Download End semester examination BSE652, Developmental Biology 21

End semester examination
4:00 PM
BSE652, Developmental Biology
21-4-2015, Tuesday,
Question 1, 2 and 7are compulsory. Attempt any one question between 3 and 4 and 5 and
6 respectively. Please be brief and to the point when answering questions.
Question 1: (15 points)
For proportionate growth of limbs the signaling pathways that regulate
development/growth along one axis or the other must cross-talk. Cite one such example in
the case of early limb bud development. The answer must have a schematic with bullet
points and no more than 4-5 sentences explaining the schematic and connecting the bullet
points. Unnecessarily long answers will be penalized.
Question 2: (20 points)
Match the items listed on the left hand column (a-j) with the most appropriate item in the
middle column (1-10) and in the right hand column (i-x). Also provide a justification for each
match. Only one item the left will be the best match with one item in the middle and one item
on the right. All three correctly matched with the correct justification provided will be
awarded +2.
a. Ultraviolet radiation
treatment in anterior
of egg
b. Epithelialmesenchymal
transition
c. Anterio-posterior
polarity
d. Posterior blastema
e. Teratogen
f. Proximo-distal
polarity
g. Evolution of the
forelimb of bats
h. Dorsal blastopore lip
i. Ultraviolet radiation
treatment of egg
j. Heterometry
in
evolution
1.
FGF
i
Embryo is ventralized
2.
Retinoic acid
ii
Apical ectodermal ridge
3.
Wnt 11
iii
Develops into a head
4.
5.
6.
7.
Inhibition of BMP
iv
Bicoid
v
Downregulation of cell vi
adhesion molecules
Sonic Hedgehog
vii
8.
9.
High amount of BMP
Inhibition of Wnt activity
viii
ix
Failure of neural
migration
No Apoptosis
Embryo with two tails
10.
Noggin
x
Wide and deep beak
Rescue of ventralized embryo
Zone of polarizing activity
Cancer stem cells
Please attempt any ONE question between Questions 3 and 4:
Question 3: (40 points). The freshwater lakes of Mexico have a species of fish which has two
variants. One is the surface variety and is present in the lakes and the other is the cave variety
as it is present in water filled caves underground. These surface and cave varieties differ in
many ways one of which is the absence of pigments in the cave variety.
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crest
A) Describe the method that you would use to identify the gene which might be
responsible for this lack of pigment in the cave variety. (16 points)
B) You find that this identified gene is an enzyme essentially required for synthesis of a
neurotransmitter in certain neurons as well as being required for synthesis of pigment
in melanocytes. Provide a possible explanation of how this gene could be associated
with loss of pigmentation in the cave variety. (12 points)
C) How would you demonstrate that the gene you have identified is the one associated
with lack of pigment formation in the cave variety? (12 points)
Question 4: (40 points)
The figure below shows the genes and their relationship to one another with respect to
establishment of dorsal-ventral polarity in the Drosophila embryo. A) Shows events in the egg
chamber and B) in the perivitelline space and the ventral side of the embryo. Please answer
the following questions based on this information.
A)
Devise
a
set
of
experiments which can be used to
distinguish which of the above
mentioned genes are maternal
effect genes and which of them
are required in the zygote.(8
points)
B)
The events in panel A are
separated in time and space than
those in panel B. Explain the
mechanism by which information
regarding the dorsal-ventral
identity of the embryo is
transferred from A to B. (8 points)
C) Some of the genes in the above two panels are required in the follicle cells (somatic
tissue) and others in the oocyte (germline). Describe a method to demonstrate which
ones are required to be somatically provided and which ones are required to be
provided by the germline. (12 points)
D) Provide explanation of how injection of perivitelline fluid from a Toll mutant embryo
into gd embryos produces ventral structures at the site of injection. Hint: GD
(gastrulation defective) binds to sulphated vitelline membrane proteins on the ventral
side. Bound GD then binds to and activates Snake, which then binds and activates
Easter by cleaving it. Activated Easter cleaves Spatzle to activate it. Toll is the receptor
for cleaved Spatzle. (12 points).
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Please attempt any ONE question between Questions 5 and 6:
Question 5: (20 points) A small molecule “X” is acting as an agonist for a endogenous
hormone “Y”. This hormone other than being required in the adult is also required for the
normal development of reproductive organs in the vertebrate embryo. Y is synthesized by an
enzyme Y-synthase and is inactivated by another enzyme Y-hydrolase. The amount of “Y” is
very strictly controlled during development through feedback mechanisms that regulate the
transcription of Y-synthase and Y-hydrolase. It was observed that if the developing embryo is
exposed to X then reproductive organs are not formed properly. Surprisingly, in loss of
function mutants of Y-synthase the same phenotype is observed.
A) Do you think X is acting as a “teratogen” or an “endocrine disrupter”? Explain your
answer by highlighting the differences if any between teratogens and endocrine
disrupters. (8 points)
B) Explain the observation that exposure to “X” leads to the same phenotype as loss of
function of Y-synthase. (12 points)
Question 6: (20 points)
Unlike the flatworm where the regeneration blastema tissue comes from pluripotent stem
cells, in the salamander most of the regeneration blastema appears to arise from
dedifferentiation of adult cells followed by cell division and redifferentiation of those cells
back into their original cell types. The blastema is not simply a collection of homogenous fully
dedifferentiated cells, in fact the blastema cells keep a “memory” of what they have been.
A) Devise an experiment to show that the dedifferentiated cells of the blastema indeed
keep a memory of what they have been. (10 points)
B) Devise an experiment to find out if in the salamander the newly regenerated limb
tissue is only coming from dedifferentiation of differentiated cells or if adult stem cells
present in the limb contribute to it at all. Hint: You can use any of the techniques that
you have been taught before the mid-semester examination. (10 points).
Question 7: (5 points)
The adjoining figure depicts
experiments
where
transplantation of dorsal lip from
early gastrula to blastocoel of
another early gastrula led to
formation of secondary heads (E).
Whereas transplantation of dorsal
lip from a late gastrula to and early
gastrula led to formation of
secondary tails (F). What can be
concluded from this experiment? Describe an experimental approach that you can use
to isolate the gene products responsible for the induction of secondary heads and tails
respectively.
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