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 nonjunctional (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.Connexin proteins are the major constituents of gap junctions and are four-pass transmembrane proteins. Six connexin proteins make up a hexamer called a connexon, which acts as a hemichannel at the cell membrane. Each gap junction is a large molecular unit formed by the docking of connexons, allowing ϳ1,000-Da small molecules to be transferred between neighboring cells (1,2). Approximately 20 connexins exist in mammalian genomes, and connexins are categorized into five subgroups (␣, ␤, ␥, ␦, and ), depending on their molecular weight and amino acid sequences (3, 4). In zebrafish, ϳ36 connexins are predicted to exist (5). This higher gene number might be due to genome duplication events during fish evolution. As in mammals, connexins are expressed in tissue-specific but overlapping patterns. A combination of connexins in the same or adjacent cells can lead to several types of gap junctions. Uniform connexins create homomeric homotypic gap junctions, whereas two or more types of connexins form gap junctions that are heteromeric (different connexins within a connexon), heterotypic (different connexins in two opposing connexons), or a combination of both. The composition of heteromeric and heterotypic gap junctions is expected to create gap junctions with a wide range of properties in vivo, although relatively little is known about their importance or complexity due to technical difficulties associated with their analysis (6 -12).The zebrafish i...

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The striped pigmentation pattern of zebrafish is determined by the interaction between pigment cells with different colors. Recent studies show the behaviors of pigment cells are substantially different according to the environment. Interestingly, the resulting patterns are almost identical, suggesting a robustness of the patterning mechanism. To know how this robustness originates, we investigated the behavior of melanophores in various environments including different developmental stages, different body positions, and different genetic backgrounds. Normally, when embryonic melanophores are excluded from the yellow stripe region in the body trunk, two different cellular behaviors are observed. Melanophores migrate to join the black stripe or disappear (die) in the position. In environments where melanophore migration was restricted, we observed that most melanophores disappeared in their position, resulting in the complete exclusion of melanophores from the yellow stripe. In environments where melanophore cell death was restricted, most melanophores migrated to join the black stripes, also resulting in complete exclusion. When both migration and cell death were restricted, melanophores remained alive in the yellow stripes. These results show that migration and cell death complement each other to achieve the exclusion of melanophores. This flexibility may be the basis of the mechanistic robustness of skin pattern formation.