03-P010 TBX5 AND GATA-4 responsive genes in cardiac development

microscopy. Quantitative analysis of the movies revealed a clear posterior-to-anterior gradient of cell motility and directionality in the PSM. We tracked the movement of the PSM extracellular matrix (ECM) in parallel to the labelled cells and substracted the ECM movement to the global motion of cells. After substraction, cell movements remained consistently graded but lacked directionality. The gradient of random cell motion along the PSM parallels the FGF/MAPK gradient, which has been implicated in the control of cell motility in this tissue. Both FGF signaling and gain and loss-of-function experiments in the chicken embryo lead to a disruption of the motility gradient and to a slowing down of axis elongation. Furthermore, embryos treated with a cell movement inhibitor, also show a slowing down of axis elongation. We propose that the gradient of random cell motility downstream of FGF signaling in the PSM controls posterior elongation in the amniote embryo.