Functional regeneration of the optic nerve occurs after injury in lower vertebrates. This regenerative capacity is not observed for the optic nerves of higher vertebrates such as humans. This proposal is concerned with the involvement of intermediate filament proteins in the development and regeneration of the optic nerve in the goldfish visual pathway, a system which is particularly amenable to a molecular analysis. The intermediate filament protein composition of the goldfish optic nerve does not match the conventional composition of mammalian optic nerves. The intermediate filament proteins of the goldfish optic nerve consist predominantly of a group of four proteins of 58kD, two of neuronal origin, and two of glial origin. The glial intermediate filament protein in the goldfish optic nerve is a keratin K8, not the expected glial fibrillary acidic protein. The expression of this protein in goldfish optic nerve glial cells may impart a unique structural morphology which serves to guide axonal outgrowth during the regeneration of optic axons. The two proteins of neuronal origin are synthesized in retinal ganglion cells and their expression is greatly elevated during optic nerve regeneration. These proteins are distinct from the mammalian neurofilament proteins, but are structurally related to vimentin, an intermediate filament protein expressed in mammalian optic nerves during embryogenesis. Thus, the intermediate filament protein composition in the neurons and surrounding glial of the adult goldfish optic nerve is unusual. However this composition is expressed in other systems during embryogenesis, and may be a molecular link between optic nerve development and regeneration. Molecular cloning techniques will be used to complete the primary structure of the neuronal proteins in order to determine their structural similarities and differences to other conventional intermediate filament proteins. The expression of the genes for the neuronal and nonneuronal proteins will be quantiated by analyzing their mRNA transcription in order to determine at what level, when and where they are regulated during optic nerve regeneration. Promoter and regulatory regions for the genes of the proteins will be defined and assessed in order to determine the mechanism by which these proteins are controlled at the level of transcription. The long term goal of these studies is to understand, at the molecular level, why some visual systems possess the ability to regenerate while other visual systems lack this regenerative capacity.