Multiple connexins participate in preimplantation mouse development

This study attempted to identify connexins present in preimplantation mouse embryos. Transcripts for Cx30.3, Cx31, Cx31.1, Cx40, Cx43, and Cx45 were detected by RT-PCR in the blastocyst. These connexins are transcribed after fertilization, and show differences in onset of accumulation. Cx31, Cx43, and Cx45 accumulate continuously from the 2- to 4-cell stage while Cx30.3, Cx31, and Cx40 accumulate beginning in the 8-cell stage. All six mRNAs were found to cosediment with polyribosomes, indicating they are translated. Immunocytochemistry detected Cx31.1, Cx40, Cx43, and Cx45 in pre- and post-compaction embryos. Cx31.1 was detected in gap junctions in 8-cell embryos and morulae, while Cx31.1, Cx43 and Cx45 were detected in gap junctions of compacted morulae. Only Cx31.1 and Cx43 were detected in blastocyst gap junctions with Cx40 and Cx45 remaining localized in the cytoplasm. Expression of multiple connexin genes during early embryogenesis raises new questions about their functional significance in preimplantation development.