We studied pigment pattern formation in zebrafish on the cellular level and found that both, xanthophores and iridophores, come in two different forms, specific for the light and dark stripes, respectively (Fig.2). We found that the patterning process is regulated by galanin signalling in the brain, which in turn regulates thyroid hormone release and thus influences the behaviour of pigment cells (Fig.3). Inter-specific complementation tests using hybrids between zebrafish mutants and other Danio fish showed that one gene, kcnj13, is an important genetic hub with functional differences in three species (Fig.4). To further study the role of kcnj13, which encodes an inwardly rectifying potassium channel, we generated mutants in the corresponding gene in Danio aesculapii, the species most closely related to zebrafish. We could show that kcnj13 is also required for patterning in this species, but the function of the gene must have shifted (Fig.5). Analysing the mutant phenotype in zebrafish in more detail, we found that although the gene function is only required in melanophores the shapes of all three types of pigment cells are altered in the mutants ( Fig.6). This underlines the importance of cell-cell interactions in the patterning process. We could show that the functional differences between zebrafish and Danio aesculapii are based on cis-regulatory evolution and we assume that lower expression in the latter species leads to weakened cellular interactions and contributes to the differences in patterns. We have published our results in four papers, so far, with two more in preparation. In addition, the results were presented at several conferences as talks or in poster form.
