Quail MyoD Is Regulated by a Complex Array of cis-Acting Control Sequences

Abstract

Quail myoD (QmyoD) is the earliest myoD family member expressed in quail somites and its transcription is initiated in response to early developmental signals. We have investigated the transcriptional regulation of QmyoD to define the cis-acting sequences required for tissue-specific and correct developmental expression. The QmyoD gene locus was isolated and sequenced and its regulatory properties were characterized. We identified three distinct regions of cis-acting regulatory sequences that control the expression of reporter gene constructs following DNA transfection into cell lines and cultured primary quail cells. The first, a complex distal control region (DCR), 11.5 kb upstream of the gene, contains three separable enhancer activities. Two of these DCR enhancer activities are tissue specific and can be autoactivated. In addition, these same two enhancers and the entire DCR direct somite- and muscle-specific expression of a reporter gene in transgenic mice. Sequence analysis of the DCR enhancers reveals clusters of E-boxes, MEF2 binding motifs, and stretches of sequence identity with the human myoD enhancer. Second, the promoter region has sequences which act positively to direct expression in both muscle and nonmuscle cells as well as sequences that repress expression specifically in nonmuscle cells. The third control region, the PR, is located -3.3 to -5 kb from the transcription start site and directs muscle-specific expression in cultured cells. This analysis demonstrates that QmyoD has multiple control regions and that some features of myoD regulation are conserved between mammals and birds.