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The callipyge phenotype in sheep involves substantial postnatal muscle hypertrophy and other changes to carcass composition. A single nucleotide polymorphism in the DLK1- DIO3 imprinted gene cluster alters gene expression of the paternal allele-specific protein-coding genes and several maternal allele-specific long noncoding RNA and micro RNA when the mutation is inherited in cis. The inheritance pattern of the callipyge phenotype is polar overdominant because muscle hypertrophy only occurs in heterozygous animals that inherit a normal maternal allele and the callipyge SNP on the paternal allele ( +/C). We examined the changes of gene expression of four major transcripts from the DLK1- DIO3 cluster and four myosin isoforms during the development of muscle hypertrophy in the semimembranosus as well as in the supraspinatus that does not undergo hypertrophy. The homozygous ( C/C) animals had an intermediate gene expression pattern for the paternal allele-specific genes and two myosin isoforms, indicating a biological activity that was insufficient to change muscle mass. Transcriptome analysis was conducted by RNA sequencing in the four callipyge genotypes. The data show that homozygous animals ( C/C) have lower levels of gene expression at many loci relative to the other three genotypes. A number of the downregulated genes are putative targets of the maternal allele-specific micro RNA with gene ontology, indicating regulatory and cell signaling functions. These results suggest that the trans-effect of the maternal noncoding RNA and associated mi RNA is to stabilize the expression of a number of regulatory genes at a functional, but low level to make the myofibers of homozygous ( C/C) lambs less responsive to hypertrophic stimuli of the paternal allele-specific genes. [ABSTRACT FROM AUTHOR]

The ruminant developmental transition from late foetus to lamb is associated with marked changes in skeletal muscle structure and function that reflect programming for new physiological demands following birth. To determine whether epigenetic changes are involved in this transition, we investigated the genomic architecture of the chromatin modification, histone 3 lysine 27 trimethylation (H3K27me3), which typically regulates early life developmental processes; however, its role in later life processes is unclear. Chromatin immunoprecipitation coupled with next-generation sequencing was used to map H3K27me3 nucleosomes in ovine longissimus lumborum skeletal muscle at 100 days of gestation and 12 weeks post-partum. In both states, H3K27me3 modification was associated with genes, transcription start sites and CpG islands and with transcriptional silencing. The H3K27me3 peaks consisted of two major categories, promoter specific and regional, with the latter the dominant feature. Genes encoding homeobox transcription factors regulating early life development and genes involved in neural functions, particularly gated ion channels, were strongly modified by H3K27me3. Gene promoters differentially modified by H3K27me3 in the foetus and lamb were enriched for gated ion channels, which may reflect changes in neuromuscular function. However, most modified genes showed no changes, indicating that H3K27me3 does not have a large role in late muscle maturation. Notably, promyogenic transcription factors were strongly modified with H3K27me3 but showed no differences between the late gestation foetus and lamb, likely reflecting their lack of involvement in the myofibre fusion process occurring in this transition. H3K27me3 is a major architectural feature of the epigenetic landscape of ruminant skeletal muscle, and it comments on gene transcription and gene function in the context of late skeletal muscle development. [ABSTRACT FROM AUTHOR]

Rtl1 and Dlk1 are two genes in an imprinted gene cluster on mouse chromosome 12. Rtl1 is a paternally expressed gene encoding a retrotransposon-like protein, but as yet, there is no evidence that a protein is produced by this gene although a transcript is produced. Dlk1 is also paternally expressed and it encodes a plasma membrane-bound protein known to act as a negative regulator of adipogenesis. Genes at other imprinted loci often show coordinate expression and may interact at a functional level. We tested the hypothesis that Dlk1 and Rtl1 are functionally related. Rtl1 and Dlk1 mRNA expression patterns show similar time courses of down-regulation during induced adipogenesis of 3T3L1 cells. Despite the coordinate down-regulation of Dlk1 and Rtl1 mRNA levels, Rtl1 over-expression did not affect the time course of adipogenesis or Dlk1 expression. It is concluded that these two genes are neither directly nor indirectly functionally related. [ABSTRACT FROM AUTHOR]

The callipyge mutation causes postnatal muscle hypertrophy in heterozygous lambs that inherit a paternal callipyge allele ( +/CLPG). Our hypothesis was that the up-regulation of one or both of the affected paternally expressed genes ( DLK1 or PEG11) initiates changes in biochemical and physiological pathways in skeletal muscle to induce hypertrophy. The goal of this study was to identify changes in gene expression during the onset of muscle hypertrophy to identify the pathways that are involved in the expression of the callipyge phenotype. Gene expression was analysed in longissimus dorsi total RNA from lambs at 10, 20, and 30 days of age using the Affymetrix Bovine Expression Array. An average of 40.6% of probe sets on the array was detected in sheep muscle. Data were normalized and analysed using a two-wayanova for genotype and age effects with a false discovery rate of 0.10. From theanova, 13 genes were significant for the effect of genotype and 13 were significant for effect of age ( P < 0.10). No significant age-by-genotype interactions were detected ( P > 0.10). Of the 13 genes indicating an effect of genotype, quantitative PCR assays were developed for all of them and tested on a larger group of animals from 10 to 200 days of age. Nine genes had significantly elevated transcript levels in callipyge lambs. These genes included phosphofructokinase, a putative methyltransferase protein, a cAMP phosphodiesterase, and the transcription factor DNTTIP1. [ABSTRACT FROM AUTHOR]

Introduction: Sarcopenia is associated with morbidity and mortality. Cellular pathways involved in the regulation of growth and atrophy affect myofibre size and subsequently, muscle strength. The objective of this study was to investigate whether skeletal muscle gene expression was associated with altered lean mass and grip strength in community-dwelling older men.Methods: 99 men (mean age 72 years) consented for detailed characterisation of muscle mass and strength as well as a muscle biopsy of the vastus lateralis. Tissue suitable for molecular analysis was available from 88 participants. PCR arrays on muscle tissue were used to determine the expression of 44 genes implicated in the cellular regulation of skeletal muscle. The relationships between gene expression, lean mass and grip strength were described.Results: Participant groups with extreme values of lean mass (n = 18) and grip strength (n = 20) were used in the analysis of fold change in gene expression. Expression of VDR (vitamin D receptor) (fold change [FC] 0.52, standard error for fold change [SE] ±0.08, p = 0.01) and INFG (interferon gamma) mRNA (FC 0.31; SE ±0.19, p = 0.01) were lower in those with higher lean mass. Expression of IL6 (interleukin 6) (FC 0.43; SE ±0.13, p = 0.02), TNF (tumour necrosis factor) (FC 0.52; SE ±0.10, p = 0.02), IL1R (interleukin 1 receptor) (FC 0.63; SE ±0.09, p = 0.04) and MSTN (myostatin) (FC 0.64; SE ±0.11, p = 0.04) were lower in those with higher grip strength. No other significant changes in fold change were seen.Conclusion: Lower expression of VDR and INFG associated with higher lean mass and lower expression of IL6, TNF, IL1R and myostatin associated with higher grip strength. These results suggest a role for inflammation in the regulation of muscle mass and strength. Replication studies in larger study samples of men and women are now needed. [ABSTRACT FROM AUTHOR]

Introduction: Sarcopenia is associated with morbidity and mortality. Cellular pathways involved in the regulation of growth and atrophy affect myofibre size and subsequently, muscle strength. The objective of this study was to investigate whether skeletal muscle gene expression was associated with altered lean mass and grip strength in community-dwelling older men.Methods: 99 men (mean age 72 years) consented for detailed characterisation of muscle mass and strength as well as a muscle biopsy of the vastus lateralis. Tissue suitable for molecular analysis was available from 88 participants. PCR arrays on muscle tissue were used to determine the expression of 44 genes implicated in the cellular regulation of skeletal muscle. The relationships between gene expression, lean mass and grip strength were described.Results: Participant groups with extreme values of lean mass (n = 18) and grip strength (n = 20) were used in the analysis of fold change in gene expression. Expression of VDR (vitamin D receptor) (fold change [FC] 0.52, standard error for fold change [SE] ±0.08, p = 0.01) and INFG (interferon gamma) mRNA (FC 0.31; SE ±0.19, p = 0.01) were lower in those with higher lean mass. Expression of IL6 (interleukin 6) (FC 0.43; SE ±0.13, p = 0.02), TNF (tumour necrosis factor) (FC 0.52; SE ±0.10, p = 0.02), IL1R (interleukin 1 receptor) (FC 0.63; SE ±0.09, p = 0.04) and MSTN (myostatin) (FC 0.64; SE ±0.11, p = 0.04) were lower in those with higher grip strength. No other significant changes in fold change were seen.Conclusion: Lower expression of VDR and INFG associated with higher lean mass and lower expression of IL6, TNF, IL1R and myostatin associated with higher grip strength. These results suggest a role for inflammation in the regulation of muscle mass and strength. Replication studies in larger study samples of men and women are now needed. [ABSTRACT FROM AUTHOR]