Male Reproductive Physiology Review - Raff

Question 1

1. Expression of what peptide hormone in the male embryo results in the generation of testes?
2. What results in the generation of ovaries in the female embryo?

Answer 1

1. Müllerian-Inhibiting Factor (MIF)
2. **Lack of **MIF expression will default to a female embryo.

Question 2

What is the specific function of Müllerian-Inhibiting Factor (MIF) in embryogenesis?

When does MIF expression occur?

Answer 2

• Inhibits the development of the paramesonephric (aka Müllerian) ducts
  
  • In the female, these ducts develop into the uterine tubes, uterus, cervix, and upper third of the vagina.
  • (Wiki) MIF binds a cell-surface receptor to induce apoptosis in the Müllerian duct cells.
• Peak expression around 8 weeks

Question 3

What are the Wolffian Ducts?

Answer 3

• aka Mesonephric ducts
• Male equivalent of the Müllerian (paramesonephric) ducts
• Develops into male reproductive structures including the epididymis, vas deferens, and seminal vesicles

Question 4

Other than MIF, what other hormone is required for generation of the male reproductive system during embryogenesis?

What does it do?

Answer 4

Testosterone

Supports the development of the Wolffian (mesonephric) ducts. Without testosterone (i.e., in the female embryo), the Wolffian ducts will regress.

Question 5

What hormone is important regarding the formation of the actual genitalia (penis or vagina)?

When during embryogenesis does the expression of this hormone for this purpose occur?

Answer 5

Dihydrotestosterone (DHT)

• Presence of DHT causes formation of male genitalia.
• Lack of DHT causes formation of female genitalia.

Peak occurs at ~11-17 weeks

Question 6

A second peak of steroidogenesis from the testes occurs during the first year of life.

1. What is this surge implicated to be important for?
2. When does a third increase of steroidogenesis occur?

Answer 6

1. Sex differentiation of the brain
2. Onset of puberty

Question 7

In the steroid synthesis pathway, two important estrogens are derived from two androgens (in females):

1. What are the the two estrogens and then androgens they are converted from?
2. What enzyme catalyzes the conversion?

Answer 7

1. Steroids:
   
   • Estrone from Androstenedione
   • Estradiol from Testosterone
2. Aromatase

Question 8

Which is a more potent androgen: DHT or T?

What else differs between the function of DHT and T?

Answer 8

• DHT is more potent
• Know that DHT and T each are responsible for a set of unique fetal and pubertal developments; both cooperate to the total development of the male reproductive system and later, secondary sex characteristics
  
  • ​[We were told not to worry about memorizing the specifics]

Question 9

What biological functions for males are normally accomplished by testosterone during puberty?

Answer 9

• Lineal growth and, later, epiphyseal fusion
  
  • [For both boys and girls, I think]
• Spermatogenesis (in males)
• Generation of secondary sex characteristics (in males)

Question 10

What pituitary hormone is affected by testosterone other than negative feedback oLH/FSH?

Answer 10

Testosterone stimulates the release of Growth Hormone.

Question 11

1. What cells in the testes produce inhibin?
2. What does inhibin inhibit? What doesn’t it inhibit?
3. Why does the asnwer to #2 make sense?

Answer 11

1. Sertoli cells
2. Inhibits FSH but not LH or GnRH
3. Sertoli cells support spermatogenesis are are themselves stimulated by FSH. Inhibin allows for a normal negative feedback loop on spermatogenesis without affecting the production of testosterone from Leydig cells via LH.

Question 12

What common signalling cascade mediates both increased spermatogenesis by Sertoli cells and testosterone production by Leydig cells?

Answer 12

Increased cAMP –> Increased PKA