Name Student ID Page 1 Zoology 470 Exam 2 2015 This exam has 6 pages and a total of 50 points You will have 90 minutes to complete it Answer all short answer questions as briefly as possible Make sure your name and ID number are on all pages 1 5 points Provide concise definitions for each of the following a midblastula transition period during the blastula stage during which zygotic gene transcription is activated In many embryos the MBT is accompanied by loss of synchronous cell divisions In frogs MBT is triggered by crossing a threshold nucleus cytoplasm ratio b involution Inward rolling of a sheet of tissue during morphogenesis c maskin Protein involved in regulating translatability of mRNAs which forms a complex connecting the 3 and 5 regions of mRNAs thereby effectively masking them from the translational machinery After fertilization maskin s association with the mRNA is altered allowing it to be translated d primordial germ cell Cells that are committed to generating germ cells sperm or oocyte precursors e micromere Generally any cells that are smaller in a cleavage stage embryo compared with other cells as a result of asymmetric cell division In sea urchin embryos micromeres form at the vegetal pole give rise to skeletogenic mesenchyme and appear to have gut inducing capabilities 2 Multiple intracellular signaling events are required for egg activation Please answer the following questions regarding these signaling events In each case explain your answer briefly a 2 points If a sea urchin egg is fertilized in sea water that is made mildly acidic with acetic acid what effects on the events of egg activation would you predict This would decrease the normal pH increase partially suppressing upregulation of macromolecular synthesis b 2 points You treat amphibian oocytes with xestospongin C a drug that interferes with inositol triphosphate IP3 signaling What effects would pretreatment with the drug have on the eggs after fertilization If IP3 signaling is inhibited calcium won t be released from the ER and the slow block and subsequent egg activation events will be impeded c 1 point You examine mammalian oocytes after they are fertilized using a transmission electron microscope You find that numerous specific membrane enclosed structures are absent from these oocytes What are these structures Structures missing cortical granules Name Student ID Page 2 3 7 points Circle true T or false F for each of the following T Humans like other chordates are deuterostomes F T A weak mutation in the mouse pax 6 gene would be expected to result in loss of posterior structures since the fly homologue is involved in patterning the posterior of the embryo The Wolffian duct is normally retained in male mammals F F Pronuclear migration in a fertilized sea urchin egg is inhibited by the actin depolymerizing drug cytochalasin B since it requires functional actin microfilaments This is a microtubule dependent process requiring dynein Nodal proteins which encode key transcription factors act to pattern the dorsoventral axis of sea urchin embryos T Enhancers are proteins that can act 5 upstream or 3 downstream to their associated gene T If the poly A tail of a mRNA were removed the stability of that mRNA would be expected to decrease F If the bicoid RNA is engineered such that it is missing most of its 3 UTR it would be expected to localize normally in the oocyte F A microRNA miRNA that is an exact match to a sequence in the 3 untranslated region 3 UTR of a mRNA will tend to block translation of that mRNA but will not affect its stability F A sox 9 knockout mouse with two X chromosomes would be expected to have testes sox 9 is needed in XY mice to make testes Injecting a fertilized sea urchin egg with C3 transferase a Rho inhibitor would be expected to block cytokinesis but not mitosis Normal zebrafish primordial germ cells placed into an embryo lacking the function of the chemokine receptor CXCR4 would be expected to migrate abnormally signal still produced T F T Adding ubiquitin to a protein would make it more likely to be degraded F Loss of cadherin complex function in C elegans embryos has no significant defects on morphogenesis since other cell surface proteins are more important in worms they blow up 4 You are studying sex determination in mammals a 2 points In a rare human genetic disorder a chromosomal translocation takes the small region of the Y chromosome containing the sry gene and inserts it into the X chromosome What would the consequences be regarding the sex of the offspring from such a man in the case when the offspring is derived from sperm carrying an X chromosome Assume the mother is normal If the offspring is XX but one X has the sry locus the offspring would be male b 1 point Androgen insensitivity syndrome results from mutations in a hormone receptor required for cells to respond to testosterone Where does this receptor act once it has bound testosterone Primary site of action within the cell nucleus c 1 point Female mammals produce the sex hormone estrogen from another sex hormone What is this hormone Hormone testosterone Name Student ID Page 3 5 The product of the skn 1 gene in C elegans is thought to act like a determinant for the MS blastomere If necessary please refer to the diagram for reference a 1 point Where is the SKN 1 protein found within the cells in which it is present what is its subcellular location Location of SKN 1 Nucleus b 2 points SKN 1 is found in two of the four cells of the early C elegans embryo EMS and P2 Why does SKN 1 only affect cells derived from EMS and not P2 The presence of PIE 1 in P2 suppresses the activity of SKN 1 in that cell restricting the activity of SKN1 to EMS and its progeny c 2 points EMS forms two daughter cells MS and E both of which are derived from a cell in which SKN 1 is present yet which adopt different fates You work in Bob Goldstein s lab and you are learning how to use blastomere isolations to study specification in early C elegans embryos What would happen to the differentiation of the daughters of EMS if you placed a P2 cell from a mom 5 Frizzled mutant mother next to an EMS cell from an embryo derived from a mom 2 Wnt mutant mother Explain your answer P2 normally produces a Wnt signal encoded by mom 2 which causes EMS upon receiving the signal to produce an MS cells and an E cell with the E cell being closer to the source of the Wnt signal Since in this case the EMS cells is mutant for mom 2 still can receive the signal