THE LEVELS OF RETINAL MESSENGER-RNA FOR GEFILTIN, A NEURONAL INTERMEDIATE FILAMENT PROTEIN, ARE REGULATED BY THE TECTUM DURING OPTIC FIBER REGENERATION IN THE GOLDFISH

Reorganization of the intermediate filament (IF) network during axonal regeneration is accompanied by changes in the expression of various I F proteins:. An increase in expression of the neuronal if subunit gefi ltin in goldfish retinal ganglion cells (RGCs) has been linked to the unique ability of the goldfish optic nerve to regenerate following inj ury. Evidence suggests that the optic tectum, the target of optic fibe rs, may regulate the expression of gefiltin during regeneration. To ad dress this issue we examined gefiltin mRNA levels during optic fiber r egeneration in the presence or absence of the tectum. We found that ge filtin mRNA levels in the RGCs of animals that received an optic nerve crush (ONC group) began increasing by 10 days, peaked from 20 to 38 d ays at 5.5-fold over normal, and declined to near normal values by 115 days. In animals that had the entire tectum removed as well as an opt ic nerve crush (ETR group), gefiltin mRNA levels increased by 10 days, peaked at 20 days at 5.5 to 6.5-fold over normal, and although they d ropped slightly thereafter, they remained elevated at 5-fold over norm al for at lease 115 days. When axons regenerated to the ipsilateral te ctal lobe as a result of a left rectal lobe removal and left eye remov al surgery (LTR/LER group), the expression pattern of gefiltin mRNA pa ralleled that of the ONC group. We also Found that the abundance of ge filtin subunits in the retina was elevated at 30 days of regeneration In ONC and ETR animals, and that levels in the nerve were reconstitute d to 80% of normal by 30 days. These results demonstrate that increase s in gefiltin mRNA and protein levels during optic nerve regeneration are independent of the tectum, whereas the downregulation of gefiltin mRNA levels in the late stages of regeneration is entirely dependent u pon the tectum. (C) 1998 Elsevier Science B.V. All rights reserved.