The roles of bioelectric signaling in developmental patterning remain largely unknown, although recent work has implicated bioelectric signals in cellular processes such as proliferation and migration. Here, we report a mutation in the inwardly rectifying potassium channel (kir) gene, kcnj13/kir7.1, that causes elongation of the fins in the zebrafish insertional mutant Dhi2059. A viral DNA insertion into the noncoding region of kcnj13 results in transient activation and ectopic expression of kcnj13 in the somite and dermomyotome, from which the fin ray progenitors originate. We made an allele-specific loss-of-function kcnj13 mutant by CRISPR (clustered regularly interspaced short palindromic repeats) and showed that it could reverse the long-finned phenotype, but only when located on the same chromosome as the Dhi2059 viral insertion. Also, we showed that ectopic expression of kcnj13 in the dermomyotome of transgenic zebrafish produces phenocopies of the Dhi2059 mutant in a gene dosage-sensitive manner. Finally, to determine whether this developmental function is specific to kcnj13, we ectopically expressed three additional potassium channel genes: kcnj1b, kcnj10a, and kcnk9 We found that all induce the long-finned phenotype, indicating that this function is conserved among potassium channel genes. Taken together, our results suggest that dermomyotome bioelectricity is a new fin-patterning mechanism, and we propose a two-stage bioelectricity model for zebrafish fin patterning. This ion channel-regulated bioelectric developmental patterning mechanism may provide with us new insight into vertebrate morphological evolution and human congenital malformations.
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