The calcium (Ca²⁺) signals that help to regulate neuro-muscular development consist of a complex interaction between signal transduction pathways and gene transcription. The challenge when exploring, modulating, and visualizing these Ca²⁺ signals, lies in their spatial and temporal nature, as well as in the variety of Ca²⁺ mobilizing agents and receptors that come into play. The most recently identified agonist/ receptor pair that has been reported to be involved in skeletal muscle differentiation and nervous system development is nicotinic acid adenine dinucleotide phosphate (NAADP) and the two-pore channel (TPC), respectively, where NAADP has been shown to be the most potent intracellular Ca²⁺ mobilizing agent described to date. Here, I present new data that describe what app...[ Read more ]

The calcium (Ca²⁺) signals that help to regulate neuro-muscular development consist of a complex interaction between signal transduction pathways and gene transcription. The challenge when exploring, modulating, and visualizing these Ca²⁺ signals, lies in their spatial and temporal nature, as well as in the variety of Ca²⁺ mobilizing agents and receptors that come into play. The most recently identified agonist/ receptor pair that has been reported to be involved in skeletal muscle differentiation and nervous system development is nicotinic acid adenine dinucleotide phosphate (NAADP) and the two-pore channel (TPC), respectively, where NAADP has been shown to be the most potent intracellular Ca²⁺ mobilizing agent described to date. Here, I present new data that describe what appears to be a complex relationship between Ca²⁺ released via TPC2, and that released via the well-known ryanodine receptor (RyR) and inositol trisphosphate receptor (IP₃R) during zebrafish neuro-muscular development. I show that their differential couplings and interactions, which were deduced from: 1) Various molecular, genetic, and pharmacological manipulations; in conjunction with 2) Ca²⁺ imaging; and 3) immunolabelling followed by either confocal or stimulated emission depletion super-resolution microscopy, are necessary for myogenesis, motor axonogenesis, and spinal circuitry maturation during the segmentation period of zebrafish development. In addition, I suggest that the neuromuscular junctions that form the functional link between the motor network and muscle are also regulated by TPC2-mediated Ca²⁺ signalling. Furthermore, I identify the putative enzyme responsible for NAADP synthesis (i.e., ADP-ribosyl cyclase; ARC), in zebrafish embryos in silico. I then confirm the expression of the ARC homolog at the transcript and protein levels across the segmentation stages in embryos. My study, therefore, demonstrates the robust requirement of NAADP/TPC2/Ca²⁺ signalling throughout the formation and onset of function of the motor neurons and muscle cells in zebrafish embryos, which results in the development of their motility.