GABA type-A (GABA-A) receptors containing the α2 subunit (GABRA2) are expressed in most brain regions and are critical in modulating inhibitory synaptic function. Genetic variation at the GABRA2 locus has been implicated in epilepsy, affective and psychiatric disorders, alcoholism and drug abuse. Gabra2 expression varies as a function of genotype and is modulated by sequence variants in several brain structures and populations, including F2 crosses originating from C57BL/6J (B6J) and the BXD recombinant inbred family derived from B6J and DBA/2J. Here we demonstrate a global reduction of GABRA2 brain protein and mRNA in the B6J strain relative to other inbred strains, and identify and validate the causal mutation in B6J. The mutation is a single base pair deletion located in an intron adjacent to a splice acceptor site that only occurs in the B6J reference genome. The deletion became fixed in B6J between 1976 and 1991 and is now pervasive in many engineered lines, BXD strains generated after 1991, the Collaborative Cross, and the majority of consomic lines. Repair of the deletion using CRISPR- Cas9 -mediated gene editing on a B6J genetic background completely restored brain levels of GABRA2 protein and mRNA. Comparison of transcript expression in hippocampus, cortex, and striatum between B6J and repaired genotypes revealed alterations in GABA-A receptor subunit expression, especially in striatum. These results suggest that naturally occurring variation in GABRA2 levels between B6J and other substrains or inbred strains may also explain strain differences in anxiety-like or alcohol and drug response traits related to striatal function. Characterization of the B6J private mutation in the Gabra2 gene is of critical importance to molecular genetic studies in neurobiological research because this strain is widely used to generate genetically engineered mice and murine genetic populations, and is the most widely utilized strain for evaluation of anxiety-like, depression-like, pain, epilepsy, and drug response traits that may be partly modulated by GABRA2 function.

Summary How lifespan and body weight vary as a function of diet and genetic differences is not well understood. Here we quantify the impact of differences in diet in a genetically diverse family of female mice, split into matched isogenic cohorts fed a low-fat chow (CD, n = 663) or a high-fat diet (HFD, n = 685). We further generate key metabolic data in a parallel cohort sacrificed at four time points. HFD feeding shortens lifespan by 12%— equivalent to a decade in humans. Initial body weight and early weight gains account for longevity differences of ~4–6 days/g. At 500 days, animals on a HFD typically gain 4× as much weight as control, but variation in weight gain does not correlate with lifespan. Classic serum metabolites, often regarded as health biomarkers, are not necessarily strong predictors of longevity. Our data indicate that responses to a high fat diet are substantially modulated by gene-by-environmental interactions, highlighting the importance of genetic variation in making accurate individualized dietary recommendations.

Diet and environmental factors profoundly modulate lifespan. We measured longevity as a function of diet, and weight gain across a large genetically diverse BXD cohort which segregates for over 6 million variants, making it ideal for the analysis of gene-by-diet interactions that modulate lifespan. We followed 1348 females from parental strains, C57BL/6J and DBA/2J, and 76 BXD progeny strains on a standard low fat diet (CD, 18% calories from fat) or a widely used high fat diet (HFD, 60% calories from fat) across their natural life span. A diet rich in saturated fats shortens lifespan by an average of 85 days (HFD 605 ± 6, n = 685; CD 690 ± 8, n = 663), roughly equivalent to a 7-year decrease in humans. This diet is associated with an average two-fold higher age-adjusted risk of death compared to CD. Individual strains show remarkably wide variation in responses to diet, ranging from -54% on HFD in BXD65 to +37% on HFD in BXD8.Baseline weight and early weight gain on HFD associates negatively with longevity, with a gram increase causing lifespan to decrease by 4 days. By 500 days of age, BXDs on HFD gained 4X more weight than those on CD. However, strain-specific variation in the change in body weight does not significantly correlate with strain-specific life span. Major morbidities appear to be influenced by diet, with cases on HFD showing increased prevalence and severity of cardiovascular disease and lesions. Overall, we find that diet significantly impacts longevity even after adjusting for weight gain.

Aging is a complex and highly variable process. Heritability of longevity among humans and other species is low, and this finding has given rise to the idea that it may be futile to search for DNA variants that modulate aging. We argue that the problem in mapping longevity genes is mainly one of low power and the genetic and environmental complexity of aging. In this review we highlight progress made in mapping genes and molecular networks associated with longevity, paying special attention to work in mice and humans. We summarize 40 years of linkage studies using murine cohorts and 15 years of studies in human populations that have exploited candidate gene and genome-wide association methods. A small but growing number of gene variants contribute to known longevity mechanisms, but a much larger set have unknown functions. We outline these and other challenges and suggest some possible solutions, including more intense collaboration between research communities that use model organisms and human cohorts. Once hundreds of gene variants have been linked to differences in longevity in mammals, it will become feasible to systematically explore gene-by-environmental interactions, dissect mechanisms with more assurance, and evaluate the roles of epistasis and epigenetics in aging. A deeper understanding of complex networks-genetic, cellular, physiological, and social-should position us well to improve healthspan.

Coenzyme Q (CoQ) is a well-studied molecule, present in every cell membrane in the body, best known for its roles as a mitochondrial electron transporter and a potent membrane anti-oxidant. Much of the previous work was done in vitro in yeast and more recent work has suggested that CoQ may have additional roles prompting calls for a re-assessment of its role using in vivo systems in mammals. Here we investigated the putative role of Coenzyme Q in ethanol-induced effects in vivo using BXD RI mice. We examined hippocampal expression of Coq7 in saline controls and after an acute ethanol treatment, noting enriched biologic processes and pathways following ethanol administration. We also identified 45 ethanol-related phenotypes that were significantly correlated with Coq7 expression, including six phenotypes related to conditioned taste aversion and ethanol preference. This analysis highlights the need for further investigation of Coq7 and related genes in vivo as well as previously unrecognized roles that it may play in the hippocampus.

32GABA type-A (GABA-A) receptors containing the α2 subunit (Gabra2) are expressed in most brain regions and are 33 critical in modulating inhibitory synaptic function. Genetic variation at the GABRA2 locus has been implicated in epilepsy, 34 affective and psychiatric disorders, alcoholism and drug abuse. Gabra2 expression varies as a function of genotype and is 35 modulated by sequence variants in several brain structures and populations, including F2 crosses originating from 36 C57BL/6J (B6J) and the BXD recombinant inbred family derived from B6J and DBA/2J. Here we demonstrate a global 37 reduction of Gabra2 brain mRNA and protein in the B6J strain relative to other inbred strains, and identify and validate 38 the causal mutation in B6J. The mutation is a single base pair intronic deletion located adjacent to a splice acceptor site 39 that only occurs in the B6J reference genome. The deletion became fixed in B6J between 1976 and 1991 and is now 40 pervasive in many engineered lines, BXD strains generated after 1991, the Collaborative Cross, and the majority of 41 consomic lines. Repair of the deletion using CRISPR-Cas9 mediated gene editing on a B6J genetic background completely 42 restored brain levels of Gabra2 mRNA and protein. Comparison of transcript expression in hippocampus, cortex, and 43 striatum between B6J and repaired genotypes revealed alterations in GABA-A receptor subunit expression, especially in 44 striatum. These results suggest that naturally occurring variation in GABRA2 levels between B6J and other substrains or 45 inbred strains may also explain strain differences in anxiety-like or alcohol and drug response traits related to striatal 46 function. Characterization of the B6J private mutation in the Gabra2 gene is of critical importance to molecular genetic 47 studies in neurobiological research as this strain is widely used to generate genetically engineered mice and murine genetic 48 populations, and is the most widely utilized strain for evaluation of anxiety-like, depression-like, pain, epilepsy, and drug 49