Lecture 6: Cleavage I

Question 1

Compaction

Answer 1

Outer blastomeres adhere via gap junctions and appear to lose their individual identity; E-cadherins, CAMs involved

Question 2

What is the mechanism behind blastocoel formation?

Answer 2

Water transported into ball of cells due to Na+/K+ transporters around 4 days after fertilization

Question 3

At one point is an embryo referred to as a blastocyst?

Answer 3

At the 58 cell stage

Question 4

What are the components of the blastocyst?

Answer 4

Blastocoel, trophoblast, inner cell mass

Question 5

What structures does the trophoblast give rise to?

Answer 5

Extraembryonic structures including placenta

Question 6

What structures does the inner cell mass give rise to?

Answer 6

Embryo proper, other embryonic structures such as yolk sac and amnion

Question 7

What is the difference in genetic control between non-mammals and mammals

Answer 7

In non-mammals: most early control of cleavage is through maternal genome until after blastulation; mammals: embryonic genome by 4 cell stage

Question 8

Methylation

Answer 8

Inactivates genes by addition of methyl groups to specific regions of DNA molecules; can cause imprinting

Question 9

Inside-Out Hypothesis

Answer 9

Fate of blastomere is determined by its position within the embryo, not from intrinsic properties

Question 10

Cell Polarity Model

Answer 10

Fate of blastomere depends on plane of cell division during cleavage

Cleavage plane parallel: outer daughter cell becomes trophoblast, inner becomes inner cell mass

Cleavage plane perpendicular: both daughter cells become trophoblast cells

Question 11

Which of the following genes is required to permit cleavage to proceed to 2-cell stage?

A. Cdx-2
B. Oct-4
C. Nanog
D. Sox2

Answer 11

B. Oct-4

Question 12

Cdx-2

Answer 12

Gene essential for trophoblast cell differentiation, antagonistic toward Oct-4

Question 13

Oct-4

Answer 13

Expressed in developing oocyte/zygote, required to permit cleavage to proceed to 2-cell stage, expressed in all morula cells, maintenance of undifferentiated state

Question 14

Nanog

Answer 14

Produced by inner cells in later morula stage, maintains integrity of ICM with Oct-4; without Nanog inner cells differentiate into endoderm, wihtout Oct-4 inner cells differentiate into trophoblast

Question 15

Sox2

Answer 15

First expressed in 8-cell stage, controls regulation of genes involved in differentiation