Endocytosis, membrane recycling and sorting of GPI-anchored proteins: Trypanosoma brucei as a model system.

In the flagellated protozoon Trypanosoma brucei, endo- and exocytosis are restricted to a small area of the plasma membrane, the flagellar pocket. All endosomal compartments and the single Golgi complex are located within the posterior part of the cell between the flagellar pocket and the nucleus. The use of reverse genetic tools, including RNA interference, in combination with quantitative 3D-fluorescence and electron microscopic techniques has provided an insight into endosomal membrane traffic, which occurs at a very high rate and appears to exhibit a lower level of complexity than in mammalian cells. The flagellate is an excellent model system for studies on endocytosis, sorting and recycling of glycosylphosphatidylinositol-anchored glycoproteins, because 10(7) molecules of the variant surface glycoprotein form a dense coat at the cell's surface. Because the endocytic rate varies widely at different stages in the parasite's life cycle, trypanosomes may be used for investigating developmental aspects of their endocytic system.