Expression profiles of muscle genes in postnatal skeletal muscle in lines of chickens divergently selected for high and low body weight.

Long-term genetic selection for BW has generated high weight select (HWS) and low weight select (LWS) lines of chickens. These lines show an approximate 10-fold difference in BW at selection age (d 56). The objective of this study was to profile the expression of master regulators of early lineage specification (Pax3, Pax7) and myogenic regulatory factors (Myf5, MyoD1, MyoG, and Mrf4) on day of hatch and d 7, 28, and 56 in pectoralis major and gastrocnemius muscles. There was a line × age interaction for expression of all 6 genes in both muscles. In pectoralis major muscle, Pax3, MyoD1, and Mrf4 showed greater expression in LWS than HWS at day of hatch, whereas all 6 genes showed greater expression in HWS than LWS at d 28. In gastrocnemius muscle, Pax3, Myf5, MyoD1, and MyoG showed greater expression in LWS than HWS at day of hatch, whereas Pax7, Myf5, MyoD1, and Mrf4 showed greater expression in HWS than LWS at d 28. At day of hatch there was no difference in fiber number in gastrocnemius muscle between HWS and LWS; however, HWS had greater fiber diameter than LWS. These results indicate that in LWS there is enhanced expression of genes that are necessary for proliferation of progenitor muscle cells and muscle cell differentiation at day of hatch compared with HWS, but by d 28 these genes are expressed greater in HWS than LWS. Thus, long-term selection for growth has altered the pattern of muscle gene expression.