LAUSR

The egress and fertilization of Plasmodium gametes and development of a motile ookinete are the first crucial steps that mediate the successful transmission of the malaria parasites from humans to the Anopheles vector. However, limited information exists about the cell biology and regulation of this process. Technical impediments in the establishment of in vitro conditions for ookinete maturation in Plasmodium falciparum and other human malaria parasites further constrain a detailed characterization of ookinete maturation. Here, using fluorescence microscopy and immunolabeling, we compared P. falciparum ookinete maturation in Anopheles coluzzii mosquitoes in vivo and in cell culture in vitro. Our results identified two critical steps in ookinete maturation that are regulated by distinct mosquito factors, thereby highlighting the role of the mosquito environment in the transmission efficiency of malaria parasites. Graphical Abstract Ookinete development within the mosquito blood bolus is a critical step in malaria transmission. Using time-series approaches, we identified two limiting steps of Plasmodium falciparum ookinete development in vitro: (i) inhibition of transition from round forms (stage I) to knobs (stage II), likely caused by an inefficient fertilization, and (ii) arrest of transition between stages III and IV, associated with morphological abnormalities during protuberance elongation and enlargement. The abnormal protuberance at stage IV prevents further nuclear migration from the round body to the appendage.