Beef cattle are raised for their lean tissue, and excessive fat accumulation accounts for large amounts of waste. On the other hand, intramuscular fat or marbling is essential for the palatability of beef. In addition, tender beef is demanded by consumers, and connective tissue contributes to the background toughness of beef. Recent studies show that myocytes, adipocytes, and fibroblasts are all derived from a common pool of progenitor cells during embryonic development. It appears that during early embryogenesis, multipotent mesenchymal stem cells first diverge into either myogenic or adipogenic-fibrogenic lineages; myogenic progenitor cells further develop into muscle fibers and satellite cells whereas adipogenic-fibrogenic lineage cells develop into the stromal-vascular fraction of skeletal muscle where reside adipocytes, fibroblasts, and resident fibro-adipogenic progenitor cells (the counterpart of satellite cells). Strengthening myogenesis (i.e., formation of muscle cells) enhances lean growth, promoting intramuscular adipogenesis (i.e., formation of fat cells) increases marbling, and reducing intramuscular fibrogenesis (i.e., formation of fibroblasts and synthesis of connective tissue) improves overall tenderness of beef. Because the abundance of progenitor cells declines as animals age, it is more effective to manipulate progenitor cell differentiation at an early developmental stage. Nutritional, environmental, and genetic factors shape progenitor cell differentiation; however, up to now, our knowledge regarding mechanisms governing progenitor cell differentiation remains rudimentary. In summary, altering mesenchymal progenitor cell differentiation through nutritional management of cows, or fetal programming, is a promising method to improve cattle performance and carcass value.

In the present manuscript, the methods required to generate purified cultures of mature adipocytes, as well as stromal vascular cells, from the same isolation are detailed. Also, we describe the in vitro conditions for the dedifferentiation of the isolated mature adipocytes. These two types of cells may be used to reevaluate differences between presently available cellular models for lipogenesis/lipolysis and might provide a new cellular physiological system for studies utilizing the proliferative progeny from mature adipocyte dedifferentiation. Alternative possibilities to the dedifferentiation phenomenon are proposed, as this new area of research is novel.Abbreviations: DMEM -Dulbecco's modified Eagle medium; DMEM/F12 -1:1 ratio; Dulbecco's modified Eagle medium + Ham's F12; FBS -fetal bovine serum; HBSS -Hank's balanced salt solution; HS -horse serum; PBS -phosphate buffered saline, pH 7.08; PSG -pigskin gelatin; SC -satellite cell

Thirteen reference genes were investigated to determine their stability to be used as a housekeeping in gene expression studies in skeletal muscle of chickens. Five different algorithms were used for ranking of reference genes and results suggested that individual rankings of the genes differed among them. The stability of the expression of reference genes were validated using samples obtained from the Pectoralis major muscle in chicken. Samples were obtained from chickens in different development periods post hatch and under different nutritional diets. For gene expression calculation the ΔΔCt approach was applied to compare relative expression of pairs of genes within each of 52 samples when normalized to mitochondrially encoded cytochrome c oxidase II (MT-CO2) target gene. Our findings showed that hydroxymethylbilane synthase (HMBS) and hypoxanthine phosphoribosyl transferase 1 (HPRT1) are the most stable reference genes while transferrin receptor (TFRC) and beta-2-microglobulin (B2M) ranked as the least stable genes in the Pectoralis major muscle of chickens. Moreover, our results revealed that HMBS and HPRT1 gene expression did not change due to dietary variations and thus it is recommended for accurate normalization of RT-qPCR data in chicken Pectoralis major muscle.

The effect of breed and diet on insulin response to glucose challenge and its relation to intramuscular fat deposition was determined in 36 steers with 12 each of greater than 87% Wagyu (referred to as Wagyu), Wagyu x Limousin, and Limousin breeds. Weaned steers were blocked by weight into heavy, medium, and light calves and placed in six pens with two pens per weight type and with two steers of each breed per pen. Three pens with steers from each weightclass were fed backgrounding and finishing diets for 259 d, while the other three pens were fed the same diets where 6% of the barley grain was replaced with sunflower oil. Prior to initiation of the finishing phase of the study the intravenous glucose tolerance test (VGTIT) was conducted in all steers. Once steers were judged as carrying adequate 12th-rib fat, based on weight and days on feed, they were harvested and graded and samples of the longissimus muscle were procured for determination of fat content and fatty acid composition. Dietary oil improved (P = 0.011; 0.06) ADG and feed conversion efficiency of steers during the latter part of backgrounding and only ADG during early part ofthe finishing period. Generally percent kidney, pelvic, and heart fat was the only adiposity assessment increased (P = 0.003) by dietary oil. The IVGTT results indicated that insulin response to intravenous glucose was lower in Limousin steers than in Wagyu steers. Dietary oil decreased (P = 0.052) fasting plasma insulin concentration in Wagyu steers compared with Limousin steers. The correlation coefficients among the IVGTT measures and intramuscular fat content or marbling score were less than 0.4, and only a negative trend existed between fasting insulin and USDA marbling scores. However, the carcasses of the Wagyu steers graded US Choice, and 66% of the Wagyu carcasses graded US Prime, which were substantially better than the quality grades obtained for the carcasses from the other breed types. Dietary oil did not affect muscle fat content but increased (P = 0.01) conjugated linoleic acid (CLA) concentrations by 339%. Results indicated that IVGTT measures were not appropriate indices of marbling potential in cattle and that dietary oil can enhance CLA content of beef.

Background:The mechanisms eliciting metabolic activation in satellite cells are unclear. Results: Noncanonical Sonic Hedgehog is activated following muscle injury, which activates AMPK␣1 to induce Warburg-like glycolysis and promote satellite cell activation and proliferation. Conclusion: AMPK␣1 is required for Warburg-like glycolysis in satellite cells, which promotes satellite cell activation and muscle regeneration. Significance: AMPK promotes satellite cell activation during muscle regeneration.