PROJECT SUMMARY/ABSTRACT The cardiogenic fate is established as a bilateral heart field (HF) within the anterior mesoderm through an inductive inter-germ layer signaling interaction. Many genetic pathways responsible for fate specification and differentiation of the HF have been extensively studied. However, where cells of the HF originate, how they precisely arrive at bilateral HF, or how they receive fate specification cues, remains obscured. Using live imaging of both wild type and somatic trans-genetic embryos with molecular sensors, this proposal will identify a coupling of: axis inducing signals with HF precursor positioning in the PS (Aim 1), the earlier onset of bilateral patterning (Aim 2); and a direct cell-cell contact with HF fate specification signaling transfer (Aim 3). Taken together, the proposed study will establish a novel view for the importance of coordinated positioning and interactions in the PS and at the HF forming site to define ultimate cardiogenic fate.