title: Temperature-induced in vitro transformation of Leishmania mexicana. I. Ultrastructural comparison of culture-transformed and intracellular amastigotes.
abstract: Promastigotes of Leishmania mexicana growing exponentially in vitro at 26 degrees C in mammalian cell culture medium with 10% serum were transformed to amastigote-like forms by elevating the incubation temperature to 34 degrees C. During the first 24-48 h of the transformation process the slender flagellated promastigotes lost their flagella and became smaller and more ovoid. By 72 h, transformation was complete with greater than 95% of the parasites viable as judged by vital dye exclusion. Moreover, these newly transformed parasites were capable of infecting the macrophage-like tumor cell line P388D1, and could reconvert to the promastigote stage upon return to an incubation temperature of 26 degrees C. The transformed amastigote-like parasites survived only 3 days in culture even with daily renewal of the culture medium, possibly indicating the requirement for some factor or factors normally present in the intracellular milieu. Ultrastructural studies revealed the same gross changes observed under light microscopy, and also demonstrated a close similarity in cellular organelles and membrane structure between amastigotes within phagolysosomes of P388D1 and the culture-derived amastigote forms. By these biologic and morphologic criteria the transformed parasites appear to be amastigotes, though further biochemical studies are needed to confirm their strict analogy to intracellular forms. However, the temperature-induced transformation process itself should provide an excellent model system for studying the effects of environment on eukaryotic gene expression.
mesh_terms: D000818:Animals; D002460:Cell Line; D003470:Culture Media; D005407:Flagella / Q000648:ultrastructure; D007891:Leishmania / Q000254:growth & development* / Q000648:ultrastructure; D008264:Macrophages / Q000469:parasitology; D008928:Mitochondria / Q000648:ultrastructure; D013696:Temperature; D013997:Time Factors
chemical_list: D003470:Culture Media