TGFbeta receptor types I and II and the substrate proteins Smad 2 and 3 are present in human oocytes.

We have recently found that values of the transforming growth factor (TGF)beta1 in human ovarian follicular fluid obtained during ovarian stimulation for IVF were higher in women who subsequently became pregnant following embryo transfer. We therefore postulated that TGFbeta1 may have a beneficial effect on the preimplantation embryo and improve the chances of a successful implantation. We have used reverse transcription-polymerase chain reaction (RT-PCR) and immunohistochemistry to investigate the presence in human oocytes and preimplantation embryos of the essential components of the TGFbeta signalling pathway, TGFbeta receptors type I and II and the substrate proteins Smad 2 and 3. We found that both receptors, as well as Smad 2 and 3, were present in the unfertilized oocyte, whereas only the type I receptor and Smad 2 and 3 were present at the blastocyst stage. At the 4-cell and 8-cell stages neither of the receptors was present, but Smad 2 and 3 were present at both stages. These findings support our hypothesis that the TGFbeta1 in follicular fluid may interact with the oocyte and preimplantation embryo via TGFbeta receptors, and that TGFbeta signalling may be important for the development of the oocyte and the preimplantation embryo.