A DEVELOPMENTAL DEFECT IN PLASMODIUM-FALCIPARUM MALE GAMETOGENESIS

Asexually replicating populations of Plasmodium parasites, including t hose from cloned lines, generate both male and female gametes to compl ete the malaria life cycle through the mosquito. The generation of the se sexual forms begins with the induction of gametocytes from haploid asexual stage parasites in the blood of the vertebrate host. The molec ular processes that govern the differentiation and development of the sexual forms are largely unknown. Here we describe a defect that affec ts the development of competent male gametocytes from a mutant clone o f P. falciparum (Dd2). Comparison of the Dd2 clone to the predecessor clone from which it was derived (W2'82) shows that the defect is a mut ation that arose during the long-term cultivation of asexual stages in vitro. Light and electron microscopic images, and indirect immunofluo rescence assays with male-specific anti-alpha-tubulin II antibodies, i ndicate a global disruption of male development at the gametocyte leve l, with at least a 70-90% reduction in the proportion of mature male g ametocytes by the Dd2 clone relative to W2'82. A high prevalence of ab normal gametocyte forms, frequently containing multiple and unusually large vacuoles, is associated with the defect. The reduced production of mature male gametocytes may reflect a problem in processes that com mit a gametocyte to male development or a progressive attrition of via ble male gametocytes during maturation. The defect is genetically link ed to an almost complete absence of male gamete production and of infe ctivity to mosquitoes. This is the first sex-specific developmental mu tation identified and characterized in Plasmodium.