NORMAL DEVELOPMENT OF PREIMPLANTATION MOUSE EMBRYOS DEFICIENT IN GAP JUNCTIONAL COUPLING

The connexin multigene family (13 characterized members in rodents) en codes the subunits of gap junction channels, Gap junctional intercellu lar coupling, established during compaction of the preimplantation mou se embryo, is assumed to be necessary for development of the blastocys t, One member of the connexin family, connexin43, has been shown to co ntribute to the gap junctions that form during compaction, yet embryos homozygous for a connexin43 null mutation develop normally, at least until implantation, We show that this can be explained by contribution s from one or more additional connexin genes that are normally express ed along with connexin43 in preimplantation development, Immunogold el ectron microscopy confirmed that roughly 30% of gap junctions in compa cted morulae contain little or no connexin43 and therefore are likely to be composed of another connexin(s), Confocal immunofluorescence mic roscopy was then used to demonstrate that connexin45 is also assembled into membrane plaques, beginning at the time of compaction, Correspon dingly, embryos homozygous for the connexin43 null mutation were found to retain the capacity for cell-to-cell transfer of fluorescent dye ( dye coupling), but at a severely reduced level and with altered permea bility characteristics. Whereas mutant morulae showed no evidence of d ye coupling when tested with 6-carboxyfluorescein, dye coupling could be demonstrated using 2',7'-dichlorofluorescein, revealing permeabilit y characteristics previously established for connexin45 channels, We c onclude that preimplantation development in the mouse can proceed norm ally even though both the extent and nature of gap junctional coupling have been perturbed, Despite the distinctive properties of connexin43 channels, their role in preimplantation development can be fulfilled by one or more other types of gap junction channels.