Ferreira Ludmila R P, Dossin Fernando de M, Ramos Thiago C, Freymüller Edna, Schenkman Sergio
Departamento de Microbiologia, Imunologia e Parasitologia, Universidade Federal de São Paulo, São Paulo, SP, Brazil.
An Acad Bras Cienc. 2008 Mar;80(1):157-66. doi: 10.1590/s0001-37652008000100011.
The differentiation of proliferating epimastigote forms of Trypanosoma cruzi , the protozoan parasite that causes Chagas disease, into the infective and non-proliferating metacyclic forms can be reproduced in the laboratory by incubating the cells in a chemically-defined medium that mimics the urine of the insect vector. Epimastigotes have a spherical nucleus, a flagellum protruding from the middle of the protozoan cell, and a disk-shaped kinetoplast -- an organelle that corresponds to the mitochondrial DNA. Metacyclic trypomastigotes have an elongated shape with the flagellum protruding from the posterior portion of the cell and associated with a spherical kinetoplast. Here we describe the morphological events of this transformation and characterize a novel intermediate stage by three-dimensional reconstruction of electron microscope serial sections. This new intermediate stage is characterized by a kinetoplast compressing an already elongated nucleus, indicating that metacyclogenesis involves active movements of the flagellar structure relative to the cell body. As transcription occurs more intensely in proliferating epimastigotes than in metacyclics, we also examined the presence of RNA polymerase II and measured transcriptional activity during the differentiation process. Both the presence of the enzyme and transcriptional activity remain unchanged during all steps of metacyclogenesis. RNA polymerase II levels and transcriptional activity only decrease after metacyclics are formed. We suggest that transcription is required during the epimastigote-to-metacyclic trypomastigote differentiation process, until the kinetoplast and flagellum reach the posterior position of the parasites in the infective form.
克氏锥虫是一种导致恰加斯病的原生动物寄生虫，其增殖型上鞭毛体形式向感染性且非增殖型循环后期形式的分化，可在实验室中通过将细胞置于模拟昆虫媒介尿液的化学限定培养基中孵育来重现。上鞭毛体有一个球形细胞核、一条从原生动物细胞中部伸出的鞭毛以及一个盘状动质体——一种对应于线粒体DNA的细胞器。循环后期锥鞭毛虫呈细长形，鞭毛从细胞后部伸出并与一个球形动质体相连。在此，我们描述了这种转变的形态学事件，并通过电子显微镜连续切片的三维重建来表征一个新的中间阶段。这个新的中间阶段的特征是动质体挤压已经拉长的细胞核，这表明循环后期发育涉及鞭毛结构相对于细胞体的主动运动。由于增殖型上鞭毛体中的转录比循环后期形式更为活跃，我们还检测了RNA聚合酶II的存在情况，并测量了分化过程中的转录活性。在循环后期发育的所有步骤中，该酶的存在和转录活性均保持不变。只有在循环后期形式形成后，RNA聚合酶II水平和转录活性才会下降。我们认为，在上鞭毛体向循环后期锥鞭毛虫的分化过程中需要转录，直到动质体和鞭毛到达感染形式的寄生虫的后部位置。
