Quick sequence of events - Mammalian Development

Question 1

Sequence of events that lead up to blastocyst implantation

Answer 1

Note: its the blastocyst that is being implanted into the uterus

Question 2

Quick overview of events that lead up to Organogenesis

Answer 2

1. Oogenesis
2. Ovulation
3. Fertilization
4. Cleavage
5. Blastocyst Formation
6. Gastrulation
7. Organogenesis

Question 3

Steps involved in Gastrulation

Answer 3

Gastrulation occurs in the following sequence:

(1) the embryo becomes asymmetric;
(2) the primitive streak forms;
(3) cells from the epiblast at the primitive streak undergo an epithelial to mesenchymal transition [EMT] and ingress at the primitive streak to form the 3 germ layers that will give rise to different tissues and organs.

Question 4

How does Cleavage occur? What are the two divisions involved? When is the genome activated?

Answer 4

Before fertilization, mammalian oocyte is released from the ovary and swept by the fimbriae into the oviduct.

Meiosis is completed after sperm entry

Fertilization occurs in the ampulla of the oviduct.

Cilia in the oviduct pushes the embryo toward the uterus, first cleavage occurs along this journey.

First cleavage is a normal meridional division

Second cleavage - one blastomere divides meridionally and the other divides equatorially. [this is called rotational cleavage]

Genome is activated during early cleavage and newly formed nuclei produce proteins necessary for cleavage and development.

Question 5

When does the embryo switch from maternal to zygotic control of genes?

Answer 5

switch from maternal to zygotic control occurs at the 2 cell stage and zygotic genes are activated between 4 and 8 cell stage.

Question 6

Describe the embryo at the 8 cell stage?

Answer 6

1. embryo cells are called blastomeres
2. cells are together in a loose arrangement with a lot of space between them.
3. Cell adhesion proteins like E cadherin become expressed and cells become tightly compacted to one another.
4. Compaction is stabalized by tight junctions on the outside and gap junctions on the inside of the zona pellucida.
5. 8 cell embryo divides into a 16 cell morula

Question 7

What happens at the 16 cell morula?

Answer 7

1. small group of internal cells is surrounded by a large group of external cells.

2.