Potassium Channel-Associated Bioelectricity of the Dermomyotome Determines Fin Patterning in Zebrafish

Abstract

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 dermomyotome, from which the fin ray progenitors originate. We made an allele-specific loss-of-function kcnj13 CRISPR mutant 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 us new insight into vertebrate morphological evolution and human congenital malformations.

Evolution of the potassium channel gene Kcnj13 underlies colour pattern diversification in Danio fish

“…The potassium channel gene Kcnj13. Potassium channels have important roles in tissue patterning 59 , notably in the regulation of allometric growth of fins in D. rerio 57,[60][61][62] . Kcnj13 encodes an inwardly rectifying potassium channel (Kir7.1) conserved in vertebrates ( Supplementary Fig.…”

“…So far, five Kcnj13 alleles, all of which are dominant, have been identified in D. rerio in several independent genetic screens (Supplementary Figs. 4 and 5 ) 37 , 38 , 40 , 56 , 57 . We used the CRISPR/Cas9 system to generate novel mutations in Kcnj13 in D. rerio .…”

longfincausescis-ectopic expression of thekcnh2a ether-a-go-goK+channel to autonomously prolong fin outgrowth

“…Mutations in kcnk5b (K + channel, (Perathoner et al, 2014)), kcc4a / slc12a7A (K + Cl − co-transporter, (Lanni et al, 2019)), or over/ectopic expression of the K + channels kcnj13, kcnj1b , kcnj10a , kcnk9c (Silic et al, 2020), and now kcnh2a (this study) all cause fin overgrowth. Each model may disrupt a common “ion signaling” pathway featuring the fin outgrowth-restraining Ca 2+ -dependent phosphatase calcineurin (Daane et al, 2018; Harris et al, 2020; Kujawski et al, 2014; Lanni et al, 2019; Yi et al, 2020).…”

“…Further, fin overgrowth in the schleier mutant is caused by loss of kcc4a/ slc12a7a , a K + Cl − cotransporter (Lanni et al, 2019). Ectopic expression of kcnj13 , coding for a K + channel, caused by a viral insertion or transgene-mediated expression of the Kcnj1b, Kcnj10a, and Kcnk9c K + channels also causes overgrowth (Silic et al, 2020). Finally, loss of gap junction protein alpha 1b ( gja1 , also known as connexin 43 ) in shortfin mutants suggests involvement of intercellular ion exchange (Iovine and Johnson, 2000).…”

“…Rather, lof t2 fins fail to return to isometric growth as animals reach maturity (Goldsmith et al, 2006; Iovine and Johnson, 2000). Unlike kcnk5b ( alf ) and kcc4a/ slc12a7a ( schlier ) mutants as well as calcineurin inhibition, lof t2 overgrown fins lack other defects such as tissue hyper-vascularization and elongated ray segments (Kujawski et al, 2014; Lanni et al, 2019; McMillan et al, 2018; Perathoner et al, 2014; Silic et al, 2020). The latter phenotype likely reflects the independent disruption of joint formation rather than overgrowth since ray segment number and fin size are not correlated; evx1 mutants, devoid of all fin joints, have normal fin sizes (Schulte et al, 2011; Ton and Iovine, 2013).…”