Unformatted text preview: Problem set 1 (10 questions, 50 points) 1) In no more than two sentences define each of the following concept pairs and the connection between them (3 points each pair (1 point for getting each concept right, 1 point for getting the connection right, 12 points altogether) Example: Concept pair: cleavage mitosis promoting factor (MPF) Cleavage is the stage of embryonic development that follows after fertilization and is characterized by rapid cell divisions. MPF is a complex consisting of Cyclin B and cdc 2 protein kinase, which is stabilized at the end of fertilization, and is necessary for the beginning of the cleavage stage. Pair 1. Acrosome - species-specific recognition Species specific recognition is the situation where a certain interaction can occur only if the two partners are from the same species. In the sea urchin, species-specific recognition between the egg jelly and the sperm, results in the exocytosis of the acrosome, a secretory vesicle in sperm that contains enzymes that digest the egg jelly Pair 2. Cortical reaction bindin Bindin is a protein on the sperm's acrosomal process that is recognized by the egg vitelline mebrane in a species-specific way. Cortical reaction is a release of the contents of the cortical granules into the spaces between the cell and the vitelline membranes of the egg, and it is triggered by the binding of bindin by the egg's receptors Pair 3. Blastula mesoderm Blastula is an embryonic stage that follows after the cleavage. During the blastula, mesoderm, which is a germ layer that will give rise to muscle, blood, notochord, is starting to differentiate. Pair 4. Germ layer triplobastic animal Germ layers are three basic layers of the animal embryo: ectoderm, mesoderm, endoderm. Triplobalstic animal is an animal that contains all three of these germ layers (optional: as opposed to the diploblastic animal, which contains no true mesoderm). 2) Using the following table, compare fertilization process in the sea urchins and mammals (8 points) External envelopes of the egg Sea urchins (will be blank) 1. Vitelline membrane 2. Jelly layer Mammals (will be blank) 1. Zona pellucida 2. cumulus Acrosome reaction is stimulated by the interaction between (will be blank) Polysaccharide on the egg jelly and its receptors on the sperm Polyspermy is prevented by 1. Changes in egg's cell membrane potential 2. Exocytosis of the corticle granules that triggers the formation of fertilization envelope (will be blank) Exocytosis of the cortical granules releases proteases that cleave ZP3 and ZP2 proteins, thus preventing other sperm from binding zona pellucida ZP3 glycoprotein in the zona pellucida and its receptors on the sperm 3. Waves of high internal Ca2+ that sweep through the egg following the sperm-egg fusion trigger dramatic changes in the egg metabolism (besides triggering the cortical reaction). List 4 major differences in the metabolic and genetic state of the egg before and after fertilization: (there are more than 4 differences. Pick your favorite 4). (8 points, 2 points each) A. The nucleus becomes diploid instead of haploid B. DNA synthesis resumes C. Transcription resumes D. Protein translation is activated Other possible answers: cell division initiated, cell cycle re-activated, NADP+ level increases, lipid (membrane) synthesis increases, mitosis-promoting factor (MPF) is generated. 4. Which embryonic germ layer has as one of its fates to become brain and nervous system (2 points) A. B. C. D. mesoderm ectoderm endoderm blastocoel 5. What DOES NOT normally happen during gastrulation? (5 points) A. Three embryonic germ layers are established B. The embryo undergoes rapid cell divisions C. The embryo increases dramatically in size D. Embryonic germ layers begin to be committed toward distinct developmental fates E. Cell migrations are a prominent feature of this developmental stage 5. Fill in the blanks (4 points): Cleavage of the bird embryo is an example of a meroblastic cleavage, otherwise called an incomplete cleavage. This type of cleavage is characterized by cell divisions happening only in one restricted part of the embryo. It is typical for eggs containing large amounts of yolk. 6. You have isolated a gene a mutation in which causes infertility in mice. The gene encodes a Ca2+ channel (10 points). A. In which two processes it might be involved? (4 points) 1. Acrosome reaction of the mouse sperm 2. Cortical reaction and activation of the egg metabolism in the egg. B. Propose one experiment to distinguish between the two possibilities (6 points). Determine the expression pattern of the gene. If it is expressed in the sperm it is involved in process 1, if it's expressed in the egg process 2. Alternative: fertilize the eggs from the mutant with the sperm from a wild type animal. If the fertilization happens normally the mutated Ca2+ channel is involved in process 1. If the fertilization does not happen it is involved in process 2. Also, perform the inverse experiment, using the wild type eggs with the mutant sperm. In this case, if the mutated channel plays role in process 1, you would expect the fertilization not to happen, whereas if the mutated channel is involved in process 2, the fertilization will happen normally. ...
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- Winter '09
- Developmental Biology, Germ layer, germ layers, Embryo, cortical reaction, zona pellucida