Although mice are the most widely used model organism, genetic studies have suffered from limited mapping resolution due to extensive linkage disequilibrium (LD) that is characteristic of crosses among inbred strains. Carworth Farms White (CFW) mice are a commercially available outbred mouse population that exhibit rapid LD decay compared to other available mouse populations. We performed a genome-wide association study (GWAS) of behavioral, physiological and gene expression phenotypes using 1,200 male CFW mice. We used genotyping-by-sequencing (GBS) to obtain genotypes at 92,734 single nucleotide polymorphisms (SNPs). We also measured gene expression using RNA-Sequencing in three brain regions. Our study identified numerous behavioral, physiological and expression quantitative trait loci (QTLs). We integrated the behavioral QTL and eQTL results to implicate specific genes, including Azi2 in sensitivity to methamphetamine and Zmynd11 in anxiety-like behavior. The combination of CFW mice, GBS and RNA-Sequencing constitutes a powerful approach to GWAS in mice.

Two bottlenecks impeding the genetic analysis of complex traits in rodents are access to mapping populations able to deliver gene-level mapping resolution, and the need for population specific genotyping arrays and haplotype reference panels. Here we combine low coverage sequencing (0.15X) with a novel method to impute the ancestral haplotype space in 1,887 commercially available outbred mice. We mapped 156 unique quantitative trait loci for 92 phenotypes at 5% false discovery rate. Gene-level mapping resolution was achieved at about a fifth of loci, implicating Unc13c and Pgc1-alpha at loci for the quality of sleep, Adarb2 for home cage activity, Rtkn2 for intensity of reaction to startle, Bmp2 for wound healing, Il15 and Id2 for several T-cell measures and Prkca for bone mineral content. These findings have implications for diverse areas of mammalian biology and demonstrate how GWAS can be extended via low-coverage sequencing to species with highly recombinant outbred populations.

Exercise and contractions of isolated skeletal muscle induce phosphorylation of mitogen‐activated protein kinases (MAPKs) by undefined mechanisms. The aim of the present study was to determine exercise‐related triggering factors for the increased phosphorylation of MAPKs in isolated rat extensor digitorum longus (EDL) muscle. Concentric or eccentric contractions, or mild or severe passive stretches were used to discriminate between effects of metabolic/ionic and mechanical alterations on phosphorylation of two MAPKs: extracellular signal‐regulated kinase 1 and 2 (MAPKerk1/2) and stress‐activated protein kinase p38 (MAPKp38). Concentric contractions induced a 5‐fold increase in MAPKerk1/2 phosphorylation. Application of the antioxidants N‐acetylcysteine (20 mM) or dithiothreitol (5 mM) suppressed concentric contraction‐induced increase in MAPKerk1/2 phosphorylation. Mild passive stretches of the muscle increased MAPKerk1/2 phosphorylation by 1.8‐fold, whereas the combination of acidosis and passive stretches resulted in a 2.8‐fold increase. Neither concentric contractions, nor mild stretches nor acidosis significantly affected phosphorylation of MAPKp38. High force applied upon muscle by means of either eccentric contractions or severe passive stretches resulted in 5.7‐ and 9.5‐fold increases of phosphorylated MAPKerk1/2, respectively, whereas phosphorylation of MAPKp38 increased by 7.6‐ and 1.9‐fold (not significant), respectively. We conclude that in isolated rat skeletal muscle an increase in phosphorylation of both MAPKerk1/2 and MAPKp38 is induced by mechanical alterations, whereas contraction‐related metabolic/ionic changes (reactive oxygen species and acidosis) cause increased phosphorylation of MAPKerk1/2 only. Thus, contraction‐induced phosphorylation can be explained by the combined action of increased production of reactive oxygen species, acidification and mechanical perturbations for MAPKerk1/2 and by high mechanical stress for MAPKp38.

The mitogen-activated protein (MAP) kinase pathways have been highlighted as a possible link between exercise and adaptive changes in skeletal muscle. In this study, the effect of exercise intensity on the activation of the ERK/MAP kinase pathway was investigated in human skeletal muscle. One-leg exercise at low (40% maximal oxygen consumption, VO2max for 30 min) and high (75% VO2max for 30 min) intensity resulted in 11.5+8. I-fold and 39.7+/-6.3-fold (mean +/-SEM) increases in ERK1/2 phosphorylation (P<0.001), respectively. The phosphorylation of MEK1/2, the upstream kinase of ERK1/2, increased with exercise intensity (P<0.05) to 2.5+/-0.9 and 4.8+/-1.1 times the basal level at the low and high intensity, respectively. The statistical analysis revealed a systematic difference between basal, low and high intensity exercise levels for both kinases. There was no change in the phosphorylation of either kinase in the non-exercised leg. The phosphorylation of the transcription factor cyclic AMP response element binding protein (CREB), a possible downstream target of the ERK/MAP kinase signalling pathway, was unaffected by exercise. The phosphorylation of ERK1/2 was significantly higher in purified freeze-dried compared to crude wet muscle after exercise, whereas the opposite pattern was observed for CREB. In conclusion, phosphorylation of ERK1/2 and MEK1/2 increases in an exercise intensity-dependent manner in human skeletal muscle and this seems to originate in the muscle fibres themselves.

Lionikas A, Cheng R, Lim JE, Palmer AA, Blizard DA. Finemapping of muscle weight QTL in LG/J and SM/J intercrosses.