Only a truncated epidermal growth factor receptor protein is present in porcine endometrium

The epidermal growth factor receptor (EGF-R) is a 170-kDa transmembrane protein, of which a truncated 100-kDa form (trEGF-R) lacking the cytoplasmic and the transmembrane domains, and an oncogenic 68-kDa form (v-erb) lacking the extracellular domain have been described. The trEGF-R is secreted and not able to transmit signals into the cell. Growth factors of the EGF family have been shown in porcine uterine fluids and blastocyst. Employing differential immunohistochemistry, we found the extracellular domain, but not the cytoplasmic domain, of the EGF-R in porcine endometrium on Days 9-11 of pregnancy. Blastocysts from Days 9 to 11 post coitum (p.c.) were positive for both antibodies, indicating the presence of the full-size receptor. Western Blotting of endometrial protein resulted in a 100-kDa band, but no 170-kDa band. No evidence for a coexpression of the 170- or 68-kDa forms of the receptor was found. ELISA analysis demonstrated trEGF-R in porcine uterine flushings. We conclude that 1) the trEGF-R is the only EGF-R form present in porcine endometrium, and 2) growth factors of the EGF family in porcine uterine fluids can exert their function via the EGF-R only on blastocysts, not on the endometrium.