L5- Germ cells and sex determination Flashcards
What are germline cells?
Cells that develop into the eggs and the sperm
What is germplasm?
Specialised cytoplasm in the egg that contains cytoplasmic determinants (posterior pole cells) which specify germ cells
Oskar gene key in this
Found in flies, nematode worm, fish and frogs (not mammals or chick)
What determines germ cells in mammals and chick?
Mechanisms are in place to suppress somatic cell programming and help protect posterior pole cells.
Blimp1/Prdm1 are genes that suppress somatic cell programme.
How do primordial germ cells migrate?
PGC’s express a G protein coupled receptor CXCR4 which binds to a secreted ligand SDF1
This ligand-receptor complex formation makes PGC’s bind to areas expressing SDF1
Areas such as the genital ridge in mammals
What is sex determination?
The decision to develop as a male or female
What is sex differentiation?
How the decision is translated into all the differences between the sexes
What are the ways in which sex is determined?
- Environment, many species of fish and reptiles are temperature sensitive
- Chromosomal/Genetic, number of chromosome sets, ratio of X chromosomes to autosomes
What is the SRY protein?
Characterised by a HMG box DNA binding domain
Gene specific to mammals
Member of SOX gene family (highly conserved)
Most SRY function in sex determination is conferred by HMG box
How is SRY involved in sex determination?
SRY gene is present on the Y chromosome only and determines the male sex
What is SOX9?
A gene whose expression causes male development. Its repression causes female development
How is SOX9 transcriptionally regulated?
SF1 (transcription factor) and SRY causes increased transcription of SOX9.
If there is no SRY then there is no SOX9 and no male development
What happens in the absence of SRY?
Increased Wnt4 causes increased suppression of SOX9 due to the production of beta-catenin.
No SOX9 to suppress FOX12 (ovary maintenance) so ovaries develop.
