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Schizophrenia is a debilitating psychiatric condition often associated with poor quality of life and decreased life expectancy. Lack of progress in improving treatment outcomes has been attributed to limited knowledge of the underlying biology, although large-scale genomic studies have begun to provide insights. We report a new genome-wide association study of schizophrenia (11,260 cases and 24,542 controls), and through meta-analysis with existing data we identify 50 novel associated loci and 145 loci in total. Through integrating genomic fine-mapping with brain expression and chromosome conformation data, we identify candidate causal genes within 33 loci. We also show for the first time that the common variant association signal is highly enriched among genes that are under strong selective pressures. These findings provide new insights into the biology and genetic architecture of schizophrenia, highlight the importance of mutation-intolerant genes and suggest a mechanism by which common risk variants persist in the population. A new GWAS of schizophrenia (11,260 cases and 24,542 controls) and meta-analysis identifies 50 new associated loci and 145 loci in total. The common variant association signal is highly enriched in mutation-intolerant genes and in regions under strong background selection.

Approximately one-third of all mammalian genes are essential for life. Phenotypes resulting from knockouts of these genes in mice have provided tremendous insight into gene function and congenital disorders. As part of the International Mouse Phenotyping Consortium effort to generate and phenotypically characterize 5,000 knockout mouse lines, here we identify 410 lethal genes during the production of the first 1,751 unique gene knockouts. Using a standardized phenotyping platform that incorporates high-resolution 3D imaging, we identify phenotypes at multiple time points for previously uncharacterized genes and additional phenotypes for genes with previously reported mutant phenotypes. Unexpectedly, our analysis reveals that incomplete penetrance and variable expressivity are common even on a defined genetic background. In addition, we show that human disease genes are enriched for essential genes, thus providing a dataset that facilitates the prioritization and validation of mutations identified in clinical sequencing efforts. Identification and characterization, using a comprehensive embryonic phenotyping pipeline, of 410 lethal alleles during the generation of the first 1,751 of 5,000 unique gene knockouts produced by the International Mouse Phenotyping Consortium. Embryonic phenotypes and lethal genes Stephen Murray and colleagues, including those from the International Mouse Phenotyping Consortium, report on the first phase of the project to generate and phenotypically characterize 5,000 knockout mouse lines, the first systematic efforts to characterize the phenotypes of embryonic lethal mutations. They identify 410 lethal genes during the production of the first 1,751 unique gene knockouts, and characterize these in a comprehensive phenotyping pipeline that includes high-resolution 3D imaging methods. Unexpectedly, given the defined genetic background, they find a number of phenotypes with incomplete penetrance, including some gene knockouts with subviability. The authors also show that orthologues of these mouse essential genes are enriched in genes associated with human disease and show evidence of purifying selection in the human population.

Gene targeting in embryonic stem cells has become the principal technology for manipulation of the mouse genome, offering unrivalled accuracy in allele design and access to conditional mutagenesis. To bring these advantages to the wider research community, large-scale mouse knockout programmes are producing a permanent resource of targeted mutations in all protein-coding genes. Here we report the establishment of a high-throughput gene-targeting pipeline for the generation of reporter-tagged, conditional alleles. Computational allele design, 96-well modular vector construction and high-efficiency gene-targeting strategies have been combined to mutate genes on an unprecedented scale. So far, more than 12,000 vectors and 9,000 conditional targeted alleles have been produced in highly germline-competent C57BL/6N embryonic stem cells. High-throughput genome engineering highlighted by this study is broadly applicable to rat and human stem cells and provides a foundation for future genome-wide efforts aimed at deciphering the function of all genes encoded by the mammalian genome. Knockout mice with potential Knockout mice in which a specific gene is inactivated are central to the analysis of gene function. An important resource is reported here in the form of a high-throughput gene targeting pipeline that has already produced thousands of conditional mutations in the C57BL/6 embryonic stem-cell line, suitable for the creation of mutant mice for large-scale phenotyping programmes. The strategy is also applicable to rat and human stem cells and provides a foundation for deciphering the function of all genes encoded by the mammalian genome.

The evolution of reproductive barriers is the first step in the formation of new species and can help us understand the diversification of life on Earth. These reproductive barriers often take the form of hybrid incompatibilities, in which alleles derived from two different species no longer interact properly in hybrids 1 – 3 . Theory predicts that hybrid incompatibilities may be more likely to arise at rapidly evolving genes 4 – 6 and that incompatibilities involving multiple genes should be common 7 , 8 , but there has been sparse empirical data to evaluate these predictions. Here we describe a mitonuclear incompatibility involving three genes whose protein products are in physical contact within respiratory complex I of naturally hybridizing swordtail fish species. Individuals homozygous for mismatched protein combinations do not complete embryonic development or die as juveniles, whereas those heterozygous for the incompatibility have reduced complex I function and unbalanced representation of parental alleles in the mitochondrial proteome. We find that the effects of different genetic interactions on survival are non-additive, highlighting subtle complexity in the genetic architecture of hybrid incompatibilities. Finally, we document the evolutionary history of the genes involved, showing signals of accelerated evolution and evidence that an incompatibility has been transferred between species via hybridization. Analysis of naturally hybridizing swordtail fish species reveals a mitonuclear genetic incompatibility among three genes that encode components of mitochondrial respiratory complex I, providing insights into the emergence of hybrid incompatibilities and reproductive barriers.

Whole-genome doubling (WGD) is common in human cancers, occurring early in tumorigenesis and generating genetically unstable tetraploid cells that fuel tumour development 1 , 2 . Cells that undergo WGD (WGD + cells) must adapt to accommodate their abnormal tetraploid state; however, the nature of these adaptations, and whether they confer vulnerabilities that can be exploited therapeutically, is unclear. Here, using sequencing data from roughly 10,000 primary human cancer samples and essentiality data from approximately 600 cancer cell lines, we show that WGD gives rise to common genetic traits that are accompanied by unique vulnerabilities. We reveal that WGD + cells are more dependent than WGD − cells on signalling from the spindle-assembly checkpoint, DNA-replication factors and proteasome function. We also identify KIF18A , which encodes a mitotic kinesin protein, as being specifically required for the viability of WGD + cells. Although KIF18A is largely dispensable for accurate chromosome segregation during mitosis in WGD – cells, its loss induces notable mitotic errors in WGD + cells, ultimately impairing cell viability. Collectively, our results suggest new strategies for specifically targeting WGD + cancer cells while sparing the normal, non-transformed WGD − cells that comprise human tissue. Cancer cells that have undergone whole-genome doubling are more reliant than their near-diploid counterparts on DNA-replication factors, the spindle-assembly checkpoint and a mitotic kinesin protein, KIF18A.

Synthetic lethality is an approach to study selective cell killing based on genotype. Previous work in our laboratory has shown that loss of RAD52 is synthetically lethal with BRCA2 deficiency, while exhibiting no impact on cell growth and viability in BRCA2-proficient cells. We now show that this same synthetically lethal relationship is evident in cells with deficiencies in BRCA1 or PALB2, which implicates BRCA1, PALB2 and BRCA2 in an epistatic relationship with one another. When RAD52 was depleted in BRCA1- or PALB2-deficient cells, a severe reduction in plating efficiency was observed, with many abortive attempts at cell division apparent in the double-depleted background. In contrast, when RAD52 was depleted in a BRCA1- or PALB2-wildtype background, a negligible decrease in colony survival was observed. The frequency of ionizing radiation-induced RAD51 foci formation and double-strand break-induced homologous recombination (HR) was decreased by 3- and 10-fold, respectively, when RAD52 was knocked down in BRCA1- or PALB2-depleted cells, with minimal effect in BRCA1- or PALB2-proficient cells. RAD52 function was independent of BRCA1 status, as evidenced by the lack of any defect in RAD52 foci formation in BRCA1-depleted cells. Collectively, these findings suggest that RAD52 is an alternative repair pathway of RAD51-mediated HR, and a target for therapy in cells deficient in the BRCA1–PALB2–BRCA2 repair pathway.

DNA repair role in cell differentiation The DNA repair enzyme thymine DNA glycolase (TDG) has been implicated in gene regulation, but its biological functions are unclear. Tdg gene knockouts in mice now reveal that the enzyme is essential for embryonic development, acting to maintain active and bivalent chromatin states during cell differentiation. TDG-dependent DNA repair may therefore have evolved to maintain epigenetic stability in lineage-committed cells. TDG is a member of the uracil DNA glycosylase family of DNA repair enzymes. It has been implicated in gene regulation but its biological functions have been unclear. Here, a knockout of the Tdg gene in mice reveals functions in embryonic development and in the maintenance of chromatin states. Thymine DNA glycosylase (TDG) is a member of the uracil DNA glycosylase (UDG) superfamily of DNA repair enzymes. Owing to its ability to excise thymine when mispaired with guanine, it was proposed to act against the mutability of 5-methylcytosine (5-mC) deamination in mammalian DNA 1 . However, TDG was also found to interact with transcription factors 2 , 3 , histone acetyltransferases 4 and de novo DNA methyltransferases 5 , 6 , and it has been associated with DNA demethylation in gene promoters following activation of transcription 7 , 8 , 9 , altogether implicating an engagement in gene regulation rather than DNA repair. Here we use a mouse genetic approach to determine the biological function of this multifaceted DNA repair enzyme. We find that, unlike other DNA glycosylases, TDG is essential for embryonic development, and that this phenotype is associated with epigenetic aberrations affecting the expression of developmental genes. Fibroblasts derived from Tdg null embryos (mouse embryonic fibroblasts, MEFs) show impaired gene regulation, coincident with imbalanced histone modification and CpG methylation at promoters of affected genes. TDG associates with the promoters of such genes both in fibroblasts and in embryonic stem cells (ESCs), but epigenetic aberrations only appear upon cell lineage commitment. We show that TDG contributes to the maintenance of active and bivalent chromatin throughout cell differentiation, facilitating a proper assembly of chromatin-modifying complexes and initiating base excision repair to counter aberrant de novo methylation. We thus conclude that TDG-dependent DNA repair has evolved to provide epigenetic stability in lineage committed cells.

Essential genes represent critical cellular components whose disruption results in lethality. Characteristics shared among essential genes have been uncovered in fungal and metazoan model systems. However, features associated with plant essential genes are largely unknown and the full set of essential genes remains to be discovered in any plant species. Here, we show that essential genes in Arabidopsis thaliana have distinct features useful for constructing within- and cross-species predictionmodels. Essential genes in A. thaliana are often single copy or derived from older duplications, highly and broadly expressed, slow evolving, and highly connected within molecular networks compared with genes with nonlethal mutant phenotypes. These gene features allowed the application of machine learning methods that predicted known lethal genes as well as an additional 1970 likely essential genes without documented phenotypes. Prediction models from A. thaliana could also be applied to predict Oryza sativa and Saccharomyces cerevisiae essential genes. Importantly, successful predictions drew upon many features, while any single feature was not sufficient. Our findings show that essential genes can be distinguished from genes with nonlethal phenotypes using features that are similar across kingdoms and indicate the possibility for translational application of our approach to species without extensive functional genomic and phenomic resources.

Hong Xu and colleagues demonstrate reduced germline replication and selection against the transmission of mitochondria encoding a temperature-sensitive cytochrome c oxidase subunit. Although mitochondrial DNA (mtDNA) is prone to mutation and few mtDNA repair mechanisms exist 1 , crippling mitochondrial mutations are exceedingly rare 2 . Recent studies have demonstrated strong purifying selection in the mouse female germline 3 , 4 . However, the mechanisms underlying positive selection of healthy mitochondria remain to be elucidated. We visualized mtDNA replication during Drosophila melanogaster oogenesis, finding that mtDNA replication commenced before oocyte determination during the late germarium stage and was dependent on mitochondrial fitness. We isolated a temperature-sensitive lethal mtDNA allele, mt:CoI T300I , which resulted in reduced mtDNA replication in the germarium at the restrictive temperature. Additionally, the frequency of the mt:CoI T300I allele in heteroplasmic flies was decreased, both during oogenesis and over multiple generations, at the restrictive temperature. Furthermore, we determined that selection against mt:CoI T300I overlaps with the timing of selective replication of mtDNA in the germarium. These findings establish a previously uncharacterized developmental mechanism for the selective amplification of wild-type mtDNA, which may be evolutionarily conserved to limit the transmission of deleterious mutations.

A multi-genomic approach identifies the addiction of KRAS -mutant lung cancer cells to XPO1-dependent nuclear export, offering a new therapeutic opportunity. Druggable targets in KRAS-driven tumours These authors use RNA interference screening of more than a hundred human non-small-cell lung cancer cell lines to identify phenotypic variations selectively required for the survival of cells carrying mutations in the KRAS gene. They find that KRAS-driven cancers are dependent on the nuclear export machinery. This vulnerability can be exploited by clinically available drugs targeting nuclear export receptor XPO-1, which inhibit tumour growth at least in part by promoting nuclear accumulation of NF-κB inhibitors. Conversely, some KRAS-driven tumours bypass this dependence through co-occurring mutations that result in YAP1 activation. This resistance mechanism can be countered by coadministration of the YAP1/TEAD inhibitor verteporfin. The common participation of oncogenic KRAS proteins in many of the most lethal human cancers, together with the ease of detecting somatic KRAS mutant alleles in patient samples, has spurred persistent and intensive efforts to develop drugs that inhibit KRAS activity 1 . However, advances have been hindered by the pervasive inter- and intra-lineage diversity in the targetable mechanisms that underlie KRAS-driven cancers, limited pharmacological accessibility of many candidate synthetic-lethal interactions and the swift emergence of unanticipated resistance mechanisms to otherwise effective targeted therapies. Here we demonstrate the acute and specific cell-autonomous addiction of KRAS -mutant non-small-cell lung cancer cells to receptor-dependent nuclear export. A multi-genomic, data-driven approach, utilizing 106 human non-small-cell lung cancer cell lines, was used to interrogate 4,725 biological processes with 39,760 short interfering RNA pools for those selectively required for the survival of KRAS -mutant cells that harbour a broad spectrum of phenotypic variation. Nuclear transport machinery was the sole process-level discriminator of statistical significance. Chemical perturbation of the nuclear export receptor XPO1 (also known as CRM1), with a clinically available drug, revealed a robust synthetic-lethal interaction with native or engineered oncogenic KRAS both in vitro and in vivo . The primary mechanism underpinning XPO1 inhibitor sensitivity was intolerance to the accumulation of nuclear IκBα (also known as NFKBIA), with consequent inhibition of NFκB transcription factor activity. Intrinsic resistance associated with concurrent FSTL5 mutations was detected and determined to be a consequence of YAP1 activation via a previously unappreciated FSTL5–Hippo pathway regulatory axis. This occurs in approximately 17% of KRAS -mutant lung cancers, and can be overcome with the co-administration of a YAP1–TEAD inhibitor. These findings indicate that clinically available XPO1 inhibitors are a promising therapeutic strategy for a considerable cohort of patients with lung cancer when coupled to genomics-guided patient selection and observation.