Résumé
During muscle maturation, isoform switching of contractile proteins to attain the adult phenotype involves both stage-specific and muscle-specific regulatory mechanisms. Chicken pectoralis major (PM) provides an interesting model to study the latter since a specific pattern of tropomyosin (TM) with repression of the β TM isoform is displayed by the adult PM. The developmental pattern of α and β fast skeletal muscle tropomyosins' (α
f and β TM) RNAs was investigated with 3' untranslated region specific probes. In PM, the β TM messenger ceased to accumulate after hatching through a transcriptional control, as shown by run-on assays, so that, at Day 8
ex ovo, no β TM mRNA was detected. In this same muscle, in parallel with the disappearance of the β TM mRNA, there was a boost in the accumulation of the α
f TM mRNA. In the leg muscles, following hatching, there was only a moderate increase in the level of the α
f TM mRNA, together with a slight decrease in the accumulation of the β TM mRNA. Taken together, these results show that chicken muscle maturation involves tissue-specific transcriptional control of tropomyosin genes and could suggest a possible coordinate regulation of the two genes.