Involved in the Notch signaling pathway as Notch ligand. Activates NOTCH1 and NOTCH4. Involved in angiogenesis; negatively regulates endothelial cell proliferation and migration and angiogenic sprouting. Essential for retinal progenitor proliferation is required for suppressing rod fates in late retinal progenitors as well as for proper generation of other retinal cell types. During spinal cord neurogenesis, inhibits V2a interneuron fate (By similarity). Expression restricted to anterior ectodermal derivatives, namely the ventral forebrain, the cranial neural crest and the cement gland. Also expressed in the developing eye. Belongs to the distal-less homeobox family.