COLOCALIZATION OF TRANSFORMING GROWTH FACTOR-ALPHA AND A FUNCTIONAL EPIDERMAL GROWTH-FACTOR RECEPTOR (EGFR) TO THE INNER CELL MASS AND PREFERENTIAL LOCALIZATION OF THE EGFR ON THE BASOLATERAL SURFACE OF THE TROPHECTODERM IN THE MOUSE BLASTOCYST

Results of previous studies suggested that responses of mouse blastocysts to TGF-α/EGF treatment are mediated by EGF receptors (EGFR) located on the apical surface of the trophectoderm (TE). We report here results of experiments using gold-labeled EGF that confirm the presence of these apically located EGFRs. In addition, immunoelectron microscopy (IEM) studies using anti-EGFR antibodies indicate that the receptor is preferentially distributed on the basolateral surface of the TE. Furthermore, the receptor is also present on the inner cell mass (ICM) and is likely to be functional, since treatment of isolated ICMs with TGF-α affects [35S]methionine uptake and incorporation into acid-insoluble material. IEM was also used to demonstrate that EGF, which is not synthesized by the mouse preimplantation embryo, is present in both the oviduct and the uterus. Maternally derived EGF is present in both ICM and TE cells in freshly isolated blastocysts, but is present in greatly reduced amounts following overnight culture of blastocysts in vitro. Last, IEM was also used to demonstrate that TGF-α is preferentially localized to the ICM and polar TE. The co-localization of TGF-α and functional EGFRs to the ICM and polar TE suggests potential autocrine, juxtacrine, and paracrine roles for TGF-α in blastocyst development. © 1992.