Identification of α-11 giardin as a flagellar and surface component of Giardia lamblia

Identification of target genes regulated by encystation-induced transcription factor Myb2 using knockout mutagenesis in Giardia lamblia

BACKGROUND

Encystation is one of the two processes comprising the life cycle of Giardia lamblia, a protozoan pathogen with tetraploid genome. Giardia lamblia Myb2 (GlMyb2) is a distinct encystation-induced transcription factor whose binding sites are found in the promoter regions of many encystation-induced genes, including its own.

METHODS

Two sequential CRISPR/Cas9 experiments were performed to remove four glmyb2 alleles. The expression level of G. lamblia cyst wall protein 1 (GlCWP1), a well-known target gene of GlMyb2, was measured via western blotting and immunofluorescence assays. Chromatin immunoprecipitation experiments using anti-GlMyb2 antibodies were performed on the encysting G. lamblia cells. Quantitative real-time PCR was performed to confirm an expression of candidate GlMyb2-regulated genes by comparing the transcript level for each target candidate in wild-type and knockout mutant Giardia. The promoter region of glcwp1 was analyzed via deletion and point mutagenesis of the putative GlMyb2 binding sites in luciferase reporters.

RESULTS

Characterization of the null glmyb2 mutant indicated loss of functions related to encystation, i.e. cyst formation, and expression of GlCWP1. The addition of the wild-type glmyb2 gene to the null mutant restored the defects in encystation. Chromatin immunoprecipitation experiments revealed dozens of target genes. Nineteen genes were confirmed as GlMyb2 regulons, which include the glmyb2 gene, six for cyst wall proteins, five for signal transduction, two for transporter, two for metabolic enzymes, and three with unknown functions. Detailed analysis on the promoter region of glcwp1 defined three GlMyb2 binding sites important in its encystation-induced expression.

CONCLUSIONS

Our data confirm that GlMyb2 acts as a transcription activator especially during encystation by comparing the glmyb2 knockout mutant with the wild type. Further investigation using glmyb2 null mutant will provide knowledge regarding transcriptional apparatus required for the encystation process of G. lamblia.

Kinesin-13, a Motor Protein, is Regulated by Polo-like Kinase in Giardia lamblia

Kinesin-13 (Kin-13), a depolymerizer of microtubule (MT), has been known to affect the length of Giardia. Giardia Kin-13 (GlKin-13) was localized to axoneme, flagellar tips, and centrosomes, where phosphorylated forms of Giardia polo-like kinase (GlPLK) were distributed. We observed the interaction between GlKin-13 and GlPLK via co-immunoprecipitation using transgenic Giardia cells expressing Myc-tagged GlKin-13, hemagglutinin-tagged GlPLK, and in vitro-synthesized GlKin-13 and GlPLK proteins. In vitro-synthesized GlPLK was demonstrated to auto-phosphorylate and phosphorylate GlKin-13 upon incubation with [γ-32P]ATP. Morpholino-mediated depletion of both GlKin-13 and GlPLK caused an extension of flagella and a decreased volume of median bodies in Giardia trophozoites. Our results suggest that GlPLK plays a pertinent role in formation of flagella and median bodies by modulating MT depolymerizing activity of GlKin-13.

Characterization of Metronidazole-Resistant Giardia intestinalis Lines by Comparative Transcriptomics and Proteomics

Metronidazole (MTZ) is a clinically important antimicrobial agent that is active against both bacterial and protozoan organisms. MTZ has been used extensively for more than 60 years and until now resistance has been rare. However, a recent and dramatic increase in the number of MTZ resistant bacteria and protozoa is of great concern since there are few alternative drugs with a similarly broad activity spectrum. To identify key factors and mechanisms underlying MTZ resistance, we utilized the protozoan parasite Giardia intestinalis, which is commonly treated with MTZ. We characterized two in vitro selected, metronidazole resistant parasite lines, as well as one revertant, by analyzing fitness aspects associated with increased drug resistance and transcriptomes and proteomes. We also conducted a meta-analysis using already existing data from additional resistant G. intestinalis isolates. The combined data suggest that in vitro generated MTZ resistance has a substantial fitness cost to the parasite, which may partly explain why resistance is not widespread despite decades of heavy use. Mechanistically, MTZ resistance in Giardia is multifactorial and associated with complex changes, yet a core set of pathways involving oxidoreductases, oxidative stress responses and DNA repair proteins, is central to MTZ resistance in both bacteria and protozoa.

A polo-like kinase modulates cytokinesis and flagella biogenesis in Giardia lamblia

BACKGROUND

Polo-like kinases (PLKs) are conserved serine/threonine kinases that regulate the cell cycle. To date, the role of Giardia lamblia PLK (GlPLK) in cells has not been studied. Here, we report our investigation on the function of GlPLK to provide insight into the role of this PKL in Giardia cell division, especially during cytokinesis and flagella formation.

METHODS

To assess the function of GIPLK, Giardia trophozoites were treated with the PLK-specific inhibitor GW843286X (GW). Using a putative open reading frame for the PLK identified in the Giardia genomic database, we generated a transgenic Giardia expressing hemagglutinin (HA)-tagged GlPLK and used this transgenic for immunofluorescence assays (IFAs). GlPLK expression was knocked down using an anti-glplk morpholino to observe its effect on the number of nuclei number and length of flagella. Giardia cells ectopically expressing truncated GlPLKs, kinase domain + linker (GlPLK-KDL) or polo-box domains (GlPLK-PBD) were constructed for IFAs. Mutant GlPLKs at Lys51, Thr179 and Thr183 were generated by site-directed mutagenesis and then used for the kinase assay. To elucidate the role of phosphorylated GlPLK, the phosphorylation residues were mutated and expressed in Giardia trophozoites RESULTS: After incubating trophozoites with 5 μM GW, the percentage of cells with > 4 nuclei and longer caudal and anterior flagella increased. IFAs indicated that GlPLK was localized to basal bodies and flagella and was present at mitotic spindles in dividing cells. Morpholino-mediated GlPLK knockdown resulted in the same phenotypes as those observed in GW-treated cells. In contrast to Giardia expressing GlPLK-PBD, Giardia expressing GlPLK-KDL was defective in terms of GIPLK localization to mitotic spindles and had altered localization of the basal bodies in dividing cells. Kinase assays using mutant recombinant GlPLKs indicated that mutation at Lys51 or at both Thr179 and Thr183 resulted in loss of kinase activity. Giardia expressing these mutant GlPLKs also demonstrated defects in cell growth, cytokinesis and flagella formation.

CONCLUSIONS

These data indicate that GlPLK plays a role in Giardia cell division, especially during cytokinesis, and that it is also involved in flagella formation.

Characterisation of the in vitro activity of a Nitazoxanide-N-methyl-1H-benzimidazole hybrid molecule against albendazole and nitazoxanide susceptible and resistant strains of Giardia intestinalis and its in vivo giardicidal activity

BACKGROUND

It was previously demonstrated that CMC-20, a nitazoxanide and N-methyl-1H-benzimidazole hybrid molecule, had higher in vitro activity against Giardia intestinalis WB strain than metronidazole and albendazole and similar to nitazoxanide.

OBJETIVES

To evaluate the in vitro activity of CMC-20 against G. intestinalis strains with different susceptibility/resistance to albendazole and nitazoxanide and evaluate its effect on the distribution of parasite cytoskeletal proteins and its in vivo giardicidal activity.

METHODS

CMC-20 activity was tested against two isolates from patients with chronic and acute giardiasis, an experimentally induced albendazole resistant strain and a nitazoxanide resistant clinical isolate. CMC-20 effect on the distribution of parasite cytoskeletal proteins was analysed by indirect immunofluorescence and its activity was evaluated in a murine model of giardiasis.

FINDINGS CMC-20

showed broad activity against susceptible and resistant strains to albendazole and nitaxozanide. It affected the parasite microtubule reservoir and triggered the parasite encystation. In this process, alpha-7.2 giardin co-localised with CWP-1 protein. CMC-20 reduced the infection time and cyst load in feces of G. muris infected mice similar to albendazole.

MAIN CONCLUSIONS

The in vitro and in vivo giardicidal activity of CMC-20 suggests its potential use in the treatment of giardiasis.

Microtubule organelles in Giardia

Giardia lamblia is a widespread parasitic protist with a complex MT cytoskeleton that is critical for motility, attachment, mitosis and cell division, and transitions between its two life cycle stages-the infectious cyst and flagellated trophozoite. Giardia trophozoites have both highly dynamic and highly stable MT organelles, including the ventral disc, eight flagella, the median body and the funis. The ventral disc, an elaborate MT organelle, is essential for the parasite's attachment to the intestinal villi to avoid peristalsis. Giardia's four flagellar pairs enable swimming motility and may also promote attachment. They are maintained at different equilibrium lengths and are distinguished by their long cytoplasmic regions and novel extra-axonemal structures. The functions of the median body and funis, MT organelles unique to Giardia, remain less understood. In addition to conserved MT-associated proteins, the genome is enriched in ankyrins, NEKs, and novel hypothetical proteins that also associate with the MT cytoskeleton. High-resolution ultrastructural imaging and a current inventory of more than 300 proteins associated with Giardia's MT cytoskeleton lay the groundwork for future mechanistic analyses of parasite attachment to the host, motility, cell division, and encystation/excystation. Giardia's unique MT organelles exemplify the capacity of MT polymers to generate intricate structures that are diverse in both form and function. Thus, beyond its relevance to pathogenesis, the study of Giardia's MT cytoskeleton informs basic cytoskeletal biology and cellular evolution. With the availability of new molecular genetic tools to disrupt gene function, we anticipate a new era of cytoskeletal discovery in Giardia.

Prokaryotic Expression of α-13 Giardin Gene and Its Intracellular Localization in Giardia lamblia

To study prokaryotic expression and subcellular localization of α-13 giardin in Giardia lamblia trophozoites, α-13 giardin gene was amplified and cloned into prokaryotic expression vector pET-28a(+). The positive recombinant plasmid was transformed into E. coli BL21(DE3) for expression by using IPTG and autoinduction expression system (ZYM-5052). The target protein was validated by SDS-PAGE and Western blotting and purified by Ni-NTA Resin. Rabbits were immunized with purified fusion proteins for preparation of polyclonal antibody; then the intracellular location of α-13 giardin was determined by fluorescence immunoassay. The results showed that the length of α-13 giardin gene was 1038 bp, encoding a polypeptide of 345 amino acids. The expressed product was a fusion protein with about 40 kDa largely present in soluble form. The target protein accounted for 21.0% of total proteins after being induced with IPTG, while it accounted for 28.8% with ZYM-5052. The anti-α13-giardin polyclonal antibody possessed good antigenic specificity as well as excellent binding activity with recombinant α-13 giardin. Immunofluorescence assays revealed that α-13 giardin was localized in the cytoplasm of G. lamblia trophozoite, suggesting that it is a cytoplasm-associated protein. The present study may lay a foundation for further functional research on α-13 giardin of G. lamblia.

Immunolocalization of α18- and α12-giardin in Giardia lamblia trophozoites

To study subcellular localization of α18- and α12-giardin in Giardia lamblia trophozoites, the α18- and α12-giardin genes were amplified from G. lamblia assemblage A, respectively. The PCR products were cloned into the prokaryotic expression vector pET-28a(+), and the positive recombinant plasmids were transformed into E. coli Rosetta (DE3) strain for the expression, and expressed α18- and α12-giardin fusion protein were purified by Ni-Agarose resin, respectively. Mice were immunized with purified fusion proteins for preparation of polyclonal antibody, and then the subcellular localization of α18- and α12-giardin was determined by fluorescence immunoassay. Results showed that the concentrations of purified α18- and α12-giardin fusion proteins were 1.20 and 0.86 mg/ml, respectively. The titers of anti-α18- and anti-α12-giardin polyclonal antibody were both as high as 1:25600 dilutions. Immunofluorescent analysis showed that α18- and α12-giardin proteins were mainly localized at four pairs of flagella and the cytoplasm of G. lamblia trophozoites, suggesting that α18- and α12-giardin are the flagella and cytoplasm-associated proteins, respectively. The above information would lay the foundation for research about the crystal structure and biological function of α18- and α12-giardin.

Sequence analysis and prokaryotic expression of Giardia lamblia α-18 giardin gene

To study the genetic variation and prokaryotic expression of α18 giardin gene of Giardia lamblia zoonotic assemblage A and host-specific assemblage F, the α18 genes were amplified from G. lamblia assemblages A and F by PCR and sequenced. The PCR product was cloned into the prokaryotic expression vector pET-28a(+) and the positive recombinant plasmid was transformed into Escherichia coli Rosetta (DE3) strain for the expression. The expressed α18 giardin fusion protein was validated by SDS-PAGE and Western blot analysis, and purified by Ni-Agarose resin. The putative sequence of α18 giardin amino acid was analyzed by bioinformatics software. Results showed that the α18 giardin gene was 861 bp in length, encoding 286 amino acids; it was 100% homologous between human-derived and dog-derived G. lamblia assemblage A, but it was 86.8% homologous with G. lamblia assemblage F (cat-derived). Giardin α18 was about 36 kDa in molecular weight, with good reactivity. Prediction based on in silico analyses: it had hydrophobicity, without signal peptide and transmembrane domain, and contained 11 alpha regions, 13 beta sheets, 1 beta turn and 7 random coils in secondary structure. The above information would lay the foundation for research about the subcellular localization and biological function of α18 giardin in G. lamblia.