Sexual Differentiation

Question 1

How does the Y chromosome lead to the development of male (and not female) genitalia?

Answer 1

• Y chromosome contains SRY gene, which promotes SOX-9 protein expression
• This promotes differentiation of pre-sertoli cells, which produce antimullerian hormones (which removes the mullerian duct) and promotes sertoli cell development
• Wolffian duct develops in to seminal vesicles, epididymis and vas deferens under the influence of T from ? cells
• DHT (converted from ?) promots urethra to form prostate and bulbourethral gland

Question 2

Describe female sexual differentiaion. What key gene is absent?

Answer 2

• SRY gene is absent. No SOX-9 protein
• No pre-sertoli cells; germ cells differentiate into female gonad and enter meiosis
• In the absence of AMH, mullerian ducts develop into fallopian tubes, uterus and superior vagina
• W/ no T (since no leydig cells), wolffian ducts regress

Question 3

What is the role of DHT and T in male external genitalia development? Which androgen is stronger? What happens in their absence?

Answer 3

• These hormones cause the phallus to grow and become a penis. Labioscrotal folds close, penile urethra elongates, ano-genital distance increases (this makes sense)
• DHT is more potent than T in this instance
• Without androgens, female phenotype develops

Question 4

why do women produce AMH if their mullerian ducts do not regress?

Answer 4

• Because evolution is efficient
• They don’t produce AMH during development
• Instead, it’s mostly produced by granulosa cells during folliculogenesis to inhibit growth of other follices/reduce sensitivity of FSH
• It’s an indicator of ovarian reserve