[Regulation of the expression of alpha and beta tropomyosin genes during development of the pectoral muscle in the chicken].

Accumulation of mRNAs coding for alpha and beta skeletal tropomyosins was investigated using specific probes and normalized to muscle creatine kinase (M-CK) mRNA by slot-blot assays. In developing pectoralis muscle, the ratio of alpha TM messenger/M-CK remained constant until hatching, at which time the messenger disappeared within a week. However, in the leg, this ratio remained constant until 8 days after hatching, whereafter it decreased progressively to reach 30% in the adult. The alpha TM/M-CK ratios were almost the same in the embryonic leg and pectoralis muscle. After hatching, there was a large increase in pectoralis muscle (x 3 at day +4, x 0 at day +21) whereas, the increase was less pronounced and more progressive in the leg (x 3 at day 21). Run-on assays showed that nuclei isolated from 15-day in ovo leg and pectoralis muscles had similar patterns of muscle specific gene transcription whereas post-hatched pectoralis muscle nuclei were shown to have a higher rate of alpha to beta tropomyosin gene transcription. These data are in accordance with the results obtained for protein analysis of leg and pectoralis muscles and support the notion that changes in the protein pattern of developing muscle can be relevant to coordinate regulation of gene transcription.