1. Exam 3 on Thursday
90% lecture material
10% reading

2. T F Xenopus animal pole cells grown in isolation make endoderm.

3. T F When animal pole cells are cultured. with vegetal pole cells, the
T F When animal pole cells are cultured with vegetal pole cells, the vegetal pole cells become mesoderm.

4. What is the difference between the germ line
and a germ layer?

5. What are the differences between follicle cells
and nurse cells?

6. The Drosophila ovary is composed of both
somatic follicle cells and germ line nurse cells and oocyte

7. follicle cells nurse cells N urse cells synthesize macromolecules
and pump them into the oocyte
through the cytoplasmic bridges
follicle cells
oocyte
nurse cells

8. Nurse cells are mitotic sisters of the oocyte
Figure 19.4

9. dorsal
anterior
posterior
ventral

10. Molecules synthesized by the nurse cells and
specifically localized in the oocyte determine
the anterior/posterior axis of the embryo
Specific mRNAs are bound by proteins and transported along microtubules by motor proteins to their destinations
Oocyte
Anterior
Posterior
Determinant
(bicoid)
Determinant
(nanos)

11. Ventral follicle cells build a signal into the egg shell that determines the dorsal/ventral axis of the embryo
Dorsal
torpedo receptor-
inhibits pipe
See Fig. 9.11
for more details
gurken mRNA
nucleus
Anterior
Posterior
pipe protein
Oocyte signals follicle cells,
follicle cells signal back to oocyte
cytoplasm
Ventral
Ventral follicle cells

13. Localized maternal mRNAs also influence
vertebrate development
Vg1 mRNA

14. Vg1 mRNA localizes to the vegetal pole of the Xenopus oocyte
Figure 5.38

15. Model for mesoderm induction and organizer formation
Figure 10.26

16. C. elegans: P granules are segregated at each division and make the
cell that
inherits them
the germline
Figure 8.44
cell nuclei P-granules

17. mother cell of germline = P4
The germ line is set aside early in development as a separate cell lineage
"P granule"
This can sometimes be visualized by the segregation of putative "determinants”
as in C. elegans
Fertilized egg P1
HOW are P-granules segregated?
PAR proteins & microfilaments see p. 246 and Fig. 8.43
mother cell of germline = P4

18. What is the role of the protein Bindin
in blocking polyspermy?

19. Example 1-- the sea urchin
Sperm-eggshell contact triggers the acrosome reaction
Example 1-- the sea urchin
Species specificity
(equivalent to zona pellucida)
enzymes

20. Mid-blastula transition
and the N/C ratio
Lets say you have an organism which normally
undergoes 4 cell divisions before the MBT
pre-cleavage: N/C ratio = 1/16 = (close to 0)
after 4 cell divisions (1 > 2 > 4 > 8 > 16): 16/16 = 1

21. Question:
6.) (4 pts, Circle one) In Drosophila, if an embryo is manipulated so that it is now haploid (has ½ the amount of nuclear material), it will undergo one more or one fewer cell division than an embryo with the normal amount of nuclear material. Explain in terms of the N/C ratio. ________________________________________________________________________________________________________________________________________________________________________________________________________________________________

22. Blastopore
Blastocoel
Blastocyst
Blastomere

23. EARLY CLEAVAGE
rapid increase in the number of cells after fertilization
egg contents distributed to cells, often asymmetrically
blastomeres

24. Development of a Human Embryo From Fertilization to Implantation
hatch from zona pellucida
Fig
Fig

25. Early cleavage in Xenopus
animal
vegetal
Two functions of the blastocoel:
1. Prevents cells from interacting too soon
2. allows space for cell migrations during gastrulation

26. Apical constriction and changes in the extracellular matrix create a
Step 2:
Apical constriction and changes in the extracellular matrix create a
dome-shaped invagination =
archenteron
(primitive gut)
blastopore = opening
Figure 8.19

27. bicoid mutants have no head!!
wildtype larva
bicoid mutant
Figure 9.23

28. (ECM)
Fertilization:
a multistep
process

29. Example 1-- the sea urchin
Sperm-eggshell contact triggers the acrosome reaction
Example 1-- the sea urchin
Species specificity
(equivalent to zona pellucida)
enzymes

30. attracts/activates sperm
Figure 7.8

31. Sperm-eggshell contact triggers the acrosome reaction Example 2:
Mammals
Sperm have
ZP3 receptor

32. Figure 7.8