RBPJ binding sites in the promoters of HEY1, HEY2 and HEYL genes are conserved between humans and mice (Maier and Gessler 2000), and expression of human NICD1 was directly shown to activate transcription from human HEY2 and HEYL promoters (Arnett et al. 2010). Based on the evolutionary conservation of RBPJ sites and the existing findings from human and mouse studies, NOTCH1 is expected to directly stimulate transcription of HEY1, HEY2 and HEYL (Fischer et al. 2004, Leimeister et al. 2000).