Molecular cloning of the partial cDNA coding sequences of the four erbB receptors and the epidermal growth factor (EGF)-like ligands EGF, transforming growth factor α (TGF), and heparin-binding EGF (HB-EGF) has provided the basis for a comprehensive analysis of the spatiotemporal expression pattern of the EGF receptor/ligand system during the peri-implantation period in the rabbit. Employing nonradioactive in situ hybridization and immunolocalization, we observed differential expression of erbB1–erbB3 within the trophectoderm of the blastocyst. ErbB1 was strongly expressed in the cytotrophoblast but was downregulated upon syncytium formation. ErbB3 was a product of both the cyto- and syncytiotrophoblast. Despite the expression of erbB2 mRNA, the trophectoderm was devoid of immunoreactive ErbB2. ErbB4 gene activity was exclusively detected in the trophoblast at midpregnancy. The luminal and glandular epithelium and stroma of the nonpregnant, pseudopregnant, and pregnant rabbit uterus at Day 6 of gestation also expressed ErbB1–ErbB3. In the peri-implantation period, gene activities of erbB1–erbB3 were upregulated upon decidualization. At the site of implantation, uterine luminal epithelial cells apposing the preimplantation blastocyst displayed a distinct membrane immunolocalization of ErbB2, identifying the uterine epithelium as target for EGF, TGFα, and HB-EGF derived from both the embryonic trophectoderm and the uterine epithelium. In the luminal epithelium at the antimesometrial uterine site, HB-EGF gene activity was upregulated at the time of blastocyst attachment, but this upregulation was not reflected in an increase in immunoreactive HB-EGF. The detection of tyrosine phosphorylated ErbB2 in the rabbit placenta indicated the presence of a functional ErbB/EGF-like system in the pregnant rabbit uterus. This study provides strong evidence for a role of the ErbB/EGF-like system in embryo/maternal interactions during the peri-implantation period in the rabbit.
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