Members of the Entamoeba genus synthesize several proteins, which are secreted. Cisternae of the endoplasmic reticulum and a putative Golgi have been identified by confocal microscopy of cellslabeled with NBD-ceramide ands by transmission electron microscopy (Mazzuco et al. 1997). Biochemical and molecular studies have shown the presence of an endoplasmic reticulum retention receptor ERD2, a cis-Golgi-associated transmembrane protein (Sanchez-Lopez et al. 1998). BiP, a known marker of the ER, has also been identified in E. histolytica (Ghosh et al. 1999). Proteins present on the surface of E. histolytica, as the Ser-rich protein and the Gal or GalNAc lectin are inserted into the plasma membrane via fusion of secretory vesicles to the membrane. During the process of encystation, which has been studied mainly inE. invadens, proteins such as chitinase, localized using an immunocytochemical approach, were seen in many secretory vesicles (Ghosh et al. 1999). During encystation of E. histolytica trophozoites large vacuoles with a densely packed filamentous content were observed. They contained chitin since were labeled when cells were incubated in the presence of calcofluor (Chávez-Munguía et al. 2004). It was suggested that these vacuoles are equivalent to the encystation vesicles described during encystation of G. lamblia.
The work carried out in the author's laboratory has been supported by Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq), Fundação Carlos Chagas Filho de Amparo à Pesquisado Estado do Rio de Janeiro (FAPERJ) and Programa de Núcleos de Excelência (PRONEX).