REGENERATION Of injured axons at neuromuscular junctions has been assu
med to be regulated by extracellular factors that promote neurite outg
rowth. We report here the cloning of a novel neurite outgrowth factor,
designated neurocrescin, from chick denervated skeletal muscle. A rec
ombinant neurocrescin promoted neurite outgrowth from cultured neurons
of spinal cord and telencephalon of chick embryo. It was expressed pr
edominantly in neural tissue and muscle, and was secreted extracellula
rly after intramolecular cleavage. This truncated form was detected in
denervated muscle but not in innervated muscle. Thus, neurocrescin ap
pears to be a novel neurite outgrowth factor that is secreted in an ac
tivity-dependent fashion. A highly homologous counterpart was also clo
ned from mouse brain.