Commitment to sexual differentiation in the human malaria parasite, Plasmodium falciparum

The differentiation of the two sexes in the gametocytogenesis of Plasmodium falciparum was investigated using a plaque assay and antibodies specific f or various stages and sexes of gametocytes. Immunofluorescence assays on pl aques of cultured parasites grown in monolayers of erythrocytes revealed th at the merozoites released from a single sexually-committed schizont became either all male or all female gametocytes. Thus, the commitment of this sp ecies to differentiate into one sex or the other is likely to occur prior t o the nuclear division of the sexually-committed schizont. The characterist ic female-biased gametocyte sex ratio observed for many Plasmodium species is manifested in P. falciparum by a greater percentage of schizonts that pr oduce female gametocytes (67-71 %) than those that yield males. From the pl aque assay, it tvas determined that the number of gametocytes produced per sexually-committed schizont was similar for both sexes, indicating that all ocation of parasite resources was equal for each sex of gametocyte. The tim ing of sexual differentiation and features of the gametocyte sex ratio is d iscussed in relation to previous observations on P. falciparum and related malaria parasites.