells
B. Su(H) is inactivated by E(spl)
C. Delta expression is activated by proneural genes
D. Notch activated in sending cells
11) Neuroblast cell division is characterized by:
A. Symmetric cell division
B. Asymmetric localization of some proteins
C. Mitotic recombination
D. Production of neurons and glia
12) Transplantation of an extra notochord near the vertebrate neural tube will result in:
A. no change
B. an extra roof plate
C. an extra floor plate
D. fewer motor neurons
13) Sonic hedgehog regulates neural identity in the neural tube by:
A. concentration gradient
B. activation of transcription factors
C. repression of BMPs
D. A and B
E. A, B, C
14) A naturally occurring gradient of retinoic acid (RA) in the developing vertebrate nervous
system helps to create an anterior posterior pattern because a high concentration of RA:
A. Represses anterior Hox genes
B. Activates anterior Hox genes
C. Represses posterior Hox genes
D. All of the above
E. None of the above
15) Dynamic microtubules are essential for:
A. Filipodia retraction
B. Growth cone turning
C. Forward growth cone movement
D. Filipodia extenision
16) Which cell adhesion molecule(s) have the potential to affect directly the actin cytoskeleton?
A. NCAM
B. NrCAM
C. Integrin
D. Fibronectin
E. All of the above
17) Netrins can mediate both repulsive and attractive cues because they:
A. Bind to multiple receptor types
B. Do not contribute actin dynamics
C. Equalize the ratio of g-actin and f-actin
D. Promote stable microtubules
18) Regulation of small GTPases by GAPs results in:
A. increased actin branching
B. faster activation of GTPase activity
C. capping of f-actin
D. slower removal of GDP
19) The signal transduction pathway for the Slit / Robo ligand receptor complex may include:
A. Rac
B. Cdc42
C. Rho
D. A and B
E. A, B and C
20) Semaphorin3A causes growth cone collapse by:
A. Reducing the activity of profilin
B. Increasing cofilin activity
C. Reducing the amount of filipodial F-actin
D. Increasing the amount of stable microtubules in lammelipodia
END OF TEST
E. A, B and C