Abnormal cardiac inflow tract remodeling can result in total anomalous pulmonary venous return (TAPVR), a life-threatening congenital heart defect. My human genetic studies and my preliminary expression and functional data in chick and mouse embryos suggest that PDGF-signaling is required for inflow tract remodeling and correct pulmonary venous connection. Asymmetric accumulation of cells in the heart stalk is thought to be important for inflow tract and pulmonary vein (PV) development. My data in chick show that Pdgfra and its ligand Pdgfa are expressed in mesenchyme on opposite sides of the heart stalk during PV formation and later around the PV as it matures. I hypothesize that asymmetric expression of PDGF signaling molecules in the heart stalk is required for normal inflow tract and PV development. The transcription factor PITX2 is a key player in asymmetric organogenesis. Mice lacking asymmetric expression of PITX2 have TAPVR. I hypothesize that downstream targets of PITX2 in the heart stalk, likely to include PDGF-signaling molecules, mediate inflow tract remodeling and PV development. My long-term objective is to understand the genetic pathways that regulate inflow tract remodeling and the pulmonary venous connection to the left atrium. I propose the following specific aims 1. Characterize PDGF-signaling in the mouse heart stalk: define the temporal and spatial expression patterns of the PDGF receptors and ligands in the developing mouse heart stalk;determine the requirement of PDGF-signaling in heart stalk patterning and PV development using PDGFRA deficient mouse mutants;examine the cellular mechanisms underlying the leftward shift of the PV. 2. Identify PITX2-regulated genes during mouse inflow tract remodeling: define the expression pattern of PDGF-signaling molecules in Pitx2 mutants lacking an asymmetric enhancer;use these Pitx2AASE mutants to identify PITX2-regulated genes in the inflow tract and heart stalk by microarray analysis. A well structured career development plan, extensively supported with institutional resources and internationally known mentors, has been designed to allow me to transition during the tenure of the K award to an independent tenure-track faculty investigator. Thus, I will receive the necessary training both to direct an active research program and provide state-of-the-art clinical care. (End of Abstract)