Exploiting CRISPR-Cas9 technology to investigate individual histone modifications

Epigenetic Modifications of Hormonal Signaling Pathways in Plant Drought Response and Tolerance for Sustainable Food Security

Drought significantly challenges global food security, necessitating a comprehensive understanding of plant molecular responses for effective mitigation strategies. Epigenetic modifications, such as DNA methylation and histone modifications, are key in regulating genes and hormones essential for drought response. While microRNAs (miRNAs) primarily regulate gene expression post-transcriptionally, they can also interact with epigenetic pathways as potential effectors that influence chromatin remodeling. Although the role of miRNAs in epigenetic memory is still being explored, understanding their contribution to drought response requires examining these indirect effects on epigenetic modifications. A key aspect of this exploration is epigenetic memory in drought-adapted plants, offering insights into the transgenerational inheritance of adaptive traits. Understanding the mechanisms that govern the maintenance and erasure of these epigenetic imprints provides nuanced insights into how plants balance stability and flexibility in their epigenomes. A major focus is on the dynamic interaction between hormonal pathways-such as those for abscisic acid (ABA), ethylene, jasmonates, and salicylic acid (SA)-and epigenetic mechanisms. This interplay is crucial for fine-tuning gene expression during drought stress, leading to physiological and morphological adaptations that enhance plant drought resilience. This review also highlights the transformative potential of advanced technologies, such as bisulfite sequencing and CRISPR-Cas9, in providing comprehensive insights into plant responses to water deficit conditions. These technologies pave the way for developing drought-tolerant crops, which is vital for sustainable agriculture.

CRISPR-Cas9 Gene Editing: Curing Genetic Diseases by Inherited Epigenetic Modifications

Introduction  CRISPR-Cas9 gene editing, leveraging bacterial defense mechanisms, offers precise DNA modifications, holding promise in curing genetic diseases. This review critically assesses its potential, analyzing evidence on therapeutic applications, challenges, and future prospects. Examining diverse genetic disorders, it evaluates efficacy, safety, and limitations, emphasizing the need for a thorough understanding among medical professionals and researchers. Acknowledging its transformative impact, a systematic review is crucial for informed decision-making, responsible utilization, and guiding future research to unlock CRISPR-Cas9's full potential in realizing the cure for genetic diseases. Methods  A comprehensive literature search across PubMed, Scopus, and the Web of Science identified studies applying CRISPR-Cas9 gene editing for genetic diseases, following the Preferred Reporting Items for Systematic Reviews and Meta-Analyses guidelines. Inclusion criteria covered in vitro and in vivo models targeting various genetic diseases with reported outcomes on disease modification or potential cure. Quality assessment revealed a generally moderate to high risk of bias. Heterogeneity prevented quantitative meta-analysis, prompting a narrative synthesis of findings. Discussion  CRISPR-Cas9 enables precise gene editing, correcting disease-causing mutations and offering hope for previously incurable genetic conditions. Leveraging inherited epigenetic modifications, it not only fixes mutations but also restores normal gene function and controls gene expression. The transformative potential of CRISPR-Cas9 holds promise for personalized treatments, improving therapeutic outcomes, but ethical considerations and safety concerns must be rigorously addressed to ensure responsible and safe application, especially in germline editing with potential long-term implications.

Mitotic inheritance of genetic and epigenetic information via the histone H3.1 variant

The replication-dependent histone H3.1 variant, ubiquitous in multicellular eukaryotes, has been proposed to play key roles during chromatin replication due to its unique expression pattern restricted to the S phase of the cell cycle. Here, we describe recent discoveries in plants regarding molecular mechanisms and cellular pathways involving H3.1 that contribute to the maintenance of genomic and epigenomic information. First, we highlight new advances concerning the contribution of the histone chaperone CAF-1 and the TSK-H3.1 DNA repair pathway in preventing genomic instability during replication. We then summarize the evidence connecting H3.1 to specific roles required for the mitotic inheritance of epigenetic states. Finally, we discuss the recent identification of a specific interaction between H3.1 and DNA polymerase epsilon and its functional implications.

Direct assessment of histone function using histone replacement

Histones serve many purposes in eukaryotic cells in the regulation of diverse genomic processes, including transcription, replication, DNA repair, and chromatin organization. As such, experimental systems to assess histone function are fundamental resources toward elucidating the regulation of activities occurring on chromatin. One set of important tools for investigating histone function are histone replacement systems, in which endogenous histone expression can be partially or completely replaced with a mutant histone. Histone replacement systems allow systematic screens of histone regulatory functions and the direct assessment of functions for histone residues. In this review, we describe existing histone replacement systems in model organisms, the benefits and limitations of these systems, and opportunities for future research with histone replacement strategies.

MG149 Inhibits MOF-Mediated p53 Acetylation to Attenuate X-Ray Radiation-Induced Apoptosis in H9c2 Cells

Cardiomyocyte apoptosis is involved in the pathogenesis of radiation-induced heart disease, but the underlying epigenetic mechanism remains elusive. We evaluated the potential mediating role of males absent on the first (MOF) in the association between epigenetic activation of p53 lysine 120 (p53K120) and X-ray radiation-induced apoptosis in H9c2 cells. H9c2 cells were pretreated for 24 h with the MOF inhibitor MG149 after 4 Gy irradiation, followed by assessment of cell proliferation, injury, and apoptosis. MOF expression was upregulated by X-ray radiation. MG149 suppressed the proliferation inhibition, reduction of mitochondrial membrane potential, ROS production, and cell apoptosis. MG149 may promote the survival of H9c2 cells via inhibition of MOF-mediated p53K120 acetylation in response to X-ray radiation-induced apoptosis. Our data indicates a MOF-associated epigenetic mechanism in H9c2 cells that promotes attenuation of X-ray radiation-induced injury.

CRISPR-Cas9: Taming protozoan parasites with bacterial scissor

The invention of CRISPR-Cas9 technology has opened a new era in which genome manipulation has become precise, faster, cheap and more accurate than previous genome editing strategies. Despite the intricacies of the genomes associated with several protozoan parasites, CRISPR-Cas9 has made a substantial contribution to parasitology. The study of functional genomics through CRISPR-Cas9 mediated gene knockout, insertion, deletion and mutation has helped in understanding intrinsic parasite biology. The invention of CRISPR-dCas9 has helped in the programmable control of protozoan gene expression and epigenetic engineering. CRISPR and CRISPR-based alternatives will continue to thrive and may aid in the development of novel anti-protozoan strategies to tame the protozoan parasites in the imminent future.

Improved loss-of-function CRISPR-Cas9 genome editing in human cells concomitant with inhibition of TGF-β signaling

Strategies to modulate cellular DNA repair pathways hold immense potential to enhance the efficiency of CRISPR-Cas9 genome editing platform. In the absence of a repair template, CRISPR-Cas9-induced DNA double-strand breaks are repaired by the endogenous cellular DNA repair pathways to generate loss-of-function edits. Here, we describe a reporter-based assay for expeditious measurement of loss-of-function editing by CRISPR-Cas9. An unbiased chemical screen performed using this assay enabled the identification of small molecules that promote loss-of-function editing. Iterative rounds of screens reveal Repsox, a TGF-β signaling inhibitor, as a CRISPR-Cas9 editing efficiency enhancer. Repsox invariably increased CRISPR-Cas9 editing in a panel of commonly used cell lines in biomedical research and primary cells. Furthermore, Repsox-mediated editing enhancement in primary human CD4+ T cells enabled the generation of HIV-1-resistant cells with high efficiency. This study demonstrates the potential of transiently targeting cellular pathways by small molecules to improve genome editing for research applications and is expected to benefit gene therapy efforts.

Oligo targeting for profiling drug resistance mutations in the parasitic trypanosomatids

Trypanosomatids cause the neglected tropical diseases, sleeping sickness, Chagas disease and the leishmaniases. Studies on these lethal parasites would be further facilitated by new and improved genetic technologies. Scalable precision editing methods, for example, could be used to improve our understanding of potential mutations associated with drug resistance, a current priority given that several new anti-trypanosomal drugs, with known targets, are currently in clinical development. We report the development of a simple oligo targeting method for rapid and precise editing of priority drug targets in otherwise wild type trypanosomatids. In Trypanosoma brucei, approx. 50-b single-stranded oligodeoxynucleotides were optimal, multiple base edits could be incorporated, and editing efficiency was substantially increased when mismatch repair was suppressed. Resistance-associated edits were introduced in T. brucei cyclin dependent kinase 12 (CRK12, L482F) or cleavage and polyadenylation specificity factor 3 (N232H), in the Trypanosoma cruzi proteasome β5 subunit (G208S), or in Leishmania donovani CRK12 (G572D). We further implemented oligo targeting for site saturation mutagenesis, targeting codon G492 in T. brucei CRK12. This approach, combined with amplicon sequencing for codon variant scoring, revealed fourteen resistance conferring G492 edits encoding six distinct amino acids. The outputs confirm on-target drug activity, reveal a variety of resistance-associated mutations, and facilitate rapid assessment of potential impacts on drug efficacy.

Is There a Histone Code for Cellular Quiescence?

Many of the cells in our bodies are quiescent, that is, temporarily not dividing. Under certain physiological conditions such as during tissue repair and maintenance, quiescent cells receive the appropriate stimulus and are induced to enter the cell cycle. The ability of cells to successfully transition into and out of a quiescent state is crucial for many biological processes including wound healing, stem cell maintenance, and immunological responses. Across species and tissues, transcriptional, epigenetic, and chromosomal changes associated with the transition between proliferation and quiescence have been analyzed, and some consistent changes associated with quiescence have been identified. Histone modifications have been shown to play a role in chromatin packing and accessibility, nucleosome mobility, gene expression, and chromosome arrangement. In this review, we critically evaluate the role of different histone marks in these processes during quiescence entry and exit. We consider different model systems for quiescence, each of the most frequently monitored candidate histone marks, and the role of their writers, erasers and readers. We highlight data that support these marks contributing to the changes observed with quiescence. We specifically ask whether there is a quiescence histone “code,” a mechanism whereby the language encoded by specific combinations of histone marks is read and relayed downstream to modulate cell state and function. We conclude by highlighting emerging technologies that can be applied to gain greater insight into the role of a histone code for quiescence.

CRISPRing protozoan parasites to better understand the biology of diseases

Precise gene editing techniques are paramount to gain deeper insights into the biological processes such as host-parasite interactions, drug resistance mechanisms, and gene-function relationships. Discovery of CRISPR-Cas9 system has spearheaded mechanistic understanding of protozoan parasite biology as evident from the number of reports in the last decade. Here, we have described the use of CRISPR-Cas9 in understanding the biology of medically important protozoan parasites such as Plasmodium, Leishmania, Trypanosoma, Babesia and Trichomonas. In spite of intrinsic difficulties in genome editing in these protozoan parasites, CRISPR-Cas9 has acted as a catalyst for faster generation of desired transgenic parasites. Modifications in the CRISPR-Cas9 system for improving the efficiency have been useful in better understanding the molecular mechanisms associated with repair of double strand breaks in the parasites. Moreover, improvement in reagents used for CRISPR mediated gene editing have been instrumental in addressing the issue of non-specificity and toxicity for therapeutic use. These application-based modifications may help in further increasing the efficiency of gene editing in protozoan parasites.

A CRISPR-Cas9 based shuffle system for endogenous histone H3 and H4 combinatorial mutagenesis

Post-translational modifications of histone proteins greatly impact gene expression and cell fate decisions in eukaryotes. To study these, it is important to develop a convenient, multiplex, and efficient method to precisely introduce mutations to histones. Because eukaryotic cells usually contain multiple copies of histone genes, it is a challenge to mutate all histones at the same time by the traditional homologous recombination method. Here, we developed a CRISPR-Cas9 based shuffle system in Saccharomyces cerevisiae, to generate point mutations on both endogenous histone H3 and H4 genes in a rapid, seamless and multiplex fashion. Using this method, we generated yeast strains containing histone triple H3–K4R–K36R–K79R mutants and histone combinatorial H3–K56Q–H4–K59A double mutants with high efficiencies (70–80%). This CRISPR-Cas9 based mutagenesis system could be an invaluable tool to the epigenetics field.

Application of CRISPR/Cas9-Based Reverse Genetics in Leishmania braziliensis: Conserved Roles for HSP100 and HSP23

The protozoan parasite Leishmania (Viannia) braziliensis (L. braziliensis) is the main cause of human tegumentary leishmaniasis in the New World, a disease affecting the skin and/or mucosal tissues. Despite its importance, the study of the unique biology of L. braziliensis through reverse genetics analyses has so far lagged behind in comparison with Old World Leishmania spp. In this study, we successfully applied a cloning-free, PCR-based CRISPR–Cas9 technology in L. braziliensis that was previously developed for Old World Leishmania major and New World L. mexicana species. As proof of principle, we demonstrate the targeted replacement of a transgene (eGFP) and two L. braziliensis single-copy genes (HSP23 and HSP100). We obtained homozygous Cas9-free HSP23- and HSP100-null mutants in L. braziliensis that matched the phenotypes reported previously for the respective L. donovani null mutants. The function of HSP23 is indeed conserved throughout the Trypanosomatida as L. majorHSP23 null mutants could be complemented phenotypically with transgenes from a range of trypanosomatids. In summary, the feasibility of genetic manipulation of L. braziliensis by CRISPR–Cas9-mediated gene editing sets the stage for testing the role of specific genes in that parasite’s biology, including functional studies of virulence factors in relevant animal models to reveal novel therapeutic targets to combat American tegumentary leishmaniasis.

Histone Modifications and Other Facets of Epigenetic Regulation in Trypanosomatids: Leaving Their Mark

Histone posttranslational modifications (PTMs) modulate several eukaryotic cellular processes, including transcription, replication, and repair. Vast arrays of modifications have been identified in conventional eukaryotes over the last 20 to 25 years. While initial studies uncovered these primarily on histone tails, multiple modifications were subsequently found on the central globular domains as well. Histones are evolutionarily conserved across eukaryotes, and a large number of their PTMs and the functional relevance of these PTMs are largely conserved.

Histone posttranslational modifications (PTMs) modulate several eukaryotic cellular processes, including transcription, replication, and repair. Vast arrays of modifications have been identified in conventional eukaryotes over the last 20 to 25 years. While initial studies uncovered these primarily on histone tails, multiple modifications were subsequently found on the central globular domains as well. Histones are evolutionarily conserved across eukaryotes, and a large number of their PTMs and the functional relevance of these PTMs are largely conserved. Trypanosomatids, however, are early diverging eukaryotes. Although possessing all four canonical histones as well as several variants, their sequences diverge from those of other eukaryotes, particularly in the tails. Consequently, the modifications they carry also vary. Initial analyses almost 15 years ago suggested that trypanosomatids possessed a smaller collection of histone modifications. However, exhaustive high resolution mass spectrometry analyses in the last few years have overturned this belief, and it is now evident that the “histone code” proposed by Allis and coworkers in the early years of this century is as complex in these organisms as in other eukaryotes. Trypanosomatids cause several diseases, and the members of this group of organisms have varied lifestyles, evolving diverse mechanisms to evade the host immune system, some of which have been found to be principally controlled by epigenetic mechanisms. This minireview aims to acquaint the reader with the impact of histone PTMs on trypanosomatid cellular processes, as well as other facets of trypanosomatid epigenetic regulation, including the influence of three-dimensional (3D) genome architecture, and discusses avenues for future investigations.

A transient CRISPR/Cas9 expression system for genome editing in Trypanosoma brucei

OBJECTIVE

Generation of knockouts and in situ tagging of genes in Trypanosoma brucei has been greatly facilitated by using CRISPR/Cas9 as a genome editing tool. To date, this has entailed using a limited number of cell lines that are stably transformed to express Cas9 and T7 RNA polymerase (T7RNAP). It would be desirable, however, to be able to use CRISPR/Cas9 for any trypanosome cell line.

RESULTS

We describe a sequential transfection expression system that enables transient expression of the two proteins, followed by delivery of PCR products for gRNAs and repair templates. This procedure can be used for genome editing without the need for stable integration of the Cas9 and T7RNAP genes.

Culturing and Transfection of Pleomorphic Trypanosoma brucei

Cultivation of pleomorphic Trypanosoma brucei strains was introduced in 1996 when matrix dependence of growth of natural isolates was recognized. Semisolid agarose or liquid methylcellulose are currently used and here we provide optimized protocols for these culture methods and for transfection of pleomorphic strains. Although more laborious than standard liquid culture, culture of native pleomorphic strains is important for a number of research questions including differentiation, virulence, tissue tropism, and regulated metabolism. Some subclones of pleomorphic strains have acquired matrix independence upon passage in culture but maintained a pleomorphic phenotype. It appears that matrix dependence and pleomorphism are not tightly linked traits, yet phenotypes have to be verified before choosing one of these subclones for given experiments. Based on direct comparisons, we give recommendations for pleomorphic strain selection and culture conditions that guarantee truly pleomorphic and differentiation competent Trypanosoma brucei.

A single amino acid substitution (H451Y) in Leishmania calcium-dependent kinase SCAMK confers high tolerance and resistance to antimony

Background

For almost a century, antimonials have remained the first-line drugs for the treatment of leishmaniasis. However, little is known about their mode of action and clinical resistance mechanisms.

Objectives

We have previously shown that Leishmania nicotinamidase (PNC1) is an essential enzyme for parasite NAD+ homeostasis and virulence in vivo. Here, we found that parasites lacking the pnc1 gene (Δpnc1) are hypersusceptible to the active form of antimony (SbIII) and used these mutant parasites to better understand antimony’s mode of action and the mechanisms leading to resistance.

Methods

SbIII-resistant WT and Δpnc1 parasites were selected in vitro by a stepwise selection method. NAD(H)/NADP(H) dosages and quantitative RT–PCR experiments were performed to explain the susceptibility differences observed between strains. WGS and a marker-free CRISPR/Cas9 base-editing approach were used to identify and validate the role of a new resistance mutation.

Results

NAD+-depleted Δpnc1 parasites were highly susceptible to SbIII and this phenotype could be rescued by NAD+ precursor or trypanothione precursor supplementation. Δpnc1 parasites could become resistant to SbIII by an unknown mechanism. WGS revealed a unique amino acid substitution (H451Y) in an EF-hand domain of an orphan calcium-dependent kinase, recently named SCAMK. When introduced into a WT reference strain by base editing, the H451Y mutation allowed Leishmania parasites to survive at extreme concentrations of SbIII, potentiating the rapid emergence of resistant parasites.

Conclusions

These results establish that Leishmania SCAMK is a new central hub of antimony’s mode of action and resistance development, and uncover the importance of drug tolerance mutations in the evolution of parasite drug resistance.

State-of-the-art CRISPR/Cas9 Technology for Genome Editing in Trypanosomatids

CRISPR/Cas9 technology has revolutionized biology. This prokaryotic defense system against foreign DNA has been repurposed for genome editing in a broad range of cell tissues and organisms. Trypanosomatids are flagellated protozoa belonging to the order Kinetoplastida. Some of its most representative members cause important human diseases affecting millions of people worldwide, such as Chagas disease, sleeping sickness and different forms of leishmaniases. Trypanosomatid infections represent an enormous burden for public health and there are no effective treatments for most of the diseases they cause. Since the emergence of the CRISPR/Cas9 technology, the genetic manipulation of these parasites has notably improved. As a consequence, genome editing is now playing a key role in the functional study of proteins, in the characterization of metabolic pathways, in the validation of alternative targets for antiparasitic interventions, and in the study of parasite biology and pathogenesis. In this work we review the different strategies that have been used to adapt the CRISPR/Cas9 system to Trypanosoma cruzi, Trypanosoma brucei, and Leishmania spp., as well as the research progress achieved using these approaches. Thereby, we will present the state-of-the-art molecular tools available for genome editing in trypanosomatids to finally point out the future perspectives in the field.

Programmed knockout mutation of liver fluke granulin attenuates virulence of infection-induced hepatobiliary morbidity

Infection with the food-borne liver fluke Opisthorchis viverrini is the principal risk factor (IARC Working Group on the Evaluation of Carcinogenic Risks to Humans, 2012) for cholangiocarcinoma (CCA) in the Lower Mekong River Basin countries including Thailand, Lao PDR, Vietnam and Cambodia. We exploited this link to explore the role of the secreted growth factor termed liver fluke granulin (Ov-GRN-1) in pre-malignant lesions by undertaking programmed CRISPR/Cas9 knockout of the Ov-GRN-1 gene from the liver fluke genome. Deep sequencing of amplicon libraries from genomic DNA of gene-edited parasites revealed Cas9-catalyzed mutations within Ov-GRN-1. Gene editing resulted in rapid depletion of Ov-GRN-1 transcripts and the encoded Ov-GRN-1 protein. Gene-edited parasites colonized the biliary tract of hamsters and developed into adult flukes, but the infection resulted in reduced pathology as evidenced by attenuated biliary hyperplasia and fibrosis. Not only does this report pioneer programmed gene-editing in parasitic flatworms, but also the striking, clinically-relevant pathophysiological phenotype confirms the role for Ov-GRN-1 in virulence morbidity during opisthorchiasis.

Simplified inducible system for Trypanosoma brucei

Nowadays, most reverse genetics approaches in Trypanosoma brucei, a protozoan parasite of medical and veterinary importance, rely on pre-established cell lines. Consequently, inducible experimentation is reduced to a few laboratory strains. Here we described a new transgene expression system based exclusively on endogenous transcription activities and a minimum set of regulatory components that can easily been adapted to different strains. The pTbFIX vectors are designed to contain the sequence of interest under the control of an inducible rRNA promoter along with a constitutive dicistronic unit encoding a nucleus targeted tetracycline repressor and puromycin resistance genes in a tandem “head-to-tail” configuration. Upon doxycycline induction, the system supports regulatable GFP expression (170 to 400 fold) in both bloodstream and procyclic T. brucei forms. Furthermore we have adapted the pTbFIX plasmid to perform RNAi experimentation. Lethal phenotypes, including α-tubulin and those corresponding to the enolase and clathrin heavy chain genes, were successfully recapitulated in procyclic and bloodstream parasites thus showing the versatility of this new tool.