DENERVATED CHICKEN BREAST MUSCLE DISPLAYS DISCOORDINATE REGULATION AND DIFFERENTIAL PATTERNS OF EXPRESSION OF ALPHA-F AND BETA-TROPOMYOSIN GENES

The expression of the alpha fast (alphaf) and beta tropomyosin (TM) ge nes has been analysed with muscle-specific and common cDNA probes afte r unilateral nerve section of the pectoralis major muscle (PM) in 4-we ek-old chickens. The following were observed in denervated muscles. (1 ) The betaTM mRNA, which was repressed during development, reaccumulat es in a biphasic curve with the increase in the betaTM protein lagging behind the changes in its mRNA. Accordingly, no betaTM is seen in pro ducts translated in vitro from total and polyA+ RNA obtained 1 week af ter denervation. No such translation block is seen with RNA obtained f rom control or muscles denervated for 6 weeks. (2) No changes in the a lphafTM mRNA and corresponding protein are observed. (3) RNA processin g of the two genes is not changed. (4) In the contralateral muscles, t ransitory increases in alphaf and betaTM mRNAs are observed while the corresponding proteins remain unchanged. Our data suggest that muscle fibres display early and long-term responses to the loss of neural inp ut which might result from a combination of changes produced by regene rative processes and reprogramming of existing fibres. Moreover, in co ntrast to normal development, no reciprocal changes of alphaf and beta TM expression are seen in denervated muscles.