A reporter allele for investigating connexin 26 gene expression in the mouse brain

A variety of connexins are expressed in the diverse cell types of the central nervous system and are thought to regulate some of the functional properties exhibited by immature and mature cells. A proper understanding of the role of specific connexins in these processes requires an unambiguous characterization of their spatial and temporal pattern of expression. In order to define the cellular distribution of connexin 26 (Cx26) in the mouse we have generated a reporter allele (Cx26lacZ) by genetically manipulating the locus so that the beta-galactosidase (lacZ) gene is expressed from the endogenous Cx26 promoter. This modification decreased expression from the allele and resulted in embryonic lethality for the Cx26lacZ/lacZ genotype in accordance with previous studies on Cx26 knock-out animals indicating that Cx26-containing gap junctions are necessary for embryonic development. Despite the lower than expected transcript levels, the amount of lacZ protein produced in heterozygous mice was sufficient to label tissues known to contain Cx26, such as liver, kidney, skin, cochlea, small intestine, placenta and thyroid gland. In the embryonic and mature central nervous system, however, lacZ was restricted to meningeal cells and could not be detected in either neurons or glia. The absence of Cx26 mRNA in these cells could also be confirmed by reverse transcription-polymerase chain reaction and in situ hybridization. Our experiments indicate that the Cx26lacZ mouse line can be used as a reporter of Cx26 gene expression and suggest that Cx26, contrary to previous reports, is restricted to the meninges in both embryonic and adult brain.