Studies on development of the sexual stages in Plasmodium

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Induction mechanisms of gametogenesis and in vitro development of ookinetes to oocysts in a rodent malaria parasite, Plasmodium berghei, were investigated.1)Induction of gametogenesis was regulated by two distinct mechanisms, one is a low-temperature-dependent DNA synthesis and the other is a pH-dependent control of developmental events leading to microgamete assembly and exflagellation. In these events, Ca^<2+> and cGMP were found to act as second messengers.2)DNA synthesis and axoneme formation in microgametocytes were regulated by Ca^<2+>/calmodulin-dependent metabolic pathways, whereas further events to exflagellation was controlled by cGMP.3)Two separate ion exchangers, i. e., Na^+-dependent HCO_3^-(influx)/ H^+(efflux)and nonspecific-cation-dependent Cl^-(influx)/HCO_3-(efflux)exchangers, were involved in the ionic regulation in the induction of gametogenesis.4)Electron microscopy revealed that ookinetes penetrate the midgut wall of a mosquito, Anopheles omorii, by the intracellular route, although the intracellular occurrence of the parasite was also observed.5)Development of ookinetes to young oocysts was achieved in in vitro culture with or without co-cultivation of mosquito's cells. However, all of transformed young oocysts failed to develop further, i. e., neither deposition of the oocysts capsule nor nuclear division was observed.