Sexual Differentiation Flashcards
(36 cards)
What is the SRY gene?
Sex determining gene on the Y chromosome
Encodes for a DNA-binding protein that functions as a transcription factor for male testis differentiation
Located close to the pseudoautosomal region on the Y
What are indifferent gonads?
Gonads prior to 7th week of gestation are identical
Composed of external cortex and internal medulla
What are primordial germ cells?
Originate outside of the gonad
Begin migrating from the yolk sac endoderm to the indifferent gonad early in 5th week
What occurs after the PGCs enter the developing genital ridge?
They are rapidly surrounded by cords of somatic cells
The sex chromosomes in these somatic cells determine the type of gonad the genital ridge will become
What is the gene product of the SRY gene and what is its function?
SOX9 transcription factor that is the principal regulator of Sertoli cell differentiation
How are the testis cords formed?
The primitive sex cords penetrate deep into the medulla and form the testis cords
Subsequently, they become separated from the genital ridge by a mesenchymal layer that later becomes the tunica albuginea
What is the first histologically discernable event of testis differentiation?
Appearance of Sertoli Cells in the medulla between weeks 6-7
What are gonocytes?
PGCs transition to gonocytes within the testis cords and enter mitotic arrest at 10-12 weeks
By this time the gonocytes will have differentiated into prespermatogonia
Male germ cells are prevented from entering meiosis until puberty
What are the testis cords?
Precursors to seminiferous tubules
Remain as solid structures until puberty, when the develop a lumen and mature into fully functional seminiferous tubules
What is the role of paracrine factors released by sertoli cells?
Recruiting mesenchymal cells to differentiate into:
Peritbuluar myoid cells
Male-specific vasculature endothelial cells
Leydig cells
What do Leydig cells produce?
Testosterone
Insulin-like 3 (INSL3)
What is the relationship between seminiferous tubules and germ cells?
Presence of germ cells is not a requirement for seminiferous tubule development
What is Klinefelter syndrome?
Males with XXY karyotype caused by nondisjunction
Small, firm testes with hyalinized seminiferous tubules
What three things does the differentiation of an ovary require?
Invasion of the cortex by PGCs
Reactivation of the inactivated X chromosome in germ cells
Absence of the SRY gene
What is Turner Syndrome?
Ovarian disgenesis associated with a 45, X karyotype
What do the PGCs do in ovarian differentiation?
Migrate to presumptive ovary and differentiate into oogonia
At week 11, some of the oogonia will leave the pool of proliferating cells and enter into meiosis (primary oocytes)
When is meiosis arrested in primary oocytes?
Prophase I
What is atresia?
Form of programmed cell death
Occurs to some oogonia when with the onset of oogonial meiosis
What occurs in the ovary after week 13?
Primordial follicles arise as pregranulosa cells affregate to form a single layer of cells around the primary oocyte
What are the three reasons for decline of germ cells in the ovary post-20 weeks?
Decrease in the rate of oogonial mitosis
Atresia of oogonia that are not incorporated into follicles
Atresia of follicles that start to mature
What are cortical cords?
Represent a second wave of cord formation that occurs at week 7
Extend into underlying mesenchyme
PGCs are incorporated into cortical cords and during month three, the cortical cords break up into distinct cell clusters (primordial follicles)
What are primordial follicles?
Primary oocyte surrounded by a single layer of pregranulosa cells
What is the pathway responsible for ovarian differentiation in the absence of SRY?
B-catenin/WNT4
What are the two sets of genital ducts in the undifferentiated reproductive tract of both sexes?
Mesonephric/wolffian ducts
Paramesonephric/mullerian ducts
