The characteristic striped pigment pattern in zebrafish is formed by three types of pigment cells: black melanophores, yellow xanthophores, and iridescent iridophores. The patterning process depends on self-organizing properties of pigment cells, as well as extrinsic cues. By now most of the known pigment pattern formation mutations in zebrafish act cell autonomously in pigment cells, and our knowledge of the patterning regulation by surrounding tissues is scarce.
Here, we describe four dominant missense mutations in mau/Aquaporin 3a (Aqp3a), which is one of the main aquaporins in zebrafish skin and epithelia, known to transport water, glycerol and some other solutes. All four mutations lead to a similar phenotype: although all three types of pigment cells are present in the skin, the mutants display irregularities and broken stripes. In addition, they have short fins with fewer, but normally sized, fin ray segments. Blastula transplantations indicate that all the pigment cells types of mau mutants are capable of forming a wild-type-like pattern, but the mutant tissue environment prevents them from doing so. CRISPR-Cas9 knock-out of mau, which leads to no phenotypic consequences, and experiments in Xenopus oocytes as well as expression of mutant variants of Aqp3a in mammalian cells and zebrafish embryos indicated that mau mutations are neomorphic and their effect is dose-dependent. Based on transcriptome analysis and visualization of calcium distribution in the tissues of mau and wild-type fish, we suggest calcium signaling as a factor influencing behavior of pigment cells and their communication with surrounding tissues.