Download Bi117 problem set 4 Grader: Jon

Bi117 problem set 4
Due: Tuesday, March 11,2014
Grader: Jon Schor and Monisha Dilip
Jon OH: Monday, 2PM-3PM Red door
Jon OH: Monday, 1PM-2PM Red door
I. Heart Development (7pts)
a.
In the chick embryo:
i. Briefly describe the morphogenetic steps by which the early two-chambered
heart tube is able to develop into a functional four-chambered organ and the
changes that occur in each step. What overall change in polarity does the heart
undergo? (0.5pt)
Figure 1. At stage 7, retinaldehyde dehydroxylase-2 is expressed in the posterior mesoderm (Blentic et al. 2003)
ii. Based on the figure above, what important natural product is important in
specifying the posterior cardiac precursor cells? (0.5pt)
iii. Before the posterior cardiac precursors enter this realm as seen in the figure,
their fates are not fixed. As transplantation or rotation experiments show these
cells have a greater developmental potential in which they can regulate and
differentiate in accordance with a new environment. Explain what this realm
accomplishes, with respect to these specific precursors, in heart formation,
from their initial migration to complete differentiation. Also, in terms of
developmental fate, what happens to these precursors when they enter this
realm? (2 pt)
b.
Mouse embryos that lack the essential transcription factor Hand2 die at
embryonic day 10.5 from right ventricular hypoplasia and vascular defects, while mice
that lack the related gene hand1 die at embryonic day 8.5 from placental and extraembryonic abnormalities.
i.
Given that embryonic lethality precludes analysis of the role of Hand1 and
Hand2 during the later stages of cardiac development, describe one way
in which you could circumvent this problem. (1pt)
ii.
It is possible to delay the embryonic lethality in mice caused by Hand2 null
mutants through repression of the gene Apaf1, a downstream regulator of
mitochondrially-induced apoptosis (Aiyer, 2005). What does this suggest
about the role of Hand2 in ventricular formation? (1pt)
iii.
Interestingly, Nkx2.5 regulates both the Hand1 and Hand2 transcription
factors. Though both Hand proteins are actively transcribed in the early
heart tube, as looping commences, Hand1 becomes restricted to the
future left ventricle and Hand2 to the right. How is left/right asymmetry
established in heart formation? Specifically, what two major factors are
involved in the distinction of these two sides and what is the path that
leads to this point of distinction in the developing mouse embryo? (2pt)
II. Limb Development (3pts)
a.
In the developing chick limb bud, replacement of the ZPA with tissue from the
notochord results in the rescue of the limb. What signaling molecule could be
responsible for this rescue? Design a similar rescue experiment with a
cellular/molecular method, testing specifically the possible signaling molecule.
(1pt)
b.
The difference between the feet of a chicken and a duck is the presence of
webbing. What type cellular process is responsible for the freeing of the digits.
You are interested in generating a chicken with feet like a duck. Design an
experiment in which the resulting morphology of the feet exhibit inter-digital
webbing like that of a duck. (1pt)
Figure 2. Whole-mount forelimb from 10-12 day chick embryo (Honig 1981).
c.
From the picture above, explain what experiment resulted in this unusual limb
morphology in the developing chicken. (1pt)