Expression of Sox8, Sf1, Gata4, Wt1, Dax1, and Fog2 in the mouse ovarian follicle: implications for the regulation of Amh expression.

Anti-Mullerian hormone (Amh) is expressed in the granulosa cells of growing and preovulatory follicles in the mouse ovary where it acts to decrease responsiveness to follicle stimulating hormone (FSH) and plays a role in inhibiting primordial follicle recruitment. Recently, co-culture of isolated oocytes and granulosa cells has demonstrated that Amh expression is up-regulated in the presence of oocytes and, at preantral stages, this effect is dependent upon close contact. In Sertoli cells, Amh expression is regulated by several transcription factors including SOX9, SF1, GATA4, WT1, and DAX1, which, with the exception of SOX9, are also expressed in granulosa cells where GATA4 is known to up-regulate Amh expression antagonised by FOG2. Here, we demonstrate that Sox8, which is closely related to Sox9 and encodes the protein SOX8 which can transactivate Amh, is expressed in the postnatal mouse ovarian follicle but is not co-expressed with Amh in the granulosa cells of preantral follicles. Sox8 expression was found only in the oocytes of preantral follicles and in the oocytes, cumulus cells, and mural granulosa cells of preovulatory follicles. Also, increased expression of Amh in granulosa cells co-cultured with oocytes was not associated with increased mRNA levels of the transcription factors Sf1, Gata4, Wt1, Dax1, or Fog2. These findings reveal Sox8 expression in the ovarian follicle and show that oocyte regulation of Amh expression is not due to oocyte regulation of Sf1, Gata4, Wt1, Dax1, or Fog2 expression in granulosa cells.