Voltage-gated calcium channels generate blastema Ca2+ fluxes restraining zebrafish fin regenerative outgrowth

ABSTRACT Adult zebrafish fins regenerate to their original size regardless of damage extent, providing a tractable organ size control model. Gain-of-function of voltage-gated K+ channels in fibroblast-lineage blastema cells or inhibition of the Ca2+-dependent phosphatase calcineurin causes dramatic fin regenerative overgrowth. However, Ca2+ fluxes and their potential origins from dynamic membrane voltages have not been directly linked to fin size restoration. We used fibroblast-lineage GCaMP imaging of regenerating fins to identify widespread Ca2+ transients in distal blastema cells. Membrane depolarization of isolated fin fibroblasts triggered voltage-gated Ca2+ channel-dependent Ca2+ spikes. Single cell transcriptomics identified cacna1c (L-type channel), cacna1ba (N-type) and cacna1g (T-type) as candidate mediators of fibroblast-lineage Ca2+ signaling. Small molecule inhibition revealed that L- and/or N-type channels act during regenerative outgrowth to restore fins to their original scale. Strikingly, cacna1g homozygous mutant zebrafish regenerated extraordinarily long fins due to prolonged outgrowth. GCaMP imaging showed Cacna1g enables Ca2+ dynamics in the distal blastema. We conclude that ‘bioelectricity’ for fin size control reflects voltage-modulated Ca²+ fluxes in fibroblast-lineage blastemal cells that decelerate outgrowth at a rate tuned to restore the original scale of the fin.