Characterization of ADP-ribosyl cyclase 1-like (ARC1-like) activity and NAADP signaling during slow muscle cell development in zebrafish embryos

We recently demonstrated the requirement of two-pore channel type 2 (TPC2)-mediated Ca ²⁺ release during slow muscle cell differentiation and motor circuit maturation in intact zebrafish embryos. However, the upstream trigger(s) of TPC2/Ca ²⁺ signaling during these developmental processes remains unclear. Nicotinic acid adenine dinucleotide phosphate (NAADP) is a potent Ca ²⁺ mobilizing messenger, which is suggested to target TPC2 in mediating the release of Ca ²⁺ from acidic vesicles. Here, we report the molecular cloning of the zebrafish ADP ribosyl cyclase (ARC) homolog (i.e., ARC1-like), which is a putative enzyme for generating NAADP. We characterized the expression of the arc1-like transcript and the NAADP levels between ~ 16 h post-fertilization (hpf) and ~ 48 hpf in whole zebrafish embryos. We showed that if ARC1-like (when fused with either EGFP or tdTomato) was overexpressed it localized in the plasma membrane, and associated with intracellular organelles, such as the acidic vesicles, Golgi complex and sarcoplasmic reticulum, in primary muscle cell cultures. Morpholino (MO)-mediated knockdown of arc1-like or pharmacological inhibition of ARC1-like (via treatment with nicotinamide), led to an attenuation of Ca ²⁺ signaling and disruption of slow muscle cell development. In addition, the injection of arc1-like mRNA into ARC1-like morphants partially rescued the Ca ²⁺ signals and slow muscle cell development. Together, our data might suggest a link between ARC1-like, NAADP, TPC2 and Ca ²⁺ signaling during zebrafish myogenesis.