Expression patterns of gap junctional proteins connexin 32 and 43 suggest new communication compartments in the gastrulating rabbit embryo

A central problem in embryological research is the identification of mechanisms by which control over the development of a viable individual is maintained. An important role in this process is attributed to intercellular communication the preconditions of which were examined in the present study. Using a range of monoclonal antibodies, the expression patterns of the gap junctional proteins connexin 32 (Cx32) and connexin 43 (Cx43) were examined in whole-mount preparations and cryosections of gastrulating rabbit embryos between 6.0 and 7.5 days post conception. Distinct distribution patterns for Cx32 and Cx43, respectively, were found: Cx32 was exclusively expressed in the hypoblast and yolk sac epithelium (the lower layer of the embryo) whereas Cx43-expression was limited to the epiblast (in the upper layer) and its derivatives. Moreover, the dynamics of the Cx32 and Cx43 expression patterns indicate the existence of smaller tissue compartments within the three embryonic cell layers present at the beginning of gastrulation (epiblast, mesoderm and hypoblast). The most striking one of these smaller compartments is a belt-like area within the lower layer which straddles the epiblast-trophoblast border seen in the upper layer of the embryonic disc. The significance of these compartments for initiating and maintaining the gastrulation process is discussed.