To further examine the hypothesis that activin is an in-trafollicular paracrine signal between granulosa cells and oocytes, we examined mRNA levels of the inhibin/activin subunits, FS315, and activin receptors in individual human oocytes to determine which of these molecules are synthesized. While mRNAs for each of the four activin receptor subtypes were easily detected, we found no significant mRNA for any of the inhibin/activin subunits, suggesting that neither inhibin nor activin is produced by oocytes.
On the other hand, all mRNAs examined were found in cumulus cells, suggesting that these cells are the primary source of activin within the growing follicle. Thus, the presence of activin receptor mRNA, but the absence of activin subunit transcripts, suggests that oocytes are capable of receiving an activin signal emitted by surrounding cumulus cells, but not of transmitting one. These results are consistent with the recent observation that bovine COC secrete significant amounts of activin whereas no activin was detectable from denuded oocytes. buy cheap antibiotics
Inhibin/activin subunit, activin receptor, and FS mRNA levels were also investigated in mouse oocytes so that we could examine these undetectable targets at the greater RNA concentrations afforded by the more readily available mouse oocytes.