Mammalian Jagged proteins are homologs of the Drosophila Notch ligand, Serrate, and together with Delta-like proteins, constitute ligands for the mammalian Notch proteins. Jagged 1 and 2 are 180 kDa and 150 kDa type I transmembrane glycoproteins, respectively, that possess extracellular DSL (delta, serrate, lag-2 consensus sequence) domains necessary for binding to Notch receptors, along with 15-16 calcium-binding EGF-like repeats which modulate the binding affinity. Jagged-Notch signaling specifies cell fate, regulates pattern formation, defines boundaries between different cell types, and modulates cell proliferation and differentiation, especially during hematopoiesis, myogenesis, neurogenesis and development of the vasculature. Since both the ligands and receptors are transmembrane proteins, direct cell-cell interactions are thought to be required for functional Notch signaling.