Biology 205 problem set B: Gastrulation, Signaling

(* = hand in answers in recitations)

11) From which tissue layer (endoderm, mesoderm, ectoderm) do the following develop?

stomach

heart

spinal cord

lung

ribs

12) In sea urchin embryos,

a) Name three cell surface characteristics that change in the vegetal plate cells that become primary mesenchyme cells.

b) Do all vegetal plate cells undergo these changes?

c) What tissue layer do these cells become?

13) How does the animal pole of a Xenopus oocyte differ from the vegetal pole? What kind of symmetry does the oocyte have? What effect does fertilization have on the symmetry?

14) What kinds of tadpoles will be produced by the following treatments of recently fertilized Xenopus eggs:

a) no special treatment?

b) UV light irradiation?

c) UV irradiation followed by turning the egg on its side?

d) turning the egg (without UV irradiation)?

15) On the following diagram of a gastrulating frog embryo, label the future ectoderm, mesoderm, and endoderm. Label the cells that will give rise to the brain.

16) Raymond is trying to map the developmental fates of different cells in an amphibian species. To do this, he cuts a 16-cell embryo into clumps of tissue, cultivates the clumps of cells, and observes how they develop.

a) What do you expect the indicated cells will develop into in this experiment?

b) Is the map that Raymond develops an accurate representation of the future fates of these cells in the normal embryo? Explain your answer.

c) Describe the experimental method you would use to determine a fate map for an embryo with 1000 cells.

17) When molecule X is injected into a certain spot in a Xenopus embryo, a second dorsal axis forms. Does this mean that X is the inducer of a dorsal axis during normal development? Briefly explain your reasoning.

18) A student is studying inductive events in Xenopus embryo development. On Monday, he removes a piece of animal pole tissue from an embryo and discovers that he can induce it to become mesoderm by incubating it in the presence of a purified protein factor X. The next day, he removes another piece of animal pole tissue to repeat the experiment, but this time he sees no induction of mesoderm tissue. He does not understand this result because he was careful to keep the embryo alive and growing overnight. Can you account for the difference in the two results?

19) The following experiments refer to tissues taken from a 32-cell Xenopus blastula.

a) Animal pole cells are incubated with vegetal pole cells from the future ventral side of the embryo. What happens to each cell population?

b) Animal pole cells are incubated with vegetal pole cells from the future dorsal side of the embryo. What happens to each cell population?

c) Two days later, the animal poles from part a) are cultured with the vegetal cells from part b). No further changes in cell fates are seen. Why not?

*20) For the following pair of questions, include a sketch as part of your answer:

a) Describe a way that one can manipulate a fertilized Xenopus egg so that it develops into a two-headed tadpole.

b) Describe a way that one can manipulate a Xenopus blastula so that it develops into a two-headed tadpole.

21) How is it possible for different cells to use common signaling mechanisms for different purposes?