General and conditional replacement of connexin43-coding DNA by a lacZ reporter gene for cell-autonomous analysis of expression.

Using the Cre/loxP system, we have circumvented early postnatal lethality and possible pleiotropic effects of general Cx43 gene deletion, in order to determine the expression and function of connexin43 (Cx43) in defined cell types. General or cell type-specific, Cre-mediated deletion of the floxed (i.e. flanked by loxP sites) Cx43-coding region led to activation of the inserted lacZ reporter gene in cells with transcriptional activity of the Cx43 gene. As deduced from lacZ expression in mice with general deletion, transcriptional activity of the Cx43 gene was not only found in a broad range of cell types known to a express Cx43, but also inpancreatic duct cells and vascular cells of the gut and skeletal muscle. Cre-mediated deletion restricted to defined cell types led to lacZ activation highlighting corresponding subsets of cells expressing Cx43, such as vascular endothelial cells, hepatic duct cells and putative neural crest cells, which were otherwise masked by strong Cx43 expression in neighbouring cells. In Cx43 expressing cell types, the floxed Cx43 allele was useful as a Cre-excision reporter for the characterization of Cre transgenes.