Persephin is a disulfide-linked homodimeric neurotrophic factor belonging to the Transforming Growth Factor-beta (TGF-beta) superfamily and the GDNF sub-family. One cysteine residue, out of the seven conserved, is used for inter-chain disulfide bridging while the others form a cysteine knot ring formation. It signals through RET and one of the four GFR-alpha (alpha-1, alpha-2, alpha-3, alpha-4) receptors to promote the proper development and maintenance of the nervous system. Persephin promotes survival of dopaminergic neurons in the midbrain as well as some motor neurons, and promotes branching of ureteric buds.