REGULATION OF SKELETAL ALPHA-ACTIN PROMOTER IN YOUNG CHICKENS DURING HYPERTROPHY CAUSED BY STRETCH OVERLOAD

Anterior latissimus dorsi (ALD) muscles of S-wk-old male chickens were injected with plasmids containing various lengths of the chicken skel etal alpha-actin promoter (ranging from -2,090 to -77 relative to the transcription start site) driving luciferase. Hypertrophy of the left ALD muscle was induced by attaching a weight (11% of body wt) to the l eft wing of each chicken, with the unweighted contralateral wing servi ng the control. Six days of stretch overload significantly increased m uscle mass 110%. Luciferase activity from the -2,090 actin-luciferase chimeric gene increased 127% compared with the contralateral control A LD muscle. Luciferase activities driven by the -424, -202, and -99 act in promoters were 179, 134, and 378% higher, respectively, in the stre tched ALD muscle than in the contralateral control ALD muscle. Lucifer ase activity from the -77 deletion construct was not different between stretched and control muscles. These data indicate that the gene regi on responding to stretch is downstream of -99 and imply, but do not co nclusively prove, that the region between -99 and -77, which contains serum response element 1, contributes to the stretch-induced increase in skeletal alpha-actin promoter activity in the ALD muscle.