This period of
Sertoli cell proliferation up to 6.5 wk of age corresponds with declining estrogen and androgen secretion by the testis and as observed here. Our past and present data therefore
indicate that blockade of both androgen and estrogen receptor
activation further promotes Sertoli cell proliferation during this
crucial developmental interval in the boar. This further
suggests that the converse may also be true, namely, that
androgens and estrogens may promote differentiation of Sertoli
cells by closing the proliferative window. Estrogens acting
through ESR2 were recently hypothesized to promote Sertoli
cell differentiation, although estrogen signaling through ESR1
was believed to stimulate proliferation in cultured rat Sertoli
cells, an effect of estrogen that directly contrasts with that
observed in vivo in the pig.