UNSUSPECTED ROLE FOR THE T-CELL LEUKEMIA PROTEIN SCL TAL-1 IN VASCULAR DEVELOPMENT/

The transcription factor SCL/tal-1 is essential for blood cell develop ment. Though it is also expressed in vascular endothelium, SCL has bee n considered dispensable for vessel formation. Through transgenic resc ue of hematopoietic defects of SCL-/- embryos and analysis of chimeras generated with SCL-/- ES cells tagged with a transgene expressed in v ascular endothelial cells, we show that SCL is essential for angiogeni c remodeling of the yolk sac capillary network into complex vitelline vessels. These findings establish a role for SCL in embryonic angiogen esis and argue for critical functions in both embryonic blood and vasc ular cells, the descendents of the presumptive hemangioblast.