CLONING AND EXPRESSION OF A NOVEL NEUROTROPHIN, NT-7, FROM CARP

Neurotrophins have been demonstrated to play important roles in the de velopment and functioning of the nervous system. This family of protei ns consists of four homologous members in mammals: NGF, BDNF, NT-3, an d NT-4/5. A new member, called NT-6, was recently cloned from the plat yfish Xiphophorus maculatus. This protein shares closer structural rel ationship to NGF than the other neurotrophins, but contains a characte ristic insertion of 22 amino acids that constituted the heparin-bindin g domain. Here we report the cloning of a novel neurotrophin from the fish Cyprinus carpio (carp), which shared about 66% amino acid identit y to Xiphophorus NGF and NT-6. The neurotrophin, designated NT-7, poss esses structural characteristics common to all known neurotrophins, su ch as the presence of six conserved cysteine residues and the flanking conserved sequences. In addition, there is an insertion of 15 amino a cids at the position corresponding to that observed for NT-6. The neur otrophic activity of NT-7 was demonstrated by its ability to promote n eurite outgrowth and neuronal survival of chick dorsal root ganglia. P hosphorylation assay of various Trk receptors overexpressed in fibrobl asts suggested that NT-7 could activate TrkA but not TrkB or TrkC. Nor thern blot analysis revealed that NT-7 was predominantly expressed in peripheral tissues, though weak expression was also detected in the br ain. Like NT-6, this novel neurotrophin might represent yet another NG F-like neurotrophin in lower vertebrates.