Muscle-specific Transcriptional Regulation of theslowpoke Ca2+-activated K+Channel Gene

Abstract

Transcriptional regulation of the Drosophila slowpoke calcium-activated potassium channel gene is complex. To date, five transcriptional promoters have been identified, which are responsible for slowpoke expression in neurons, midgut cells, tracheal cells, and muscle fibers. The slowpoke promoter called Promoter C2 is active in muscles and tracheal cells. To identify sequences that activate Promoter C2 in specific cell types, we introduced small deletions into the slowpoke transcriptional control region. Using transformed flies, we asked how these deletions affected the in situ tissue-specific pattern of expression. Sequence comparisons between evolutionarily divergent species helped guide the placement of these deletions. A section of DNA important for expression in all cell types was subdivided and reintroduced into the mutated control region, a piece at a time, to identify which portion was required for promoter activity. We identified 55-, 214-, and 20-nucleotide sequences that control promoter activity. Different combinations of these elements activate the promoter in adult muscle, larval muscle, and tracheal cells.

The Smooth Muscle Cell-restricted KCNMB1 Ion Channel Subunit Is a Direct Transcriptional Target of Serum Response Factor and Myocardin

“…Recently, the cardiac muscle-specific channel, hyperpolarization-activated cyclic nucleotide-gated potassium channel 4, was shown to be a direct target of the MEF2 (myocyte-specific, enhancer-binding factor 2) transcription factor (56). In Drosophila, the Kcnma1 gene (slowpoke) is controlled by multiple promoters, including one directing expression of this channel in muscle fibers and tracheal cells through sequences containing MEF2 and E-box binding sites (57). The orthologous mouse Kcnma1 gene is also under the control of several promoters that contain E-boxes, MEF2 sites, and putative CArG boxes (58), some of which are conserved in the human ortholog (59).…”

Drug-Induced Epigenetic Changes Produce Drug Tolerance

“…Both 55b and 6b are non–promoter-containing DNA sequences that were originally identified because of their conservation between two Drosophila species [19,63]. Conservation alone is a strong indicator that these sequences have important roles in the regulation of the slo gene.…”

“…(A) Alignment of the 55b box [63] and (B) the 6b box [19] across eight Drosophila species. Areas of highest identity (80%) are boxed, and black bars below the line denote transcription factor binding motifs that are conserved in these species.…”

Regulation of Mouse Slo Gene Expression

“…In many instances these multiple promoters behave differentially under different cellular conditions. For example, Drosophila Slo gene (dSlo) has multiple promoters whose expression is differentially regulated in muscle or the central nervous system (16,18). However, the role of multiple TSSs or exactly how they are regulated in mammals is not clear.…”

“…Answering this question had as a prerequisite the establishment of the promoter(s) architecture. In this regard, studies of the Drosophila homolog gene, slowpoke (dSlo), have shown that this gene contains multiple promoters that regulate dSlo expression in a tissue-specifie (15)(16)(17)(18) and developmental stage-specific manner (19). However, no studies * This work was supported by National Institutes of Health Grants HL54970…”