longfin causes cis-ectopic expression of the kcnh2a ether-a-go-go K+ channel to autonomously prolong fin outgrowth

Abstract

Organs stop growing to achieve a characteristic size and shape in scale with the body of an animal. Likewise, regenerating organs sense injury extents to instruct appropriate replacement growth. Fish fins exemplify both phenomena through their tremendous diversity of form and remarkably robust regeneration. The classic zebrafish mutant longfint2 develops and regenerates dramatically elongated fins and underlying ray skeleton. We show longfint2 chromosome 2 overexpresses the ether-a-go-go-related voltage-gated potassium channel kcnh2a. Genetic disruption of kcnh2a in cis rescues longfint2, indicating longfint2 is a regulatory kcnh2a allele. We find longfint2 fin overgrowth originates from prolonged outgrowth periods by showing Kcnh2a chemical inhibition during late stage regeneration fully suppresses overgrowth. Cell transplantations demonstrate longfint2-ectopic kcnh2a acts tissue autonomously within the fin intra-ray mesenchymal lineage. Temporal inhibition of the Ca2+-dependent phosphatase calcineurin indicates it likewise entirely acts late in regeneration to attenuate fin outgrowth. Epistasis experiments suggest longfint2-expressed Kcnh2a inhibits calcineurin output to supersede growth cessation signals. We conclude ion signaling within the growth-determining mesenchyme lineage controls fin size by tuning outgrowth periods rather than altering positional information or cell-level growth potency.

Evolution of inwardly rectifying potassium channels and their gene expression in zebrafish embryos

“…Recently, we demonstrated that the ectopic expression of the kcnj13 gene in zebrafish somites could lead to elongated fins in zebrafish 23 . Additionally, kcnk5 , slc12a7a , and knnh2a mutant zebrafish develop long fins in zebrafish 46‐48 . Thus, the temporal and transient kir genes' expression could be a cellular bioelectric signal for developmental patternings, such as seen in the ectopic somite gene expression of kcnj13 in our long‐fin mutant Dhi2059.…”

“…23 Additionally, kcnk5, slc12a7a, and knnh2a mutant zebrafish develop long fins in zebrafish. [46][47][48] Thus, the temporal and transient kir genes' expression could be a cellular bioelectric signal for developmental patternings, such as seen in the ectopic somite gene expression of kcnj13 in our long-fin mutant Dhi2059. It is reasonable to speculate that the somite expression of kcnj2a, kcnj11, kcnj5, and other K+ channels (eg, KCa) 49 could be part of a general endogenous fin patterning regulation system for zebrafish fins.…”

The genetic architecture of phenotypic diversity in the Betta fish ( Betta splendens )

“…The smg8 protein acts as a regulator of kinase activity involved in nonsense-mediated decay of mRNAs ( 35 ) and is an unlikely candidate of the long-fin phenotype. In contrast, kcnj15 encodes a potassium channel, which is a much better candidate, as several genes encoding potassium channels, including kcnk5b ( 36 ), kcnh2a ( 37 ), kcnj13 ( 38 ), and kcc4a ( 39 ), have been identified to cause various long-fin phenotypes in zebrafish. Moreover, when comparing the expression profiles of the two candidate genes in caudal fin between long-fin and short-fin individuals by RNA sequencing (RNA-seq), we found that the expression levels of smg8 were similar between different fish groups, while kcnj15 showed a significant difference as it is highly expressed in long-fin breeds ( Fig.…”

Bioelectricity in Developmental Patterning and Size Control: Evidence and Genetically Encoded Tools in the Zebrafish Model

“…The causal mutant gene of the lof has remained unknown for decades until recently. Two independent reports pinpointed Kcnh2a, a voltage-gated potassium channel [ 105 , 106 ]. There is a 0.9 Mb chromosomal reversion upstream of the kcnh2a gene on chromosome 2 [ 106 ].…”