Localized survival of ciliary ganglionic neurons identifies neuronotrophic factor bands on nitrocellulose blots

A novel and sensitive method has been developed to identify ciliary neuronotrophic factors (CNTFs) from tissue extracts after blotting to nitrocellulose paper. The CNTF proteins are required for the in vitro survival of embryonic chick ciliary ganglionic neurons. Tissue extracts containing such CNTFs are electrophoresed using sodium dodecyl sulfate-polyacrylamide gel electrophoresis and transferred to nitrocellulose paper. Purified ciliary ganglionic neurons are seeded on the surface of the nitrocellulose blot, and the culture is incubated for 24 hr in medium lacking CNTF. CNTF can be localized on the blot because it retains its ability to support the survival of the neurons cultured on the nitrocellulose. A band of viable neurons, easily visualized by staining with a vital dye, is supported by the blotted CNTF polypeptide. The number of neurons surviving on the blotted CNTF is related to the amount of CNTF originally loaded on the electrophoretic gel. As little as 2 ng (16 trophic units) of CNTF protein contained in crude tissue extracts can be loaded on the sodium dodecyl sulfate gel and still be recognized by the cultured neurons. This method was used to identify CNTF polypeptides from extracts of adult rat nerve (24,000 and 19,000 daltons) and from tissue found near experimentally induced adult rat brain lesions (24,000 daltons). The electrophoretic mobilities of these peptides are distinct from the previously purified chick eye CNTF polypeptide (20,400 daltons).