AN OCT-LIKE BINDING-FACTOR REGULATES MYF-5 EXPRESSION IN PRIMARY AVIAN CELLS

Myogenic regulatory factors (MRFs) are hierarchical regulators of skel etal myogenesis. Many MRF promoters have been well characterized with respect to flanking sequences that control their expression. Yet the p romoter elements that regulate Myf-5, the first MRF expressed during m ammalian embryogenesis, are still largely unknown. Comparison of Myf-5 5' flanking regions from bovine, mouse, and chicken genes revealed th ree evolutionarily conserved elements proximal to the transcription st art site: the TATA box, an octamer motif, termed OLS, and a 6-bp C-ric h element. Mobility shift assays and DNase I footprinting analysis dem onstrated that a nuclear factor(s) present in both bovine and avian mu scle and nonmuscle tissues specifically recognized OLS. Furthermore, t his binding activity reacted with a polyclonal Oct-1 antibody. In avia n primary myoblast and fibroblast cultures, CAT reporter constructs un der regulation of the proximal Myf-5 5' flanking sequence were express ed preferentially in myoblasts with CAT levels approximately la-fold h igher than in fibroblasts. The TATA box and octamer motif were importa nt for expression in both myoblasts and fibroblasts: loss of the TATA box abolished activity, and disruption of the OLS resulted in 50-75% l oss of promoter activity. (C) 1998 Academic Press.