Plasma membrane specializations in a trypanosomatid flagellate

A spiralling cytoskeleton of microtubules closely underlies the plasma membrane of the trypanosomatid Leptomonas collosoma. Links between the membrane and the microtubules can be seen in thin sections of whole cells and in negatively stained isolated membrane-microtubule complexes. Freeze-fracture images of the membrane reveal occasional rows of intramembrane particles on the PF face aligned with the microtubules, but the majority of particles on the cell body are randomly distributed. Organized particles are also found on a membrane fold of the flagellar pocket with which microtubules are closely associated. The basal region of the flagellum possesses a modified flagellar necklace on the PF face and, in the same area, aggregates of large particles that cleave with the EF face and are aligned with flagellar projections. Where the flagellum emerges from the pocket, its membrane contains a patch of particles corresponding to the desmosome between the flagellum and the lip of the pocket. The density and size of the intramembrane particles are different for the body, pocket, and flagellar membrane regions.