The long-term goal of this proposal is to understand the genetic mechanisms that lead to the formation and functional differentiation of the heart in the model system of the fruit fly Drosophila. This is the first genetic model system in which a defined set of genes has been identified that specify and correctly position the heart within the embryo. In pursuit of this goal, we have established that global embryonic positioning cues, encoded by the secreted factors wingless (Wnt) and dpp (TGF-beta), act in conjunction with the transcription factors Tinman (homeodomain protein) and Pannier (GATA factor), which provide essential mesodermal context information, to allow initiation of heart specification. Remarkably, molecular mechanisms and gene identities responsible to make a fly heart are conserved within the animal kingdom, and have paved the way for understanding fundamental aspects of congenital heart disease. Congenital heart defects are the most common developmental anomaly and are the leading non-infectious cause of mortality in newborns. The Drosophila heart has become an excellent model for unraveling the basic mechanisms of cardiogenesis, and for finding crucial components involved in cardiac differentiation. Here, we propose to continue to exploit the genetic tools and reagents available in Drosophila to elucidate the basis of heart formation (aim 1) and function (aim 2). In aim 1, we propose to examine the genetic and biochemical interactions among the mesodermal transcription factors Tinman, Pannier and a new set of players, the T-box factors Neuromancer 1 (H15) and 2 (H15r), in specifying heart. In aim 2, we plan to examine the role of these transcriptional regulators and select targets in establishing normal heart function. To begin to understand the genetic controls of cardiac physiology, we will also identify and study new gene functions that affect this process.