The role of the cytoskeleton in Plasmodium falciparum merozoite biology: an electron-microscopic view.

The biochemical, ultrastructural and experimental data concerning the organization and biological roles of the merozoite cytoskeleton are briefly reviewed. Actin is known to be expressed in the asexual erythrocytic stages, and has also been demonstrated in Plasmodium falciparum merozoites biochemically and visualized by fluorescence microscopy after appropriate labelling. Experimental evidence indicates that actin-myosin-based motility is important in merozoite locomotion during red-cell invasion. Microtubules also occur in P. falciparum merozoites in the form of a small longitudinal band of subpellicular microtubules, and experiments with anti-microtubule drugs indicate that microtubules are involved in some aspect of invasion. In the late-stage schizont, microtubules are also important in merozoite morphogenesis. The numbers and positions of the merozoite apices within the schizont are spatially related to the spindle poles of the final mitotic division, and extranuclear microtubules are probably responsible for the trafficking of vesicles from a single Golgi cisterna to form the apical organelles. In addition to these cytoskeletal structures, numerous short cytoskeletal filaments of unknown composition attach the merozoite plasma membrane to the underlying pellicular cisterna, and this process may drive the budding of merozoites from the parent schizont.