L43 Origin and Development of Germ Cells

Question 1

Primordial germ cells can be found in the yolk sac in week 3 p.c.

Where do they migrate to for spermatogenesis?

Answer 1

Commence ‘migration’ from yolk sac, through hind gut to genital ridge.

Enter presumptive seminiferous tubes (hoops) with pro-Sertoli cells.

PGCs initially settle on tubule wall. Therefore spermatogonia are outside blood-testis barrier (BTB).

Question 2

Are spermatogonia inside or outside the blood-testis barrier?

Answer 2

Outside

Question 3

Primordial germ cells proliferate via __1__ and develop into __2__.

These proliferate by __3__ and develop into __4__.

Answer 3

1) mitosis
2) gonocytes
3) mitosis
4) pro-spermatogonia

Question 4

PGC’s develop into gonocytes, which develop into prospermatogonia.

What do prospermatogonia develop into?

Answer 4

Prospermatogonia develop into spermatogonia by the end of the foetal stage.

Question 5

Spermatogonia undergo peri-natal division to produce __?__

Answer 5

spermatocytes

Question 6

Spermatogonia are classified as A-dark and A-pale.

A-__1__ are considered to be stem cells, while A-__2__ are proliferative.

Answer 6

1) A-dark

2) A-pale

Question 7

True or false: All post-stem cell development is as a syncytia (single cell; multiple nuclei) until just before sperm release.

Answer 7

True.

Question 8

True or false: Spermatocytes arrest in interphase of 1st meiotic division.

Answer 8

False.

Spermatocytes arrest in prophase of 1st meiotic division.

Question 9

What are the stages of prophase in meiosis?

Answer 9

1. Leptotene
2. Zygotene
3. Pachytene
4. Diplotene

After diplotene, the cells enter meiosis. There are 2 stages of meiosis.

Question 10

What occurs during meiosis?

Answer 10

2 stages of cell division:

Primary spermatocyte (diploid) splits into 2 secondary spermatocytes (haploid). These secondary spermatocytes undergo a second round of meiosis to form spermatids (haploid) which mature into sperm.

Question 11

What is spermiogenesis?

Answer 11

The development of spermatids.

Question 12

True or false: Round spermatids are transcriptionally active

Answer 12

True

Question 13

True or false: Elongating spermatids are transcriptionally active

Answer 13

False.

Transition proteins are replaced by protamines as the nucleus shrinks dramatically. Cytoplasm also shrinks away as the flagellum develops fully.

Question 14

True or false: Maturing spermatids are transcriptionally active

Answer 14

False. They lost transcription capability in elongation phase of development.

Maturation phase spermatids have the morphology of mature spermatozoa and shed from Sertoli cell into lumen of seminiferous tubule (spermiation).

Question 15

The primordial germ cells in females are known as __?__

Answer 15

oogonia

Question 16

In which stage of cell cycle is the primary oocyte arrested?

Answer 16

Diplotene (part of meiotic prophase)

Question 17

At each of the meiotic division stages, what is produced?

Answer 17

Meiosis I:

a) secondary oocyte
b) first polar body

Meiosis II:

a) ovum
b) second polar bodies

Polar bodies are little ‘buds’ that come off during meiosis, but never form into ovum.

Question 18

What is a germinal vesicle?

Answer 18

The nucleus of an oocyte that is arrested in prophase of meiosis I.

Question 19

What is primordial follicle?

Answer 19

Following arrest of cell cycle in prophase, the primary oocyte is surrounded by granulosa cells, forming the primary follicle.

Question 20

What happens to primordial follicles at puberty?

Answer 20

They begin to recommence development into primary (pre-antral), secondary, and pre-ovulatory follicles.

Question 21

At which stage of folliculogenesis does the zona pellucida begin to form?

Answer 21

Primary (pre-antral) follicle stage,

Primary follicle secretes glycoproteins that form the zona pellucida.

Question 22

What type of cell junctions are found between the dividing granulosa cells of the pre-antral follicle?

Answer 22

Gap junctions

Question 23

What type of cell forms a theca around the pre-antral follicle?

Answer 23

Ovarian stromal cells

Question 24

In what type of follicle do the granulosa cells increase secrete mucopolysaccharides and serum?

Answer 24

Secondary (antral, or graafian) follicle.

The follicular fluid secreted by granulosa cells fills the follicular cavity known as an ‘antrum’.

This fluid-filled antrum is characteristic of a secondary follicle.

Question 25

What is ‘cumulus oophorus’?

Answer 25

A thick layer of granulosum cells that surrounds the oocyte.

Forms part of the secondary (antral, Graafian) follicle.

Question 26

True or false: The secondary follicle is gonadotropin-dependent

Answer 26

True

Question 27

What event stimulates ovulation?

Answer 27

Peak of LH

Question 28

When does meiosis I occur in females?

Answer 28

During ovulation.

Peak in LH stimulates breakdown of nuclear membrane, separation of chromosomes and unequal division of cytoplasm (forms 1st polar body).

Oocyte continues in metaphase until meiosis II (after fertilisation)

Question 29

Fertilisation by a sperm triggers what in the female germ cell?

Answer 29

Meiosis II - formation of the ovum and 2nd polar body.