A role for estrogen in somatic cell fate of the mammalian gonad.

Estrogen is both necessary and sufficient to drive ovarian development in many nonmammalian vertebrates. However, the role of estrogen in the mammalian gonad is less clear. Mouse ovarian development can proceed in the absence of estrogen signaling, but granulosa cell fate cannot be maintained. Estrogen receptor expression is conserved in the indifferent gonad of all mammals and many species also express the CYP19 gene that encodes aromatase, in the early ovary. Furthermore, estrogen is sufficient to drive ovarian development of the indifferent gonad in marsupial mammals. Here we review the function of estrogen in the mammalian gonad and propose a model for its action in establishing and maintaining ovarian somatic cell fate.