Molecular and cellbiological studies on gametocytogenesis of a malaria parasite, Plasmodium falciparum

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Induction mechanism of gametocytogenesis in a malaria parasite, Plasmodium falciparum was investigated cell-biologically and molecularly, using wild isolates.1. Induction of gametocytogenesis in wild isolates : Induction methods of gametocytogenesis was studied, using wild isolates collected from Myanmar and Indonesia.Gametocytogenesis was observed when the parasite density reached to ca. 5% and then they were cultivated at 3-4 times higher concentrations of RBC than normal culture condition. All wild isolates adapted for in vitro cultivation were capable in forming gametocytes, and their transformation rates reached to 50-70%.2. Induction ofgametocytogenesis by glucose deficiency : As gametocytogenesis was induced by cultivation at higher RBC concentration, it was speculated that nutrient deficiency, particularly glucose, may play important role in triggering this phenomenon. In fact, addition of glucose into the medium inhibited the induction of gametocytogenesis. Furthermore, addition of 2-deoxy glucose was capable in inducing it under a normal culture condition, although a great decrease ofparasitaemia was observed. These results indicated that glucose deficiency might play an important role in inducing gametocytogenesis.3. Trials of induction ofgametocytogenesis in established strains : Using FCR-3 and K-l strains, induction of gametocytogenesis was examined as like in wild isolates, but no gametocyte was formed, suggesting that important genes for induction of gametocytogenesis might be deleted in these strains.4. Identification of master gene(s) for induction of gametocytogenesis : Using a subtraction method between mRNA isolated from gametocyogenesis-induced and non-induced parasites, master gene(s) which may regulate gametocytogenesis was investigated. However, all clones obtained after the subtraction were only heat shock protein genes, and expected genes, such as cAMP-dependent kinases, were not detected.