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Adipose tissue and muscle are endocrine organs releasing signalling and mediator proteins termed adipokines and myokines, enabling functioning of the organism and its adaption to a wide range of different challenges such as starvation, overfeeding, stress and diseases. They also contribute to the "adipose-muscular" cross-talk for an integrated control of body mass composition. This article integrates transcriptomic and proteomic data available in ruminant species (mainly in bovine, and when available in ovine and caprine) to computationally predict the large-scale secretome of adipose tissues and muscles. For this purpose predictive bioinformatics algorithms were employed to identify proteins putatively secreted by tissues thanks to a signal peptide. We predicted 1749 secreted proteins that were found from adipose tissues and muscles, more than a half of them being already declared as secreted proteins in public repositories. We also identified 188 and 357 proteins in the predictive secretome of adipose tissues and muscles respectively, only a minor part (3-11%) of them being reported in the overlap of public repositories used for comparison. Functional analysis of these proteins highlights their involvement in biological pathways known to sustain tissue growth and functioning. This strategy allowed us to identify some known and putative novel adipomyokines, adipokines and myokines. However their role and their expression signature depending on rearing practices remain largely to be explored.

Array technology has been increasingly used to monitor global gene expression patterns in various tissues and cell types. However, applications to muscle development and pathology as well as meat production in livestock species have been hampered by the lack of appropriate cDNA collections. To overcome this problem, a directed cDNA library was constructed starting from 23 muscles of meat-producing bovines to derive a collection of 3573 clones. A preliminary sequence characterization of this collection indicated that the most abundant transcripts correspond to genes encoding proteins involved in energy metabolism (COX and NADH dehydrogenase subunits) and belonging to the contractile apparatus (myosin chains and troponin isoforms). From this cDNA library, we selected a set of 435 clones representing 340 unique genes, of which 24 were novel. This collection was subsequently completed with 75 specific cDNA probes for genes of interest already studied in our laboratory. The bovine 'muscle' cDNA repertoire thus designed was spotted onto a nylon membrane (macroarray) in order to test its utility to further investigate the transcriptome of bovine muscles in relation to meat quality traits. It is also anticipated that this type of collection might be useful for the study of chronic myologic diseases in other mammalian species, including humans.

The aim of the present study was to precise the origin of the particular muscle characteristics of double-muscled cattle by comparing muscle properties of Holstein and double-muscled Belgian Blue (BB) foetuses. Ten 100-day-old foetuses of each genotype were studied. The weight and length of foetuses and the length, weight and area of the Semitendinosus (ST) muscle were analysed. Contractile differentiation of the different fibre types was studied by immunohistochemistry using several monoclonal antibodies raised against different myosin heavy chain isoforms (MHC slow, fast, foetal) and by electrophoresis. Proliferation phase of myoblasts from each genotype was analysed in primary culture. On 100 days of foetal life, the foetuses of both genotypes did not show any significant differences in their weight and length. However, BB cattle already present muscle hypertrophy, which seems to originate from a higher myoblast proliferation observed in primary culture. The use of anti-MHC antibodies shows that ST muscle of BB contained a smaller proportion of primary fibres and a higher proportion of secondary fibres which will give principally fast fibres in adult muscle. Electrophoresis analysis confirms a lower proportion of slow MHC in ST of BB.

With the aim to identify the oncoprotein partners implicated in the c-Jun myogenic influence, we carried out stable transfection experiments of c-Jun and/or ATF2, Fra2, c-Fos overexpression in avian myoblasts. Before induction of differentiation, c-Jun repressed myoblast withdrawal from the cell cycle, as did a TPA treatment. However, after serum removal, unlike TPA, c-Jun significantly stimulated myoblast differentiation. In search for specific partners involved in this dual influence, we found that a reduction in the amounts of c-Fos and Fra2 and an increase in c-Jun proteins occurred at cell confluence, a situation likely to favor cooperation between c-Jun and ATF2 during terminal differentiation. Whereas c-Fos and Fra2 cooperated with c-Jun to abrogate myoblast withdrawal from the cell cycle and terminal differentiation, ATF2 co-expression potentiated the positive myogenic c-Jun influence. In addition, myogenin expression was a positive target of this cooperation and this regulation occurred through a stimulation of myogenin promoter activity: (1) whereas c-Fos or Fra2 co-expression abrogated c-Jun stimulatory activity on this promoter, ATF2 co-expression potentiated this influence; (2) using a dominant negative ATF2 mutant, we established that c-Jun transcriptional activity required functionality of endogenous ATF2. These data suggest that through this dual myogenic influence due to cooperations with different partners, c-Jun is involved in the control of duration of myoblast proliferation and thereafter of fusion efficiency.

The v-erbA oncoprotein represents a mutated version of a thyroid hormone receptor, responsible for the induction of a differentiation arrest in chicken erythroid cells. We have studied the influence of v-erbA on proliferation and differentiation of avian myoblasts. Secondary quail myoblast cultures were infected either with an avian retrovirus carrying the v-erbA oncogene in association with the neomycin resistance gene, or with a control deleted v-erbA/neoR alpha retrovirus. We report here that v-erbA expression led to an increase in myoblast proliferation and to a surprising stimulation of quail myoblast terminal differentiation. In addition, these effects occurred in the presence or absence of T3, and v-erbA did not suppress T3 influence on myoblasts. Transient transfection assays demonstrated that, in contrast to its action in HeLa cells, v-erbA was unable to repress the transcriptional activation of a TRE-CAT reporter gene by liganded c-erbA alpha receptors in quail myoblasts. We also observed that the AP-1/c-erbA/v-erbA interactions are not functional in quail myoblasts. These data suggest that, in these cells, v-erbA action does not interfere with T3 induced mechanisms. They also demonstrate a cell specificity for the v-erbA pathway. Lastly, expression of c-erbA/v-erbA chimeric proteins and of the S61G v-erbA mutant indicates that the DNA binding domain of v-erbA, and more specifically serine 61, is directly involved in the enhancement of myoblast differentiation by the oncoprotein.

The influence of triiodothyronine (T3) on avian myoblast proliferation and differentiation was studied in secondary cultures using plating densities of 2,500 and 7,000 cells/cm2. Culture media were depleted of T3 (control myoblasts) and increasing amounts were then added to concentrations of 0.6, 3 and 15 nM T3 (treated myoblasts). Independent of the cell density, T3 induced a dose-related decrease in myoblast proliferation measured by cell number, doubling time and 3H-thymidine incorporation. However, with the lower plating density, this influence was delayed, occurring only after the third day of culture for 0.6 nM T3-treated myoblasts and simultaneous with the onset of myosin heavy chain accumulation. Moreover, when myoblasts were exposed to BrdU for 48 h, the T3 growth inhibitory effect disappeared, thus showing that this effect was clearly linked to differentiation. In addition, we have shown that T3 induced an early fusion of myoblasts: 65% of the maximal value of the fusion index was reached on day 3 in the T3-treated cells in comparison to 25% in the control myoblasts. This hormone also enhanced accumulation of muscle-specific proteins (connectin, acetylcholine receptors, myosin heavy chain), tested by cytoimmunofluorescence, ELISA, binding experiments and Western blot. All these results show that T3 increased myoblast differentiation through a pathway including myoblast withdrawal from the cell cycle. The influence of T3 could partly explain its previously reported positive effect on the number of muscle fibers.

We investigated the myogenic properties of rabbit myoblasts in culture, and examined particularly the expression of acetylcholinesterase (AChE). In the presence of horse serum, myoblasts proliferate quickly and begin to fuse by day 3 of culture. Differentiated myotubes presenting some spontaneous contractions are clearly visible from days 6 to 9. The cultures degenerate from day 10 onwards. The specific activity of AChE is low during the proliferation phase of myogenic cells, increases sharply as myotubes differentiated, then decreases as cultures degenerate. In 7-day-old cultures, globular forms are largely predominant and asymmetric forms, detected as A12, represent only 1% of the total activity.

The lean-to-fat ratio, that is, the relative masses of muscle and adipose tissue, is a criterion for the yield and quality of bovine carcasses and meat. This review describes the interactions between muscle and adipose tissue (AT) that may regulate the dynamic balance between the number and size of muscle v. adipose cells. Muscle and adipose tissue in cattle grow by an increase in the number of cells (hyperplasia), mainly during foetal life. The total number of muscle fibres is set by the end of the second trimester of gestation. By contrast, the number of adipocytes is never set. Number of adipocytes increases mainly before birth until 1 year of age, depending on the anatomical location of the adipose tissue. Hyperplasia concerns brown pre-adipocytes during foetal life and white pre-adipocytes from a few weeks after birth. A decrease in the number of secondary myofibres and an increase in adiposity in lambs born from mothers severely underfed during early pregnancy suggest a balance in the commitment of a common progenitor into the myogenic or adipogenic lineages, or a reciprocal regulation of the commitment of two distinct progenitors. The developmental origin of white adipocytes is a subject of debate. Molecular and histological data suggested a possible transdifferentiation of brown into white adipocytes, but this hypothesis has now been challenged by the characterization of distinct precursor cells for brown and white adipocytes in mice. Increased nutrient storage in fully differentiated muscle fibres and adipocytes, resulting in cell enlargement hypertrophy), is thought to be the main mechanism, whereby muscle and fat masses increase in growing cattle. Competition or prioritization between adipose and muscle cells for the uptake and metabolism of nutrients is suggested, besides the successive waves of growth of muscle v. adipose tissue, by the inhibited or delayed adipose tissue growth in bovine genotypes exhibiting strong muscular development. This competition or prioritization occurs through cellular signalling pathways and the secretion of proteins by adipose tissue (adipokines) and muscle (myokines), putatively regulating their hypertrophy in a reciprocal manner. Further work on the mechanisms underlying cross-talk between brown or white adipocytes and muscle fibres will help to achieve better understanding as a prerequisite to improving the control of body growth and composition in cattle. [ABSTRACT FROM AUTHOR]

An experiment was conducted with 42 Montbéliard steers to determine if nutritionally induced interrupted growth could influence muscle characteristics of steers and hence meat quality. A restriction/refeeding path was designed in order to induce a discontinuous growth path. At 9 months of age, 21 steers were given a restricted amount of diet for 3 months and were then slaughtered (R steers; no. = 10; intake: 5.28 kg dry matter (DM) per day) or sgerowthubjected to a 4-month ad libitum refeeding period (R/F steers; no. = 11; intake: 8.99 kg DM per day) with the same diet (11.03 to 11.12 MJ metabolizable energy (ME) per kg DM) prior to slaughter. An additional 21 control steers were offered the same diet but in amounts that allowed them to gain continuously between 9 and 12 months of age, and were then slaughtered (C steers; no. = 10; intake: 7.08 kg DM per day) or maintained on a continuous feeding protocol through to 16 months of age prior to slaughter (C/C steers; no. = 11; intake : 8.07 kg DM per day). M. semitendinosus (ST), m. longisssimus thoracis and m. triceps brachii (TB) were collected for biochemical and histochemical analyses. R steers had a lower average daily gain (ADG; P < 0.001), a lower final weight (P < 0.01) and a leaner carcass (P < 0.01) than C steers. Upon refeeding, R/F steers had a higher ADG than C/C steers (P < 0.05) and underwent compensatory growth resulting in compensation of body weight and composition at 16 months. In muscles, glycolytic lactate dehydrogenase activity was lower in R steers (P < 0.01) and restored in R/F steers compared with control steers. Among oxidative enzymes, cytochrome-c oxidase activity was higher in the TB of R/F compared with C/C steers (P < 0.001) indicating a muscle-specific metabolic adaptation to the feeding level. There was little effect of the nutritional treatment on muscle fibre size and type except for an increase in the frequency of hybrid fibres in R and R/F groups... [ABSTRACT FROM AUTHOR]

Information on clone offspring F1 is limited, especially in species with a long inter-generation interval such as cattle. As cloned cattle exhibit a slight delay in muscle maturation until puberty (Jurie et al.2009 Animal 3, 244-250), the present study aimed to investigate the contractile and metabolic muscle characteristics of F1 at 8, 12, and 18 months of age. Repeated biopsies of the semitendinosus muscle were collected on 10 F1 heifers born after AI of cloned cows at the experimental farm of INRA. Muscle characteristics of these offspring were compared with those of 9 female clones and 8 AI control heifers previously biopsied at the same ages. All animals (clones, F1, and controls) were female Holstein, born and raised under the same conditions in the same farm. Biopsy samples were stored frozen at -80°C until analysis for contractile and metabolic characteristics. The type of contractile fibers was determined from the proportion of the different myosin heavy chain (MyHC) isoforms separated by electrophoresis. Oxidative metabolism was assessed by isocitrate dehydrogenase (ICDH) and cytochrome-c oxidase (COX) activities (μmol min-1per gram of muscle). Data were analyzed separately for each time of biopsy using the GLM procedure of SAS (SAS Institute, Cary, NC, USA). The statistical model contained the group as fixed effect. When a significant effect was detected, differences between least squares means were further separated by the PDIFF option of SAS. Comparison of contractile characteristics from the 3 groups of animals is presented in Table 1. The proportion of MyHC I (slow oxidative isoform) and MyHC IIx (fast glycolytic isoform) in the muscles of F1 was not significantly different from those of controls at 8 and 12 months of age. F1 had different muscle contractile properties compared with clones at 12 months of age. At 8 months of age, F1 had greater ICDH activity than controls (1.39 ± 0.22 v.0.54 ± 0.007; P≤ 0.002) and greater COX activities (11.4 ± 1.6 v.4.2 ± 0.9; P≤ 0.003), but this was not observed later on. Altogether, these data indicate that the muscles of F1 were more oxidative than those of controls. This was not related to a higher percentage of type I fibers but rather to a higher percentage of type IIA fibers. A delay in muscle maturation was only partially found in F1. Table 1.Contractile characteristics (mean ± SE) of the semitendinosus muscle from controls (n= 8), clones (n= 9) and clone offspring (F1, n= 10) heifers [ABSTRACT FROM AUTHOR]