Identification of two distinct functions for TGF-beta in early mouse development

In this study the function of transforming growth factor-beta (TGF-beta) in preimplantation mouse embryos was examined. By RT-PCR, mRNA for the signal ling type I (T beta R-I) and type II (T beta R-II) receptors for TGF-beta w as shown to be present in two distinct time windows: in fertilized oocytes and at the blastocyst stage. The function of TGF-beta at these times was an alysed in two ways. Firstly, the TGF-beta signalling pathway was blocked by injecting a DNA construct encoding a truncated T beta R-II, that acts as a dominant-negative receptor, in fertilized oocytes, and the effect on devel opment was determined. Secondly, inner cell masses isolated at the blastocy st stage were cultured in vitro with and without TGF-beta under conditions that favour the outgrowth of parietal endoderm. The results show that TGF-b eta signalling mediated by maternally expressed receptors is important for development of preimplantation embryos beyond the two-cell stage, and sugge st a regulatory role for TGF-beta in the outgrowth of parietal endoderm.