Problem Set 3
Due Feb. 25, 2014
Graders: Stan (sschor@caltech.edu) and Jing (jjxu@caltech.edu)
Office hours:
Stan: Friday 3-4 PM, Monday 3-4 PM at Red Door
Jing: Sunday, 2-3 PM, Monday 3-4 PM at Red Door
Note: Do not use the Internet to answer these questions. It is good practice for the final,
which is open book and notes but no Internet.
1. Which tissues are involved in neural crest induction? Is there a way to induce neural
crest in the absence of one of these tissues? (.75)
2. There is evidence that suggests neural crest fate is determined before they migrate to their
final location, but there is contradicting evidence that suggests their fate is determined by
their environment. How is this possible? Briefly describe some of the evidence that
supports each view. (1)
3. You’re studying the anchor cell in C. elegans, which uses signaling molecules to induce
the fate of adjacent cells. C. elegans mutants that have a deficient anchor cell lack vulvas.
a. Given a collection of cells which you know induces the anchor cell, how would
you deduce which cell is the anchor cell? (1)
b. You’ve narrowed the anchor cell-signaling molecule down to two molecules, both
of which seem to be expressed in the cell population. How would you test which
of the two molecules gives the anchor cell its inductive ability? (1)
c. Now that you have figured out which cell is the anchor cell and the likely
signaling molecule, you’d like to know when and where the signaling molecule is
expressed. How would you do this (techniques using either mRNA or protein are
acceptable)? (1.25)
4. A theory in evolutionary development postulates that the insect hexapod body plan
evolved from crustacean-like ancestors.
a. Look at the figure below and propose a theory to explain how such changes in
homeotic gene expression can give rise to a hexapod body plan. Would
expression changes of Ubx and abdA alone account for the shift to a hexapod
body plan or would there need to be other changes to one or both of these genes
as well? (1)
b.
You want to know if the Drosophila and Artemia homeotic genes have a new
function or if the change in the expression pattern is enough to cause a change to a
hexapod body plan. You decide to make transgenic flies which either have a
DmUbx or a AfUbx expressed in the thorax, where normally only Antp is
expressed, using an arm-Gal4 construct (arm is thorax specific promoter). You
find that both Ubx proteins are able to induce abdominal features in the thoracic
segments. You also observe that DmUbx is 90 % better at suppressing leg
development than AfUbx. What do these finding suggest? (1.25)
Dm= Drosophila melanogastar Af = Artemia franciscana
c. Describe how DmUbx might suppress leg formation. Design an experiment to
uncover the molecular target of this new leg suppressing function. You do not
need to name specific targets. (1.25)
d. Design an experiment to investigate which changes in the Ubx gene are
responsible for this difference in the ability to suppress leg formation. The
genomes of both organisms have been sequenced so you have access to genome
and protein sequence information. (1.5)