Form and function in the trypanosomal secretory pathway.

Recent advances in secretory biology of African trypanosomes reveal both similarities and striking differences with other model eukaryotic organisms. Secretion is streamlined for rapid and selective transport of the major cargo, VSG. Selectivity in the early and post-Golgi compartments is dependent on glycosylphosphatidyl inositol anchors. Streamlining includes reduced organellar abundance, and close association of ER exit sites with Golgi and with unique flagellar cytoskeletal elements that govern organellar replication and segregation. These elements include a novel centrin containing bilobe structure. Innate signals for post-Golgi sorting of biosynthetic lysosomal cargo trafficking have been defined, as have pathways for both biosynthetic and endocytic trafficking to the lysosome. Less well-defined secretory organelles such as the multivesicular body and acidocalcisomes are receiving closer scrutiny.