Up-Regulated Scr Expression in the Drosophila Prothoracic Leg is Regulated by Two Cis-Regulatory Elements

The Drosophila Hox gene Sex combs reduced (Scr) functions during embryonic development to specify regional identity along the anterior/posterior (A/P) axis which is well-studied. Scr also functions to specify the morphology of the prothoracic leg specifically the bristle pattern of the leg which is not well studied. This work examines the genetic regulation of Scr and two cis-regulatory modules (CRMs) that direct the expression of Scr. The expression of up-regulate Scr is regulated along all three axis in the prothoracic leg. This study shows that the transcription factors Dachshund (Dac) and Distalless (Dll) activate Scr expression along the Proximal/Distal (Pr/Di) axis and Bric-a-brac (Bab) refines the distal edge. Decapentaplegic (Dpp), Wingless (Wg) and Engralied refine the expression of Scr along the A/P and Dorsal/Ventral (D/V) axes to the anterior-ventral region of the prothoracic leg. This up-regulated expression of Scr is regulated by two cis-regulatory elements (CRM), one intronic CRM and one CRM 5’ to the Scr transcription start site. The intronic CRM directs expression in the transverse row (T-row) bristle primordium with the 5’ CRM directing expression in the T-row and sex comb primordium. A smaller sub clone of the 5’ CRM, E fragment, fully recapitulates the up-regulated Scr expression and contains punitive binding sites for Dpp, En and Bab.