JAG1 (Jagged 1): JAG1 is a crucial ligand in the Notch signaling pathway, playing a role in regulating cell fate and tissue development. Mutations in JAG1 can lead to Alagille syndrome, a disorder that affects the liver, heart, and other organs. Through its involvement in Notch signaling, JAG1 also plays a part in processes such as vascular development, blood cell formation, and cancer progression.