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.

28Aging is associated with an increased risk of cardiovascular disease and death. Here we 29show that oral supplementation of the natural polyamine spermidine extends the lifespan of 30 mice and exerts cardioprotective effects, reducing cardiac hypertrophy and preserving 31 diastolic function in old mice. Spermidine feeding enhanced cardiac autophagy, mitophagy 32 and mitochondrial respiration, and it also improved the mechano-elastical properties of 33 cardiomyocytes in vivo, coinciding with increased titin phosphorylation and suppressed 34 subclinical inflammation. Spermidine feeding failed to provide cardioprotection in mice that 35 lack the autophagy-related protein Atg5 in cardiomyocytes. In Dahl salt-sensitive rats that 36 were fed a high-salt diet, a model for hypertension-induced congestive heart failure, 37 spermidine feeding reduced systemic blood pressure, increased titin phosphorylation and 38 prevented cardiac hypertrophy and a decline in diastolic function, thus delaying the 39 progression to heart failure. In humans, high levels of dietary spermidine, as assessed from 40 food questionnaires, correlated with reduced blood pressure and a lower incidence of 41 cardiovascular disease. Our results suggest a new and feasible strategy for the protection 42 from cardiovascular disease. 43Author's manuscript to Eisenberg et al.

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.

Degenerative disorders of motor neurons include a range of progressive fatal diseases such as amyotrophic lateral sclerosis (ALS), spinal-bulbar muscular atrophy (SBMA), and spinal muscular atrophy (SMA). Although the causative genetic alterations are known for some cases, the molecular basis of many SMA and SBMA-like syndromes and most ALS cases is unknown. Here we show that missense point mutations in the cytoplasmic dynein heavy chain result in progressive motor neuron degeneration in heterozygous mice, and in homozygotes this is accompanied by the formation of Lewy-like inclusion bodies, thus resembling key features of human pathology. These mutations exclusively perturb neuron-specific functions of dynein.