Exam 3 on Thursday

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

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

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

What are the differences between follicle cells and nurse cells?

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

Nurse cells synthesize macromolecules and pump them into the oocyte

through the cytoplasmic bridges

oocyte

nurse cells

follicle cells

Nurse cells are mitotic sisters of the oocyte

Figure 19.4

dorsal

ventral

anterior posterior

Molecules synthesized by the nurse cells and specifically localized in the oocyte determine

the anterior/posterior axis of the embryo

Posterior Determinant(nanos)

Anterior Determinant(bicoid)

Oocyte

Specific mRNAs are bound by proteins and transported along microtubules by motor proteins to their destinations

Ventral follicle cells build a signal into the egg shell that determines the dorsal/ventral axis of the embryo

Ventral follicle cells

Oocyte signals follicle cells,follicle cells signal back to oocytecytoplasm

nucleus

gurken mRNA

PosteriorAnterior

Dorsal

Ventral

torpedo receptor- inhibits pipe

pipe protein

See Fig. 9.11for more details

Localized maternal mRNAs also influencevertebrate development

Vg1 mRNA

Vg1 mRNA localizes to the vegetal poleof the Xenopusoocyte

Figure 5.38

Model for mesoderm induction and organizer formation

Figure 10.26

C. elegans:

P granulesare segregated at each divisionand make thecell that inherits them the germline

Figure 8.44 cell nuclei P-granules

The germ line is set aside early in development as a separate cell lineage

This can sometimes be visualized by the segregation of putative "determinants”as in C. elegans

Fertilized egg

"P granule"

mother cell of germline = P4

P1HOW are P-granules segregated?

PAR proteins & microfilaments see p. 246 and Fig. 8.43

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

Sperm-eggshell contact triggers the acrosome reaction

Example 1-- the sea urchin

enzymes

Species specificity (equivalent to zona pellucida)

Mid-blastula transition

and the N/C ratioLets say you have an organism which normally undergoes 4 cell divisions before the MBT

pre-cleavage: N/C ratio = 1/16 = 0.0625 (close to 0)after 4 cell divisions (1 > 2 > 4 > 8 > 16): 16/16 = 1

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. ________________________________________________________________________________________________________________________________________________________________________________________________________________________________

BlastoporeBlastocoelBlastocystBlastomere

EARLY CLEAVAGE rapid increase in the number of cells after fertilization

egg contents distributed to cells, often asymmetrically

blastomeres

hatch from zona pellucida

Fig. 11.27

Fig. 11.25

Development of a Human Embryo From Fertilization to

Implantation

Two functions of the blastocoel: 1. Prevents cells from interacting too soon2. allows space for cell migrations during gastrulation

animal

vegetal

Early cleavage in Xenopus

Step 2:Apical constriction and changes in the extracellular matrix create a dome-shaped invagination =archenteron (primitive gut)

blastopore = openingFigure 8.19

wildtype larva

bicoid mutant

bicoid mutants have no head!!

Figure 9.23

Fertilization: a multistepprocess

(ECM)

Sperm-eggshell contact triggers the acrosome reaction

Example 1-- the sea urchin

enzymes

Species specificity (equivalent to zona pellucida)

attracts/activates sperm

Figure 7.8

Sperm-eggshell contact triggers the acrosome reaction

Example 2: Mammals

Sperm have ZP3 receptor

Figure 7.8