Olomu, Charles
(2018)
Molecular and metabolic regulation of skeletal muscle growth in chicken.
PhD thesis, University of Nottingham.
Abstract
Broiler chicken has been bred for meat production and is characterised with a very fast skeletal muscle growth rate, whilst the layer type have been bred for the production of eggs. This study aimed to understand how intense breeding programmes have developed commercial meat type chickens that have resulted in a fast muscle growth phenotype by a comparative analysis of gene expression between fast-growing broiler and slow-growing layer type chicken. Two chicken trials were carried out. In Trial 1 from fast-growing broiler Ross 308 genotype (R) fast-growing breast Pectoralis major (RPM) and slow-growing leg Peroneus tertius (RPT) muscles were collected at day 14, 36 and 42 post-hatch. In Trial 2, from fast-growing broiler Ross 308 (R) or slow growing layer Hy-Line (H) Pectoralis major (either RPM or HPM) and Peroneus tertius (either RPT or HPM) were collected at day 4, 14, 23, 35 and 42 post-hatch.
In Trial 1, there was a muscle type x age interaction in muscle weights with the RPM having the highest value at day 43 (P<0.001). This effect was also reflected in the protein content with RPM having more protein than RPT. However, RPT had a higher DNA content per unit tissue weight (muscle type x age interaction, P=0.003) with highest value seen at day 43. This suggests that muscle cells of RPM are bigger than those in RPT and that as a result they contain more protein, potentially reflecting RPM hypertrophy compare to RPT. In Trial 1, genes associated with glycolysis, GAPDH and -enolase, were significantly higher in the faster growing RPM (P<0.05). Genes involved in serine biosynthesis PHGDH, PSAT and PSPH, as well as P70S6K involved in protein translation, also had a significantly higher expression in the RPM when compared to the RPT (P<0.05) indicating a greater rate of protein synthesis in the faster growing RPM. Expression of genes associated with smaller muscles (myostatin) or protein degradation (calpastatin, the specific endogenous inhibitor of calpain proteinases) were not different between muscles. LIM domain proteins, CSRP3 and FHL2, had a higher expression in the slower growing muscle, indicating the possibility of those two genes being negative regulators of muscle growth, or may be involved in the upregulation of muscle regenerative physiological processes, as a result of the strain on the leg muscles induced by physical activities during locomotion.
In Trial 2 there was a three-way interaction between genotype, muscle type and age in muscle growth (P<0.001) with the highest value seen at day 42 in the RPM. There was a 3-way interaction between genotype, muscle type and age in the expression of -enolase (P=0.036) with the highest value seen at day 42 in the HPM. For -Enolase mRNA expression, there was a separate genotype and a muscle type effect (both P<0.001) with HPM and HPT been higher than RPM and RPT, and PM muscles having a higher expression than PT muscles in both genotypes. When the serine synthesis pathway was examined, there was a genotype x age interaction (P=0.046) for PSAT and PSPH gene expression, with the highest expression at day 35 in both muscles of the Ross 308 genotype for the former, whilst the latter had the highest expression in the RPM at day 35. For ASNS mRNA expression there were significant genotype (P=0.004) and muscle type effects (P=0.014), with the Ross 308 genotype having the higher expression and the PM being greater than PT. For P70S6K mRNA expression, PM was higher than PT (P=0.012). For P70S6K total protein there was a significant muscle type x age interaction (P=0.049), RPM and HPM being higher than RPT and HPT at days 14 and 35.
For calpain activity only at day 35 was there significant genotype x isoform interaction (P<0.001), with the Hy-Line genotype having a higher micro and milli calpain activity than the Ross 308 genotypes, irrespective of muscle. For trypsin, chymotrypsin and caspase – like activities of the proteasome, there was a significant genotype effects (P<0.001). In all three assays Ross 308 muscles had a higher activity when compared muscles from Hy-Line at both time points. For the ubiquitin ligases there was a borderline muscle type x time interaction (P=0.05) in the expression of MAFbx mRNA, with the RPT and HPT having a higher expression than the RPM and HPM respectively at day 14. For MuRF1 mRNA there was a significant genotype x age interaction (P<0.001) with the HPM and HPT having a higher expression than the RPM and RPT at day 14 and 35. For CSRP3 there was a genotype x age interaction (P<0.001), with the highest expression seen in the HPT at day 42. There was also muscle type effect within genotypes with the RPT and HPT having a higher expression than the RPM and HPM (P<0.001).
Trial 2 indicated that there is an increase in protein synthesis which leads to clear increase in protein accretion in faster growing chicken muscles, thereby supporting the wealth of literature detailing protein turnover in chicken skeletal muscles. There also appears to be an interaction between protein synthesis and degradation, however in most cases protein synthesis seems to be more dynamic and these changes seem to appear around day 35. The novel findings of this study were the observed increase in the expression genes that could limit the synthetic capacity of non-essential amino acid (non-EEA) in fast growing muscles.
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