Differential expression of genes characterizing myofibre phenotype.

Skeletal muscle is composed of metabolically heterogeneous myofibres that exhibit high plasticity at both the morphological and transcriptional levels. The objective of this study was to employ microarray analysis to elucidate the differential gene expression between the tonic-'red' anterior latissimus dorsi (ALD) muscle, the phasic-'white' posterior latissimus dorsi (PLD) and 'mixed'-phenotype biceps femoris (BF) in 1-week-and 19-week-old male turkeys. A total of 170 differentially expressed genes were identified in the muscle samples analysed (P < 0.05). Gene GO analysis software was utilized to identify top gene networks and metabolic pathways involving differentially expressed genes. Quantitative real-time PCR for selected genes (BAT2D, CLU, EGFR and LEPROT) was utilized to validate the microarray data. The largest differences were observed between ALD and PLD muscles, in which 32 genes were over-expressed and 82 genes were under-expressed in ALD1-PLD1 comparison, and 70 genes were over-expressed and 70 under-expressed in ALD19-PLD19 comparison. The largest number of genes over-expressed in ALD muscles, as compared to other muscles, code for extracellular matrix proteins such as dystroglycan and collagen. The gene analysis revealed that phenotypically 'red' BF muscle has high expression of glycolytic genes usually associated with the 'white' muscle phenotype. Muscle-specific differences were observed in expression levels of genes coding for proteins involved in mRNA processing and translation regulation, proteosomal degradation, apoptosis and insulin resistance. The current findings may have large implications in muscle-type-related disorders and improvement of muscle quality in agricultural species.

Fiber phenotype and coenzyme Q10 content in Turkey skeletal muscles.

Phenotypical differences between muscle fibers are associated with a source of cellular energy. Coenzyme Q(10) (CoQ(10)) is a major component of the mitochondrial oxidative phosphorylation process, and it significantly contributes to the production of cellular energy in the form of ATP. The objective of this study was to determine the relationship between whole-tissue CoQ(10) content, mitochondrial CoQ(10) content, mitochondrial protein, and muscle phenotype in turkeys. Four specialized muscles (anterior latissimus dorsi, ALD; posterior latissimus dorsi, PLD; pectoralis major, PM, and biceps femoris, BF) were evaluated in 9- and 20-week-old turkey toms. The amount of muscle mitochondrial protein was determined using the Bradford assay and CoQ(10) content was measured using HPLC-UV. The amount of mitochondrial protein relative to total protein was significantly lower (p < 0.05) at 9 compared to 20 weeks of age. All ALD fibers stained positive for anti-slow (S35) MyHC antibody. The PLD and PM muscle fibers revealed no staining for slow myosin heavy chain (S35 MyHC), whereas half of BF muscle fibers exhibited staining for S35 MyHC at 9 weeks and 70% at 20 weeks of age. The succinate dehydrogenase (SDH) staining data revealed that SDH significantly increases (p < 0.05) in ALD and BF muscles and significantly decreases (p < 0.05) in PLD and PM muscles with age. The study reveals age-related decreases in mitochondrial CoQ(10) content in muscles with fast/glycolytic profile, and demonstrates that muscles with a slow/oxidative phenotypic profile contain a higher proportion of CoQ(10) than muscles with a fast/glycolytic phenotypic profile.

The effect of early dietary amino acid levels on muscle satellite cell dynamics in turkeys.

Understanding the relationship between nutrition and satellite cell activity will be beneficial in obtaining optimal muscle growth and meat production. The objective of this study was to evaluate the effect of early post-hatch levels of dietary amino acids+/-0.88 NRC, 1.00 NRC, and 1.12 NRC), and feed deprivation on the satellite cell mitotic activity, pectoralis thoracicus muscle weight, and body weight of male turkeys (Meleagris gallopavo). Birds from each treatment were injected with 5-bromo-2'-deoxyuridine (BrdU) to label mitotically active cells. The right pectoralis thoracicus was harvested 1 h after BrdU injection for immunohistochemical and myofiber diameter analysis. On the third day post-hatch, satellite cell mitotic activity was the highest (P<0.05) in the 0.88 NRC amino acid treatment group and the lowest (P<0.05) in the feed-deprived group. On the fourth day post-hatch, feed-deprived birds exhibited the lowest (P<0.05) satellite cell mitotic activity and muscle weight. At 140 days of age, there were no significant differences (P>0.05) between treatments in body weight or pectoralis thoracicus muscle weight. Research evaluating species-related differences in apoptotic events and in genes regulating cell proliferation may be necessary to devise feeding strategies aimed at obtaining optimal pectoralis thoracicus muscle yield at market age.

Apoptosis and macrophage infiltration occur simultaneously and present a potential sign of muscle injury in skeletal muscle of nutritionally compromised, early post-hatch turkeys.

Physical stress and malnutrition may cause elimination of myonuclei and produce inflammatory response in muscle. The objective of this study was to histochemically determine the association of apoptosis and/or macrophage infiltration with changes in muscle satellite cell mitotic activity in pectoralis thoracicus muscle of early post-hatch turkey toms. Feed-deprived birds and birds provided with three different levels of crude protein and amino acids (0.88 NRC, 1.00 NRC, and 1.12 NRC) were used in this model. The number of apoptotic nuclei was significantly elevated (P<0.05) and presence of macrophage infiltration was readily detectable in feed-deprived and 0.88 NRC treatment groups 72 h and 96 h post-hatch suggesting potential muscle injury and/or muscle remodeling. The number of apoptotic nuclei was the same (P>0.05), and there was no detectable macrophage infiltration present in birds placed on 1.00 NRC and 1.12 NRC diet 72 h, 96 h, and 120 h post-hatch. At 120 h post-hatch, feed-deprived and 0.88 NRC birds were characterized by no detectable levels of macrophage infiltration and a significant drop (P<0.05) in apoptotic nuclei. Understanding mechanisms that correlate early nutrition with skeletal muscle growth and development may present a useful tool in optimizing muscle health and improving meat quality and yield.