TPC2-mediated Ca2+ signaling is required for axon extension in caudal primary motor neurons in zebrafish embryos

The role of TPC2-mediated Ca2+ release was recently characterized in zebrafish during the establishment of the early spinal circuitry, one of the key events in the coordination of neuromuscular activity. Here, we extend our study to investigate the in vivo role of TPC2 in the regulation of caudal primary motor neuron (CaP) axon extension. We used a combination of: TPC2 knock-down with a translational-blocking morpholino antisense oligonucleotide (MO); TPC2 knock-out via the generation of a tpcn2dhkz1a mutant line of zebrafish using CRISPR/Cas9 gene-editing; and pharmacological inhibition of TPC2 via incubation with bafilomycin A1 (an H+-ATPase inhibitor) or trans-ned-19 (an NAADP receptor antagonist), and showed that these treatments attenuated CaP Ca2+ signaling and inhibited axon extension. We also characterized the expression of an arc1-like transcript in CaPs grown in primary culture. MO-mediated knock-down of ARC1-like in vivo led to an attenuation of the Ca2+ transients in the CaP growth cones, and an inhibition of axon extension. Together our new data suggest a link between ARC1-like, TPC2 and Ca2+ signaling during axon extension in zebrafish.