.
The germ line cells are shaded in red, and the somatic cells are shaded in green and blue. The change from light to darker color indicates that the cell has matured or differentiated. The Sry gene acts in a subpopulation of somatic cells in the developing gonad to direct them to differentiate into Sertoli cells instead of into follicle cells. The Sertoli cells then induce primordial germ cells to commit to sperm development. They also secrete anti-Müllerian hormone, which causes the Müllerian duct to regress, and they help to induce other somatic cells to differentiate into Leydig cells, which secrete testosterone (see Figure 20-28
). In the absence of Sry, the primordial germ cells commit to egg development, and the somatic cells develop into either follicle cells, which support egg development, or theca cells, which secrete estrogen. Whereas Leydig cells begin secreting testosterone in the fetus, theca cells do not begin secreting estrogen until puberty.
). In the absence of Sry, the primordial germ cells commit to egg development, and the somatic cells develop into either follicle cells, which support egg development, or theca cells, which secrete estrogen. Whereas Leydig cells begin secreting testosterone in the fetus, theca cells do not begin secreting estrogen until puberty.