Functional Analysis Of Ca²⁺ Homeostasis During Collective Cell Migration In Vivo

Collective cell migration is an essential process for many morphogenic events during different developmental stages of multicellular organisms.Though functions and mechanisms of Ca2+ homeostasis have been well known in single cell migration system in vitro,how Ca2+ homeostasis regulate and orchestrate collective cell migration is still largely unknown,especially in the in vivo system.Here using Drosophila border cell cluster,we find a higher Ca2+ activity at stage 8 of oogenesis when the cell fate initiates to convert from stationary to migratory.The genetic screen results suggest that not mitochondrial Ca2+ homeostasis,but cytoplasmic Ca2+homeostasis is required for border cell migration,and cytoplasmic Ca2+ homeostasis is maintained by Ca2+-induced Ca2+ release(CICR),but not store-operated Ca2+ entry(SOCE).Besides intracellular Ca2+homeostasis,intercellular Ca2+homeostasis mediated by gap junction protein innexin 2(inx2)plays essential roles in the cooperativity between border cells.Border cells without inx2 show a cell-nonautonomous defect to the wildtype border cells,and the border cell cluster even fails to form in the most severe situation.Unexpectedly,calmodulin(Cam),calcineurin(Can),and protein kinase C 53E(Pkc53E),three important Ca2+-binding proteins are all dispensable for border cell migration suggesting that canonical Ca2+signaling is not the downstream mediator of cytoplasmic Ca2+ homeostasis.