This exam has 6 pages and a total of 50 points. You will have 90 min. to complete it. Make sure your name is on all pages.You will receive 1 bonus point for doing this!! Answer all short answer questions in the space provided.
1. Briefly define each of the following (5 points).
involution:
syngamy:
ICSI:
capacitation:
blastocoel:
2. Regulation of reproduction in humans involves hormonal regulation before and after fertilization.
a. Complete the following table, which refers to the approximate levels (low or high) of several hormones involved in reproduction at various times in the human reproductive cycle (3 points). Provide your reasoning in each case.
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Hormone/factor
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Stage in cycle
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Expected hormone level
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Reasoning
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human chorionic gonadotropin
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Immediately following release of oocyte from mature follicle
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luteinizing hormone
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Immediately prior to release of oocyte from mature follicle
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progesterone
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Three days after ovulation in the absence of fertilizing sperm
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b. Briefly describe how the drug RU486 acts, and why it is effective as an abortifacient. Provide molecular details where appropriate. (2 points).
3. You believe a novel sperm surface protein (which you name protein W) is required for binding to the zona pellucida during mammalian fertilization.
a. You use a variety of techniques to study protein W's function. For each piece of information you learned about protein W, state what technique you used to obtain the information. (3 points)
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Discovery
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Major Technique Used to Obtain information
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Lack of protein W gene function in mice results in sperm that cannot bind to the zona
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Protein W mRNA is not produced in any other tissue in mice expect in secondary spermatocytes and spermatids in the male testis
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In the occasional mouse sperm from a normal male that cannot bind to the zona well, protein W is in an abnormal location
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You isolate a DNA fragment from humans that corresponds to a portion of the coding region for protein W
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You discover to your surprise that the nematode C. elegans has a gene similar to the protein W gene
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You wish to block the function of the human protein W to test its function in fertilization
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b. Based on what you already know, what protein would you predict protein W interacts with in the zona? (1 point)
c. You assay sperm from male mice that lack a functional protein W gene. As expected, you discover that their acrosomal vesicles are intact, even when they are placed in contact with large quantities of zona pellucida proteins. Why did you expect this? Clearly state your reasoning (1 point)
4. The ability of sperm to bind to and fuse with eggs is a key event in fertilization, and crucial for blocking polyspermy. Please complete the following table, which asks whether or not sperm will bind to eggs under a variety of circumstances. Indicate your reasoning in the space provided (6 points):
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Type of sperm
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Type of egg
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Fertilization successful (yes/no)?
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Reasoning
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Sea urchin sperm exposed to egg jelly
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Normal sea urchin eggs from a different species
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Untreated sea urchin sperm
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sea urchin egg treated with calcium ionophore
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Human sperm directly removed from the epididymis
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human oocyte with intact zona pellucida
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Sea urchin sperm
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sea urchin egg held at -70 mV by a "voltage clamp"
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5. Answer the following questions based on your knowledge of cytostatic factor's effects on cell division.
a. If purified c-mos were injected into one cell of a two-cell embryo immediately after first cleavage, what would you predict would happen at the time of the next division? Clearly state your reasoning. (2 points)
b. Frog eggs can be artificially activated in the absence of sperm by pricking them with a needle. What would you expect would happen to levels of cytostatic factor in such an artificially activated egg? Clearly state your reasoning. (2 points)
6. Complete the following table referring to cleavage patterns in various animals.
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Animal
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Yolk distribution
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Completeness of cleavage
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Orientation of cleavage
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Ostrich
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radial (discoidal)
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Snail (a gastropod mollusc)
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holoblastic
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Human
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Sea cucumber (an echinoderm)
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7. By altering the external ionic environment or the properties of some eggs or oocytes, it is possible to study the role of signal transduction in the blocks to polyspermy and egg activation. Please answer the following questions regarding these ionic events. In all cases, briefly explain your reasoning.
a. If eggs are placed in sea water made mildly basic with ammonia in the absence of sperm, what effects would you expect on the treated eggs? (2 points)
b. A frog oocyte is injected with mRNA for serotonin receptors and allowed to undergo maturation. The oocyte is then treated with serotonin. What effects do you expect?
c. A frog oocyte is injected with a calcium chelator compound (a compound that binds to calcium ions, preventing them from moving freely within the cytoplasm) and subsequently fertilized. What effects do you expect? (2 points)
8. Circle the appropriate response (T = true, F = false) for each of the following statements, which refer to mammalian embryos (6 points):
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T
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In frog cloning experiments, the likelihood of producing a viable tadpole from a donor nucleus placed into an enucleated oocyte decreases the older the animal is from which the donor nuclei are obtained..
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F
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The inner cell mass cells of the mammalian blastocyst predominantly form the extraembryonic membranes of the later fetus.
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F
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In chicken embryos, some epiblast cells involute to form the hypoblast, which forms the floor of the embryo.
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T
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Unlike protostomes, the first opening of the gut formed in echinoderms such as sea urchins forms the anus.
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T
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Like European Union countries, the United States prohibits federal funding of human cloning experiments.
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F
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Cortical granules in sea urchin eggs are crucial in the fast block to polyspermy, because they contain components that help to produce the fertilization envelope.
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T
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Unlike mammalian sperm, sea urchin sperm produce a long acrosomal process containing bundles of actin.
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F
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Treatment of fertilized frog eggs with nocodazole prevents rotation of subcortical cytoplasm, preventing ventral structures from forming.
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F
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Pronuclear migration would likely be inhibited by cytochalasins, since it is an actin-dependent process.
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F
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"Pre-embryo" biopsy is still difficult, because current methods only allow genetic identification of homozygous embryos.
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T
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The archenteron of the sea urchin embryo is a convenient system in which to study invagination of a cell sheet.
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F
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Fate mapping indicates that extensive cell movement occurs in embryos prior to gastrulation.
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9. The developmental potential of cells in the early mammalian embryo has been examined in several ways.
a. Describe one way that primate embryonic stem cells have been produced (2 points)
b. Describe at least two experiments that demonstrate that cells in the pre-compacted mammalian embryo are totipotent (2 points)
10. Many processes in early development require proper cell adhesion. Match the appropriate responses on the right to the processes on the left. Note: There may be more than one correct answer for each event listed on the left. (3 points)
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Adhesion of frog blastula cells
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a. Requires cadherin-mediated adhesion
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Compaction of mouse embryos
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b. Requires integrin-based adhesion
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Binding of acrosome-reacted sperm and
oocyte in mammals
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c. a & b
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"Sorting out' of amphibian embryonic
cells
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d. None of the above
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Binding of sea urchin sperm to
sea urchin eggs
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