title: Ultrastructural study of encystation and excystation in Acanthamoeba castellanii.
abstract: Encystation and excystation of Acanthamoeba castellanii were studied by transmission electron microscopy. The differentiation process was induced in asynchronous cultures grown axenically. Cytoplasmic vesicles containing a dense fibrous material very similar in appearance to the cyst wall were observed in trophozoites induced to encyst. When these trophozoites were incubated with calcofluor white m2r, fluorescence was observed in cytoplasmic vesicles, suggesting that the material contained in these vesicles corresponded to cyst wall precursors. Semithin cryosections of mature cysts with the same treatment showed fluorescence in the ectocyst and a less intense fluorescence in the endocyst, suggesting the presence of cellulose in both structures of the cyst wall. In mature cysts induced to excystation, small structures very similar to electron-dense granules (EDG) previously described in other amoebae were frequently observed. The EDGs were either sparsely distributed in the cytoplasm or associated with the cytoplasmic face of the plasma membrane. Many of them were located near the ostiole. In advanced phases of excystation, endocytic activity was suggested by the formation of endocytic structures and the presence of vacuoles with fibrous content similar to that of the cyst wall. Electron-dense granules in the process of dissolution were also observed in these vacuoles. Furthermore, the formation of a pseudopod suggests a displacement of the amoeba toward the ostiole.
authors.affiliation: Departament of Experimental Pathology, Center for Research and Advanced Studies, Av. IPN 2508, Zacatenco, 07360 Mexico City, Mexico. bchavez@mail.cinvestav.mx
authors.forename: Bibiana
authors.initials: B
authors.lastname: Chávez-Munguía
authors.forename: Maritza
authors.initials: M
authors.lastname: Omaña-Molina
authors.forename: Mónica
authors.initials: M
authors.lastname: González-Lázaro
authors.forename: Arturo
authors.initials: A
authors.lastname: González-Robles
authors.forename: Patricia
authors.initials: P
authors.lastname: Bonilla
authors.forename: Adolfo
authors.initials: A
authors.lastname: Martínez-Palomo
mesh_terms: D048248:Acanthamoeba castellanii / Q000254:growth & development* / Q000648:ultrastructure*; D000818:Animals; D003470:Culture Media; D006801:Humans; D046529:Microscopy, Electron, Transmission; D008856:Microscopy, Fluorescence
chemical_list: D003470:Culture Media