A Novel Multiprotein Bridging Factor 1-Like Protein Induces Cyst Wall Protein Gene Expression and Cyst Differentiation in Giardia lamblia

Protists: Eukaryotic single-celled organisms and the functioning of their organelles

Organelles are membrane bound structures that compartmentalize biochemical and molecular functions. With improved molecular, biochemical and microscopy tools the diversity and function of protistan organelles has increased in recent years, providing a complex panoply of structure/function relationships. This is particularly noticeable with the description of hydrogenosomes, and the diverse array of structures that followed, having hybrid hydrogenosome/mitochondria attributes. These diverse organelles have lost the major, at one time, definitive components of the mitochondrion (tricarboxylic cycle enzymes and cytochromes), however they all contain the machinery for the assembly of Fe-S clusters, which is the single unifying feature they share. The plasticity of organelles, like the mitochondrion, is therefore evident from its ability to lose its identity as an aerobic energy generating powerhouse while retaining key ancestral functions common to both aerobes and anaerobes. It is interesting to note that the apicoplast, a non-photosynthetic plastid that is present in all apicomplexan protozoa, apart from Cryptosporidium and possibly the gregarines, is also the site of Fe-S cluster assembly proteins. It turns out that in Cryptosporidium proteins involved in Fe-S cluster biosynthesis are localized in the mitochondrial remnant organelle termed the mitosome. Hence, different organisms have solved the same problem of packaging a life-requiring set of reactions in different ways, using different ancestral organelles, discarding what is not needed and keeping what is essential. Don't judge an organelle by its cover, more by the things it does, and always be prepared for surprises.

A myeloid leukemia factor homolog is involved in tolerance to stresses and stress-induced protein metabolism in Giardia lamblia

BACKGROUND

The eukaryotic membrane vesicles contain specific sets of proteins that determine vesicle function and shuttle with specific destination. Giardia lamblia contains unknown cytosolic vesicles that are related to the identification of a homolog of human myeloid leukemia factor (MLF) named MLF vesicles (MLFVs). Previous studies suggest that MLF also colocalized with two autophagy machineries, FYVE and ATG8-like protein, and that MLFVs are stress-induced compartments for substrates of the proteasome or autophagy in response to rapamycin, MG132, and chloroquine treatment. A mutant protein of cyclin-dependent kinase 2, CDK2m3, was used to understand whether the aberrant proteins are targeted to degradative compratments. Interestingly, MLF was upregulated by CDK2m3 and they both colocalized within the same vesicles. Autophagy is a self-digestion process that is activated to remove damaged proteins for preventing cell death in response to various stresses. Because of the absence of some autophagy machineries, the mechanism of autophagy is unclear in G. lamblia.

RESULTS

In this study, we tested the six autophagosome and stress inducers in mammalian cells, including MG132, rapamycin, chloroquine, nocodazole, DTT, and G418, and found that their treatment increased reactive oxygen species production and vesicle number and level of MLF, FYVE, and ATG8-like protein in G. lamblia. Five stress inducers also increased the CDK2m3 protein levels and vesicles. Using stress inducers and knockdown system for MLF, we identified that stress induction of CDK2m3 was positively regulated by MLF. An autophagosome-reducing agent, 3-methyl adenine, can reduce MLF and CDK2m3 vesicles and proteins. In addition, knockdown of MLF with CRISPR/Cas9 system reduced cell survival upon treatment with stress inducers. Our newly developed complementation system for CRISPR/Cas9 indicated that complementation of MLF restored cell survival in response to stress inducers. Furthermore, human MLF2, like Giardia MLF, can increase cyst wall protein expression and cyst formation in G. lamblia, and it can colocalize with MLFVs and interact with MLF.

CONCLUSIONS

Our results suggest that MLF family proteins are functionally conserved in evolution. Our results also suggest an important role of MLF in survival in stress conditions and that MLFVs share similar stress-induced characteristics with autophagy compartments.

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.

Genome-wide characterization of the MBF1 gene family and its expression pattern in different tissues and stresses in Zanthoxylum armatum

Background

Multiprotein bridging factor 1 (MBF1) is a crucial transcriptional coactivator in animals, plants, and some microorganisms, that plays a necessary role in growth development and stress tolerance. Zanthoxylum armatum is an important perennial plant for the condiments and pharmaceutical industries, whereas the potential information in the genes related to stress resistance remains poorly understood in Z. armatum. 

Results

Herein, six representative species were selected for use in a genome-wide investigation of the MBF1 family, including Arabidopsis thaliana, Oryza sativa, Populus trichocarpa, Citrus sinensis, Ginkgo biloba, and Z. armatum. The results showed that the MBF1 genes could be divided into two groups: Group I contained the MBF1a and MBF1b subfamilies, and group II was independent of the MBF1c subfamily.. Most species have at least two different MBF1 genes, and MBF1c is usually an essential member. The three ZaMBF1 genes were respectively located on ZaChr26, ZaChr32, and ZaChr4 of Zanthoxylum chromosomes. The collinearity were occurred between three ZaMBF1 genes, and ZaMBF1c showed the collinearity between Z. armatum and both P. trichocarpa and C. sinensis. Moreover, many cis-elements associated with abiotic stress and phytohormone pathways were detected in the promoter regions of MBF1 of six representative species. The ERF binding sites were the most abundant targets in the sequences of the ZaMBF1 family, and some transcription factor sites related to floral differentiation were also identified in ZaMBF1c, such as MADS, LFY, Dof, and AP2. ZaMBF1a was observed to be very highly expressed in 25 different samples except in the seeds, and ZaMBF1c may be associated with the male and female floral initiation processes. In addition, expression in all the ZaMBF1 genes could be significantly induced by water-logging, cold stress, ethephon, methyl jasmonate, and salicylic acid treatments, especially in ZaMBF1c.

Conclusion

The present study carried out a comprehensive bioinformatic investigation related to the MBF1 family in six representative species, and the responsiveness of ZaMBF1 genes to various abiotic stresses and phytohormone inductions was also revealed. This work not only lays a solid foundation to uncover the biological roles of the ZaMBF1 family in Z. armatum, but also provides some broad references for conducting the MBF1 research in other plants.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12864-022-08863-4.

Implementation of a tunable t-CRISPRi system for gene regulation in Giardia duodenalis

Giardia duodenalis, is a binuclear and microaerophilic protozoan that causes giardiasis. Up to date, several molecular approaches have been taken to understand the molecular mechanisms of diverse cellular processes in this parasitic protozoan. However, the role of many genes involved in these processes needs further analysis. The CRISPR interference (CRISPRi) system has been widely used, as a constitutive expression system for gene silencing purposes in several parasites, including Giardia. The aim of this work was to implement a tunable t-CRISPRi system in Giardia to silence abundant, moderately and low expressed genes, by constructing an optimized and inducible plasmid for the expression of both gRNA and dCas9. A doxycycline inducible pRan promoter was used to express dCas9 and each gRNA, consistently dCas9 expression and nuclear localization were confirmed by Western-blot and immunofluorescence in transfected trophozoites. The transcriptional repression was performed on α-tubulin (high expression), giardipain-1 (moderate expression) and Sir2 and Sir4 (low expression) genes. The α-tubulin gene knock-down caused by dCas9 doxycycline-induction was confirmed by a decrease in its protein expression which was of 50% and 60% at 24 and 48 h, respectively. This induced morphological alterations in flagella. The giardipain-1 knock down, showed a decrease in protein expression of 40 and 50% at 12 and 24 h, respectively, without affecting trophozoites viability, consistent with this a zymogram analysis on giardipain-1 knock down revealed a decrease in giardipain-1 protease activity. When repressing sirtuins expression, a total repression was obtained but trophozoites viability was compromised. This approach provides a molecular tool for a tailored repression to produce specific gene knockdowns.

A Novel Spo11 Homologue Functions as a Positive Regulator in Cyst Differentiation in Giardia lamblia

Giardia lamblia persists in a dormant state with a protective cyst wall for transmission. It is incompletely known how three cyst wall proteins (CWPs) are coordinately synthesized during encystation. Meiotic recombination is required for sexual reproduction in animals, fungi, and plants. It is initiated by formation of double-stranded breaks by a topoisomerase-like Spo11. It has been shown that exchange of genetic material in the fused nuclei occurs during Giardia encystation, suggesting parasexual recombination processes of this protozoan. Giardia possesses an evolutionarily conserved Spo11 with typical domains for cleavage reaction and an upregulated expression pattern during encystation. In this study, we asked whether Spo11 can activate encystation process, like other topoisomerases we previously characterized. We found that Spo11 was capable of binding to both single-stranded and double-stranded DNA in vitro and that it could also bind to the cwp promoters in vivo as accessed in chromatin immunoprecipitation assays. Spo11 interacted with WRKY and MYB2 (named from myeloblastosis), transcription factors that can activate cwp gene expression during encystation. Interestingly, overexpression of Spo11 resulted in increased expression of cwp1-3 and myb2 genes and cyst formation. Mutation of the Tyr residue for the active site or two conserved residues corresponding to key DNA-binding residues for Arabidopsis Spo11 reduced the levels of cwp1-3 and myb2 gene expression and cyst formation. Targeted disruption of spo11 gene with CRISPR/Cas9 system led to a significant decrease in cwp1-3 and myb2 gene expression and cyst number. Our results suggest that Spo11 acts as a positive regulator for Giardia differentiation into cyst.