[Show abstract][Hide abstract] ABSTRACT: The molecular basis and control of the biochemical and biophysical properties of skeletal muscle, regarded as muscle phenotype, are examined in terms of fibre number, fibre size and fibre types. A host of external factors or stimuli, such as ligand binding and contractile activity, are transduced in muscle into signalling pathways that lead to protein modifications and changes in gene expression which ultimately result in the establishment of the specified phenotype. In skeletal muscle, the key signalling cascades include the Ras-extracellular signal regulated kinase-mitogen activated protein kinase (Erk-MAPK), the phosphatidylinositol 3'-kinase (PI3K)-Akt1, p38 MAPK, and calcineurin pathways. The molecular effects of external factors on these pathways revealed complex interactions and functional overlap. A major challenge in the manipulation of muscle of farm animals lies in the identification of regulatory and target genes that could effect defined and desirable changes in muscle quality and quantity. To this end, recent advances in functional genomics that involve the use of micro-array technology and proteomics are increasingly breaking new ground in furthering our understanding of the molecular determinants of muscle phenotype.
[Show abstract][Hide abstract] ABSTRACT: A study in 192 entire male pigs examined the effects of breed, diet and muscle on growth, fatness, sensory traits and fatty acid composition. There were four breeds: two modern breeds, Duroc and Large White and two traditional breeds, Berkshire and Tamworth. The diets differed in energy:protein ratio, being conventional (C) and low protein (LP) diets, respectively. Muscles investigated were the `white' longissimus dorsi (LD) and the `red' psoas major (PS). Breed influenced growth rate and fatness, the modern breeds being faster-growing with leaner carcasses. However, the concentrations of neutral lipid fatty acids and marbling fat (neutral lipid+phosopholipid fatty acids) were higher in Berkshire and Duroc, in both LD and PS. Relationships between marbling fat and P2 fat thickness showed clear breed effects, with Duroc having high marbling fat at low P2 and Tamworth low marbling fat at high P2. Breed effects on sensory scores given by the trained taste panel to griddled LD and PS steaks were relatively small. Breed affected the fatty acid composition of intramuscular neutral lipid, with high % values for the saturated fatty acids, 14:0 and 16:0 in Berkshire and Tamworth (fat carcasses) and high values for polyunsaturated fatty acids in Duroc and Large White (lean carcasses). Duroc had particularly high concentrations of the long-chain polyunsaturated fatty acids, 20:5n-3 and 22:6n-3 in phospholipid of both muscles. Diet influenced growth rate and fatness, the LP diet slowing growth and producing fatter meat, more so in the two modern breeds, and particularly in intramuscular rather than subcutaneous fat. This diet produced more tender and juicy meat, although pork flavour and flavour liking were reduced. The PS muscle had higher tenderness, juiciness, pork flavour, flavour liking and overall liking scores than LD. The concentration of phospholipid fatty acids was higher in PS than LD but neutral lipid fatty acid content and marbling fat were higher in LD.
[Show abstract][Hide abstract] ABSTRACT: We investigated the presence of dinucleotide repeats (microsatellites) in a porcine skeletal muscle cDNA library. In total, microsatellites were found in nearly 4% of all muscle cDNA clones, of which CT- and TG-repeats were the most prevalent. We found a near full-length desmin cDNA clone with a CT-repeat sited downstream from its stop codon. From 44 commercially reared pigs, six allelic length polymorphisms were identified at this microsatellite locus (128, 131, 134, 135, 136, and 138 bp), whose desmin genotypes were associated with pH change after slaughter (P=0.031) and colour variation of meat (P<0.001 for hue, P<0.005 for lightness, and P=0.014 for b colour). Two of the genotypes (131/131 bp and 131/135 bp) were consistent with paler meat. This finding indicates the usefulness of the cDNA library approach to generate markers for marker-assisted selection and suggests that the desmin microsatellite could be a possible selection marker.
The Veterinary Journal 03/2003; 165(2):157-63. DOI:10.1016/S1090-0233(02)00159-4 · 1.76 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: The use of DNA markers to define the genetic makeup (genotype) and predict the performance of an animal is a powerful aid to animal breeding. One strategy is known as marker-assisted selection (MAS). MAS facilitates the exploitation of existing genetic diversity in breeding populations and can be used to improve a whole range of desirable traits. DNA markers are, by definition, polymorphic, and the methods used to define DNA markers include restriction fragment length polymorphisms (RFLPs), microsatellites, and single nucleotide polymorphisms (SNPs). Linkage analysis, association analysis and analysis of gene function can be used to determine which polymorphisms are useful markers for desirable traits. Future prospects include the use of high throughput DNA microarray (DNA chip) technology which could revolutionize animal breeding in the next millennium.
The Veterinary Journal 08/2000; 160(1):42-52. DOI:10.1053/tvjl.2000.0468 · 1.76 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: The porcine perinatal myosin heavy chain (MyHC) is a major isoform in foetal skeletal muscles. We report here on its cDNA and genomic isolation, molecular characterisation and expression. Exon 2 and the first 4 bases of exon 3 of the perinatal MyHC gene. both part of the 5'-end untranslated region, showed differential splicing. About 2% of all perinatal MyHC transcripts of a 50-day-old foetus were without exon 2 and about half were without the 4 bases at the 5'-end of exon 3. Perinatal MyHC mRNA was expressed in all hind limb muscles of a 45-day-old foetus along with the slow and embryonic MyHC isoforms in the same fibres. Unlike other sarcomeric MyHCs reported to date, the porcine perinatal promoter is clustered with repeat elements (4 SINEs and 1 microsatellite) and is without a consensus TATA box at the predicted site upstream of exon 1. Nonetheless, in reporter gene transfections, its promoter was found to be highly muscle-specific. The absence of a TATA box may point to a fundamental difference in the regulatory function between the perinatal and adult MyHC isoforms.
Journal of Muscle Research and Cell Motility 03/2000; 21(2):183-8. DOI:10.1023/A:1005660718348 · 2.09 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: The porcine sarcomeric fast 2a myosin heavy chain (MyHC) gene was previously found to require a region extending 3' from the transcriptional start site for high levels of expression. Here we established the existence of two novel opposing regulatory domains in intron 2. A positive regulatory element, defined to a 75bp region, resembles a TATA-less intronic promoter, with a consensus transcription initiation element. It can up-regulate its endogenous or a heterologous muscle promoter in a position specific manner, and on its own drive a reporter gene. In tandem with it is a dominant negative regulatory element, localised to a 81bp region, which can down-regulate its native gene and a heterologous muscle promoter. Bandshift and DNase I footprinting assays demonstrated that specific nuclear factors bound to both regulatory elements are distinctly different. Both elements appear to have no counterpart in intron 2 of the porcine fast 2x and 2b MyHC genes. Taken together, we demonstrate for the first time that a 5'-end terminal intron of a sarcomeric MyHC gene contains two critical regulatory domains, which may be involved in the complexity of temporo-spatial expression.
Journal of Muscle Research and Cell Motility 02/2000; 21(5):451-61. DOI:10.1023/A:1005625302409 · 2.09 Impact Factor