Abstract: The present invention relates to nucleotide sequences of vertebrate Delta genes, and amino acid sequences of their encoded proteins, as well as derivatives (e.g., fragments) and analogs thereof. In a specific embodiment, the vertebrate Delta protein is a human protein. The invention further relates to fragments (and derivatives and analogs thereof) of Delta which comprise one or more domains of the Delta protein, including but not limited to the intracellular domain, extracellular domain, DSL domain, domain amino-terminal to the DSL domain, transmembrane region, or one or more EGF-like repeats of a Delta protein, or any combination of the foregoing. Antibodies to Delta, its derivatives and analogs, are additionally provided. Methods of production of the Delta proteins, derivatives and analogs, e.g., by recombinant means, are also provided. Therapeutic and diagnostic methods and pharmaceutical compositions are provided.