Cytoplasmic inclusions and organelles of in vitro cultured Trypanosoma theileri and Trypanosoma melophagium and some speculations on their function

Impairment of sterol biosynthesis leads to phosphorus and calcium accumulation in Leishmania acidocalcisomes

The induction of the formation of inclusion vesicles in Leishmania amazonensis by the sterol biosynthesis inhibitors (SBI) ketoconazole and terbinafine has been reported previously. These compartments were recently identified as acidocalcisomes. By the use of electron spectroscopic imaging and energy loss spectroscopy, the presence of calcium, phosphorus and oxygen in the electron-dense inclusions located within the acidocalcisomes has been demonstrated. Endoplasmic reticulum cisternae formed membrane whorls which enclosed large portions of the cytoplasm and sometimes circumscribed acidocalcisomes. In addition, acid phosphatase activity, as well as the endocytic tracers horseradish peroxidase and gold-labelled transferrin and cystatin C were detected within these organelles in both SBI-treated and untreated parasites. These data suggest that impairment of sterol biosynthesis induces the biogenesis of acidocalcisomes and triggers an autophagic process that leads to intersection of the endosomal/lysosomal system with the acidocalcisomes.

Protein uptake and digestion in bloodstream and culture forms of Trypanosoma brucei

The mechanisms of ferritin uptake and digestion differ in bloodstream and culture forms of Trypanosoma brucei. Ferritin enters bloodstream forms from the flagellar pocket by pinocytosis in large spiny-coated vesicles. These vesicles become continuous with straight tubular extensions of a complex, mostly tubular, collecting membrane membrane system where ferritin is concentrated. From the collecting membrane system the tracer enters large digestive vacuoles. Small spiny-coated vesicles, which never contain ferritin, are found in the Golgi region, fusing with the collecting membrane system, and around the flagellar pocket. Acid phosphatase activity is present in some small spiny-coated vesicles which may represent primary lysosomes. This enzymic activity is also found in the flagellar pocket, pinocytotic vesicles, the collecting membrane system, the Golgi (mature face), and digestive vacuoles of bloodstream forms. About 50 percent of the acid phosphatase activity of blood forms is latent. The remaining nonlatent activity is firmly cell-associated and probably represents activity in the flagellar pocket. The structures involved in ferritin uptake and digestion are larger and more active in the short stumpy than in the long slender bloodstream forms. The short stumpy forms also have more autophagic vacuoles. No pinocytotic large, spiny-coated vesicles or Golgi-derived, small spiny-coated vesicles are seen in culture forms. Ferritin leaves the flagellar pocket of these forms and enters small smooth cisternae located just beneath bulges in the pocket membrane. The tracer then passes through a cisternal collecting membrane network, where it is concentrated, and then into multivesicular bodies. In the culture forms, acid phosphatase activity is localized in the cisternal system, multivesicular bodies, the Golgi (mature face), and small vesicles in the Golgi and cisternal regions. The flagellar pocket has no acid phosphatase activity, and almost all the acitvity is latent in these forms. The culture forms do not release acid phosphatase into culture medium during 4 days growth. Uptake of ferritin by all forms is almost completely inhibited by low temperature. These differences among the long slender and short stumpy bloodstream forms and culture forms are undoubtedly adaptive and reflect different needs of the parasite in different life cycle stages.

Ultrastructure of Trypanosoma duttoni

Trypanosoma duttoni exhibits the typical trypanosome morphology in that it is bounded by a unit membrane which included its anterior flagellum; it is surrounded by a framework of suppellicular fibrils, and it contains a nucleus and the posteriorly located kinetoplast-blepharoplast structures along with cytoplasmic organelles (mitochondria, Golgi, and enoplasmic reticulum). Very prominently displayed in T. duttoni is the contractile vacuole, which has not previously received wide-spread recognition. The kinetoplast is clearly continuous with mitochondria in some cases. Inclusion bodies are categorized into three distinct types, none of which can be conclusively designated as the very popular volutin granules, without cytochemical evidence. The existence of a third tubule among peripheral tubule doublets of the flagellum is observed.