| Summary: | Troponin I (TnI), like many striated muscle contractile proteins, consists of multiple isoforms encoded by a multigene family whose members are differentially expressed in the different striated muscle cell types. Two TnI genes, TnIfast and TnIslow, are expressed in skeletal muscle the former in fast muscle fibers, the latter in slow fibers. The tissue- and fiber-type-specificities of the TnI fast and slow genes are driven by transcriptional enhancer elements: a Slow Upstream Regulatory Element (SURE) upstream of the TnIslow gene and a fast Intronic Regulatory Element (IRE) within the first intron of the TnIfast gene. Within the 144 bp IRE, there are 4 known cis elements, and the aim of this work was to initiate the studies to map the element(s) that are chiefly responsible for directing the fast-fiber-specificity of IRE-driven gene expression. This was approached by making IRE end-deletion constructs lacking either the left-most or right-most IRE cis-element. These IRE derivatives were coupled to a reporter gene consisting of a minimal (enhancer-dependent) TnIfast promoter linked to E. coli beta-galactosidase coding sequences. The transcriptional activity of these constructs was first evaluated in cell culture transfection experiments, and then by in vivo gene transfer into adult mouse skeletal muscles. The conclusion of these experiments was that fast-fiber-specificity of IRE-driven gene expression resides in the left-most 30 bp of the IRE, a region including an E-box binding site for myogenic regulatory factors of the MyoD family.
|
|---|
