Activation of adult myoblasts called satellite cells during muscle degeneration is an important aspect of muscle regeneration. Satellite cells are believed to be the only myogenic stem cells in adult skeletal muscle and the source of regenerating muscle fibers. Upon activation, satellite cells proliferate, migrate to the site of degeneration, and become competent to fuse and differentiate. We show here that the transcription factor polyomavirus enhancer activator 3 (PEA3) is expressed in adult myoblasts in vitro when they are proliferative and during the early stages of differentiation. Overexpression of PEA3 accelerates differentiation, whereas blocking of PEA3 function delays myoblast fusion. PEA3 activates gene expression following binding to the ets motif most efficiently in conjunction with the transcription factor myocyte enhancer factor 2 (MEF2). In vivo, PEA3 is expressed in satellite cells only after muscle degeneration. Taken together, these results suggest that PEA3 is an important regulator of activated satellite cell function.In mature muscle, activation of adult myoblasts called satellite cells is one mechanism for the maintenance of skeletal muscle mass. Although quiescent in normal muscle, these cells are activated to proliferate and differentiate in response to muscle damage or degeneration, thereby regenerating muscle fibers (5). To identify regulatory molecules in satellite cells that respond to external signals and control gene expression during satellite cell activation, we analyzed the regulation of the human ␤-enolase gene, which belongs to a relatively small group of muscle-specific genes expressed in proliferating, undifferentiated myoblasts from adult muscle (42). We showed that expression of the ␤-enolase gene in undifferentiated myoblasts is independent of the basic helix-loop-helix (bHLH) family of transcription factors, including MyoD, myogenin, myf-5, and MRF4 (42). Through comparative deletion-transfection analyses of myoblast and fibroblast cell lines, we identified an enhancer from the human ␤-enolase gene that promoted highlevel myoblast-specific expression of a reporter gene (49). After myoblast differentiation into myotubes, the activity of the enhancer declined dramatically, suggesting that other cis-regulatory elements are responsible for maintaining ␤-enolase gene expression in myotubes. Electrophoretic mobility shift assays and mutational analysis indicated that proteins present in myoblast nuclear extracts specifically bound to an ets motif within the enhancer required for high-level activity in myoblasts (49). ETS proteins comprise a family of transcription factors that share a conserved 85-amino-acid domain necessary for specific binding to purine-rich DNA sequences with a GGA core consensus (22, 38). They have been shown to be involved in regulating gene expression and controlling cell growth, differentiation, and migration in a variety of biological systems (21, 47, 52).A feature of many ETS domain proteins is that they form complexes with transcription factors of un...

Enol lactones react with an amine to give either a keto amide or a hydroxy lactam under mild conditions. Subsequent dehydration with p-toluenesulfonic acid P"SA) gives a cyclic acylated enamino ester in good yield (Tables 1 and 2, Schemes 2 and 4). The key prostaglandin analog precursor 18 and the gly-gly dipeptide analogs 26a and 26b were prepared using the reported conditions. Acetylation of the chloro hydroxy lactam 31, prepared from the chloro enol lactones 29, followed by elimination of acetic acid gave the chloro acylated enamino esters 28.

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Each of the myogenic helix-loop-helix transcription factors (MyoD, Myogenin, Myf-5, and MRF4) is capable of activating muscle-specific gene expression, yet distinct functions have not been ascribed to the individual proteins. We report here that MyoD and Myogenin mRNAs selectively accumulate in hindlimb muscles of the adult rat that differ in contractile properties: MyoD is prevalent in fast twitch and Myogenin in slow twitch muscles. The distribution of MyoD and Myogenin transcripts also differ within a single muscle and correlate with the proportions of fast glycolytic and slow oxidative muscle fibres, respectively. Furthermore, the expression of a transgene consisting of a muscle-specific cis-regulatory region from the myoD gene controlling lacZ was primarily associated with the fast glycolytic fibres. Alteration of the fast/slow fibre type distribution by thyroid hormone treatment or by cross-reinnervation resulted in a corresponding alteration in the MyoD/Myogenin mRNA expression pattern. These findings show that the expression of specific myogenic helix-loop-helix regulators is under the control of innervation and humoral factors and may mediate differential control of contractile protein gene expression in adult muscle.