Search

Inflammatory gut disorders, including inflammatory bowel disease (IBD), can be impacted by dietary, environmental and genetic factors. While the incidence of IBD is increasing worldwide, we still lack a complete understanding of the gene-by-environment interactions underlying inflammation and IBD. Here, we profiled the colon transcriptome of 52 BXD mouse strains fed with a chow or high-fat diet (HFD) and identified a subset of BXD strains that exhibit an IBD-like transcriptome signature on HFD, indicating that an interplay of genetics and diet can significantly affect intestinal inflammation. Using gene co-expression analyses, we identified modules that are enriched for IBD-dysregulated genes and found that these IBD-related modules share cis-regulatory elements that are responsive to the STAT2, SMAD3, and REL transcription factors. We used module quantitative trait locus (ModQTL) analyses to identify genetic loci associated with the expression of these modules. Through a prioritization scheme involving systems genetics in the mouse and integration with external human datasets, we identified Muc4 and Epha6 as the top candidates mediating differences in HFD-driven intestinal inflammation. This work provides insights into the contribution of genetics and diet to IBD risk and identifies two candidate genes, MUC4 and EPHA6, that may mediate IBD susceptibility in humans.

Inflammatory gut disorders, including inflammatory bowel disease (IBD), can be impacted by dietary, environmental and genetic factors. While the incidence of IBD is increasing worldwide, we still lack a complete understanding of the gene-by-environment interactions underlying inflammation and IBD. Here, we profiled the colon transcriptome of 52 BXD mouse strains fed with a chow or high-fat diet (HFD) and identified a subset of BXD strains that exhibit an IBD-like transcriptome signature on HFD, indicating that an interplay of genetics and diet can significantly affect intestinal inflammation. Using gene co-expression analyses, we identified modules that are enriched for IBD-dysregulated genes and found that these IBD-related modules sharecis-regulatory elements that are responsive to the STAT2, SMAD3, and REL transcription factors. We used module quantitative trait locus (ModQTL) analyses to identify genetic loci associated with the expression of these modules. Through a prioritization scheme involving systems genetics in the mouse and integration with external human datasets, we identifiedMuc4andEpha6as the top candidates mediating differences in HFD-driven intestinal inflammation. This work provides insights into the contribution of genetics and diet to IBD risk and identifies two candidate genes,MUC4andEPHA6, that may mediate IBD susceptibility in humans.

Mice from different genetic backgrounds have widely diverse responses to the same metabolic challenges. Only PWK/PhJ mice show significant mitochondrial dysfunction and progression to fibrotic NASH that resembles human NASH. The PWK/PhJ strain is a novel NASH mouse model., Non-alcoholic steatohepatitis (NASH) is a global health concern without treatment. The challenge in finding effective therapies is due to the lack of good mouse models and the complexity of the disease, characterized by gene-environment interactions. We tested the susceptibility of seven mouse strains to develop NASH. The severity of the clinical phenotypes observed varied widely across strains. PWK/PhJ mice were the most prone to develop hepatic inflammation and the only strain to progress to NASH with extensive fibrosis, while CAST/EiJ mice were completely resistant. Levels of mitochondrial transcripts and proteins as well as mitochondrial function were robustly reduced specifically in the liver of PWK/PhJ mice, suggesting a central role of mitochondrial dysfunction in NASH progression. Importantly, the NASH gene expression profile of PWK/PhJ mice had the highest overlap with the human NASH signature. Our study exposes the limitations of using a single mouse genetic background in metabolic studies and describes a novel NASH mouse model with features of the human NASH.

DNA variants that modulate life span provide insight into determinants of health, disease, and aging. Through analyses in the UM-HET3 mice of the Interventions Testing Program (ITP), we detected a sex-independent quantitative trait locus (QTL) on chromosome 12 and identified sex-specific QTLs, some of which we detected only in older mice. Similar relations between life history and longevity were uncovered in mice and humans, underscoring the importance of early access to nutrients and early growth. We identified common age- and sex-specific genetic effects on gene expression that we integrated with model organism and human data to create a hypothesis-building interactive resource of prioritized longevity and body weight genes. Finally, we validated Hipk1 , Ddost , Hspg2 , Fgd6 , and Pdk1 as conserved longevity genes using Caenorhabditis elegans life-span experiments.

Organisms respond to mitochondrial stress by activating multiple defense pathways including the mitochondrial unfolded protein response (UPRmt). However, how UPRmt regulators are orchestrated to transcriptionally activate stress responses remains largely unknown. Here we identified CBP-1, the worm ortholog of the mammalian acetyltransferases CBP/p300, as an essential regulator of the UPRmt, as well as mitochondrial stress-induced immune response, reduction of amyloid-β aggregation and lifespan extension in Caenorhabditis elegans. Mechanistically, CBP-1 acts downstream of histone demethylases, JMJD-1.2/JMJD-3.1, and upstream of UPRmt transcription factors including ATFS-1, to systematically induce a broad spectrum of UPRmt genes and execute multiple beneficial functions. In mouse and human populations, transcript levels of CBP/p300 positively correlate with UPRmt transcripts and longevity. Furthermore, CBP/p300 inhibition disrupts, while forced expression of p300 is sufficient to activate, the UPRmt in mammalian cells. These results highlight an evolutionarily conserved mechanism that determines mitochondrial stress response, and promotes health and longevity through CBP/p300.

Summary: The mitochondrial unfolded protein response (UPRmt) is a promising pharmacological target for aging and age-related diseases. However, the integrative analysis of the impact of UPRmt activation on different signaling layers in animals with different genetic backgrounds is lacking. Here, we applied systems approaches to investigate the effect of UPRmt induced by doxycycline (Dox) on transcriptome, proteome, and lipidome in two genetically divergent worm strains, named N2 and CB4856. From the integrated omics datasets, we found that Dox prolongs lifespan of both worm strains through shared and strain-specific mechanisms. Specifically, Dox strongly impacts mitochondria, upregulates defense response, and lipid metabolism, while decreasing triglycerides. We further validated that lipid genes acs-2/20 and fat-7/6 were required for Dox-induced UPRmt and longevity in N2 and CB4856 worms, respectively. Our data have translational value as they indicate that the beneficial effects of Dox-induced UPRmt on lifespan are consistent across different genetic backgrounds through different regulators.

The sharp increase in obesity prevalence worldwide is mainly attributable to changes in physical activity and eating behavior but the metabolic and clinical impacts of these obesogenic conditions vary between sexes and genetic backgrounds. This warrants personalized treatments of obesity and its complications, which require a thorough understanding of the diversity of metabolic responses to high-fat diet intake. By analyzing nine genetically diverse mouse strains, we show that much like humans, mice exhibit a huge variety of physiological and biochemical responses to high-fat diet. The strains exhibit various degrees of alterations in their phenotypic makeup. At the transcriptome level, we observe dysregulations of immunity, translation machinery, and mitochondrial genes. At the biochemical level, the enzymatic activity of mitochondrial complexes is affected. The diversity across mouse strains, diets, and sexes parallels that found in humans and supports the use of diverse mouse populations in future mechanistic or preclinical studies on metabolic dysfunctions.

Bile acids (BAs) are complex and incompletely understood enterohepatic-derived hormones that control whole-body metabolism. Here, we profiled postprandial BAs in the liver, feces, and plasma of 360 chow- or high-fat-diet-fed BXD male mice and demonstrated that both genetics and diet strongly influence BA abundance, composition, and correlation with metabolic traits. Through an integrated systems approach, we mapped hundreds of quantitative trait loci that modulate BAs and identified both known and unknown regulators of BA homeostasis. In particular, we discovered carboxylesterase 1c (Ces1c) as a genetic determinant of plasma tauroursodeoxycholic acid (TUDCA), a BA species with established disease-preventing actions. The association between Ces1c and plasma TUDCA was validated using data from independent mouse cohorts and a Ces1c knockout mouse model. Collectively, our data are a unique resource to dissect the physiological importance of BAs as determinants of metabolic traits, as underscored by the identification of CES1C as a master regulator of plasma TUDCA levels., Cell Metabolism, 34 (10), ISSN:1550-4131, ISSN:1932-7420

Overweight and obesity are increasingly common public health issues worldwide, leading to a wide range of diseases from metabolic syndrome to steatohepatitis and cardiovascular diseases. While the increase in the prevalence of obesity is partly attributable to changes in lifestyle (i.e. increased sedentarity and changes in eating behaviour), the metabolic and clinical impacts of these obesogenic conditions varies between sexes and genetic backgrounds. The conception of personalised treatments of obesity and its complications require a thorough understanding of the diversity of responses to conditions such as high-fat diet intake. By analysing nine genetically diverse mouse strains, we show that much like humans, mice respond to high-fat diet in a genetic- and sex-dependent manner. Physiological and molecular responses to high-fat diet are associated with expression of genes involved in immunity and mitochondrial function. Finally, we find that mitochondrial function may explain part of the diversity of physiological responses. By exploring the complex interactions between genetics and metabolic phenotypes via gene expression and molecular traits, we shed light on the importance of genetic background and sex in determining metabolic outcomes. In addition to providing the community with an extensive resource for optimizing future experiments, our work serves as an exemplary design for more generalizable translational studies.

Summary The mitochondrial unfolded protein response (UPRmt) is a promising pharmacological target for aging and age-related diseases. However, the integrative analysis of the impact of UPRmt activation on different signaling layers in animals with different genetic backgrounds is lacking. Here, we applied systems approaches to investigate the effect of UPRmt induced by doxycycline (Dox) on transcriptome, proteome, and lipidome in two genetically divergent worm strains, named N2 and CB4856. From the integrated omics datasets, we found that Dox prolongs lifespan of both worm strains through shared and strain-specific mechanisms. Specifically, Dox strongly impacts mitochondria, upregulates defense response, and lipid metabolism, while decreasing triglycerides. We further validated that lipid genes acs-2/20 and fat-7/6 were required for Dox-induced UPRmt and longevity in N2 and CB4856 worms, respectively. Our data have translational value as they indicate that the beneficial effects of Dox-induced UPRmt on lifespan are consistent across different genetic backgrounds through different regulators., Graphical abstract, Highlights • Dox extends lifespan of N2 and CB4856 via shared and strain-specific mechanisms • Dox controls mitochondria, defense responses, and lipid metabolism in both strains • Dox-mediated longevity requires acs-2/20 in N2 and fat-7/6 in CB4856 worms, Chronobiology; Proteomics; Transcriptomics

Comparing transcript levels between healthy and diseased individuals allows the identification of differentially expressed genes, which may be causes, consequences or mere correlates of the disease under scrutiny. We propose a method to decompose the observational correlation between gene expression and phenotypes driven by confounders, forward- and reverse causal effects. The bi-directional causal effects between gene expression and complex traits are obtained by Mendelian Randomization integrating summary-level data from GWAS and whole-blood eQTLs. Applying this approach to complex traits reveals that forward effects have negligible contribution. For example, BMI- and triglycerides-gene expression correlation coefficients robustly correlate with trait-to-expression causal effects (rBMI = 0.11, PBMI = 2.0 × 10−51 and rTG = 0.13, PTG = 1.1 × 10−68), but not detectably with expression-to-trait effects. Our results demonstrate that studies comparing the transcriptome of diseased and healthy subjects are more prone to reveal disease-induced gene expression changes rather than disease causing ones., Identification of gene expression changes between healthy and diseased individuals can reveal mechanistic insights and biomarkers. Here, the authors propose a bi-directional transcriptome-wide Mendelian Randomization approach to assess causal effects between gene expression and complex traits.

Organisms respond to mitochondrial stress by activating multiple defense pathways including the mitochondrial unfolded protein response (UPRmt). However, how different layers of UPRmt regulators are orchestrated to transcriptionally activate the stress responses remains largely unknown. Here we identified CBP-1, the worm ortholog of the mammalian acetyltransferases CBP/p300, as an essential regulator for UPRmt activation, as well as for mitochondrial stress-induced immune response, reduction of amyloid-β aggregation and lifespan extension in Caenorhabditis elegans. Mechanistically, CBP-1 acts downstream of histone demethylases, JMJD-1.2/JMJD-3.1, and upstream of UPRmt transcription factors including ATFS-1, to systematically induce a broad spectrum of UPRmt genes and execute multiple beneficial functions. In mouse and human populations, transcript levels of CBP/p300 positively correlate with UPRmt transcripts and longevity. Furthermore, CBP/p300 inhibition disrupts, while forced expression of p300 is sufficient to activate, the UPRmt in mammalian cells. These results highlight an evolutionarily conserved mechanism that determines mitochondrial stress response, and promotes health and longevity through CBP/p300.

Background Resistance to enteric pathogens is a complex trait at the crossroads of multiple biological processes. We have previously shown in the Drosophila Genetic Reference Panel (DGRP) that resistance to infection is highly heritable, but our understanding of how the effects of genetic variants affect different molecular mechanisms to determine gut immunocompetence is still limited. Results To address this, we perform a systems genetics analysis of the gut transcriptomes from 38 DGRP lines that were orally infected with Pseudomonas entomophila. We identify a large number of condition-specific, expression quantitative trait loci (local-eQTLs) with infection-specific ones located in regions enriched for FOX transcription factor motifs. By assessing the allelic imbalance in the transcriptomes of 19 F1 hybrid lines from a large round robin design, we independently attribute a robust cis-regulatory effect to only 10% of these detected local-eQTLs. However, additional analyses indicate that many local-eQTLs may act in trans instead. Comparison of the transcriptomes of DGRP lines that were either susceptible or resistant to Pseudomonas entomophila infection reveals nutcracker as the only differentially expressed gene. Interestingly, we find that nutcracker is linked to infection-specific eQTLs that correlate with its expression level and to enteric infection susceptibility. Further regulatory analysis reveals one particular eQTL that significantly decreases the binding affinity for the repressor Broad, driving differential allele-specific nutcracker expression. Conclusions Our collective findings point to a large number of infection-specific cis- and trans-acting eQTLs in the DGRP, including one common non-coding variant that lowers enteric infection susceptibility.

Age-associated changes in chromatin structure have a major impact on organismal longevity. Despite being a central part of the ageing process, the organismal responses to the changes in chromatin organization remain unclear. Here we show that moderate disturbance of histone balance during C. elegans development alters histone levels and triggers a stress response associated with increased expression of cytosolic small heat-shock proteins. This stress response is dependent on the transcription factor, HSF-1, and the chromatin remodeling factor, ISW-1. In addition, we show that mitochondrial stress during developmental stages also modulates histone levels, thereby activating a cytosolic stress response similar to that caused by changes in histone balance. These data indicate that histone and mitochondrial perturbations are both monitored through chromatin remodeling and involve the activation of a cytosolic response that affects organismal longevity. HSF-1 and ISW-1 hence emerge as a central mediator of this multi-compartment proteostatic response regulating longevity., Changes in chromatin structure have been linked to organismal ageing. Here the authors show that altered histone expression and mitochondrial stress during C. elegans development result in chromatin changes and a cytosolic stress response that affects organismal longevity, and depends on HSF-1 and the chromatin remodeller, ISW-1.

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.

Summary Eukaryotic genomes encode several buffering mechanisms that robustly maintain invariant phenotypic outcome despite fluctuating environmental conditions. Here we show that the Drosophila gut-associated commensals, represented by a single facultative symbiont, Lactobacillus plantarum (LpWJL), constitutes a so far unexpected buffer that masks the contribution of the host's cryptic genetic variation (CGV) to developmental traits while the host is under nutritional stress. During chronic under-nutrition, LpWJL consistently reduces variation in different host phenotypic traits and ensures robust organ patterning during development; LpWJL also decreases genotype-dependent expression variation, particularly for development-associated genes. We further provide evidence that LpWJL buffers via reactive oxygen species (ROS) signaling whose inhibition impairs microbiota-mediated phenotypic robustness. We thus identified a hitherto unappreciated contribution of the gut facultative symbionts to host fitness that, beyond supporting growth rates and maturation timing, confers developmental robustness and phenotypic homogeneity in times of nutritional stress., Graphical Abstract, Highlights • Upon nutritional stress, fly commensals buffer the effects of cryptic genetic variants • Fly gut commensals buffer transcriptional variation in developmental genes • Fly commensals buffer phenotypic heterogeneity and mediate developmental canalization • Compromising ROS activities impair microbial buffering capacity, Biological Sciences; Microbiology; Oral Microbiology

The functions of many eukaryotic genes are still poorly understood. Here, we developed and validated a new method, termed GeneBridge, which is based on two linked approaches to impute gene function and bridge genes with biological processes. First, Gene-Module Association Determination (G-MAD) allows the annotation of gene function. Second, Module-Module Association Determination (M-MAD) allows predicting connectivity among modules. We applied the GeneBridge tools to large-scale multispecies expression compendia—1700 data sets with over 300,000 samples from human, mouse, rat, fly, worm, and yeast—collected in this study. G-MAD identifies novel functions of genes—for example, DDT in mitochondrial respiration and WDFY4 in T cell activation—and also suggests novel components for modules, such as for cholesterol biosynthesis. By applying G-MAD on data sets from respective tissues, tissue-specific functions of genes were identified—for instance, the roles of EHHADH in liver and kidney, as well as SLC6A1 in brain and liver. Using M-MAD, we identified a list of module-module associations, such as those between mitochondria and proteasome, mitochondria and histone demethylation, as well as ribosomes and lipid biosynthesis. The GeneBridge tools together with the expression compendia are available as an open resource, which will facilitate the identification of connections linking genes, modules, phenotypes, and diseases.

BACKGROUND & AIMS: Renewal and patterning of the intestinal epithelium is coordinated by intestinal stem cells (ISCs); dietary and metabolic factors provide signals to the niche that control ISC activity. Bile acids (BAs), metabolites in the gut, signal nutrient availability by activating the G protein-coupled bile acid receptor 1 (GPBAR1, also called TGR5). TGR5 is expressed in the intestinal epithelium, but it is not clear how its activation affects ISCs and regeneration of the intestinal epithelium. We studied the role of BAs and TGR5 in intestinal renewal, and regulation of ISC function in mice and intestinal organoids. METHODS: We derived intestinal organoids from wild-type mice and Tgr5(-/-) mice, incubated them with BAs or the TGR5 agonist INT-777, and monitored ISC function by morphologic analyses and colony-forming assays. We disrupted Tgr5 specifically in Lgr5-positive ISCs in mice (Tgr5ISC(-/-) mice) and analyzed ISC number, proliferation, and differentiation by flow cytometry, immunofluorescence, and organoid assays. Tgr5ISC(-/-) mice were given cholecystokinin; we measured the effects of BA release into the intestinal lumen and on cell renewal. We induced colitis in Tgr5ISC(-/-) mice by administration of dextran sulfate sodium; disease severity was determined based on body weight, colon length, and histopathology analysis of colon biopsies. RESULTS: BAs and TGR5 agonists promoted growth of intestinal organoids. Administration of cholecystokinin to mice resulted in acute release of BAs into the intestinal lumen and increased proliferation of the intestinal epithelium. BAs and Tgr5 expression in ISCs were required for homeostatic intestinal epithelial renewal and fatespecification, and for regeneration after colitis induction. Tgr5ISC(-/-) mice developed more severe colitis than mice without Tgr5 disruption in ISCs. ISCs incubated with INT-777 increased activation of yes-associated protein 1 (YAP1) and of its upstream regulator SRC. Inhibitors of YAP1 and SRC prevented organoid growth induced by TGR5 activation. CONCLUSIONS: BAs promote regeneration of the intestinal epithelium via activation of TGR5 in ISCs, resulting in activation of SRC and YAP and activation of their target genes. Release of endogenous BAs in the intestinal lumen is sufficient to promote ISC renewal and drives regeneration in response to injury.

Summary Many genes and pathways have been linked to aging, yet our understanding of underlying molecular mechanisms is still lacking. Here, we measure changes in the transcriptome, histone modifications, and DNA methylome in three metabolic tissues of adult and aged mice. Transcriptome and methylome changes dominate the liver aging footprint, whereas heart and muscle globally increase chromatin accessibility, especially in aging pathways. In mouse and human data from multiple tissues and regulatory layers, age-related transcription factor expression changes and binding site enrichment converge on putative aging modulators, including ZIC1, CXXC1, HMGA1, MECP2, SREBF1, SREBF2, ETS2, ZBTB7A, and ZNF518B. Using Mendelian randomization, we establish possible epidemiological links between expression of some of these transcription factors or their targets, including CXXC1, ZNF518B, and BBC3, and longevity. We conclude that conserved modulators are at the core of the molecular footprint of aging, and variation in tissue-specific expression of some may affect human longevity., Graphical Abstract, Highlights • The molecular footprint of aging in metabolic tissues is tissue specific • Distinct omic layers have common functional enrichments of aging-related gene sets • Few conserved transcription factors (TFs) may control the molecular footprint of aging • Mendelian randomization shows evidence of these TFs’ implications in human aging, Bou Sleiman et al. use multiple genomic methods to characterize the global footprint of aging in different mouse and human tissues. They identify regulators of gene expression that may play a role in the process and show evidence of their relevance in aging in human population data.

SummaryEukaryotic genomes encode several well-studied buffering mechanisms that robustly maintain invariant phenotypic outcome despite fluctuating environmental conditions. Here we show that the gut microbiota, represented by a single Drosophila facultative symbiont, Lactobacillus plantarum (LpWJL), acts also as a broad genetic buffer that masks the contribution of the cryptic genetic variations in the host under nutritional stress. During chronic under-nutrition, LpWJL consistently reduces variation in different host phenotypic traits and ensures robust organ patterning; LpWJL also decreases genotype-dependent expression variation, particularly for development-associated genes. We further demonstrate that LpWJL buffers via reactive oxygen species (ROS) signaling whose inhibition severely impairs microbiota-mediated phenotypic robustness. We thus identified an unexpected contribution of facultative symbionts to Drosophila fitness by assuring developmental robustness and phenotypic homogeneity in times of nutritional stress.

SUMMARY The genetic regulation and physiological impact of most lipid species are unexplored. Here, we profiled 129 plasma lipid species across 49 strains of the BXD mouse genetic reference population fed either chow or a high-fat diet. By integrating these data with genomics and phenomics datasets, we elucidated genes by environment (diet) interactions that regulate systemic metabolism. We found quantitative trait loci (QTLs) for ~94% of the lipids measured. Several QTLs harbored genes associated with blood lipid levels and abnormal lipid metabolism in human genome-wide association studies. Lipid species from different classes provided signatures of metabolic health, including seven plasma triglyceride species that associated with either healthy or fatty liver. This observation was further validated in an independent mouse model of non-alcoholic fatty liver disease (NAFLD) and in plasma from NAFLD patients. This work provides a resource to identify plausible genes regulating the measured lipid species and their association with metabolic traits., In Brief Jha et al. provide a resource of genetic loci regulating individual plasma lipid species identified by studying a large mouse population and demonstrate the potential of lipid species to reflect metabolic health status of individuals. Several lipid-regulating loci in the mouse population harbor genes associated with abnormal lipid metabolism in human GWAS. The potential of lipid species to reflect health status was validated in dietary and therapeutic models of NAFLD in mice and human NAFLD patients., Graphical Abstract

Melanization contributes to arthropod-specific innate immunity through deposition of melanin at wound sites or around parasites, with concomitant release of microbicidal reactive oxygen species. Melanization requires sequential activation of proteolytic enzymes in the hemolymph, including the final enzyme pro-phenoloxidase. Black cells (BC) is a mutation causing spontaneous melanization of Drosophila crystal cells, a hemocyte cell type producing phenoloxidases. BC individuals exhibit circulating black spots but fail to melanize upon injury. Although BC is widely used as a loss-of-function mutant of phenoloxidases, the mutation causing BC remained unknown. Here, we identified a single point mutation in the prophenoloxidase I (PPO1) gene of Bc flies causing an Alanine to Valine change in the C-terminal domain of PPO1, predicted to affect the conformation of the N-terminal pro-domain cleavage site at a distance and causing uncontrolled catalytic activity. Genomic insertion of a PPO1(A480V)transgene phenocopies Black cells, proving that A480V is indeed the causal mutation of the historical Bc phenotype. (C) 2014 Elsevier Ltd. All rights reserved.

Summary: Organisms need to assess their nutritional state and adapt their digestive capacity to the demands for various nutrients. Modulation of digestive enzyme production represents a rational step to regulate nutriment uptake. However, the role of digestion in nutrient homeostasis has been largely neglected. In this study, we analyzed the mechanism underlying glucose repression of digestive enzymes in the adult Drosophila midgut. We demonstrate that glucose represses the expression of many carbohydrases and lipases. Our data reveal that the consumption of nutritious sugars stimulates the secretion of the transforming growth factor β (TGF-β) ligand, Dawdle, from the fat body. Dawdle then acts via circulation to activate TGF-β/Activin signaling in the midgut, culminating in the repression of digestive enzymes that are highly expressed during starvation. Thus, our study not only identifies a mechanism that couples sugar sensing with digestive enzyme expression but points to an important role of TGF-β/Activin signaling in sugar metabolism. : Organisms modulate their digestive processes to reflect their nutritional state. In this study, Chng et al. demonstrate that the TGF-β/Activin pathway functions as a carbohydrate-sensing mechanism in the adult Drosophila midgut to regulate digestive enzyme expression. They show that the TGF-β ligand, Dawdle, and the canonical TGF-β/Activin signaling are essential to couple carbohydrate sensing with digestive enzyme expression. Thus, their study highlights an unexpected function of TGF-β/Activin signaling that is beyond their established roles in development and immunity.

Reference EPFL-ARTICLE-212120doi:10.1111/1346-8138.12939View record in Web of Science Record created on 2015-09-28, modified on 2017-05-12

The binding of the arginine-rich motif (ARM) of HIV Rev protein to its high-affinity site in stem IIB in the Rev response element (RRE) initiates assembly of a ribonucleoprotein complex that mediates the export of essential, incompletely spliced viral transcripts. Many biochemical, genetic, and structural studies of RevRRE IIB have been published, yet the roles of many peptide residues in Rev ARM are unconfirmed by mutagenesis. Rev aptamer I (RAI) is an optimized RRE IIB that binds Rev with higher affinity and for which mutational data are sparse. Randomized-codon libraries of Rev ARM were assayed for their ability to bind RRE IIB and RAI using a bacterial reporter system based on bacteriophage N-nut antitermination. Most Rev ARM residues tolerated substitutions without strong loss of binding to RRE IIB, and all except arginine 39 tolerated substitution without strong loss of binding to RAI. The pattern of critical Rev residues is not the same for RRE IIB and RAI, suggesting important differences between the interactions. The results support and aid the interpretation of existing structural models. Observed clinical variation is consistent with additional constraints on Rev mutation. By chance, we found double mutants of two highly critical residues, arginine 35 (to glycine) and asparagine 40 (to valine or lysine), that bind RRE IIB well, but not RAI. That an apparently distinct binding mode occurs with only two mutations highlights the ability of ARMs to evolve new recognition strategies and supports the application of neutral theories of evolution to proteinRNA recognition. Copyright (c) 2013 John Wiley & Sons, Ltd.

Gut immunocompetence involves immune, stress and regenerative processes. To investigate the determinants underlying inter-individual variation in gut immunocompetence, we perform enteric infection of 140 Drosophila lines with the entomopathogenic bacterium Pseudomonas entomophila and observe extensive variation in survival. Using genome-wide association analysis, we identify several novel immune modulators. Transcriptional profiling further shows that the intestinal molecular state differs between resistant and susceptible lines, already before infection, with one transcriptional module involving genes linked to reactive oxygen species (ROS) metabolism contributing to this difference. This genetic and molecular variation is physiologically manifested in lower ROS activity, lower susceptibility to ROS-inducing agent, faster pathogen clearance and higher stem cell activity in resistant versus susceptible lines. This study provides novel insights into the determinants underlying population-level variability in gut immunocompetence, revealing how relatively minor, but systematic genetic and transcriptional variation can mediate overt physiological differences that determine enteric infection susceptibility., Animals rely on a multitude of resistance and tolerance mechanisms to resist harmful gut microbes. Here, the authors explore the genetic, molecular and physiological basis underlying the remarkable phenotypic variation in resistance to enteric bacterial infection in Drosophila melanogaster.

Identifying genetic and environmental factors that impact complex traits and common diseases is a high biomedical priority. Here, we developed, validated, and implemented a series of multi-layered systems approaches, including (expression-based) phenome-wide association, transcriptome-/proteome-wide association, and (reverse-) mediation analysis, in an open-access web server (systems-genetics.org) to expedite the systems dissection of gene function. We applied these approaches to multi-omics datasets from the BXD mouse genetic reference population, and identified and validated associations between genes and clinical and molecular phenotypes, including previously unreported links between Rpl26 and body weight, and Cpt1a and lipid metabolism. Furthermore, through mediation and reverse-mediation analysis we established regulatory relations between genes, such as the co-regulation of BCKDHA and BCKDHB protein levels, and identified targets of transcription factors E2F6, ZFP277, and ZKSCAN1. Our multifaceted toolkit enabled the identification of gene-gene and gene-phenotype links that are robust and that translate well across populations and species, and can be universally applied to any populations with multi-omics datasets.

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.

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 on lifespan in a genetically diverse family of female mice, split into matched isogenic cohorts fed a low-fat chow diet (CD, n = 663) or a high-fat diet (HFD, n = 685). We further generate key metabolic data in a parallel cohort euthanized 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 roughly 4-6 days per gram. At 500 days, animals on a HFD typically gain four times 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 HFD are substantially modulated by gene-by-environment interactions, highlighting the importance of genetic variation in making accurate individualized dietary recommendations., Roy et al. quantify the impact of a high-fat diet across genetically diverse strains of mice, revealing a generally negative effect on lifespan but also a wide variability.

Benegiamo et al. identify genetic variants of the mitochondrial supercomplex assembly factor COX7A2L in the skeletal muscle of mice and humans that promote cardiorespiratory fitness., Mitochondrial respiratory complexes form superassembled structures called supercomplexes. COX7A2L is a supercomplex-specific assembly factor in mammals, although its implication for supercomplex formation and cellular metabolism remains controversial. Here we identify a role for COX7A2L for mitochondrial supercomplex formation in humans. By using human cis-expression quantitative trait loci data, we highlight genetic variants in the COX7A2L gene that affect its skeletal muscle expression specifically. The most significant cis-expression quantitative trait locus is a 10-bp insertion in the COX7A2L 3 ' untranslated region that increases messenger RNA stability and expression. Human myotubes harboring this insertion have more supercomplexes and increased respiration. Notably, increased COX7A2L expression in the muscle is associated with lower body fat and improved cardiorespiratory fitness in humans. Accordingly, specific reconstitution of Cox7a2l expression in C57BL/6J mice leads to higher maximal oxygen consumption, increased lean mass and increased energy expenditure. Furthermore, Cox7a2l expression in mice is induced specifically in the muscle upon exercise. These findings elucidate the genetic basis of mitochondrial supercomplex formation and function in humans and show that COX7A2L plays an important role in cardiorespiratory fitness, which could have broad therapeutic implications in reducing cardiovascular mortality.

The organism Caenorhabditis elegans is a performant model system for studying human biological processes and diseases, but until now all phenome data are produced as population-averaged read-outs. Monitoring of individual responses to drug treatments would however be more informative. Here, a new strategy to track different phenotypic traits of individual C. elegans nematodes throughout their full life-cycle—i.e., embryonic and post-embryonic development, until adulthood onset, differently from life-span—is presented. In an automated fashion, single worms were synchronized, isolated, and cultured from egg to adulthood in a microfluidic device, where their identity was preserved during their whole development. Several phenotypes were monitored and quantified for each animal, resulting in high-content phenome data. Specifically, the method was validated by analyzing the response of C. elegans to doxycycline, an antibiotic fairly well-known to prolong the development and activate mitochondrial stress-response pathways in different species. Interestingly, the obtained extensive single-worm phenome not only confirmed the dramatic doxycycline effect on the worm developmental delay, but more importantly revealed subtle yet severe treatment-dependent phenotypes that are representative of minority subgroups and would have otherwise stayed hidden in an averaged dataset. Such heterogeneous response started during the embryonic development, which makes essential having a dedicated chip that allows including this early developmental stage in the drug assay. Our approach would therefore allow elucidating pharmaceutical or therapeutic responses that so far were still being overlooked.