Download Bi117 problem set 4 Grader: Benji Uy Handout: March 1, 2016 Office

Bi117 problem set 4
Handout: March 1, 2016
Due: March 8 , 2016
1)
Grader: Benji Uy
Office hours: Monday 4:30-6:30 pm
Beckman Institute Room #11
In the chick embryo:
A) 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)
B) Based on the figure above, what important natural product is important in
specifying the posterior cardiac precursor cells? (0.5pt)
C) 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? (1 pt)
2)
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.
A) 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)
B) 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 mitochondriallyinduced apoptosis (Aiyer, 2005). What does this suggest about the role of Hand2 in
ventricular formation? (1pt)
3)
Polydactyly is a conditions that an individual has 6 or more digits. It is thought that
there is an error in Shh signalling or in downstream genes.
A) Design experiments to identify potential genes directly activating or repressing shh
in those tissues if you know transcription factors expressed in the digits? How can
you see if the result of this mutation is due to cell death or increased cell
proliferation? (2pt)
B) Why would you speculate that Polydactyly is most commonly seen on finger 1
(thumb) and finger 5 (pinkie). (0.5 pt)
C) Assuming normal limb development and similar development to frog, in a three
toed sloth, how would you change the middle digit (digit 2) into another first digit?
Can this method change digit 3 into digit 2? (0.5 pt)
4)
Commonly, umbilical cords are being kept at birth. Explain how, in terms of
regeneration, this can be useful in the future. If this could be used for regeneration,
what “type of regeneration” would this fall under? (1 pt)
5)
A)
Describe the “key checkpoints” in amphibian limb regeneration (1 pt)
B)
If a digit were cut off and soaked in maximum dose retinoic acid, what would
you expect based on the information provided? What if the digit wound was
covered with a CD59 bead?(1 pt)