Cardiac enhancer activity of the homeobox gene tinman depends on CREB consensus binding sites in Drosophila

The Drosophila homeobox gene tinman plays a critical role in subdividing th e early mesoderm. In particular, tinman is absolutely required for formatio n of the heart and visceral mesoderm. tinman expression is initiated throug hout the mesoderm of the trunk region under the control of the bHLH transcr iption factor encoded by the twist gene, a determinant of all mesoderm, Lat er, tinman expression is restricted to the dorsal portion of the mesoderm, a process that is directed by decapentaplegic (dpp) whose product (a TGF-be ta-related protein) is secreted by the overlaying ectoderm, Further restric tion of tinman expression to the cardiac progenitors, in which it will pers ist throughout development, involves the secreted segmentation gene product encoded by wingless (wg, a Drosophila Wnt gene). Here, we show that strong early expression depends on the synergistic action of an enhancer element at the 5' end of the gene in conjunction with an element in the first intro n, Moreover, two distinct enhancer regions are responsible for tinman expre ssion in the heart: one region confers expression in the heat tube associat ed pericardial cells, the other element drives expression in the contractil e, myocardial cells. The latter element contains two CREB consensus binding sites that are essential for cardiac-specific expression. (C) 2000 Wiley-L iss, Inc.