Germ cells

Question 1

What do you need for Germ Cell determination

Answer 1

• A plastic cell type (totipotent)

* A cell capable of undergoing meiosis

Question 2

where are Primordial germ cells (PGCs) determined and where do they migrate too

Answer 2

• Primordial germ cells (PGCs) are determined in a specific location just ‘on the edge’ or ‘outside’ of the developing embryo
• PGCs migrate to the gonad and become the progenitor population for eggs and sperm

Question 3

in C elegans what are the P cells

Answer 3

The P cell act as a ‘pre-germ’ cell:
Through asymmetric division, P-cells inherit specialised ‘P-granules’ (a mix of proteins and RNAs) that are in the cytoplasm but can get into the nucleus.

Question 4

what do the P granules in P cells (c elegans) do

Answer 4

1. Bind to DNA of P cell and block almost all transcription, thus all differentiation
2. And in cytoplasm, also block translation (ie a fail-safe device).
3. Promote stem cell fate, and cause cells to undergo meiosis (rather than mitosis)

Question 5

features of a germ cell

Answer 5

• Little transcription or translation
• Therefore, no differentiation
• therefore have a ‘plastic/pluripotent’ identity
• Also they can undergo meiosis

Question 6

How do you control widespread transcriptional decisions?

Answer 6

Epigenetic Silencing mechanisms include:

• DNA methylation: represses gene activity
• Histone modification: histone proteins govern accessibility of gene promoters

Question 7

what do Primordial germ cells (PGCs) arise from

Answer 7

extra-embryonic mesodendodermal cells just beyond the posterior part of the embryo.

Question 8

where are the PGC’s determined and why is this important

Answer 8

The pgc’s are determined outside – at the junction of the epiblast/hypoblast– while the early embryo is forming, and the axes are being established.

This means they are protected from the signals that are specifying the axes and orchestrating cell/tissue/organ differentiation

Question 9

In drosophila whats drives the PGCs (blue) and gonad precursor cells (red) together and to a specific destination

Answer 9

In drosophila A combination of chemo attractive and repulsive cues drive the PGCs (blue) and gonad precursor cells (red) together and to a specific destination (the gonad)

Question 10

what do the PGCs attatch to in ovaries and testes?

Answer 10

In ovaries - stromal cap.

In testes - hub cells

Question 11

in vertebrates what happens to the germ cells - step by step

Answer 11

• Primordial germ cells stay out of the embryo to start
• Then, PGCs migrate though the posterior gut (hingut) along a fibronectin trail,
• Then leave the gut to move laterally to the genital ridges, where they ultimately are found in a protective ‘niche’ - the gonads
• The genital ridges/gonads provide a specialised microenvironment that protects the PGCs in their pluripotent state, then supports their meiotic divisions and the formation of either eggs or sperm cells

Question 12

what is produced if primordial germ cells fail to migrate out of the gut, and fail to be protected in the gonads

Answer 12

then a teratoma is produced.