Embryonic Germ Cells

Question 1

What are gonadal germ cells?

Answer 1

Cells which form the egg or the sperm

They have to be protected so they remain totipotent

Question 2

How are germ cells made and set aside?

Answer 2

1) They are determined in a specific location just on the edge or outside of the embryo
2) They migrate to the gonad and become the progenitor population for eggs and sperm

Question 3

What two things are needed for germ cell differentiation?

Answer 3

1) A plastic cell type

2) A cell capable of undergoing meisosis

Question 4

How do two daughter cells become different to each other in division?

Answer 4

The mother cell may have cytoplasmic determinantes so depending on the plane of division two cells could become different

Question 5

The P cell in c elegans acts as what?

Answer 5

A pre-germ cell

Question 6

What do p cells inherit that makes them specialised?

Answer 6

P granules

Question 7

What is the role of p granules?

Answer 7

They are proteins in the cytoplasm but they can get in the nucleus

1) They bind to DNA and block almost all transcription preventing differentiation
2) In the cytoplasm it blocks almost all translation
3) Promotes stem cell fate, and causes cells to undergo meiosis (rather than mitosis)

Question 8

P granule markers show what?

Answer 8

That p granules are only present in one cell during development

Question 9

Describe the equivalent of the P cell in vertebrates

Answer 9

Always lies at the posterior part of the developing embryo

Also express a translational blocker

Question 10

What is the translational blocker found in vertebrate germ cells?

Answer 10

Nanos

Question 11

Describe two features of epigentic silencing

Answer 11

1) Methyl marks added to certain DNA bases repressed gene activity
2) Histone modification where molcules are added to the tails to tightly pack the DNA

Question 12

Where do PGCs form and initially stay?

Answer 12

Posterior end in the extra embryonic epiblast and the initially stay there

Question 13

Where exactly are PGCs determined in mammals?

Answer 13

Junction between the epiblast and the hypoblast while the embryo is forming

Question 14

Why do PGCs develop where they do?

Answer 14

They are protected from signals specifying the axes and orchestrating cell differentiation in the embryo

Question 15

Where do PGCs migrate to?

Answer 15

The gonadal niche

Question 16

How do PGCs migrate to their niche?

Answer 16

They attach to the endoderm and migrate through the midgut
They passively ride the endoderm then attach to the mesoderm
There is a combination of chemoattractive and negative cues that drive the PGCs to their specific destination

Question 17

In vertebrates what causes the archenteron to form?

Answer 17

Archenteron = primitive gut

Convergent extension and involution

Question 18

What happens if PGCs fail to reach their target of the gonads?

Answer 18

The germ cells begin to differentiate, forming a teratoma

Question 19

What is the travelling stem cell niche?

Answer 19

The PGCs along with support cells which produce Stem cell factor (SCF) to maintain the undifferentiated cell phenotype

Question 20

The cells follow what two things?

Answer 20

The fibronection trail

The chemoattractant Sdf-1