The specific subject of this proposal is the regulatory regions of the gata-6 gene. The potential significance of this subject lies in the specificity of expression of this gene in the developing heart. This specificity appears to stem from control regions identified by the investigator in his preliminary studies. In particular, one reporter transgene containing the smallest fragment of control region was strikingly expressed only in the myocardium of the atrioventricular junction. The atrioventricular region is interesting area where mesenchymal transformation occurs, where connective tissue deposition is very important in later development for proper insulation of atrial from ventricular myocardium, and where valves develop. Defects in this region have been documented in many cardiovascular-associated diseases including Down Syndrome.