Embryology - Sex Differentiation Flashcards
What gene determines sex?
The Sex-determining region of the Y gene (SRY)
What bipotential precursors do gonads develop from?
Common somatic mesenchymal tissue precursors called the ‘genital ridge primordia’
What week in development do the gonads begin to form?
3.5-4.5 weeks
Gamete precursors that migrate to the genital ridge primordia are called what?
Primordial germ cells (PGCs)
Where do primordial germ cells originate from?
The allantois - so from the epiblast
In normal males, where do PGCs enter the genital ridge mesenchyme and what degenerates?
PGCs enter medulla and the cortex degenerates
In normal females, where do PGCs enter the genital ridge mesenchyme and what degenerates?
PGCs enter cortex and medulla degenerates.
What do cells derived from coelomic epithelium become?
Primitive sex cords
What effect does SRY gene expression have on primitive sex cords?
Formation of the testis cords.
these cells will eventually become Sertoli cells to support spermatogenesis
If SRY gene is not expressed, what happens to the primitive sex cords?
the cells condence as small clusters around PGCs forming oogonia which initiates the formation of primordial ovarian follicles. In the follicles the condensing cord cells give rise to granulosa cells and the oogonia will give rise to oocytes
What is the name of the transcirption factor that SRY binds to?
SOX9
What 3 molecules does SOX9 stimulate the production of?
Prostaglandin D2 by the pre-Sertoli cells, fibroblast growth factor 9 and anti-Mullerian hormone
Does the production of PGD2 have a positive or negative feedback on SOX9?
Positive feedback - this reduces the chance of ovo-testis forming
what is the function of fibroblast growth factor 9?
Acts as a chemotactic factor for third wave migration of mesonephric cells and promotes SOX9 production (positive feedback)
What gene does SOX9 inhibit?
Fox ligand 2
In the absence of SRY gene what genes are expressed to produce granulosa and theca cells?
Fox ligand 2 and Wnt4
How do PGCs behave differently in foetal testes to the ovary?
In testes, PGCs cease mitotic proliferation and enter a period of mitotic arrest until puberty. in ovaries, PGCs oogonial germ cells stop mitotic division and enter first meiotic division to become primary oocytes
What is Turner Syndrome?
Women with only one X chromosome - infertile as full oocyte growth requires 2 X chromosomes
What is Klinefelter Syndrome?
Men with XXY chromosomes. testes form (due to expression of SRY) but most germ cells die later in life when they enter meiosis due to there being 2 X chromosomes
What do Leydig cells secrete?
Androgens e.g. testosterone
What do Sertoli Cells secrete?
They secrete substances to support and nourish sperm but also secrete AMH
What are the names given to the ducts located in the mesonephros in the males?
Wolffian or Mesonephric ducts
What are the names given to the ducts located in the mesonephros in females?
Mullerian or Paramesonephric ducts
What causes the maintenance of the Wolffian ducts?
Androgens secreted by Leydig cells in the testes
What 4 structures do the Mullerian ducts give rise to?
Oviducts (uterine tubes), uterus, cervix, upper vagina
What 3 structures do the Wolffian ducts give rise to?
Epididymis, vas deferens and seminal vesicles
What is Androgen Insensitivity Syndrome (AIS)?
XY sex chromosomes - androgen secreted but target tissues fail to respond (deficient in enzyme 5-alpha reductase)- becomes phenotypically female and infertile - rising levels of androgens produced during puberty overcomes tissue insensitivity and clitoris expands into a penis (Guevedoces - ‘penis at twelve’). after puberty they function as normal males
