Differences in the expression of genes involved in skeletal muscle proteolysis between broiler and layer chicks during food deprivation

Genetic selection results in a higher growth rate and meat yield in broiler chickens than in layer chickens. We herein demonstrated differences in the effects of 24 h of fasting on the expression of genes involved in skeletal muscle proteolysis between broiler and layer chicks. The mRNA levels of proteolysis-related genes were analyzed in the pectoralis major muscle of 14-day-old chicks after 0 or 24 h of fasting. The mRNA levels of ubiquitin ligases such as atrogin-1 and muscle RING finger-1 (MuRF-1) as well as transcription factor forkhead box class O (FOXO) 1 were significantly increased by fasting in broiler and layer chicks, suggesting that the FOXO1-induced ubiquitin–proteasome system, a major proteolytic system in skeletal muscles, was activated by fasting in both chicks. The mRNA levels of atrogin-1 were significantly lower in broiler chicks than in layer chicks after fasting. Furthermore, the mRNA levels of insulin-like growth factor-1 were significantly decreased by fasting in layer chicks, but not in broiler chicks. The mRNA levels of FOXO3 were significantly increased by fasting in layer chicks, but not in broiler chicks. Therefore, the ubiquitin–proteasome system did not appear to have been fully upregulated in broiler chicks. These results suggest that differences in the expression of genes related to the ubiquitin–proteasome system in skeletal muscle proteolysis between broiler and layer chicks during food deprivation are one of the causes of the high growth rate in broiler chickens.