Differential regulation of two classes of neuronal intermediate filament proteins during optic nerve regeneration.

The regulation of expression of two different types of neuronal intermediate filament proteins, ON1/ON2 and plasticin, was studied during optic nerve regeneration in the goldfish. During regenerative growth of optic axons, there is a rapid and dramatically increased expression of plasticin, a recently cloned, novel type III intermediate filament protein, in the retinal ganglion cells. At the time when the growing axons reinnervate the optic tectum, expression of plasticin declines and there is an increased expression of ON1 and ON2. This time course suggests that the target tissue participates in the regulation of these proteins. The aim of this study was to characterize the regulatory role played by the optic tectum. To address this issue, a repeated-crush paradigm was used whereby growing axons were hindered from reaching their target. It was found that in absence of tectal contact, the increased expression of ON1 and ON2 normally seen during regeneration was not induced. In contrast, expression of plasticin increased both in the presence and in the absence of tectal contact.