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Muscle specific differences in the regulation of myogenic differentiation in chickens genetically selected for divergent growth rates.

ABSTRACT: With the human population predicted to reach 9 billion by 2050, increasing food supplies while maintaining adequate standards of animal welfare has become a global priority. In the poultry industry, broilers are genetically selected for greater pectoral but not leg muscularity yield leading to leg disorders and thereby welfare issues. It is known that the pectoralis major of broilers contains more muscle fibres of larger diameters than egg-layers but little is known about the leg gastrocnemius muscle cellular characteristics. As muscle fibre numbers are set by hatch, the molecular regulation of myogenesis was investigated in pectoral (selected) and gastrocnemius (unselected) muscles of chick embryos to help explain diverging post-hatch phenotypes. Results showed that broilers were more active from embryonic day (ED) 8 and heavier from ED12 to 18 than layers. The pectoral muscle of broilers exhibited increased myoblast proliferation on ED15 (raised myonuclei, MyoD and PCNA) followed by increased differentiation from ED16 (raised myogenin, IGF-I) leading to increased muscle fibre hyperplasia and mass by ED18 compared to layers. In the gastrocnemius muscle of broilers, cell proliferation was also raised up to ED15 accompanied by increased PCNA, MyoD and IGF-I mRNAs. However, from ED16, myogenin and IGF-I mRNAs were similar to that of layers and PCNA was reduced leading to similar fibre area, nuclei numbers and muscle mass at ED18. We conclude that genetic selection for enhanced post-hatch pectoral muscle growth has altered the temporal expression of IGF-I and thereby myogenin transcription affecting cellular characteristics and mass by hatch in a muscle specific manner. These observations should help develop intervention strategies aimed at improving leg muscle strength and thereby animal welfare to meet growing consumer demand.

SUBMITTER: Al-Musawi SL

PROVIDER: S-EPMC3181402 | biostudies-literature |

REPOSITORIES: biostudies-literature

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Project description:Chickens divergently selected for either high abdominal fat content (fat genotype) or low abdominal fat content (lean genotype) at SRA-INRA, France were used to profile pituitary gland gene expression during juvenile development (1 to 7 weeks of age) and to identify differentially expressed genes associated with genotype and age. The fat line (FL) and lean line (LL) chickens are different in various phenotypic and metabolic measurements, including abdominal fatness, plasma glycemia, and T3. The FL and LL chickens represent unique models for characterizing biomedical and agricultural traits. The Del-Mar 14K Chicken Integrated Systems microarrays were used for a transcriptional scan in the pituitary gland during juvenile development using a reference design for the hybridization of total RNA from the pituitary gland. A reference RNA pool was made from an equal amount of high-quality total RNA extracted from all of the samples. Each of the microarrays was co-hybridized with Cy3-labeled cDNA targets from one of the pituitary samples and Cy5-labled cDNA targets from the reference pituitary RNA pool. Log2-transformed fluorescence intensities were analyzed with a mixed model. Two-way ANOVA (SAS) of log2 ratios was used to detect significant (p<0.05) differences by line, age, and the line-by-age interaction. There were 1150 significantly different genes between the two lines, and 339 of these genes exhibited greater than 0.68-fold differences in their log2 ratios (highest group mean at least 160% of the lowest group mean). One thousand four hundred twenty nine genes were significantly different by age and of these, 583 exhibited fold changes greater than 0.68 in the log2 ratio. There were 145 genes that significantly differed in their line-by-age interaction, and 62 of these exhibited greater than 0.68-fold differences. There were 386 genes with significant differences by line or for line-by-age interaction with at least a 0.68-fold change in log2 ratio and n ≥ 2 for each experimental group.

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Muscle specific differences in the regulation of myogenic differentiation in chickens genetically selected for divergent growth rates.

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