What do you need for Germ Cell determination
- A plastic cell type (totipotent)
* A cell capable of undergoing meiosis
where are Primordial germ cells (PGCs) determined and where do they migrate too
- 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
in C elegans what are the P cells
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.
what do the P granules in P cells (c elegans) do
- Bind to DNA of P cell and block almost all transcription, thus all differentiation
- And in cytoplasm, also block translation (ie a fail-safe device).
- Promote stem cell fate, and cause cells to undergo meiosis (rather than mitosis)
features of a germ cell
- Little transcription or translation
- Therefore, no differentiation
- therefore have a ‘plastic/pluripotent’ identity
- Also they can undergo meiosis
How do you control widespread transcriptional decisions?
Epigenetic Silencing mechanisms include:
- DNA methylation: represses gene activity
- Histone modification: histone proteins govern accessibility of gene promoters
what do Primordial germ cells (PGCs) arise from
extra-embryonic mesodendodermal cells just beyond the posterior part of the embryo.
where are the PGC’s determined and why is this important
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
In drosophila whats drives the PGCs (blue) and gonad precursor cells (red) together and to a specific destination
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)
what do the PGCs attatch to in ovaries and testes?
In ovaries - stromal cap.
In testes - hub cells
in vertebrates what happens to the germ cells - step by step
- 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
what is produced if primordial germ cells fail to migrate out of the gut, and fail to be protected in the gonads
then a teratoma is produced.
