COEXPRESSION OF GAP JUNCTION PROTEINS IN THE CUMULUS-OOCYTE COMPLEX

The connexins constitute a family of proteins that make up the interce llular membrane channels of gap junctions. We had previously reported the presence of two members of this protein family, connexins 32 and 4 3, in mouse one-cell zygotes (Barron et al., Dev Genet 10:318-323, 198 9; Valdimarsson et al., Mol Reprod Dev 30:18-26, 1991), implying that both must be present in the mature oocyte and could be involved in med iating the intercellular coupling that occurs between the oocyte and c umulus granulosa during oogenesis. In the present report we provide ev idence for this, based on an analysis of the cumulus-oocyte complex (C OC) using reverse transcription-polymerase chain reaction (RT-PCR) and immunocytochemistry with a confocal microscope. Transcripts of both c onnexin32 (Cx32) and connexin43 (Cx43) were detected by RT-PCR in both components of the COC. Cx32 mRNA in the oocyte declined precipitously following human chorionic gonadotropin (hCG) stimulation of pregnant mare serum gonadotropin (PMSG)-primed ovaries, whereas there was no ob vious change in Cx43 mRNA. Peptide-specific antibodies against both co nnexins provided diffuse cytoplasmic staining of oocytes as well as so me punctate staining near the oocyte surface, which could not be unequ ivocally resolved as cumulus-oocyte gap junctions. However, the two an tibodies did provide clear evidence of Cx32 and Cx43 in gap junction-l ike structures between cumulus cells. We could find no evidence of the incorporation of the oocyte's store of Cx32 into gap junctions during postfertilization development. These findings make it very likely tha t intercellular coupling within the COC involves at least three types of gap junction channels (32-32, 32-43,43-43), only one of which (43-4 3) is retained by the preimplantation embryo. (C) 1993 Wiley-Liss, Inc .