Glial cell line-derived neurotrophic factor (GDNF) and the related neurotrophic factor neurturin (NTN) are potent survival factors for central and peripheral neurons. GDNF is a glycosylated, disulfide-bonded homodimer that is distantly related to the TGF(beta) superfamily of growth factors. Three receptors for these factors, GFR(alpha)-1 (also designated GDNFR-(alpha), RETL1 or TrnR-1), GFR(alpha)-2 (also designated GDNFR-(beta), RETL2, NTNR-(alpha) or TrnR-2) and GFR(alpha)-3 have been identified. The receptors do not contain transmembrane domains and are attached to the cell membrane by glycosyl-phosphoinositol linkage. Both GFR(alpha)-1 and GFR(alpha)-2 have been shown to mediate the GDNF-dependent and NTN-dependent phosphorylation and activation of the tyrosine kinase Ret. GFR(alpha)-3 is expressed only during development.