Click editing enables programmable genome writing using DNA polymerases and HUH endonucleases.

Genome editing technologies based on DNA-dependent polymerases (DDPs) could offer several benefits compared with other types of editors to install diverse edits. Here, we develop click editing, a genome writing platform that couples the advantageous properties of DDPs with RNA-programmable nickases to permit the installation of a range of edits, including substitutions, insertions and deletions. Click editors (CEs) leverage the 'click'-like bioconjugation ability of HUH endonucleases with single-stranded DNA substrates to covalently tether 'click DNA' (clkDNA) templates encoding user-specifiable edits at targeted genomic loci. Through iterative optimization of the modular components of CEs and their clkDNAs, we demonstrate the ability to install precise genome edits with minimal indels in diverse immortalized human cell types and primary fibroblasts with precise editing efficiencies of up to ~30%. Editing efficiency can be improved by rapidly screening clkDNA oligonucleotides with various modifications, including repair-evading substitutions. Click editing is a precise and versatile genome editing approach for diverse biological applications.

BioProfiling.jl: profiling biological perturbations with high-content imaging in single cells and heterogeneous populations.

MOTIVATION: High-content imaging screens provide a cost-effective and scalable way to assess cell states across diverse experimental conditions. The analysis of the acquired microscopy images involves assembling and curating raw cellular measurements into morphological profiles suitable for testing biological hypotheses. Despite being a critical step, general-purpose and adaptable tools for morphological profiling are lacking and no solution is available for the high-performance Julia programming language. RESULTS: Here, we introduce BioProfiling.jl, an efficient end-to-end solution for compiling and filtering informative morphological profiles in Julia. The package contains all the necessary data structures to curate morphological measurements and helper functions to transform, normalize and visualize profiles. Robust statistical distances and permutation tests enable quantification of the significance of the observed changes despite the high fraction of outliers inherent to high-content screens. This package also simplifies visual artifact diagnostics, thus streamlining a bottleneck of morphological analyses. We showcase the features of the package by analyzing a chemical imaging screen, in which the morphological profiles prove to be informative about the compounds' mechanisms of action and can be conveniently integrated with the network localization of molecular targets. AVAILABILITY AND IMPLEMENTATION: The Julia package is available on GitHub: https://github.com/menchelab/BioProfiling.jl. We also provide Jupyter notebooks reproducing our analyses: https://github.com/menchelab/BioProfilingNotebooks. The data underlying this article are available from FigShare, at https://doi.org/10.6084/m9.figshare.14784678.v2. SUPPLEMENTARY INFORMATION: Supplementary data are available at Bioinformatics online.

Tissue Specific DNA Repair Outcomes Shape the Landscape of Genome Editing.

The use of Clustered Regularly Interspaced Short Palindromic Repeats (CRISPR)-Cas9 has moved from bench to bedside in less than 10years, realising the vision of correcting disease through genome editing. The accuracy and safety of this approach relies on the precise control of DNA damage and repair processes to achieve the desired editing outcomes. Strategies for modulating pathway choice for repairing CRISPR-mediated DNA double-strand breaks (DSBs) have advanced the genome editing field. However, the promise of correcting genetic diseases with CRISPR-Cas9 based therapies is restrained by a lack of insight into controlling desired editing outcomes in cells of different tissue origin. Here, we review recent developments and urge for a greater understanding of tissue specific DNA repair processes of CRISPR-induced DNA breaks. We propose that integrated mapping of tissue specific DNA repair processes will fundamentally empower the implementation of precise and safe genome editing therapies for a larger variety of diseases.

Tissue specificity of DNA repair: the CRISPR compass.

CRISPR-Cas9-mediated genome editing holds great promise for the correction of pathogenic variants in humans. However, its therapeutic implementation is hampered due to unwanted editing outcomes. A better understanding of cell type- and tissue-specific DNA repair processes will ultimately enable precise control of editing outcomes for safer and effective therapies.

Genome-scale CRISPR screens are efficient in non-homologous end-joining deficient cells.

The mutagenic repair of Cas9 generated breaks is thought to predominantly rely on non-homologous end-joining (NHEJ), leading to insertions and deletions within DNA that culminate in gene knock-out (KO). In this study, by taking focused as well as genome-wide approaches, we show that this pathway is dispensable for the repair of such lesions. Genetic ablation of NHEJ is fully compensated for by alternative end joining (alt-EJ), in a POLQ-dependent manner, resulting in a distinct repair signature with larger deletions that may be exploited for large-scale genome editing. Moreover, we show that cells deficient for both NHEJ and alt-EJ were still able to repair CRISPR-mediated DNA double-strand breaks, highlighting how little is yet known about the mechanisms of CRISPR-based genome editing.

Synthetic Lethal Interactions for Kinase Deficiencies to DNA Damage Chemotherapeutics.

Kinases are signaling enzymes that regulate diverse cellular processes. As such, they are frequently mutated in cancer and therefore represent important targets for drug discovery. However, until recently, systematic approaches to identify vulnerabilities and resistances of kinases to DNA-damaging chemotherapeutics have not been possible, partially due to the lack of appropriate technologies. With the advent of CRISPR-Cas9, a comprehensive study has investigated the cellular survival of more than 300 kinase-deficient isogenic cell lines to a diverse panel of DNA-damaging agents, enriched for chemotherapeutics. Here, we discuss how this approach has allowed for the rational development of combination therapies that are aimed at using synthetic lethal interactions between kinase deficiencies and DNA-damaging agents that are used as chemotherapeutics.

Mapping the Human Kinome in Response to DNA Damage.

We provide a catalog for the effects of the human kinome on cell survival in response to DNA-damaging agents, covering all major DNA repair pathways. By treating 313 kinase-deficient cell lines with ten diverse DNA-damaging agents, including seven commonly used chemotherapeutics, we identified examples of vulnerability and resistance that are kinase specific. To investigate synthetic lethal interactions, we tested the response to carmustine for 25 cell lines by establishing a phenotypic fluorescence-activated cell sorting (FACS) assay designed to validate gene-drug interactions. We show apoptosis, cell cycle changes, and DNA damage and proliferation after alkylation- or crosslink-induced damage. In addition, we reconstitute the cellular sensitivity of DYRK4, EPHB6, MARK3, and PNCK as a proof of principle for our study. Furthermore, using global phosphoproteomics on cells lacking MARK3, we provide evidence for its role in the DNA damage response. Our data suggest that cancers with inactivating mutations in kinases, including MARK3, are particularly vulnerable to alkylating chemotherapeutic agents.

Map of synthetic rescue interactions for the Fanconi anemia DNA repair pathway identifies USP48.

Defects in DNA repair can cause various genetic diseases with severe pathological phenotypes. Fanconi anemia (FA) is a rare disease characterized by bone marrow failure, developmental abnormalities, and increased cancer risk that is caused by defective repair of DNA interstrand crosslinks (ICLs). Here, we identify the deubiquitylating enzyme USP48 as synthetic viable for FA-gene deficiencies by performing genome-wide loss-of-function screens across a panel of human haploid isogenic FA-defective cells (FANCA, FANCC, FANCG, FANCI, FANCD2). Thus, as compared to FA-defective cells alone, FA-deficient cells additionally lacking USP48 are less sensitive to genotoxic stress induced by ICL agents and display enhanced, BRCA1-dependent, clearance of DNA damage. Consequently, USP48 inactivation reduces chromosomal instability of FA-defective cells. Our results highlight a role for USP48 in controlling DNA repair and suggest it as a potential target that could be therapeutically exploited for FA.

Parallel genome-wide screens identify synthetic viable interactions between the BLM helicase complex and Fanconi anemia.

Maintenance of genome integrity via repair of DNA damage is a key biological process required to suppress diseases, including Fanconi anemia (FA). We generated loss-of-function human haploid cells for FA complementation group C (FANCC), a gene encoding a component of the FA core complex, and used genome-wide CRISPR libraries as well as insertional mutagenesis to identify synthetic viable (genetic suppressor) interactions for FA. Here we show that loss of the BLM helicase complex suppresses FANCC phenotypes and we confirm this interaction in cells deficient for FA complementation group I and D2 (FANCI and FANCD2) that function as part of the FA I-D2 complex, indicating that this interaction is not limited to the FA core complex, hence demonstrating that systematic genome-wide screening approaches can be used to reveal genetic viable interactions for DNA repair defects.

Repair of UV-Induced DNA Damage Independent of Nucleotide Excision Repair Is Masked by MUTYH.

DNA lesions caused by UV damage are thought to be repaired solely by the nucleotide excision repair (NER) pathway in human cells. Patients carrying mutations within genes functioning in this pathway display a range of pathologies, including an increased susceptibility to cancer, premature aging, and neurological defects. There are currently no curative therapies available. Here we performed a high-throughput chemical screen for agents that could alleviate the cellular sensitivity of NER-deficient cells to UV-induced DNA damage. This led to the identification of the clinically approved anti-diabetic drug acetohexamide, which promoted clearance of UV-induced DNA damage without the accumulation of chromosomal aberrations, hence promoting cellular survival. Acetohexamide exerted this protective function by antagonizing expression of the DNA glycosylase, MUTYH. Together, our data reveal the existence of an NER-independent mechanism to remove UV-induced DNA damage and prevent cell death.