Persephin (PSPN) belongs to the GDNF ligand subfamily of the TGF-beta superfamily. The amino acid sequence of human PSPN is about 30% analogous to human GDNF. PSPN is synthesized throughout the nervous system and presumably originates from both astroglial cells and neurons. It promotes the survival and growth of mesencephalic dopaminergic and motor neurons. It also plays a role in kidney development by promoting ureteric bud branching. PSPN binds to a receptor complex consisting of Ret tyrosine kinase and GFR-alpha-4.

Pleiotrophin (PTN) is a heparin-binding protein, expression of which is developmentally regulated. It is expressed primarily in brain tissues, but is also expressed in lung, kidney, gut, and bone tissues and can be induced by PDGF. PTN is expressed in some tumor cells as well. PTN is involved in a diverse array of functions including mitogenesis, angiogenesis, tissue repair, and neurite outgrowth. It exhibits strong mitogenic activity towards hepatocytes and plays a role in liver regeneration. PTN binds to several different receptors including syndecan-3, PTP-zeta, and ALK. The nucleotide sequence of Human pleiotrophin is about 50% homologous to human midkine (MDK).