MOLECULAR CHARACTERIZATION OF A DEVELOPMENTALLY-REGULATED PORCINE SKELETAL MYOSIN HEAVY-CHAIN GENE AND ITS 5' REGULATORY REGION

Members of the myosin heavy chain (MyHC) gene family show developmenta l stage- and spatial-specificity of expression. We report on the chara cterization and identification of a porcine skeletal fast MyHC gene, i ncluding its corresponding 5' end cDNA and 5' regulatory region. This MyHC isoform was found exclusively in skeletal muscles from about the last quarter of gestation through to adulthood, Expression of this iso form was higher postnatally and its spatial distribution resembled a r osette duster; each with a ring of fast fibres surrounding a central s low fibre, This rosette pattern was absent in the adult diaphragm but about 20% of the fibres continued to express this MyHC isoform, Furthe r in vivo expression studies, in a variety of morphologically and func tionally diverse muscles, showed that this particular skeletal MyHC is oform was expressed in fast oxidative-glycolytic fibres, suggesting th at it was the equivalent of the fast IIA isoform. Two domains in the u pstream regulatory region were found to confer differentiation-specifi c expression on C2 myotubes (-1007 to -828 and -455 to -101), based on in vitro transient expression assays using the chloramphenicol acetyl transferase (CAT) reporter gene. Interestingly, for high levels of CAT expression to occur, a 3' region, extending from the transcriptional start site to part of intron 2, must be present in all the DNA constru cts used.