Fig. 4

Cell-autonomy of melanophore requirement for Jam3b. (A) Fluorescently labeled wild-type cells that developed as myotome (shown here) or epidermis did not rescue the pigment pattern of jam3b mutant hosts (n ​= ​4 individuals developed these cell types of 11 informative chimeras). (B) Wild-type cells that developed as melanophores in psr mutant hosts exhibited wild-type morphologies and arrangements, whether or not these cells developed in the vicinity of wild-type iridophores (left and right details, respectively). Transplanted cells in these experiments were transgenic for actb2:EGFP, which is broadly expressed across a variety of cell types, but variegated in iridophores, and pnp4a:mem-mCherry, which is expressed reliably in iridophores (Patterson and Parichy, 2013; Spiewak et al., 2018). Images are stitched from multiple tiles and melanosomes were contracted partially towards cell centers by epinephrine treatment to facilitate detection of actb2:EGFP (n ​= ​10 individuals developed these cell types). (C) In ltk mutant fish, iridophores are absent and fewer melanophores develop, resulting in spots rather than stripes (upper right) (Frohnhofer et al., 2013; Lopes et al., 2008; Patterson and Parichy, 2013). jam3b mutant melanophore phenotypes were similar whether fish were wild-type for ltk (irid+, lower left) or mutant for ltk (irid–, lower right). (D) jam3b mutants expressing wild-type Jam3b mosaically in melanophores had partially rescued melanophore morphologies and patterns (upper panels; uninjected control, lower panel). Note that mitfa and the mitfa regulatory region used here are expressed in melanophores and melanoblasts, as well as xanthophores; the binucleate state revealed by nucVenus expression is typical of mature, well-spread melanophores (Eom et al., 2012; Saunders et al., 2019).