A role for transforming growth factor-alpha in mouse preimplantation embryo development
Growth factors and their cognate receptors are implicated in cell proliferation and differentiation in normal somatic cells. In addition, autocrine stimulation of transformed cells is likely to account for their ability to proliferate and differentiate without exogenously added growth factors. Recent observations that mouse preimplantation embryos synthesize growth factors and their cognate receptors suggests that these factors are involved in cell proliferation and differentiation during preimplantation development. Results of experiments performed in this thesis suggest that transforming growth factor-$\alpha$ (TGF-$\alpha$), which is synthesized by the preimplantation embryo, plays a role in mouse preimplantation development. Picomolar concentrations of TGF-$\alpha$ stimulate the rate of blastocoel expansion, suggesting that an initial differentiative function of the first mammalian epithelium--fluid transport--is sensitive to peptide growth factor modulation. Although TGF-$\alpha$ can elevate cAMP in other cell types, TGF-$\alpha$ (10 pM) does not elevate cAMP in blastocysts. Thus, it is unlikely that elevation of cAMP is the mechanism by which TGF-$\alpha$ stimulates the rate of blastocoel expansion. Experiments using gold-labeled epidermal growth factor (EGF) confirm the presence of apically located EGF receptors (EGFR) on the trophectoderm; immunoelectron microscopy (IEM) studies indicate that the receptor is preferentially distributed on the basolateral surface of the trophectoderm. EGFRs are also present on the inner cell mass (ICM) and are likely to be functional. IEM was used to demonstrate that TGF-$\alpha$ is preferentially localized to the ICM and polar trophectoderm. The co-localization of TGF-$\alpha$ and functional EGFRs to the ICM and polar trophectoderm suggests potential autocrine, juxtacrine, and paracrine roles for TGF-$\alpha$ in blastocyst development. To initiate studies on the protein microenvironment of the blastocoel, I examined the electrophoretic profile of newly synthesized proteins secreted into the blastocoel. Although most polypeptides reveal no relative enrichment, some proteins are enriched in the blastocoel relative to those secreted apically. The relative amount of newly synthesized protein secreted into the blastocoel is about 2.5% of total protein synthesis and TGF-$\alpha$ stimulates this secretion by about 70-100%. Zymography reveals stimulation in the secretion of several gelatinases into the blastocoel. These results suggest additional functions for TGF-$\alpha$ in mouse preimplantation development.
Cellular biology|Molecular biology
Dardik, Alan, "A role for transforming growth factor-alpha in mouse preimplantation embryo development" (1993). Dissertations available from ProQuest. AAI9321377.