The Physiological Characterization of Connexin41.8 and Connexin39.4, Which Are Involved in the Striped Pattern Formation of Zebrafish.

The zebrafish has a striped skin pattern on its body, and Connexin41.8 (Cx41.8) and Cx39.4 are involved in striped pattern formation. Mutations in these connexins change the striped pattern to a spot or labyrinth pattern. In this study, we characterized Cx41.8 and Cx39.4 after expression in Xenopus oocytes. In addition, we analyzed Cx41.8 mutants Cx41.8I203F and Cx41.8M7, which caused spot or labyrinth skin patterns, respectively, in transgenic zebrafish. In the electrophysiological analysis, the gap junctions formed by Cx41.8 and Cx39.4 showed distinct sensitivity to transjunctional voltage. Analysis of non-junctional (hemichannel) currents revealed a large voltage-dependent current in Cx39.4-expressing oocytes that was absent in cells expressing Cx41.8. Junctional currents induced by both Cx41.8 and Cx39.4 were reduced by co-expression of Cx41.8I203F and abolished by co-expression of Cx41.8M7. In the transgenic experiment, Cx41.8I203F partially rescued the Cx41.8 null mutant phenotype, whereas Cx41.8M7 failed to rescue the null mutant, and it elicited a more severe phenotype than the Cx41.8 null mutant, as evidenced by a smaller spot pattern. Our results provide evidence that gap junctions formed by Cx41.8 play an important role in stripe/spot patterning and suggest that mutations in Cx41.8 can effect patterning by way of reduced function (I203F) and dominant negative effects (M7). Our results suggest that functional differences in Cx41.8 and Cx39.4 relate to spot or labyrinth mutant phenotypes and also provide evidence that these two connexins interact in vivo and in vitro.