Research Article: Participation of Actin on Giardia lamblia Growth and Encystation

Date Published: September 23, 2009

Publisher: Public Library of Science

Author(s): Araceli Castillo-Romero, Gloria Leon-Avila, Armando Perez Rangel, Rafael Cortes Zarate, Carlos Garcia Tovar, Jose Manuel Hernandez, Stefan Bereswill.

Abstract: Microfilaments play a determinant role in different cell processes such as: motility, cell division, phagocytosis and intracellular transport; however, these structures are poorly understood in the parasite Giardia lamblia.

Partial Text: Giardia lamblia causes giardiasis worldwide, the infection may course asymptomatic but frequently it causes severe diarrhea, the principal symptom of the disease. During its life cycle, Giardia lamblia presents two stages: the trophozoite and the cyst. The trophozoites are responsible for the symptomatology [1], [2], [3]. The cyst is the infective form, it is very resistant to the environment and can be viable for two or three months in humid places at 4 to 8°C [4]. The trophozoite becomes a cyst as a consequence of some stimuli such as environmental pH changes and/or the concentration of bile salts or cholesterol in the intestine. Morphological and biochemical changes occur as a consequence of still poorly understood signaling which include the synthesis of specific new antigens and the biogenesis of new secretory compartments called encystation specific vesicles (ESV). ESV transport the cyst wall proteins (CWP) and precursor components to the surface of the newly formed cysts [5], [6], [7], [8], [9], [10], [11].

This research is a complementary study on Giardia lamblia microfilaments, it contributes with new evidence about the role of actin in both processes: growth and encystation. Previous reports, in which heterologous actin antibodies were used, described actin distributed in various specific sites of Giardia trophozoites [18], [19]. In this work we used several anti-actin from different sources without any satisfactory result, we used also a monoclonal mouse anti-actin antibody, which has been mostly used and tested to identified actin in plants, mammal cells and other parasites [39], [40], [41], [42], even though we demostrated by Western blotting the specificity of this antibody for actin Giardia in trophozoites and cysts, it was not possible by immunolfuorescence to see the actin label in the previously reported structures (data no show). We used also TRITC-phalloidin, largely used for the specific recognition of microfilaments in many species. It has been reported that actin residues E117, M119, G158, R177, D179, M355 and C374 are important for actin-phalloidin interaction [43], [44], [45], [46]. Drouin et al., (1995), found that Giardia actin has 58% identity with actin from other species, Woodson and Hawse (2002) by a systematic phylogenetic analysis included actin Giardia as a conventional actin. In this study, we confirmed Giardia actin identity by performing a BLAST and an alignment with the Vector software, using the sequence for Giardia actin (GenBank accession no. P51775) together with actin sequences from Dictyostelium (GenBank accession no. EAL62675), Rattus norvegicus ((GenBank accession no. CAA24529), rabbit (GenBank accession no. NP001095153) and human (GenBank accession no. NP001092, NP001605). The result was 99.5% positives and 55.4% identity, also the alignment revealed that Giardia actin indeed has the important residues for phalloidin interaction ( Figure S1).