NEURITE OUTGROWTH-PROMOTING FACTORS IN EXTRACTS OF DENERVATED CHICK SKELETAL-MUSCLE

1. An extract of denervated skeletal muscle contained activity for pro motion of neurite outgrowth from telencephalic neurons, as well as tha t from neurons in the spinal cord. A factor responsible for the activi ty was characterized in cultures of dissociated neurons. 2. The factor acted on neurons only when they were attached to the surface of cultu re dishes. Since treatments with proteases and lectins reduced the out growth-promoting activity, the factor was thought to be a glycoprotein . 3. Among the monoclonal antibodies raised against the partially puri fied extract, five antibodies were found to inhibit the activity for s pinal and telencephalic neurons. The most potent antibody, 4D2a, recog nized mainly a 63-kD protein and other minor proteins in the extract. Although the 63-kD protein was confirmed to be chick serum albumin by analysis of amino acid sequence, the purified albumin exhibited no act ivity. 4. From these observations, the factor was found to be a glycop rotein recognized by the neutralizing antibody as one of the minor com ponents of the extract. This factor exhibits its activity in a substra te-bound form but not in a diffusible one.