Developmental change in signal transduction regulating neurite outgrowth

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The aid of this study is to clarify signal transduction mechanisms regulating neurite outgrowth which show dynamic change in accordance with developmental process. Calcium acts important second messenger in the intracellular signal pathways in a variety of cell function. Intracellular calcium ion is strictly regulated and its optimal concentration is required for a proper neurite outgrowth. We first examined source of calcium for neurite outgrowth and calcium-dependent signaling in cultured dorsal root ganglion (DRG) neurons from early or late stages of chick embryos. In early developmental stages, calcium release from internal stores through inositol 1.4.5-trisphosphate (IP3) receptors was found to contribute on neurite outgrowth of chick DRG neuron, while calcium increases by influxes through plasma membrane and by release form internal stores through ryanodine receptors were found to be important for the neurite outgrowth. We next examined the calcium signal cascade regulating neuri … More te outgrowth in the early developmental stage. Neuronal calcium sensor-1 (NCS-1) is a high-affinity and low-capacity calcium binding protein that is specifically expressed in the nervous system. We found the clustering of NCS-1 in the growth cone that is located at a distal tip of neurite in chick DRG neurons. Immunocytochemistry revealed that NCS-1 was co-localized with type 1 IP3 receptor in the growth cone. Pharmacological inhibition of IP3 receptors decreased clustering distribution of NCS-1 in the growth cones and inhibited neurite outgrowth, but not affect growth cone morphology. Acute localized loss of NCS-1 function in the growth cone induced by chromophore-assisted laser inactivation (CALI) resulted in growth arrest of neurites and lamellipodial retraction, but not filopodial retraction. These findings suggest that calcium signaling mediated by NCS-1 in growth cone may regulate the intracellular calcium signaling regulating both of growth cone morphology and neurite outgrowth, and may functionally linked to InsP_3R1 in growth cone may promote neurite outgrowth in the earty developmental stages. Less