CELL BIOLOGY OF THE PRIMITIVE EUKARYOTE <i>GIARDIA LAMBLIA</i>

Gillin, Frances D.; Reiner, David S.; McCaffery, J. Michael

doi:10.1146/annurev.micro.50.1.679

Cited by 200 publications

(178 citation statements)

References 69 publications

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“…confirmed the general morphological description made for this protozoan by light microscope observations (Hegner 1922, Kulda & Norhýnková 1978, although some features had the proportions altered by the long and slender form of this organism, as observed by Feely and Erlandsen (1985) using the scanning electron microscope (SEM). Our results also showed that the G. agilis trophozoites had the general ultrastructural features of the genus, already described for G. muris and G. duodenalis groups in other animals (for review, see Kulda & Nohýnková 1978, Adam 1991, Gillin et al 1996. In this study some relevant aspects of its morphology are discussed, especially those which clearly show the differences when compared to other species.…”

Section: Discussionsupporting

confidence: 79%

Giardia agilis: Ultrastructure of the Trophozoites in the Frog Intestine

Sogayar¹,

Gregório

1998

Mem. Inst. Oswaldo Cruz

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Intestine samples of Bufo sp. tadpoles with parasitism confirmed for Giardia agilis were studied by transmission electron microscopy. The G. agilis trophozoites were long and thin. The plasma membrane was sometimes undulated and the cytoplasm, adjacent to the dorsal and ventral regions, showed numerous vacuoles. The two nuclei presented prominent nucleoli. The cytoplasm was electron-dense with free ribosomes, glycogen and rough endoplasmic reticulum-like structures. Polyhedral inclusions were observed in the cytoplasm and outside the protozoan; some of these inclusions exhibited membrane disruption. The flagella ultrastructure is typical, with the caudal pair accompanied by the funis. Next to the anterior pair, osmiophilic material was noticed. The ventro-lateral flange was short and thick, supported by the marginal plates that penetrated into its distal extremity; only its distal portion had adjacent osmiophilic filament. The G. agilis trophozoites showed the general subcellular feature of the genus. However, the ventro-lateral flange ultrastructure was an intermediate type between G. muris and G. duodenalis. Key words: ultrastructure -Giardia agilis -trophozoiteGiardia agilis is an intestinal parasite of tadpoles and adult anuran amphibians. It was first described by Kunstler (1822) and later by Alexeieff (1914), Hegner (1922) and Lavier (1935aLavier ( , 1942. In vitro growth for this species has not been reported; apparently they do not cause disease in their hosts (Meyer & Radulescu 1984).The trophozoites have a narrow and elongated body and the adhesive disc length is about onefifth of the body; the median bodies appear as a single club-shaped rod, as revealed by light microscopy (Kulda & Nohýnková 1978). Observations on their general morphology were described with scanning electron microscope by Feely and Erlandsen (1985); however the transmission electron microscopic studies could not be found in the literature. In the present investigation, it was described, for the first time, the subcellular structures of the G. agilis trophozoites. The understanding of its ultrastructure may help to determine the systematic relationship of this organism with G. muris and G. duodenalis. MATERIALS AND METHODSTadpoles of Bufo sp. were collected in the field (Botucatu, SP, Brazil) and maintained in aerated pond water; they were fed with fresh beaten lettuce. The animals were sacrificed by ether inhalation and the small intestine was removed. To confirm the infestation, the intestinal content was smeared on a slide, fixed in Schaudinn's solution, stained by the Heidenhain iron hematoxylin method and examined under a light microscope. Fragments of the small intestines positive for Giardia infestation were fixed in 2.5% glutaraldehyde buffered with 0.1M phosphate buffer pH 7.3 and post-fixed in 1% osmic acid in the same buffer. They were dehydrated in acetone and embedded in Araldite. Ultrathin sections were stained with uranyl acetate and lead citrate and examined with a transmission electron microscope. RESULTS

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Section: Discussionsupporting

confidence: 79%

Giardia agilis: Ultrastructure of the Trophozoites in the Frog Intestine

Sogayar¹,

Gregório

1998

Mem. Inst. Oswaldo Cruz

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“…Children with chronic diarrhea from its infection face the risk of malnutrition and delayed mental development (3). G. lamblia has two life cycle stages in response to different inhospitable environments: a pathogenic trophozoite form and a dormant infectious cyst form (4,5). The cysts are protectively walled and resistant to hypotonic lysis by fresh water and gastric acid and are responsible for transmission of giardiasis.…”

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confidence: 99%

A Novel WRKY-like Protein Involved in Transcriptional Activation of Cyst Wall Protein Genes in Giardia lamblia

Pan

Cho

Kao

et al. 2009

Journal of Biological Chemistry

101

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Synthesis of a protective cyst wall is required for survival outside of the host and for infection of Giardia lamblia. Little is known of gene regulation of the cyst wall proteins (CWPs) during differentiation into dormant cysts. WRKY homologues constitute a large family of DNA-binding proteins in plants that are involved in several key cellular functions, including disease resistance, stress response, dormancy, and development. A putative wrky gene has been identified in the G. lamblia genome. We found that wrky expression levels increased significantly during encystation. The epitope-tagged WRKY was translocated into the nuclei during encystation. Recombinant WRKY specifically bound to its own promoter and the encystation-induced cwp1 and cwp2 promoters. WRKY contains several key residues for DNA binding, and mutation analysis revealed that its binding sequences are similar to those of the known plant WRKY proteins and that two of them are positive cis-acting elements of the wrky and cwp2 promoters. Overexpression of WRKY increased the cwp1-2 and myb2 mRNA levels, and these gene promoters were bound by WRKY in vivo. Interestingly, the wrky and cwp1-2 genes were up-regulated by ERK1 (extracellular signal-related kinase 1) overexpression, suggesting that WRKY may be a downstream component of the ERK1 pathway. In addition, a WRKY mutant that cannot enter nuclei and an ERK1 mutant lacking the predicted kinase domain showed decreased cwp1-2 gene expression. Our results suggest that the WRKY family has been conserved during evolution and that WRKY is an important transactivator of the cwp1-2 genes during G. lamblia differentiation into dormant cysts.

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“…During encystation, G. lamblia synthesizes a resistant extracellular wall, which is composed of proteins and polysaccharide (2,3), protecting the parasite from hypotonic lysis by fresh water and from gastric acid during infection of the new host.…”

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confidence: 99%

Regulation of Cyst Wall Protein Promoters by Myb2 in Giardia lamblia

Su²,

Lee³

et al. 2008

Journal of Biological Chemistry

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Myb family transcription factors are important in regulating cell proliferation, differentiation, and cell cycle progression. Giardia lamblia differentiates into infectious cysts to survive outside of the host. During encystation, genes encoding cyst wall proteins (CWPs) are coordinately induced. We have identified an encystation-induced Myb2 protein, which binds to the promoter regions of the cwp genes and myb2 itself in vitro. To elucidate the role of Myb2 in G. lamblia, we tested the hypothesis that Myb2 can activate encystation-induced genes. We found that overexpression of Myb2 resulted in an increase of expression of CWP1 at both protein and mRNA levels. Interestingly, the Myb2-overexpressing trophozoites had increased capability to differentiate into cysts. In cotransfection assays, Myb2 was able to transactivate the cwp promoters and its own promoter in vivo, suggesting that its gene can be positively autoregulated. Moreover, deletion of the N-or C-terminal domain resulted in a decrease of transactivation and autoregulation function of Myb2. We also found that the promoter of a newly identified encystation-induced gene, the giardial myeloid leukemia factorlike gene, has the Myb2 binding sites and that its mRNA levels were increased by Myb2 overexpression. Chromatin immunoprecipitation assays confirmed that Myb2 was bound to the promoters with its binding sites. Transfection of the myb2 antisense construct reduced the levels of the cwp1 transcripts and cyst formation. Our results suggest that Myb2 is a potent transactivator of the cwp genes and other endogenous genes and plays an important role in G. lamblia differentiation into cysts.

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CELL BIOLOGY OF THE PRIMITIVE EUKARYOTE GIARDIA LAMBLIA

Cited by 200 publications

References 69 publications

Giardia agilis: Ultrastructure of the Trophozoites in the Frog Intestine

Giardia agilis: Ultrastructure of the Trophozoites in the Frog Intestine

A Novel WRKY-like Protein Involved in Transcriptional Activation of Cyst Wall Protein Genes in Giardia lamblia

Regulation of Cyst Wall Protein Promoters by Myb2 in Giardia lamblia

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