Induction of arylhydrocarbon receptor expression in embryoblast cells of rabbit preimplantation blastocysts upon degeneration of Rauber's polar trophoblast

The arylhydrocarbon receptor (AhR) is a ligand-activated transcription fact or and mediates carcinogenic, teratogenic, and toxic effects of xenobiotics such as dioxin and coplanar polychlorinated biphenyls. The AhR nuclear tra nslocator (ARNT) is involved in AhR signal transduction. We have analyzed t he expression of AhR and ARNT mRNA and AhR protein in Day 3 pc (postcoitum) rabbit morulae and Days 4 and 6 pc blastocysts using RT-PCR, nested PCR, w hole mount in situ hybridization, and whole mount immunohistochemistry with subsequent confocal laser scanning analysis. AhR and ARNT transcripts were detected in all stages investigated, indicating coexpression of both trans cription factors. AhR protein was localized in the cytoplasm. It was detect ed in Day 3 pc morulae and in blastocysts. In Day 4 pc blastocysts, only tr ophoblast cells but not embryoblast cells were immunopositive. However, at Day 6 pc, the embryoblast cells also expressed AhR protein and this express ion was correlated with the degeneration of Rauber's trophoblast layer. (C) 1999 Academic Press.