Oosporogenesis by Lagenidium giganteum: induction and maturation are regulated by calcium and calmodulin.

Induction and maturation of the sexual stage (oospores) of the facultative mosquito parasite Lagenidium giganteum (Oomycetes: Lagenidiales) are complex developmental processes regulated by calcium-dependent events. Use of developmentally synchronized cultures of L. giganteum allowed stage-specific disruption of calcium metabolism. A calcium chelator (EGTA), an ionophore (chlortetracycline), and inhibitors of the calcium-binding protein calmodulin (dibucaine, trifluoperazine, chlorpromazine) disrupted several discrete developmental steps associated with oosporogenesis: induction of antheridia, gametangial fusion, meiosis, oospore wall formation, and subsequent spore maturation. Extracellular calcium is necessary for oosporogenesis to proceed normally and under some conditions magnesium has a synergistic effect with calcium on oospore induction. Results are discussed in relation to calcium mediation of fusion events in a number of model membrane and biological systems.