Abstract
The development of the pigmentation pattern in zebrafish is a tightly regulated process that depends on both the self-organizing properties of pigment cells and extrinsic cues from other tissues. Many of the known mutations that alter the pattern act cell-autonomously in pigment cells, and our knowledge about external regulators is limited. Here, we describe novel zebrafish mau mutants, which encompass several dominant missense mutations in Aquaporin 3a (Aqp3a) that lead to broken stripes and short fins. A loss-of-function aqp3a allele, generated by CRISPR-Cas9, has no phenotypic consequences, demonstrating that Aqp3a is dispensable for normal development. Strikingly, the pigment cells from dominant mau mutants are capable of forming a wild-type pattern when developing in a wild-type environment, but the surrounding tissues in the mutants influence pigment cell behaviour and interfere with the patterning process. The mutated amino acid residues in the dominant alleles line the pore surface of Aqp3a and influence pore permeability. These results demonstrate an important effect of the tissue environment on pigment cell behaviour and, thereby, on pattern formation.
Highlights
The zebrafish adult colour pattern of alternating blue and gold stripes is the result of spatially and temporarily controlled interactions among pigment cells: yellow xanthophores, silvery iridophores and black melanophores
We describe novel mutations in aqp3a in zebrafish that result in an aberrant pigmentation pattern as well as short fins
We show that pigment cells are not directly affected, but that the tissue environment is changed by the mutations
Summary
The zebrafish adult colour pattern of alternating blue and gold stripes is the result of spatially and temporarily controlled interactions among pigment cells (chromatophores): yellow xanthophores, silvery iridophores and black melanophores. RESULTS mau mutants have missense mutations in aqp3a In several screens for zebrafish mutants with pigment pattern defects we identified four mau mutant alleles (tVE1, tXGU1, tVBU1, tWGU2), which exhibited similar phenotypes with undulating, broken stripes and short fins (Fig. 1A-E,K-M). We created a transgenic line expressing sfGFP-Aqp3a wild type (WT) or R220Q under the epidermis-specific keratin promoters krtt1c19e [basal layer of epidermis, which gives rise to all the strata of adult skin (Lee et al, 2014)] and krt4 [ known as krt, enveloping layer and periderm-specific (Gong et al, 2002)] Neither of these transgenes had any effect on the trunk patterning, Tg(krtt1c19e: sfGFP-Aqp3aR220Q) fish showed slight defects in fin pigmentation (e.g. the stripes do not reach the margin of the caudal fin). The krt promoter is known to drive expression in the periderm and simple epithelia (Imboden et al, 1997; Gong et al, 2002), we observed weak fluorescence in fin ray segments of post-metamorphic and adult fish (Fig. 6G,H), and this expression is likely to be responsible for the short fin phenotype
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