four-jointed interacts with dachs, abelson and enabled and feeds back ontothe Notch pathway to affect growth and segmentation in the Drosophila leg

The molecular basis of segmentation and regional growth during morphogenesi s of Drosophila legs is poorly understood. We show that four-jointed is not only required for these processes, but also can direct ectopic growth and joint initiation when its normal pattern of expression is disturbed. These effects are non-autonomous, consistent with our demonstration of both trans membrane and secreted forms of the protein in vivo. The similarities betwee n four-jointed and Notch phenotypes led us to further investigate the relat ionships between these pathways. Surprisingly, we find that although four-j ointed expression is regulated downstream of Notch activation, four-jointed can induce expression of the Notch ligands, Serrate and Delta, and may the reby participate in a feedback loop with the Notch signaling pathway. We al so show that four-jointed interacts with abelson, enabled and dachs, which leads us to suggest that one target of four-jointed signaling is the actin cytoskeleton. Thus, four-jointed may bridge the gap between the signals tha t direct morphogenesis and those that carry it out.