Delta like protein (Dlk), also known as Preadipocyte factor-1 (Pref-1) or zona glomerulosa-specific factor (ZOG), is an EGF-like transmembrane protein expressed preadipocytes but not in mature adipocytes. It is highly expressed in fetal liver, the adrenal gland, and placenta, as well as some neuroendocrine tumors and small cell lung carcinomas, where it plays a role in differentiation and proliferation. Dlk positively and negatively regulates adipocyte differentiation via at least four major variants (45-60 kDa) of Dlk generated by alternatively splicing. Constitutive expression of Dlk inhibits adipogenesis, but insulin or insulin like growth factor-1 (IGF-1) can circumvent this inhibition. Regulated processing of Dlk releases a 50 kDa soluble form that was previously characterized as Fetal Antigen-1, a protein involved in pancreatic island cell differentiation.Synonyms: DLK, DLK-1, PREF1, Preadipocyte factor 1, Protein delta homolog 1, pG2