TGF beta 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)b eta 1 in human ovarian follicular fluid obtained during ovarian stimulation for IVF were higher in women who subsequently became pregnant following em bryo transfer. We therefore postulated that TGF beta 1 may have a beneficia l effect on the preimplantation embryo and improve the chances of a success ful implantation. We have used reverse transcription-polymerase chain react ion (RT-PCR) and immunohistochemistry to investigate the presence in human oocytes and preimplantation embryos of the essential components of the TGF beta signalling pathway, TGF beta 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 recept or 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 TGF beta 1 in follicular fluid may interact with the oocyte and preimplantation embryo via TGF beta receptors, and that TGF beta signalling may be importa nt for the development of the oocyte and the preimplantation embryo.