Analysis of HeyL expression in wild-type and Notch pathway mutant mouse embryos

In vertebrates Notch signaling regulates cell fate decisions and boundary f ormation and it underlies several murine and human diseases. Gene targeting experiments point to key roles of Notch receptors. ligands, modulators and downstream targets in somitogenesis, neurogenesis and vascular development . Here we report the embryonic expression of the hairy-related basic helix- loop-helix gene HeyL in wild-type and Notch pathway mutant mice. We show th at HeyL is strongly expressed in the presomitic mesoderm, the somites, the peripheral nervous system and smooth muscle of all arteries. Loss of HeyL e xpression at the level of nascent somites in Notch1 and Delta-like1 knockou t mutants implicates HeyL as a Notch effector during somite formation. Furt hermore, HeyL expression in vascular smooth muscle cells and in the thymus strikingly overlaps with that of Notch3, mutations of which underlie the CA DASIL vascular disorder. (C) 2000 Elsevier Science Ireland Ltd. All rights reserved.