Intrinsic properties of muscle satellite cells are changed in response to long-term selection of mice for different growth traits

Effects of residual feed intake on the economic traits of fast-growing meat ducks

Feed efficiency (FE) is a crucial economic indicator of meat duck production. The objective of this study was to assess the impact of residual feed intake (RFI), defined as the difference between the actual and expected feed intake based on animal's production and maintenance requirements, on the growth performance (GP), slaughter and internal organ characteristics of fast-growing meat ducks. In total, 1,300 healthy 14-day-old male fast-growing meat ducks were housed in individual cages until slaughter at the age of 35 d. The characteristics of the carcass and internal organs of 30 ducks with the highest RFI (HRFI) and the lowest RFI (LRFI) were respectively determined. RFI, the feed conversion ratio (FCR), and average day feed intake (ADFI) were significantly lower in the LRFI group than the HRFI group (P < 0.001), while there were no significant differences in marketing BW or BW gain (BWG) (P > 0.05). The thigh muscle and lean meat yields were higher, and the abdominal fat content was lower (P < 0.001) in the LRFI group, while there were no significant differences in other carcass traits between the groups (P > 0.05). The liver and gizzard yields were significantly higher (P < 0.001) in the LRFI group, while there were no significant differences (P > 0.05) in intestinal length between the groups. RFI was highly positively correlate with FCR and ADFI (P < 0.01), but negatively correlated the yields of thigh muscle, lean meat, liver, and gizzard, and positively correlated with abdominal fat content. These results indicate that selection for low RFI could improve the FE of fast-growing meat ducks without affecting the marketing BW and BWG, while increasing yields of thigh muscle and lean meat and reducing abdominal fat content. These findings offer useful insights into the biological processes that influence FE of fast-growing meat ducks.

L-arginine upregulates the gene expression of target of rapamycin signaling pathway and stimulates protein synthesis in chicken intestinal epithelial cells

L-arginine (Arg) is an indispensable amino acid in avians and is required for growth. The aim of this study was to investigate the effects of L-Arg on protein synthesis and genes expression involved in target of rapamycin (TOR) signaling pathway in chicken enterocytes. Cells were cultured for 4 days in L-Arg-free Dulbecco's modified Eagle's medium containing 10, 100, 200, 400, or 600 μM L-Arg. Cell growth, cell cycle, protein synthesis, and protein degradation as well as mRNA expression levels of TOR, ribosomal protein S6 kinase 1 (S6K1), and eukaryotic initiation factor 4E-binding protein 1 (4E-BP1) were determined. The results showed that cell viability was enhanced by L-Arg with a maximal response at 10 to 400 μM. Increasing extracellular concentrations of L-Arg from 10 to 400 μM increased the cells in S and G2/M phase to a significant extent and decreased cell numbers in G0/G1 phase. Further more, addition of 100, 200, or 400 μM L-Arg to culture medium increased protein synthesis and reduced protein degradation in chicken intestinal epithelial cells. Consistent with the data on cell growth and protein turnover, supplementation of 100, 200, or 400 μM L-Arg increased the mRNA abundances of TOR, 4E-BP1, and S6K1. It was concluded the action of L-Arg involves in upregulating the genes expression of TOR cell signaling pathway which increases protein synthesis and reduces protein degradation.

Locomotion in response to shifting climate zones: not so fast

Although a species' locomotor capacity is suggestive of its ability to escape global climate change, such a suggestion is not necessarily straightforward. Species vary substantially in locomotor capacity, both ontogenetically and within/among populations, and much of this variation has a genetic basis. Accordingly, locomotor capacity can and does evolve rapidly, as selection experiments demonstrate. Importantly, even though this evolution of locomotor capacity may be rapid enough to escape changing climate, genetic correlations among traits (often due to pleiotropy) are such that successful or rapid dispersers are often limited in colonization or reproductive ability, which may be viewed as a trade-off. The nuanced assessment of this variation and evolution is reviewed for well-studied models: salmon, flying versus flightless insects, rodents undergoing experimental evolution, and metapopulations of butterflies. This work reveals how integration of physiology with population biology and functional genomics can be especially informative.

Dose-dependent effects of genistein and daidzein on protein metabolism in porcine myotube cultures

This study was conducted to investigate whether the isoflavones genistein and daidzein, which are components of soy-based diets, and the estrogen 17beta-estradiol affect differentiation and protein metabolism of porcine skeletal muscle cells in vitro. Serum-free porcine myotube cultures expressing the estrogen receptors ERalpha and ERbeta were treated with various concentrations of genistein, daidzein, or 17beta-estradiol for 26 h. The degree of differentiation by creatine phosphokinase activity was not altered by treatment. At 100 micromol/L both genistein and daidzein caused decreases in protein amount due to cell loss. In addition, 100 micromol/L genistein reduced protein synthesis rate of the surviving cells (P < 0.05) measured as [3H]-phenylalanine incorporation. Interestingly, genistein (0.1 micromol/L), daidzein (10, 100 micromol/L), and 17beta-estradiol (0.1, 1 nmol/L) slightly reduced protein degradation (P < 0.05). The results suggest that both genistein and daidzein affect protein metabolism in a dose-dependent manner and that estrogenic actions may play a role in decreasing protein degradation in porcine skeletal muscle.

Regulation of hypoxic response elements on the expression of vascular endothelial growth factor gene transfected to rat skeletal myoblasts under hypoxic environment

The regulation of hypoxic response elements on the expression of vascular endothelial growth factor (VEGF) gene transfected to primary cultured rat skeletal myoblasts under hypoxic environment was investigated. pEGFP-C3-9HRE-CMV-VEGF vector was constructed with molecular biology technique and transfected to primary cultured rat skeletal myoblasts by lipofectamine in vitro. Gene expression of transfected myoblasts was detected by RT-PCR, Western blot and fluorescence microscope under different oxygen concentrations and different hypoxia time. The results showed that in hypoxia group, the VEGF gene bands were seen and with the decrease of oxygen concentrations and prolongation of hypoxia time, the expression of VEGF mRNA was obviously increased. Under hypoxic environment, the expression of VEGF protein in the transfected myoblasts was significantly increased. EGFP was expressed only under hypoxic environment but not under normoxic environment. It was concluded that hypoxia promoter could be constructed with HRE and regulate the expression of VEGF gene under hypoxic and normoxic environment, which could enhance the reliability of gene therapy.

Developmental changes and the impact of isoflavones on mRNA expression of IGF-I receptor, EGF receptor and related growth factors in porcine skeletal muscle cell cultures

OBJECTIVE

Soy that is widely used in human nutrition and in livestock production is a rich source of isoflavones. In addition to the estrogenic or antiestrogenic effects, isoflavones are suggested to affect cell growth via inhibition of protein tyrosine kinases (e.g. growth factor receptors). Therefore, the present in vitro-study was undertaken to determine, whether genistein and daidzein affect the mRNA expression of growth factor receptors (IGF-I receptor and EGF receptor) and their related growth factors in porcine skeletal muscle cell cultures.

DESIGN

First, we investigated the basal mRNA expression of IGF-I, IGF-II, EGF, IGF-I receptor, and EGF receptor in proliferating and differentiating porcine skeletal muscle cell cultures using real-time PCR. Secondly, we measured the changes in the mRNA expression in these cell cultures treated with 0 (control), 1, 10, 100 microM genistein or daidzein over 26 h in serum-free medium (n=3).

RESULTS

The mRNA expression of IGF-I was slightly decreased, whereas transcript concentrations of IGF-II and EGF were increased during differentiation compared with the proliferating stage of porcine muscle cell cultures. IGF-I receptor transcripts tended to be increased, whereas EGF receptor mRNA expression remained unchanged from proliferation to differentiation. Genistein and daidzein at 1 microM and 10 microM showed no effects on the mRNA expression of these genes, neither in proliferating nor in differentiating cells. However, high-concentrated isoflavones (100 microM) decreased the mRNA expression of IGF-I receptor and of the growth factors examined.

CONCLUSIONS

The present study confirms the role of the IGF and EGF system in proliferation and differentiation of skeletal muscle cell culture especially under serum-free culture conditions. Furthermore, the results of this in vitro-study suggest that there is no effect of isoflavones at concentrations resulting from dietary consumption (1 and 10 microM) on IGF- and EGF-associated gene expression in porcine skeletal muscle tissue. Genistein and daidzein at high concentration (100 microM) reduced the mRNA expression of the IGF-I receptor and the growth factors examined, and therefore, may modify their autocrine and paracrine actions in skeletal muscle tissue.

Establishment and conditions for growth and differentiation of a myoblast cell line derived from the semimembranosus muscle of newborn piglets

To establish an adequate model to study the proliferation and differentiation of porcine skeletal muscle in response to bioactive compounds, a pool of satellite cells was derived from the semimembranosus muscle (SM) of newborn piglets using a Percoll gradient centrifugation. The final yield amounted to 4.1 x 10(6) cells/g muscle tissue. The percentage of muscle satellite cells has been determined by immunostaining for desmin and subsequent fluorescence analysis by flow cytometry, which revealed 95% of desmin-positive cells. For proliferation studies, satellite cell born myoblasts were seeded in gelatin-coated 96-well microplates at about 5 x 10(3) cells per well. Cells were grown for 1 day in MEMalpha plus 10% fetal bovine serum (FBS) and 10% horse serum (HS), followed by 2 d cultivation in serum-free growth medium. For differentiation studies, myoblasts were cultured in matrigel-coated 24-well plates for 4 d with growth medium containing 10% FBS and 10% HS. At 80% confluence, cells were grown for 24 h in medium plus 10% FBS and 1 microM insulin to initiate differentiation. Subsequently, the cells were cultured in serum-free differentiation medium (SFDM) for 3 d to form myotubes. Cultures reached a maximum fusion rate of approximately 20% after 96 h. By establishing this culture system, we provide an advanced and appropriate in vitro model to study porcine skeletal muscle cell growth and differentiation including the responses to various bioactive compounds.

Phenotypic characterisation of extreme growth-selected mouse lines: An important prerequisite for future QTL analysis

A unique set of seven mouse lines, long-term selected for high growth, from different laboratories around the world has been comprehensively compared to evaluate these resources for future QTL and gene mapping for growth traits. The heaviest line (DUH) was 40% (males) to 44% (females) heavier than the smallest line (ROH) at birth, and 105% (males) to 114% (females) heavier at 98 d. Body conformation (body length and width, body areas), body composition (dry matter, fat, fatty acid composition, organ weights), and skeletal muscle cellularity also differed substantially. DUH was more than 20% longer (12.3 cm) compared to the shortest line ROH (9.7 cm). DAH (22.5%) had the highest percentage of gonadal fat and the leanest was BEH (7.7%). Line BEH (0.49 g) showed the highest weight for the left M. rectus femoris, which was 2.1 times higher, compared to ROH (0.23 g). These results suggest that different alleles, and possibly different physiological pathways, have contributed to the selection response in the different lines. Therefore these selection lines are an important tool with which to identify the genetic and physiological basis of growth as they may contain many, if not all, growth promoting alleles.

Evidence for estrogen receptor α and β expression in skeletal muscle of pigs

Recent research suggests that estrogen receptors (ERs) are of significance in skeletal muscle function. The aim of the present study was to investigate, whether ERalpha and ERbeta are expressed in different porcine skeletal muscles and in satellite cells derived from semimembranosus muscle (SM) at the protein and mRNA level. Immunohistochemistry demonstrated positive staining for ERalpha in the nuclei of skeletal muscle cells, while the ERbeta stain showed positive signals in nuclei and cytoplasm of skeletal myofibers and myoblasts derived from satellite cells. Additionally, a weak expression of both ER subtypes was seen in skeletal muscle tissue and SM satellite cells with Western blot analysis. A clear expression of the ERalpha mRNA and a weak expression of the ERbeta mRNA was seen in skeletal muscle tissue and SM satellite cell cultures, as determined by reverse transcription (RT)-PCR. The present study shows for the first time that both ERalpha and ERbeta are expressed in porcine skeletal muscle, which, consequently, could be considered as a target tissue for estrogens or estrogen-like compounds. However, more detailed studies on the functional impact of both receptor subtypes in skeletal muscle are necessary. The porcine SM satellite cell culture provides a suitable in vitro model to investigate estrogenic effects on pig skeletal muscle.

Molecular genetic and physiologic background of the growth hormone-IGF-I axis in relation to breeding for growth rate and leanness in pigs

The GH-IGF-I axis is of major importance for the regulation of body growth and composition, and cellular proliferation and differentiation processes. Selective breeding aiming to improve growth rate and/or body composition is accompanied by changes of the GH-IGF-I axis. Research aiming to elucidate the genetic and physiologic mechanism(s) underlying these changes may best use single-trait selection lines. Two such pig selection lines, one for growth rate and one for high lean content, were used in experiments to investigate the mechanisms of the GH-IGF-I axis change during selection. This contribution reviews the selection-related changes in the GH-IGF-I axis as the consequences of selection for whole body growth rate or body composition and effects on local tissue growth rate. A model explaining the observed effects and consequences for the pressure on the physiology is presented. In short, selection related demand for GH induces GH synthesis until a limit is reached. After that the pulsatile GH plasma profile changes, which may also affect expression profiles of genes regulating body composition.