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Caloric restriction extends healthy lifespan in multiple species 1 . Intermittent fasting, an alternative form of dietary restriction, is potentially more sustainable in humans, but its effectiveness remains largely unexplored 2-8 . Identifying the most efficacious forms of dietary restriction is key for developing interventions to improve human health and longevity 9 . Here we performed an extensive assessment of graded levels of caloric restriction (20% and 40%) and intermittent fasting (1 and 2 days fasting per week) on the health and survival of 960 genetically diverse female mice. We show that caloric restriction and intermittent fasting both resulted in lifespan extension in proportion to the degree of restriction. Lifespan was heritable and genetics had a larger influence on lifespan than dietary restriction. The strongest trait associations with lifespan included retention of body weight through periods of handling-an indicator of stress resilience, high lymphocyte proportion, low red blood cell distribution width and high adiposity in late life. Health effects differed between interventions and exhibited inconsistent relationships with lifespan extension. 40% caloric restriction had the strongest lifespan extension effect but led to a loss of lean mass and changes in the immune repertoire that could confer susceptibility to infections. Intermittent fasting did not extend the lifespan of mice with high pre-intervention body weight, and two-day intermittent fasting was associated with disruption of erythroid cell populations. Metabolic responses to dietary restriction, including reduced adiposity and lower fasting glucose, were not associated with increased lifespan, suggesting that dietary restriction does more than just counteract the negative effects of obesity. Our findings indicate that improving health and extending lifespan are not synonymous and raise questions about which end points are the most relevant for evaluating aging interventions in preclinical models and clinical trials., (© 2024. The Author(s).)

Individuals of a specified pedigree relationship vary in the proportion of the genome they share identical by descent, i.e. in their realised or actual relationship. Predictions of the variance in realised relationship have previously been based solely on the proportion of the map length shared, which requires the implicit assumption that both recombination rate and genetic information are uniformly distributed along the genome. This ignores the possible existence of recombination hotspots, and fails to distinguish between coding and non-coding sequences. In this paper, we therefore quantify the effects of heterogeneity in recombination rate at broad and fine-scale levels on the variation in realised relationship. Variance is usually greater on a chromosome with a non-uniform recombination rate than on a chromosome with the same map length and uniform recombination rate, especially if recombination rates are higher towards chromosome ends. Reductions in variance can also be obtained, however, and the overall pattern of change is quite complex. In general, local (fine-scale) variation in recombination rate, e.g. hotspots, has a small influence on the variance in realised relationship. Differences in rates across longer regions and between chromosome ends can increase or decrease the variance in a realised relationship, depending on the genomic architecture.

Purinergic signalling plays an important role in the regulation of bladder smooth muscle (BSM) contractility, and P2X 4 receptor is expressed in the bladder wall, where it may act by forming heteromeric receptors with P2X 1 , the major purinergic force-generating muscle receptor. To test this hypothesis, we examined mouse BSM contractile properties in the absence and presence of selective P2X 1 (NF449 & NF279) and P2X 4 antagonists (5-BDBD). These drugs inhibited BSM purinergic contraction only partially, suggesting the possibility of a heteromeric receptor. However, carefully controlled co-immunoprecipitation experiments indicated that P2X 1 and P2X 4 do not form physically linked heteromers. Furthermore, immunofluorescence staining showed that P2X 4 is not present in mouse BSM per se, but in an unknown cellular structure among BSM bundles. To investigate whether deletion of P2X 4 could impact voiding function in vivo, P2X 4 null mice were characterized. P2X 4 null mice had normal bladder weight and morphology, normal voiding spot size and number by voiding spot assay, normal voiding interval, pressure and compliance by cystometrogram, and normal BSM contractility by myography. In conclusion, these data strongly suggest that P2X 4 is not present in mouse BSM cells, does not affect smooth muscle contractility and that mice null for P2X 4 exhibit normal voiding function.

Oxidative damage caused by reactive oxygen species has been hypothesised to underpin the trade-off between reproduction and somatic maintenance, i.e., the life-history-oxidative stress theory. Previous tests of this hypothesis have proved equivocal, and it has been suggested that the variation in responses may be related to the tissues measured. Here, we measured oxidative damage (protein carbonyls, 8-OHdG) and antioxidant protection (enzymatic antioxidant activity and serum antioxidant capacity) in multiple tissues of reproductive (R) and non-reproductive (N) mice from two mouse strains selectively bred for high (H) or low (L) food intake, which differ in their reproductive performance, i.e., H mice have increased milk energy output (MEO) and wean larger pups. Levels of oxidative damage were unchanged (liver) or reduced (brain and serum) in R versus N mice, and no differences in multiple measures of oxidative protection were found between H and L mice in liver (except for Glutathione Peroxidase), brain or mammary glands. Also, there were no associations between an individual's energetic investment (e.g., MEO) and most of the oxidative stress measures detected in various tissues. These data are inconsistent with the oxidative stress theory, but were more supportive of, but not completely consistent, with the 'oxidative shielding' hypothesis.

There is evidence across several species for genetic control of phenotypic variation of complex traits, such that the variance among phenotypes is genotype dependent. Understanding genetic control of variability is important in evolutionary biology, agricultural selection programmes and human medicine, yet for complex traits, no individual genetic variants associated with variance, as opposed to the mean, have been identified. Here we perform a meta-analysis of genome-wide association studies of phenotypic variation using ∼170,000 samples on height and body mass index (BMI) in human populations. We report evidence that the single nucleotide polymorphism (SNP) rs7202116 at the FTO gene locus, which is known to be associated with obesity (as measured by mean BMI for each rs7202116 genotype), is also associated with phenotypic variability. We show that the results are not due to scale effects or other artefacts, and find no other experiment-wise significant evidence for effects on variability, either at loci other than FTO for BMI or at any locus for height. The difference in variance for BMI among individuals with opposite homozygous genotypes at the FTO locus is approximately 7%, corresponding to a difference of ∼0.5 kilograms in the standard deviation of weight. Our results indicate that genetic variants can be discovered that are associated with variability, and that between-person variability in obesity can partly be explained by the genotype at the FTO locus. The results are consistent with reported FTO by environment interactions for BMI, possibly mediated by DNA methylation. Our BMI results for other SNPs and our height results for all SNPs suggest that most genetic variants, including those that influence mean height or mean BMI, are not associated with phenotypic variance, or that their effects on variability are too small to detect even with samples sizes greater than 100,000.

The power to detect quantitative trait loci (QTL) using the double haploid (DH), full-sib (FS) and hierarchical (HI) designs implemented in outbred fish populations was assessed for interval mapping using deterministic methods. The predictions were tested using simulation. The DH design was most efficient for the range of designs and parameters considered and was most beneficial when the FS design was not very powerful. The difference between the design was largest for a low amount of residual genetic variation. Accounting for an increase of the environmental variance due to the genetic constitution of the double haploid progeny changed the magnitude of the power, but the ranking of the designs remained the same. As large full sib family sizes can be obtained in fish, the practical value of HI designs as a strategy for increasing the power of QTL mapping experiments is limited when compared with the FS design. Overall, the results suggested that the DH design could be a very useful tool for QTL mapping in fish, and of particular importance when the effect of the QTL is low and the residual genetic variation from other chromosomes can be controlled by using multiple markers.

Until recently, the estimation of the heritability of a trait has required knowledge of the pedigree within a population. In natural populations such knowledge is often unknown. Two techniques have been developed which use marker information to estimate heritabilities without reference to the exact nature of the relationships: a regression-based estimator that regresses phenotypic similarity for a pair of individuals against an estimate of their relationship and a likelihood-based estimator that maximizes the probability of the genotypic and phenotypic data given a known population structure. Computer simulation was used to compare the behaviour of these estimators. Bias in estimates of heritability decreased with increasing marker information, decreasing simulated heritability, increasing relatedness and increasing sample size. The techniques displayed reasonable tolerance to the percentage of missing data. The regression-based technique shows least average bias, but largest variance over simulations. Likelihood-based techniques show larger average bias, but smaller variances over estimates. A modified form of the likelihood technique, requiring fewer initial assumptions about population parameters, is presented. The modified form shows less bias in its estimates of heritability than the likelihood technique originally proposed.

Analysis was undertaken using Restricted Maximum Likelihood (REML) with an animal model of the results of selection for 20 generations for predicted lean mass in 10-week-old male mice. There were three replicates, each comprising high, low and unselected control lines. The overall estimates of heritability (h2) and common environmental correlations (c2) from results of the first seven generations were 0.51 +/- 0.03 and 0.21 +/- 0.01, respectively. Analyses of data from different lines and different numbers of generations were undertaken but with all pedigrees and data included, which enabled inferences to be drawn on changes in variance that were not due simply to inbreeding or short-term effects of selection. Estimates of h2 were lower in selected lines than the control, increasingly so in later generations, indicating departure from the infinitesimal model assumption of unlinked additive genes each of very small effect. In addition, values of c2 became higher in high than in control or low selected lines.

Restricted Maximum Likelihood (REML) with an animal model was used to estimate genetic parameters of body weight, body consumption and litter size of lines of mice selected for 20 generations on an index of lean mass at 10 weeks in males, highly correlated with body weight, and for a further 18 generations on body weight at 10 weeks in males and females. Univariate and multivariate estimates of heritability were about 0.5 and those of common environment correlations were about 0.25 for both body weight and composition. Body weight and fat pad weight had genetic and phenotypic correlations of about 0.5. The heritability estimate of litter size was about 0.15 from univariate analysis, rather lower from multivariate, and the estimate of its genetic correlation with body weight was about 0.25. There were reductions in heritability of both body weight and litter size in later generations, even though full pedigrees were fitted and inferences made to the base population, but a plateau in response to selection for increased body weight could not be explained by a complete attenuation of genetic variance.

The method of genotype assay, proposed by Jinks and Towey (1976) for estimating the number of effective factors in a polygenic system, assumes independent segregation if applied to number of genes. Their results are extended to include the case of linked genes, and the ratio of expected number of effective factors to number of genes is computed for a range of models. Unless all genes are on different chromosomes or many generations of inbreeding are used, the estimate of gene number is biased downwards.

Experimental checks on theoretical predictions of the build up of negative linkage disequilibrium with directional selection were made using abdominal bristle number in Drosophila melanogaster. Selection was practised for three generations before relaxation. Realized heritabilities and thus genotype variances were estimated by divergent selection. In one replicate, little change of variance occurred but in the other it increased substantially on relaxation. This result is compatible with a model of one or more genes of large effect at extreme frequencies in the base population. This is illustrated with Monte Carlo simulations. Interpretations of results was aided by considering the build up of negative disequilibrium.