Ferroptosis is a form of regulated necrotic cell death controlled by glutathione peroxidase 4 (GPX4). At present, mechanisms that could predict sensitivity and/or resistance and that may be exploited to modulate this form of cell death are needed. We applied two independent approaches, a genome-wide CRISPR-based genetic screen and microarray analysis of ferroptosis-resistant cell lines to uncover acyl-CoA synthetase long-chain family member 4 (Acsl4) as an essential component for ferroptosis execution. Specifically, Gpx4/Acsl4 double knockout cells presented an unprecedented resistance to ferroptosis. Mechanistically, Acsl4 enriches cellular membranes with long polyunsaturated ω6 fatty acids. Moreover, Acsl4 is preferentially expressed in a panel of basal-like breast cancer cell lines and predicts their sensitivity to ferroptosis. We further demonstrate that pharmacological targeting of Acsl4 with the antidiabetic compound class, thiazolidinediones, ameliorates tissue demise in a murine model of ferroptosis, suggesting that Acsl4 inhibition is a viable therapeutic approach to prevent ferroptosis-related diseases.

Approximately one third of all mammalian genes are essential for life. Phenotypes resulting from mouse knockouts of these genes have provided tremendous insight into gene function and congenital disorders. As part of the International Mouse Phenotyping Consortium effort to generate and phenotypically characterize 5000 knockout mouse lines, we have identified 410 lethal genes during the production of the first 1751 unique gene knockouts. Using a standardised phenotyping platform that incorporates high-resolution 3D imaging, we identified novel 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 identified in our screen, thus providing a novel dataset that facilitates prioritization and validation of mutations identified in clinical sequencing efforts.

Oxidative stress in conjunction with glutathione depletion has been linked with various acute and chronic degenerative disorders, yet the molecular mechanisms have remained unclear. In contrast to the belief that oxygen radicals are detrimental to cells and tissues by unspecific oxidation of essential biomolecules, we now demonstrate that oxidative stress is sensed and transduced by glutathione peroxidase 4 (GPx4) into a-yet-unrecognized cell-death pathway. Inducible GPx4 inactivation in mice and cells revealed 12/15-lipoxygenase-derived lipid peroxidation as specific downstream event, triggering apoptosis-inducing factor (AIF)-mediated cell death. Cell death could be entirely prevented either by alpha-tocopherol (alpha-Toc), 12/15-lipoxygenase inhibitors, or siRNA-mediated AIF silencing. Accordingly, 12/15-lipoxygenase-deficient cells were highly resistant to glutathione depletion. Neuron-specific GPx4 depletion caused neurodegeneration in vivo and ex vivo, highlighting the importance of this pathway in neuronal cells. Since oxidative stress is common in the etiology of many human disorders, the identified pathway reveals promising targets for future therapies.

The insertion of precise genetic modifications by genome editing tools such as CRISPR-Cas9 is limited by the relatively low efficiency of homology-directed repair (HDR) compared with the higher efficiency of the non-homologous end joining (NHEJ) pathway. To enhance HDR, enabling the insertion of precise genetic modifications, we suppressed the NHEJ key molecules KU70, KU80 or DNA Ligase IV by gene silencing, the Ligase IV inhibitor SCR7 or the coexpression of adenovirus 4 E1B55K and E4orf6 proteins in a `traffic light´ and other reporter systems. Suppression of KU70 and DNA Ligase IV promotes the efficiency of HDR 4-5-fold. When co-expressed with the Cas9 system, E1B55K and E4orf6 improved the efficiency of HDR up to 8-fold and essentially abolished NHEJ activity in both human and mouse cell lines. Our findings provide useful tools to improve the frequency of precise gene modifications in mammalian cells.The clustered, regularly interspaced, short palindromic repeats (CRISPRs)-Cas9 endonuclease represent a versatile tool for genome engineering, enabling the induction of site-specific genomic double-strand breaks (DSBs) by single guide RNAs (sgRNAs) 1 .In mammalian cells DSBs are mostly repaired by the non-homologous end joining (NHEJ) pathway 2,3 , frequently leading to the loss of nucleotides from the DSB ends. This enables the efficient construction of knockout alleles through the induction of frameshift To quantitatively determine the outcome of CRISPR-induced DSB repair, we first generated human HEK293 cells with a `traffic light´ reporter 7 (TLR) vector integrated into the AAVS1 locus 8 (Fig. 1a). HEK293 cells were transfected with an AAVS1 targeting vector carrying the TLR insert and Cas9 and AAVS1-specific sgRNA expression plasmids ( Supplementary Fig. 1 , and up to 7-fold by the Ad4 protein pair ( Fig. 2c and Supplementary Fig. 2.2).Titration of SCR7 on AAVS1 TLR/+ cells showed an optimal effect at 1 µM concentration ( Supplementary Fig. 2.3). In the presence of two shRNAs, SCR7 or Ad4 proteins we noticed diminished fluorescence signals within the population of Venus + cells at 72h after transfection (Fig. 2a, Supplementary Fig. 2.1, 2.3c), indicating reduced Venus expression in cells undergoing NHEJ blockade, possibly caused by local chromatin remodeling through an extended DNA damage response 13,14 . However, Venus expression was normal in clones established from AAVS1 TLR/+ cells targeted in the presence of Ad4 proteins, indicating that this effect is only transient (Supplementary Fig. 2.3d). From the sample expressing the Ad4 proteins, Venus + cells were sorted, and we established 24 clones to confirm the integrity of the repaired TLR loci using PCR and sequence analysis (Supplementary Table 2). In contrast to the increase of Venus + cells, RFP + cells decreased from 3% in the controls to 1.7%, 1.4% or 0.6% in the presence of 5 shRNAs, SCR7 or Ad4 proteins, respectively (Fig. 2a, 2b). Whether the residual NHEJ activity relies on the KU/Ligase IV independent alternative end-joining mechanism 15 rem...

Selenoproteins are rare proteins among all kingdoms of life containing the 21 amino acid, selenocysteine. Selenocysteine resembles cysteine, differing only by the substitution of selenium for sulfur. Yet the actual advantage of selenolate- versus thiolate-based catalysis has remained enigmatic, as most of the known selenoproteins also exist as cysteine-containing homologs. Here, we demonstrate that selenolate-based catalysis of the essential mammalian selenoprotein GPX4 is unexpectedly dispensable for normal embryogenesis. Yet the survival of a specific type of interneurons emerges to exclusively depend on selenocysteine-containing GPX4, thereby preventing fatal epileptic seizures. Mechanistically, selenocysteine utilization by GPX4 confers exquisite resistance to irreversible overoxidation as cells expressing a cysteine variant are highly sensitive toward peroxide-induced ferroptosis. Remarkably, concomitant deletion of all selenoproteins in Gpx4 cells revealed that selenoproteins are dispensable for cell viability provided partial GPX4 activity is retained. Conclusively, 200 years after its discovery, a specific and indispensable role for selenium is provided.

Arc/Arg3.1 is robustly induced by plasticity-producing stimulation and specifically targeted to stimulated synaptic areas. To investigate the role of Arc/Arg3.1 in synaptic plasticity and learning and memory, we generated Arc/Arg3.1 knockout mice. These animals fail to form long-lasting memories for implicit and explicit learning tasks, despite intact short-term memory. Moreover, they exhibit a biphasic alteration of hippocampal long-term potentiation in the dentate gyrus and area CA1 with an enhanced early and absent late phase. In addition, long-term depression is significantly impaired. Together, these results demonstrate a critical role for Arc/Arg3.1 in the consolidation of enduring synaptic plasticity and memory storage.

Mutations in the cytosine-5 RNA methyltransferase NSun2 cause microcephaly and other neurological abnormalities in mice and human. How post-transcriptional methylation contributes to the human disease is currently unknown. By comparing gene expression data with global cytosine-5 RNA methylomes in patient fibroblasts and NSun2-deficient mice, we find that loss of cytosine-5 RNA methylation increases the angiogenin-mediated endonucleolytic cleavage of transfer RNAs (tRNA) leading to an accumulation of 5′ tRNA-derived small RNA fragments. Accumulation of 5′ tRNA fragments in the absence of NSun2 reduces protein translation rates and activates stress pathways leading to reduced cell size and increased apoptosis of cortical, hippocampal and striatal neurons. Mechanistically, we demonstrate that angiogenin binds with higher affinity to tRNAs lacking site-specific NSun2-mediated methylation and that the presence of 5′ tRNA fragments is sufficient and required to trigger cellular stress responses. Furthermore, the enhanced sensitivity of NSun2-deficient brains to oxidative stress can be rescued through inhibition of angiogenin during embryogenesis. In conclusion, failure in NSun2-mediated tRNA methylation contributes to human diseases via stress-induced RNA cleavage.

Corticotropin-releasing hormone (CRH) is a potent mediator of endocrine, autonomic, behavioural and immune responses to stress, and has been implicated in the stress-like and other aversive consequences of drug abuse, such as withdrawal from alcohol. Two CRH receptors, Crhr1 and Crhr2, have been identified in the mouse. Crhr1 is highly expressed in the anterior pituitary, neocortex, hippocampus, amygdala and cerebellum, and activation of this receptor stimulates adenylate cyclase. Here we show that in mice lacking Crhr1, the medulla of the adrenal gland is atrophied and stress-induced release of adrenocorticotropic hormone (ACTH) and corticosterone is reduced. The homozygous mutants exhibit increased exploratory activity and reduced anxiety-related behaviour under both basal conditions and following alcohol withdrawal. Our results demonstrate a key role of the Crhr1 receptor in mediating the stress response and anxiety-related behaviour.