Review Question - QID 101905

Leydig cells within the testes produce testosterone to induce the mesonephric (Wolffian) duct to develop and ultimately form the male internal reproductive organs, including the seminal vesicles, epididymides, ejaculatory ducts, and ductus deferens.

Female is the default phenotypic differentiation, with degradation of the mesonephric duct and unhindered development of the paramesoneprhic duct. For male development, the SRY gene on the Y chromosome produces the testis-determining factor (TDF) protein, which acts to induce differentiation of the gonads into testes over ovaries. The testes contain both Sertoli and Leydig cells. Sertoli cells produce Mullerian inhibitory factor (MIF), which prevents the development of the female internal genitalia by suppressing the development of the paramesonephric ducts. The Leydig cells produce testosterone, which stimulates the development of the mesonephric duct and formation of the male internal reproductive organs. Some testosterone is transformed into dihydrotestosterone (DHT), which is responsible for the development of the external male reproductive organs.

Incorrect Answers:
Answer 1: The TDF is a protein encoded by the SRY gene on the Y chromosome; it is NOT produced by Sertoli cells. Rather, TDF is responsible for gonadal differentiation into testes, which then contain Sertoli and Leydig cells.
Answer 2: Leydig cells do not excrete TDF; TDF is a genetically encoded protein that leads to the differentiation of the gonads into testes.
Answer 3: Sertoli cells do not produce testosterone; instead, they produce MIF, which suppresses the development of the female internal sex organs.
Answer 5: MIF, produced by Sertoli cells, suppresses the default development of the female internal reproductive organs.