Question

2^nd set of experiments

• You inject one micromere from a 64 cell stage sea urchin embryo with a fluorescent dye in each of 10 embryos. In all embryos at the pluteus stage only skeletal cells fluoresce.
• You isolate single micromeres from 10 different sea urchin embryos and place in a petri dish with no other signals. In each case all cells become skeleton.
• You inject one micromere from a 64 cell stage sea urchin embryo with a fluorescent dye in each of 10 embryos You move the micromere to the animal pole. In all embryos at the pluteus stage the fluorescent cells are in the skeleton.

Questions

1. Are micromeres specified at the 64 cell stage? Are they determined? What is the evidence for each?
2. Are micromeres fully differentiated at the 64 cell stage? Are they fully differentiated during ingression? Are they fully differentiated at pluteus stage? (yes/no answers for each stage)

3^rd set of experiments

• You inject one veg1 cell from a 64 cell stage sea urchin embryo with a fluorescent dye in each of 10 embryos. In embryos at the pluteus stage both ectoderm and gut endoderm cells fluoresce in all embryos.

Questions

1. Are veg1 cells in 64-cell stage sea urchin embryos specified to become endoderm only? What is the evidence?

Answer 1

1. Are micromeres specified at the 64 cell stage? - Yes

2. Are they determined? - Yes

3. What is the evidence for each? - Yes

4. Are micromeres fully differentiated at the 64 cell stage? - No

5. Are they fully differentiated during ingression? - No

6. Are they fully differentiated at pluteus stage? - Yes

7. Are veg1 cells in 64-cell stage sea urchin embryos specified to become endoderm only? What is the evidence? - No, because both veg1 and veg2 decendents of the gut tissue are not seperated into ectoderm and endoderm at 6th cleavage.