Inhibition of SOCE disrupts cytokinesis in zebrafish embryos via inhibition of cleavage furrow deepening

During the first few cell division cycles in zebrafish, distinct Ca2+ transients are localized to the early embryonic cleavage furrows, where they accompany (and are required for) furrow positioning, propagation, deepening and apposition. It has previously been shown that the endoplasmic reticulum (ER) acts as the primary store for generating these Ca2+ transients via release through inositol 1,4,5-trisphosphate receptors (IP(3)Rs). We hypothesised that maintaining the elevated levels of intracellular Ca2+ required for deepening and apposition of the cleavage furrows in these large eggs might result in the depletion of the available ER Ca2+ store, thus the role of store-operated Ca2+ entry (SOCE) was examined. Newly fertilized, dechorionated embryos were incubated with various SOCE inhibitors, starting just prior to the onset of the first cell division cycle. The effect of these inhibitors on mitosis, furrow positioning, propagation, deepening and apposition, and the generation of the cytokinetic Ca2+ transients was determined. Treatment with 2-APB or SKF 96365 had no major effect on mitosis, furrow positioning or propagation, but inhibited furrow deepening resulting in regression of the cleavage furrow. Both of these inhibitors also blocked the furrowing Ca2+ transient, with SKF 96365 having a more profound inhibitory effect than 2-APB. In zebrafish, SOCE does not appear to be required for mitosis or the early stages of cytokinesis during the early embryonic cell division cycles, but it does appear to be essential for maintaining the elevated levels of [Ca2+](i) for the extended periods that are required during furrow deepening and daughter cell apposition.