Genome-wide microhomologies enable precise template-free editing of biologically relevant deletion mutations

Exploring factors influencing choice of DNA double-strand break repair pathways

DNA double-strand breaks (DSBs) represent one of the most severe threats to genomic integrity, demanding intricate repair mechanisms within eukaryotic cells. A diverse array of factors orchestrates the complex choreography of DSB signaling and repair, encompassing repair pathways, such as non-homologous end-joining, homologous recombination, and polymerase-θ-mediated end-joining. This review looks into the intricate decision-making processes guiding eukaryotic cells towards a particular repair pathway, particularly emphasizing the processing of two-ended DSBs. Furthermore, we elucidate the transformative role of Cas9, a site-specific endonuclease, in revolutionizing our comprehension of DNA DSB repair dynamics. Additionally, we explore the burgeoning potential of Cas9's remarkable ability to induce sequence-specific DSBs, offering a promising avenue for precise targeting of tumor cells. Through this comprehensive exploration, we unravel the intricate molecular mechanisms of cellular responses to DSBs, shedding light on both fundamental repair processes and cutting-edge therapeutic strategies.

Simultaneous genetic transformation and genome editing of mixed lines in soybean (Glycine max) and maize (Zea mays)

Robust genome editing technologies are becoming part of the crop breeding toolbox. Currently, genome editing is usually conducted either at a single locus, or multiple loci, in a variety at one time. Massively parallel genomics platforms, multifaceted genome editing capabilities, and flexible transformation systems enable targeted variation at nearly any locus, across the spectrum of genotypes within a species. We demonstrate here the simultaneous transformation and editing of many genotypes, by targeting mixed seed embryo explants with genome editing machinery, followed by re-identification through genotyping after plant regeneration. Transformation and Editing of Mixed Lines (TREDMIL) produced transformed individuals representing 101 of 104 (97%) mixed elite genotypes in soybean; and 22 of 40 (55%) and 9 of 36 (25%) mixed maize female and male elite inbred genotypes, respectively. Characterization of edited genotypes for the regenerated individuals identified over 800 distinct edits at the Determinate1 (Dt1) locus in samples from 101 soybean genotypes and 95 distinct Brown midrib3 (Bm3) edits in samples from 17 maize genotypes. These results illustrate how TREDMIL can help accelerate the development and deployment of customized crop varieties for future precision breeding.

Supplementary Information

The online version contains supplementary material available at 10.1007/s42994-024-00173-5.

ACE2 knockout hinders SARS-CoV-2 propagation in iPS cell-derived airway and alveolar epithelial cells

Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2), the causative agent of COVID-19, continues to spread around the world with serious cases and deaths. It has also been suggested that different genetic variants in the human genome affect both the susceptibility to infection and severity of disease in COVID-19 patients. Angiotensin-converting enzyme 2 (ACE2) has been identified as a cell surface receptor for SARS-CoV and SARS-CoV-2 entry into cells. The construction of an experimental model system using human iPS cells would enable further studies of the association between viral characteristics and genetic variants. Airway and alveolar epithelial cells are cell types of the lung that express high levels of ACE2 and are suitable for in vitro infection experiments. Here, we show that human iPS cell-derived airway and alveolar epithelial cells are highly susceptible to viral infection of SARS-CoV-2. Using gene knockout with CRISPR-Cas9 in human iPS cells we demonstrate that ACE2 plays an essential role in the airway and alveolar epithelial cell entry of SARS-CoV-2 in vitro. Replication of SARS-CoV-2 was strongly suppressed in ACE2 knockout (KO) lung cells. Our model system based on human iPS cell-derived lung cells may be applied to understand the molecular biology regulating viral respiratory infection leading to potential therapeutic developments for COVID-19 and the prevention of future pandemics.

GHR-mutant pig derived from domestic pig and microminipig hybrid zygotes using CRISPR/Cas9 system

BACKGROUND

Pigs are excellent large animal models with several similarities to humans. They provide valuable insights into biomedical research that are otherwise difficult to obtain from rodent models. However, even if miniature pig strains are used, their large stature compared with other experimental animals requires a specific maintenance facility which greatly limits their usage as animal models. Deficiency of growth hormone receptor (GHR) function causes small stature phenotypes. The establishment of miniature pig strains via GHR modification will enhance their usage as animal models. Microminipig is an incredibly small miniature pig strain developed in Japan. In this study, we generated a GHR mutant pig using electroporation-mediated introduction of the CRISPR/Cas9 system into porcine zygotes derived from domestic porcine oocytes and microminipig spermatozoa.

METHODS AND RESULTS

First, we optimized the efficiency of five guide RNAs (gRNAs) designed to target GHR in zygotes. Embryos that had been electroporated with the optimized gRNAs and Cas9 were then transferred into recipient gilts. After embryo transfer, 10 piglets were delivered, and one carried a biallelic mutation in the GHR target region. The GHR biallelic mutant showed a remarkable growth-retardation phenotype. Furthermore, we obtained F1 pigs derived from the mating of GHR biallelic mutant with wild-type microminipig, and GHR biallelic mutant F2 pigs through sib-mating of F1 pigs.

CONCLUSIONS

We have successfully demonstrated the generation of biallelic GHR-mutant small-stature pigs. Backcrossing of GHR-deficient pig with microminipig will establish the smallest pig strain which can contribute significantly to the field of biomedical research.

Characterization of homozygous Foxn1 mutations induced in rat embryos by different delivery forms of Cas9 nuclease

BACKGROUND

The Cas9 nuclease is delivered in the form of either Cas9 protein or mRNA along with CRISPR guide RNA (gRNA: dual-crRNA:tracrRNA or chimeric single-guide RNA) or in a plasmid package encoding both Cas9 and the CRISPR gRNA.

METHODS AND RESULTS

We directly compared the efficiency of producing rat blastocysts with homozygous mutations of the Foxn1 locus by pronuclear injection of Cas9 in the form of protein, mRNA, or plasmid DNA. For highly efficient production of rat blastocysts with homozygous Foxn1 mutations, pronuclear injection of Cas9 protein at 60 ng/µl was likely optimal. While blastocyst harvest in the mRNA groups was higher than those in the protein and plasmid DNA groups, genotype analysis showed that 63.6%, 8.7-20.0%, and 25.0% of the analyzed blastocysts were homozygous mutants in the protein, mRNA, and plasmid DNA groups, respectively. The high efficiency of producing homozygous mutant blastocysts in the 60 ng/µl protein group may be associated with primary genome editing being initiated before the first cleavage. In most cases, homozygous mutations at the target Foxn1 locus are triggered by deletion and repair via nonhomologous end joining or microhomology-mediated end joining. Deletion downstream of the Cas9 break site was more likely than deletion in the upstream direction.

CONCLUSIONS

The Cas9 nuclease in protein form, when coinjected with the CRISPR gRNA (ribonucleoprotein) into a rat zygote pronucleus, can access the target genome site and induce double-strand breaks promptly, resulting in the efficient production of homozygous mutants.

Developing Bottom-Up Induced Pluripotent Stem Cell Derived Solid Tumor Models Using Precision Genome Editing Technologies

Advances in genome and tissue engineering have spurred significant progress and opportunity for innovation in cancer modeling. Human induced pluripotent stem cells (iPSCs) are an established and powerful tool to study cellular processes in the context of disease-specific genetic backgrounds; however, their application to cancer has been limited by the resistance of many transformed cells to undergo successful reprogramming. Here, we review the status of human iPSC modeling of solid tumors in the context of genetic engineering, including how base and prime editing can be incorporated into "bottom-up" cancer modeling, a term we coined for iPSC-based cancer models using genetic engineering to induce transformation. This approach circumvents the need to reprogram cancer cells while allowing for dissection of the genetic mechanisms underlying transformation, progression, and metastasis with a high degree of precision and control. We also discuss the strengths and limitations of respective engineering approaches and outline experimental considerations for establishing future models.

The origin of unwanted editing byproducts in gene editing

The rapid development of CRISPR-Cas genome editing tools has greatly changed the way to conduct research and holds tremendous promise for clinical applications. During genome editing, CRISPR-Cas enzymes induce DNA breaks at the target sites and subsequently the DNA repair pathways are recruited to generate diverse editing outcomes. Besides off-target cleavage, unwanted editing outcomes including chromosomal structural variations and exogenous DNA integrations have recently raised concerns for clinical safety. To eliminate these unwanted editing byproducts, we need to explore the underlying mechanisms for the formation of diverse editing outcomes from the perspective of DNA repair. Here, we describe the involved DNA repair pathways in sealing Cas enzyme-induced DNA double-stranded breaks and discuss the origins and effects of unwanted editing byproducts on genome stability. Furthermore, we propose the potential risk of inhibiting DNA repair pathways to enhance gene editing. The recent combined studies of DNA repair and CRISPR-Cas editing provide a framework for further optimizing genome editing to enhance editing safety.

Modulating DNA Repair Pathways to Diversify Genomic Alterations in Saccharomyces cerevisiae

Nuclease based genome editing systems have emerged as powerful tools to drive genomic alterations and enhance genome evolution via precise engineering in the various human and microbial cells. However, error-prone DNA repair has not been well studied previously to generate diverse genomic alterations and novel phenotypes. Here, we systematically investigated the potential interplay between DNA double strand break (DSB) repair and genome editing tools, and found that modulating the DSB end resection proteins could significantly improve mutational efficiency and diversity without exogenous DNA template in yeast. Deleting SAE2, EXO1, or FUN30, or overexpressing MRE11-H125N (nuclease-dead allele of MRE11), for DSB end resection markedly increased the efficiency of CRISPR/SpCas9 (more than 22-fold) and CRISPR/AsCpf1 (more than 30-fold)-induced mutagenesis. Deleting SAE2 or overexpressing MRE11-H125N substantially diversified CRISPR/SpCas9 or AsCpf1-induced mutation 2–3-fold at URA3 locus, and 3–5-fold at ADE2 locus. Thus, the error-prone DNA repair protein was employed to develop a novel mutagenic genome editing (mGE) strategy, which can increase the mutation numbers and effectively improve the ethanol/glycerol ratio of Saccharomyces cerevisiae through modulating the expression of FPS1 and GPD1. This study highlighted the feasibility of potentially reshaping the capability of genome editing by regulating the different DSB repair proteins and can thus expand the application of genome editing in diversifying gene expression and enhancing genome evolution.

IMPORTANCE Most of the published papers about nuclease-assisted genome editing focused on precision engineering in human cells. However, the topic of inducing mutagenesis via error-prone repair has often been ignored in yeast. In this study, we reported that perturbing DNA repair, especially modifications of the various DSB end resection-related proteins, could greatly improve the mutational efficiency and diversity, and thus functionally reshape the capability of the different genome editing tools without requiring an exogenous DNA template in yeast. Specifically, mutagenic genome editing (mGE) was developed based on CRISPR/AsCpf1 and MRE11-H125N overexpression, and used to generate promoters of different strengths more efficiently. Thus, this work provides a novel method to diversify gene expression and enhance genome evolution.

Strategies for Efficient Gene Editing in Protoplasts of Solanum tuberosum Theme: Determining gRNA Efficiency Design by Utilizing Protoplast (Research)

Potato, Solanum tuberosum is a highly diverse tetraploid crop. Elite cultivars are extremely heterozygous with a high prevalence of small length polymorphisms (indels) and single nucleotide polymorphisms (SNPs) within and between cultivars, which must be considered in CRISPR/Cas gene editing strategies and designs to obtain successful gene editing. In the present study, in-depth sequencing of the gene encoding glucan water dikinase (GWD) 1 and the downy mildew resistant 6 (DMR6-1) genes in the potato cultivars Saturna and Wotan, respectively, revealed both indels and a 1.3–2.8 higher SNP prevalence when compared to the heterozygous diploid RH genome sequence as expected for a tetraploid compared to a diploid. This complicates guide RNA (gRNA) and diagnostic PCR designs. At the same time, high editing efficiencies at the cell pool (protoplast) level are pivotal for achieving full allelic knock-out in tetraploids. Furthermore, high editing efficiencies reduce the downstream cumbersome and delicate ex-plant regeneration. Here, CRISPR/Cas ribonucleoprotein particles (RNPs) were delivered transiently to protoplasts by polyethylene glycol (PEG) mediated transformation. For each of GWD1 and the DMR6-1, 6–10 gRNAs were designed to target regions comprising the 5′ and the 3′ end of the two genes. Similar to other studies including several organisms, editing efficiency of the individual RNPs varied significantly, and some generated specific indel patterns. RNP’s targeting the 5′ end of GWD1 yielded significantly higher editing efficiency as compared to targeting the 3′ end. For DMR6-1, such an effect was not seen. Simultaneously targeting each of the two target regions with two RNPs (multiplexing) yielded a clear positive synergistic effect on the total editing when targeting the 3′ end of the GWD1 gene only. Multiplexing of the two genes, residing on different chromosomes, yielded no or a slightly negative effect on editing from the single or combined gRNA/RNPs. These initial findings may instigate much larger studies needed for facilitating and optimizing precision breeding in plants.

Identification of the First Single GSDME Exon 8 Structural Variants Associated with Autosomal Dominant Hearing Loss

GSDME, also known as DFNA5, is a gene implicated in autosomal dominant nonsyndromic hearing loss (ADNSHL), affecting, at first, the high frequencies with a subsequent progression over all frequencies. To date, all the GSDME pathogenic variants associated with deafness lead to skipping of exon 8. In two families with apparent ADNSHL, massively parallel sequencing (MPS) integrating a coverage-based method for detection of copy number variations (CNVs) was applied, and it identified the first two causal GSDME structural variants affecting exon 8. The deleterious impact of the c.991-60_1095del variant, which includes the acceptor splice site sequence of exon 8, was confirmed by the study of the proband’s transcripts. The second mutational event is a complex rearrangement that deletes almost all of the exon 8 sequence. This study increases the mutational spectrum of the GSDME gene and highlights the crucial importance of MPS data for the detection of GSDME exon 8 deletions, even though the identification of a causal single-exon CNV by MPS analysis is still challenging.

Distinct sequence features underlie microdeletions and gross deletions in the human genome

Microdeletions and gross deletions are important causes (~20%) of human inherited disease and their genomic locations are strongly influenced by the local DNA sequence environment. This notwithstanding, no study has systematically examined their underlying generative mechanisms. Here, we obtained 42,098 pathogenic microdeletions and gross deletions from the Human Gene Mutation Database (HGMD) that together form a continuum of germline deletions ranging in size from 1 to 28,394,429 bp. We analyzed the DNA sequence within 1 kb of the breakpoint junctions and found that the frequencies of non‐B DNA‐forming repeats, GC‐content, and the presence of seven of 78 specific sequence motifs in the vicinity of pathogenic deletions correlated with deletion length for deletions of length ≤30 bp. Further, we found that the presence of DR, GQ, and STR repeats is important for the formation of longer deletions (>30 bp) but not for the formation of shorter deletions (≤30 bp) while significantly (χ², p < 2E−16) more microhomologies were identified flanking short deletions than long deletions (length >30 bp). We provide evidence to support a functional distinction between microdeletions and gross deletions. Finally, we propose that a deletion length cut‐off of 25–30 bp may serve as an objective means to functionally distinguish microdeletions from gross deletions.

Gene Editing in Pluripotent Stem Cells and Their Derived Organoids

With the rapid rise in gene-editing technology, pluripotent stem cells (PSCs) and their derived organoids have increasingly broader and practical applications in regenerative medicine. Gene-editing technologies, from large-scale nucleic acid endonucleases to CRISPR, have ignited a global research and development boom with significant implications in regenerative medicine. The development of regenerative medicine technologies, regardless of whether it is PSCs or gene editing, is consistently met with controversy. Are the tools for rewriting the code of life a boon to humanity or a Pandora's box? These technologies raise concerns regarding ethical issues, unexpected mutations, viral infection, etc. These concerns remain even as new treatments emerge. However, the potential negatives cannot obscure the virtues of PSC gene editing, which have, and will continue to, benefit mankind at an unprecedented rate. Here, we briefly introduce current gene-editing technology and its application in PSCs and their derived organoids, while addressing ethical concerns and safety risks and discussing the latest progress in PSC gene editing. Gene editing in PSCs creates visualized in vitro models, providing opportunities for examining mechanisms of known and unknown mutations and offering new possibilities for the treatment of cancer, genetic diseases, and other serious or refractory disorders. From model construction to treatment exploration, the important role of PSCs combined with gene editing in basic and clinical medicine studies is illustrated. The applications, characteristics, and existing challenges are summarized in combination with our lab experiences in this field in an effort to help gene-editing technology better serve humans in a regulated manner. Current preclinical and clinical trials have demonstrated initial safety and efficacy of PSC gene editing; however, for better application in clinical settings, additional investigation is warranted.

CRISPR-Cas Gene Perturbation and Editing in Human Induced Pluripotent Stem Cells

Directing the fates of human pluripotent stem cells (hPSC) to generate a multitude of differentiated cell types allows the study of the genetic regulation of human development and disease. The translational potential of hPSC is maximized by exploiting CRISPR to silence or activate genes with spatial and temporal precision permanently or reversibly. Here, we summarize the increasingly refined and diverse CRISPR toolkit for the latter forms of gene perturbation in hPSC and their downstream applications. We discuss newer methods to install edits efficiently with single nucleotide resolution and describe pooled CRISPR screens as a powerful means of unbiased discovery of genes associated with a phenotype of interest. Last, we discuss the potential of these combined technologies in the treatment of hitherto intractable human diseases and the challenges to their implementation in the clinic.

Small molecule inhibition of ATM kinase increases CRISPR-Cas9 1-bp insertion frequency

Mutational outcomes following CRISPR-Cas9-nuclease cutting in mammalian cells have recently been shown to be predictable and, in certain cases, skewed toward single genotypes. However, the ability to control these outcomes remains limited, especially for 1-bp insertions, a common and therapeutically relevant class of repair outcomes. Here, through a small molecule screen, we identify the ATM kinase inhibitor KU-60019 as a compound capable of reproducibly increasing the fraction of 1-bp insertions relative to other Cas9 repair outcomes. Small molecule or genetic ATM inhibition increases 1-bp insertion outcome fraction across three human and mouse cell lines, two Cas9 species, and dozens of target sites, although concomitantly reducing the fraction of edited alleles. Notably, KU-60019 increases the relative frequency of 1-bp insertions to over 80% of edited alleles at several native human genomic loci and improves the efficiency of correction for pathogenic 1-bp deletion variants. The ability to increase 1-bp insertion frequency adds another dimension to precise template-free Cas9-nuclease genome editing.

The mutational outcome of CRISPR-Cas9 editing can be both predictable and targeted. Here the authors show that ATM inhibitor KU-60019 increases 1 bp insertions at the targeted locus.

Paving the way towards precise and safe CRISPR genome editing

As the possibilities of CRISPR-Cas9 technology have been revealed, we have entered a new era of research aimed at increasing its specificity and safety. This stage of technology development is necessary not only for its wider application in the clinic but also in basic research to better control the process of genome editing. Research during the past eight years has identified some factors influencing editing outcomes and led to the development of highly specific endonucleases, modified guide RNAs and computational tools supporting experiments. More recently, large-scale experiments revealed a previously overlooked feature: Cas9 can generate reproducible mutation patterns. As a result, it has become apparent that Cas9-induced double-strand break (DSB) repair is nonrandom and can be predicted to some extent. Here, we review the present state of knowledge regarding the specificity and safety of CRISPR-Cas9 technology to define gRNA, protein and target-related problems and solutions. These issues include sequence-specific off-target effects, immune responses, genetic variation and chromatin accessibility. We present new insights into the role of DNA repair in genome editing and define factors influencing editing outcomes. In addition, we propose practical guidelines for increasing the specificity of editing and discuss novel perspectives in improvement of this technology.

Polθ promotes the repair of 5'-DNA-protein crosslinks by microhomology-mediated end-joining

DNA polymerase θ (Polθ) confers resistance to chemotherapy agents that cause DNA-protein crosslinks (DPCs) at double-strand breaks (DSBs), such as topoisomerase inhibitors. This suggests Polθ might facilitate DPC repair by microhomology-mediated end-joining (MMEJ). Here, we investigate Polθ repair of DSBs carrying DPCs by monitoring MMEJ in Xenopus egg extracts. MMEJ in extracts is dependent on Polθ, exhibits the MMEJ repair signature, and efficiently repairs 5' terminal DPCs independently of non-homologous end-joining and the replisome. We demonstrate that Polθ promotes the repair of 5' terminal DPCs in mammalian cells by using an MMEJ reporter and find that Polθ confers resistance to formaldehyde in addition to topoisomerase inhibitors. Dual deficiency in Polθ and tyrosyl-DNA phosphodiesterase 2 (TDP2) causes severe cellular sensitivity to etoposide, which demonstrates MMEJ as an independent DPC repair pathway. These studies recapitulate MMEJ in vitro and elucidate how Polθ confers resistance to etoposide.

Rational Selection of CRISPR-Cas9 Guide RNAs for Homology-Directed Genome Editing

Homology-directed repair (HDR) of a DNA break allows copying of genetic material from an exogenous DNA template and is frequently exploited in CRISPR-Cas9 genome editing. However, HDR is in competition with other DNA repair pathways, including non-homologous end joining (NHEJ) and microhomology-mediated end joining (MMEJ), and the efficiency of HDR outcomes is not predictable. Consequently, to optimize HDR editing, panels of CRISPR-Cas9 guide RNAs (gRNAs) and matched homology templates must be evaluated. We report here that CRISPR-Cas9 indel signatures can instead be used to identify gRNAs that maximize HDR outcomes. Specifically, we show that the frequency of deletions resulting from MMEJ repair, characterized as deletions greater than or equal to 3 bp, better predicts HDR frequency than consideration of total indel frequency. We further demonstrate that tools that predict gRNA indel signatures can be repurposed to identify gRNAs to promote HDR. Finally, by comparing indels generated by S. aureus and S. pyogenes Cas9 targeted to the same site, we add to the growing body of data that the targeted DNA sequence is a major factor governing genome editing outcomes.

Deconvolution of Complex DNA Repair (DECODR): Establishing a Novel Deconvolution Algorithm for Comprehensive Analysis of CRISPR-Edited Sanger Sequencing Data

During CRISPR-directed gene editing, multiple gene repair mechanisms interact to produce a wide and largely unpredictable variety of sequence changes across an edited population of cells. Shortcomings inherent to previously available proposal-based insertion and deletion (indel) analysis software necessitated the development of a more comprehensive tool that could detect a larger range and variety of indels while maintaining the ease of use of tools currently available. To that end, we developed Deconvolution of Complex DNA Repair (DECODR). DECODR can detect indels formed from single or multi-guide CRISPR experiments without a limit on indel size. The software is accurate in determining the identities and positions of inserted and deleted bases in DNA extracts from both clonally expanded and bulk cell populations. The accurate identification and output of any potential indel allows for DECODR analysis to be executed in experiments utilizing potentially any configuration of donor DNA sequences, CRISPR-Cas, and endogenous DNA repair pathways.

Identification of Drug Resistance Genes Using a Pooled Lentiviral CRISPR/Cas9 Screening Approach

In addition to advancing the development of gene-editing therapeutics, CRISPR/Cas9 is transforming how functional genetic studies are carried out in the lab. By increasing the ease with which genetic information can be inserted, deleted, or edited in cell and organism models, it facilitates genotype-phenotype analysis. Moreover, CRISPR/Cas9 has revolutionized the speed at which new genes underlying a particular phenotype can be identified through its application in genomic screens. Arrayed high-throughput and pooled lentiviral-based CRISPR/Cas9 screens have now been used in a wide variety of contexts, including the identification of essential genes, genes involved in cancer metastasis and tumor growth, and even genes involved in viral response. This technology has also been successfully used to identify drug targets and drug resistance mechanisms. Here, we provide a detailed protocol for performing a genome-wide pooled lentiviral CRISPR/Cas9 knockout screen to identify genetic modulators of a small-molecule drug. While we exemplify how to identify genes involved in resistance to a cytotoxic histone deacetylase inhibitor, Trichostatin A (TSA), the workflow we present can easily be adapted to different types of selections and other types of exogenous ligands or drugs.

Host-Malaria Parasite Interactions and Impacts on Mutual Evolution

Malaria is the most deadly parasitic disease, affecting hundreds of millions of people worldwide. Malaria parasites have been associated with their hosts for millions of years. During the long history of host-parasite co-evolution, both parasites and hosts have applied pressure on each other through complex host-parasite molecular interactions. Whereas the hosts activate various immune mechanisms to remove parasites during an infection, the parasites attempt to evade host immunity by diversifying their genome and switching expression of targets of the host immune system. Human intervention to control the disease such as antimalarial drugs and vaccination can greatly alter parasite population dynamics and evolution, particularly the massive applications of antimalarial drugs in recent human history. Vaccination is likely the best method to prevent the disease; however, a partially protective vaccine may have unwanted consequences that require further investigation. Studies of host-parasite interactions and co-evolution will provide important information for designing safe and effective vaccines and for preventing drug resistance. In this essay, we will discuss some interesting molecules involved in host-parasite interactions, including important parasite antigens. We also discuss subjects relevant to drug and vaccine development and some approaches for studying host-parasite interactions.

DNA Damage: From Threat to Treatment

DNA is the source of genetic information, and preserving its integrity is essential in order to sustain life. The genome is continuously threatened by different types of DNA lesions, such as abasic sites, mismatches, interstrand crosslinks, or single-stranded and double-stranded breaks. As a consequence, cells have evolved specialized DNA damage response (DDR) mechanisms to sustain genome integrity. By orchestrating multilayer signaling cascades specific for the type of lesion that occurred, the DDR ensures that genetic information is preserved overtime. In the last decades, DNA repair mechanisms have been thoroughly investigated to untangle these complex networks of pathways and processes. As a result, key factors have been identified that control and coordinate DDR circuits in time and space. In the first part of this review, we describe the critical processes encompassing DNA damage sensing and resolution. In the second part, we illustrate the consequences of partial or complete failure of the DNA repair machinery. Lastly, we will report examples in which this knowledge has been instrumental to develop novel therapies based on genome editing technologies, such as CRISPR-Cas.