L5: Sex Differentiation Flashcards
What is sex determination?
Progress of development of sex differences, a natural event by which an organism is set become either a male or female.
Defined as the phenotypic development of structures consequent upon the action of hormones produced following gonadal determination.
When and how is sex determined?
Sex is determined at fertilization by the sperm. 50% chance for XX and XY
What is unique about gonadal rudiments?
All rudiment cells have just one fate, exception: gonadal rudiment. It is bipotential, can become either ovary or testis. Two organs with very different tissue architecture. At bipotential ‘indifferent’ stage Mullerian and Wolffian ducts are present.
What is the bipotential stage? How long does it last in humans?
It’s decision time in embryo develpment, gonads are indifferent and it lasts for 7 weeks.
What are the main germ cells in gonads?
- oocyte
- sperm
What are the somatic cells in gonads?
supporting cells:
- granulosa cells in oocytes
- sertoli cells in sperm development
steroidogenic cells:
- theca cells in oocytes
- leydig cells in sperm development
What are Primordial Germ Cells (PGCs)? Where are they located?
- Precursors of sperm and eggs
- located outside the body in yolk sac
When does specification of PGCs begin?
Specification of PGCs begins around 3 weeks of human gestation
How does gonadal ridge form?
PGCs migrate to gonadal ridge. Proliferation of epithelium and mesenchyme on medial side of mesonephros.
What is mesonephros?
Fetal ‘interim’ kidney
How long are gonads identical in appearance?
Until 7th week
How does PGC migration and proliferation happen at week 4-6?
PGCs migrate from yolk sac –> going up through hindgut –> dorsal mesentery (fold of tissue that attaches organs to body wall) –> genital ridges (primitive gonad)
What kind of divisions do PGC cells undergo during migration?
Undergo mitosis while migrating, from ~100 cells to 25,000
How long do PGCs proliferate in humans?
Until ~10th week
What do PGCs require for motility?
- chemotactic signals coming from gonads
- gradients of extracellular matrix glycoproteins
- PGC-PGC contact
divide into two populations –> colonise R & L gonads
What are the chemotactic signals needed for PGCs to migrate?
- TGF-beta (transforming growth factor beta)
- Kit ligand/SCF (stem cell factor)
- bFGF (basic fibroblast growth factor)
When does sex specific differentiation of PGCs begin?
During migration, germ cells are sexually bipotential.
Sex specific differentiation of PGCs begins only after colonisation of gonad (dependant on the cells that are found within the gonad)
What happens after colonisation of gonad by PGCs?
PGCs become surrounded by somatic cells, PGCs continue to proliferate