Embryonic Germ Cells Flashcards
What are gonadal germ cells?
Cells which form the egg or the sperm
They have to be protected so they remain totipotent
How are germ cells made and set aside?
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
What two things are needed for germ cell differentiation?
1) A plastic cell type
2) A cell capable of undergoing meisosis
How do two daughter cells become different to each other in division?
The mother cell may have cytoplasmic determinantes so depending on the plane of division two cells could become different
The P cell in c elegans acts as what?
A pre-germ cell
What do p cells inherit that makes them specialised?
P granules
What is the role of p granules?
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)
P granule markers show what?
That p granules are only present in one cell during development
Describe the equivalent of the P cell in vertebrates
Always lies at the posterior part of the developing embryo
Also express a translational blocker
What is the translational blocker found in vertebrate germ cells?
Nanos
Describe two features of epigentic silencing
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
Where do PGCs form and initially stay?
Posterior end in the extra embryonic epiblast and the initially stay there
Where exactly are PGCs determined in mammals?
Junction between the epiblast and the hypoblast while the embryo is forming
Why do PGCs develop where they do?
They are protected from signals specifying the axes and orchestrating cell differentiation in the embryo
Where do PGCs migrate to?
The gonadal niche
How do PGCs migrate to their niche?
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
In vertebrates what causes the archenteron to form?
Archenteron = primitive gut
Convergent extension and involution
What happens if PGCs fail to reach their target of the gonads?
The germ cells begin to differentiate, forming a teratoma
What is the travelling stem cell niche?
The PGCs along with support cells which produce Stem cell factor (SCF) to maintain the undifferentiated cell phenotype
The cells follow what two things?
The fibronection trail
The chemoattractant Sdf-1
