Giardia lamblia behavior under cytochalasins treatment

Corrêa, Gladys; Benchimol, Marlene

doi:10.1007/s00436-005-0065-z

Cited by 24 publications

(16 citation statements)

References 43 publications

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“…S2). We observed filamentous actin structures within Giardia, and in contrast to previous studies using heterologous antibodies of unknown specificity (19,20), we did not observe pronounced actin staining of the ventral disk, a microtubule structure used for parasite attachment.…”

Section: Resultscontrasting

confidence: 99%

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An actin cytoskeleton with evolutionarily conserved functions in the absence of canonical actin-binding proteins

Paredez

Assaf

Sept

et al. 2011

Proc. Natl. Acad. Sci. U.S.A.

166

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Giardia intestinalis, a human intestinal parasite and member of what is perhaps the earliest-diverging eukaryotic lineage, contains the most divergent eukaryotic actin identified to date and is the first eukaryote known to lack all canonical actin-binding proteins (ABPs). We sought to investigate the properties and functions of the actin cytoskeleton in Giardia to determine whether Giardia actin (giActin) has reduced or conserved roles in core cellular processes. In vitro polymerization of giActin produced filaments, indicating that this divergent actin is a true filament-forming actin. We generated an anti-giActin antibody to localize giActin throughout the cell cycle. GiActin localized to the cortex, nuclei, internal axonemes, and formed C-shaped filaments along the anterior of the cell and a flagella-bundling helix. These structures were regulated with the cell cycle and in encysting cells giActin was recruited to the Golgi-like cyst wall processing vesicles. Knockdown of giActin demonstrated that giActin functions in cell morphogenesis, membrane trafficking, and cytokinesis. Additionally, Giardia contains a single G protein, giRac, which affects the Giardia actin cytoskeleton independently of known target ABPs. These results imply that there exist ancestral and perhaps conserved roles for actin in core cellular processes that are independent of canonical ABPs. Of medical significance, the divergent giActin cytoskeleton is essential and commonly used actin-disrupting drugs do not depolymerize giActin structures. Therefore, the giActin cytoskeleton is a promising drug target for treating giardiasis, as we predict drugs that interfere with the Giardia actin cytoskeleton will not affect the mammalian host. cytoskeleton evolution | actin protofilaments | MreB | endocytosis | Rac

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Section: Resultscontrasting

confidence: 99%

“…Cytochalasin and latrunculin have been used previously to probe actin function in Giardia often with conflicting results; moreover, in those studies, either no attempt was made to monitor actin distribution during the experiment, or heterologous antibodies (without controls) or phalloidin were used (20,26, reviewed in ref. 8).…”

Section: Resultsmentioning

confidence: 99%

An actin cytoskeleton with evolutionarily conserved functions in the absence of canonical actin-binding proteins

Paredez

Assaf

Sept

et al. 2011

Proc. Natl. Acad. Sci. U.S.A.

166

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“…In Giardia , actin was thought to function only in the attachment to glass and cell surfaces, but recently, this protein has been implicated in morphology and cytokinesis [46]–[49]. Likewise, other reports demonstrated the importance of microfilament integrity for regulated endocytic flow and for recycling of molecules to the plasma membrane [25].…”

Section: Discussionmentioning

confidence: 99%

Rab11 and Actin Cytoskeleton Participate in Giardia lamblia Encystation, Guiding the Specific Vesicles to the Cyst Wall

et al. 2010

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Background Giardia passes through two stages during its life cycle, the trophozoite and the cyst. Cyst formation involves the synthesis of cyst wall proteins (CWPs) and the transport of CWPs into encystation-specific vesicles (ESVs). Active vesicular trafficking is essential for encystation, but the molecular machinery driving vesicular trafficking remains unknown. The Rab proteins are involved in the targeting of vesicles to several intracellular compartments through their association with cytoskeletal motor proteins.Methodology and Principal FindingsIn this study, we found a relationship between Rab11 and the actin cytoskeleton in CWP1 transport. Confocal microscopy showed Rab11 was distributed throughout the entire trophozoite, while in cysts it was translocated to the periphery of the cell, where it colocalized with ESVs and microfilaments. Encystation was also accompanied by changes in rab11 mRNA expression. To evaluate the role of microfilaments in encystation, the cells were treated with latrunculin A. Scanning electron microscopy showed this treatment resulted in morphological damages to encysted parasites. The intensity of fluorescence-labeled Rab11 and CWP1 in ESVs and cyst walls was reduced, and rab11 and cwp1 mRNA levels were down-regulated. Furthermore, knocking down Rab11 with a hammerhead ribozyme resulted in an up to 80% down-regulation of rab11 mRNA. Although this knockdown did not appear lethal for trophozoites and did not affect cwp1 expression during the encystation, confocal images showed CWP1 was redistributed throughout the cytosol.Conclusions and SignificanceOur results indicate that Rab11 participates in the early and late encystation stages by regulating CWP1 localization and the actin-mediated transport of ESVs towards the periphery. In addition, alterations in the dynamics of actin affected rab11 and cwp1 expression. Our results provide new information about the molecules involved in Giardia encystation and suggest that Rab11 and actin may be useful as novel pharmacological targets.

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“…In previous studies, the actin depolymerizing agent cytochalasin D was associated with detachment after 24 hours of exposure [19]–[21]. Here, iso-osmotic addition of cytochalasin D (0.1 mM) to Giardia growth medium had no significant effect on attachment after three minutes of exposure (Figure 2C).…”

Section: Resultsmentioning

confidence: 49%

“…Short-timescale detachment of Giardia has not been examined in the numerous studies of forced detachment, as most assays measure population attachment levels after a period of 2−24 hours incubation with a given drug or medium composition (e.g. [19]–[21],[23]). Such studies have shown that Giardia attachment and survival rates are inhibited by changes in pH and osmolality [23], but the long incubation prior to quantification of attachment makes it very difficult to separate direct effects on attachment from an overall effect on cell viability.…”

Section: Discussionmentioning

confidence: 99%

Tonic Shock Induces Detachment of Giardia lamblia

Hansen

Fletcher

2008

PLoS Negl Trop Dis

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BackgroundThe parasite Giardia lamblia must remain attached to the host small intestine in order to proliferate and subsequently cause disease. However, little is known about the factors that may cause detachment in vivo, such as changes in the aqueous environment. Osmolality within the proximal small intestine can vary by nearly an order of magnitude between host fed and fasted states, while pH can vary by several orders of magnitude. Giardia cells are known to regulate their volume when exposed to changes in osmolality, but the short-timescale effects of osmolality and pH on parasite attachment are not known.Methodology and Principal FindingsWe used a closed flow chamber assay to test the effects of rapid changes in media osmolality, tonicity, and pH on Giardia attachment to both glass and C2Bbe-1 intestinal cell monolayer surfaces. We found that Giardia detach from both surfaces in a tonicity-dependent manner, where tonicity is the effective osmolality experienced by the cell. Detachment occurs with a characteristic time constant of 25 seconds (SD = 10 sec, n = 17) in both hypo- and hypertonic media but is otherwise insensitive to physiologically relevant changes in media composition and pH. Interestingly, cells that remain attached are able to adapt to moderate changes in tonicity. By exposing cells to a timed pattern of tonicity variations and adjustment periods, we found that it is possible to maximize the tonicity change experienced by the cells, overcoming the adaptive response and resulting in extensive detachment.Conclusions and SignificanceThese results, conducted with human-infecting Giardia on human intestinal epithelial monolayers, highlight the ability of Giardia to adapt to the changing intestinal environment and suggest new possibilities for treatment of giardiasis by manipulation of tonicity in the intestinal lumen.

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Giardia lamblia behavior under cytochalasins treatment

Cited by 24 publications

References 43 publications

An actin cytoskeleton with evolutionarily conserved functions in the absence of canonical actin-binding proteins

An actin cytoskeleton with evolutionarily conserved functions in the absence of canonical actin-binding proteins

Rab11 and Actin Cytoskeleton Participate in Giardia lamblia Encystation, Guiding the Specific Vesicles to the Cyst Wall

Tonic Shock Induces Detachment of Giardia lamblia

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