This exam has 5 pages and a total of 50 points. You will have 90 min. to complete it. Answer all short answer questions as briefly as possible. Make sure your name and id number are on all pages (1 point for doing this!)
1. Briefly define each of the following (6 points):
netrin:
stem cell:
angiogenetic cell cluster:
intramembranous ossification:
coelom:
myotome:
2. Circle the appropriate response (T = true, F = false) for each of the following statements (5 points):
| Melanocytes form from neural crest cells that migrate through the posterior half of somites |
T F |
| In mammals, the embryonic endoderm forms from the hypoblast |
T F |
| In vertebrates, the lungs originate as simple outpocketings of endodermal tissue |
T F |
| The umbilical artery is important in mammals because it carries oxygenated blood from the placenta back to the fetus |
T F |
| Apoptotic elimination of neural crest cells in the trunk helps to determine which neural crest cells form cartilage structures |
T F |
| Spina bifida results from incomplete closure of the anterior neuropore |
T F |
| The steel mutation generates its characteristic phenotype because cells that normally produce melanocytes have insufficient quantities of one type of growth factor receptor |
T F |
| Unlike in the Xenopus gastrula, the superficial epithelial cells in a zebrafish gastrula do not involute |
T F |
| Lacunae form within the cytotrophoblast, allowing gas exchange between the maternal and fetal blood supplies |
T F |
| Erythropoeitin is crucial for the formation of vascular endothelial cells during development of the vasculature in vertebrates |
T F |
3. Complete the following table referring to extraembryonic membranes in amniotes (6 points).
|
Membrane
|
Type of mesoderm that contributes to it
|
Major function(s) in birds
|
Major function(s) in placental mammals
|
|
Amnion
|
|
|
|
|
Chorion
|
|
|
|
|
Yolk sac
|
|
|
|
|
Allantois
|
|
|
|
4. For each phrase referring to various morphogenetic movements on the left match ALL appropriate response(s) drawn from the column on the right. Note: in some cases, the correct answer will require more than one choice from the right-hand column. If none of the answers on the right are appropriate, write "none" (6 points).
| Characteristic |
Tissues |
| a. undergoes convergent extension_______ |
1. Deep cells of the dorsal non-involuting marginal zone of Xenopus |
| b. undergoes invagination______ |
2. Dorsal embryonic shield of zebrafish gastrula |
| c. undergoes ingression _________ |
3. Neural plate of salamanders |
| d. undergoes involution ________ |
4. Sea urchin primary mesenchyme cells |
| e. uses directed migration via filopodia or lamellipodia__________ |
5. Chick epiblast |
| |
6. Human optical vesicle |
| |
7. Mouse trunk neural crest cells |
5. You have discovered that some species of frog that are disappearing from tropical forests worldwide appear to develop defects during gastrulation.
a. Your colleague showed that healthy embryos from these species gastrulate in a manner very similar to Xenopus embryos. Based on your friend's results, describe how the overall shape of the prospective dorsal involuting marginal zone (IMZ) should change during gastrulation (2 points):
b. You believe that fibronectin may play a role similar to that in salamanders. What distribution of fibronectin would you expect to see when you immunostain healthy gastrulae from the tropical species? Assume all appropriate reagents are available (2 points).
c. Describe an experiment that you could perform to test whether fibronectin is required for successful completion of gastrulation in the tropical species. Assume all appropriate reagents are available (2 points):
6. Trunk neural crest cells of veterbrates give rise to many different types of tissues in vertebrates.
a. Describe two experiments that suggest that neural crest cells are pluripotent that do not involve the use of cells cultured in vitro (4 points):
b. Mutations in the c-kit homologues in mouse and humans result in defects in neural crest derivatives. Based on what you know about the molecular identity of c-kit, briefly provide a cellular explanation for the observed defects (2 points)
7. For each embryonic brain region listed on the right, indicate which structure on the left is generated from it. If none is appropriate, write "none" (3 points).
| Structure |
Embryonic brain region |
| 1. cerebellum__________ |
a. Prosencephalon |
| 2. pons_____________ |
b. Mesencephalon |
| 3. lens of the eye___________ |
c. Rhombencephalon |
| 4. neural crest of the pharyngeal arches___________ |
|
| 5. dorsal root ganglion__________ |
|
| 6. medulla__________ |
|
8. Growth factors and hormones are thought to be important for proper formation of the skeleton in vertebrates.
a. Describe one piece of evidence that indicates that the proper formation of skeletal elements depends on peptide growth factor signaling in the vertebrate embryo (2 points)
b. You read in the newspaper that Olympic weightlifters in lower Slobovia are using recombinant human growth hormone to improve bone strength. Why might this be a bad idea? (1 point)
9. Eph receptor tyrosine kinases and their ligands, the ephrins, are thought to be important during formation of connections between retinal axons and the optic tectum in the chick. The basic structure of the retina and tectum and their normal connections are shown in the diagram for reference.
a. Describe an experiment in vitro that demonstrates that retinal neurons respond to molecules expressed on the surface of tectal cells. Be sure to indicate the nature of the response (i.e., whether it is repulsive or attractive). (3 points)
b. Based on what you know about the distribution of Eph receptors and ephrins in the retina and tectum, are these molecules distributed in a manner consistent with them playing a role in retinal-tectal guidance? Explain your answer. (3 points)
c. The guidance of commissural neurons by the floor plate in the vertebrate spinal cord appears to operate in a different manner from the Eph/ephrin system. How do the two systems differ? (2 points)
