Jagged1 (JAG1) is one of five cell surface proteins (ligands) that interact with 4 receptors in the mammalian Notch signaling pathway. The Notch Signaling Pathway is a highly conserved pathway that functions to establish and regulate cell fate decisions in many organ systems. Once the JAG1-NOTCH (receptor-ligand) interactions take place, a cascade of proteolytic cleavages is triggered resulting in activation of the transcription for downstream target genes. Located on human chromosome 20, the JAG1 gene is expressed in multiple organ systems in the body and causes the autosomal dominant disorder Alagille syndrome (ALGS) resulting from loss of function mutations within the gene. JAG1 has also been designated as CD339 (cluster of differentiation 339).