The regulation of gefiltin mRNA expression by the tectum during optic nerve regeneration in the goldfish /

Reorganization of the intermediate filament (IF) network during axonal regeneration is accompanied by changes in the expression of various IF proteins. An increase in expression of the neuronal IF subunit gefiltin in goldfish retinal ganglion cells (RGCs) has been linked to the unique ability of the goldfish optic nerve to regenerate following injury. Evidence suggests that the optic tectum may regulate the expression of gefiltin during regeneration. The goal of this thesis was to determine the function of the tectum in the regulation of gefiltin mRNA expression during optic fiber regeneration in the goldfish. It was found that gefiltin mRNA levels in the RGCs of animals that received an optic nerve crush (ONC group) increased by 10 days, peaked from 20 to 38 days at around 5.5-fold over normal, and declined to near normal by 115 days. In animals that had the entire tectum removed and an optic nerve crush (ETR group), gefiltin mRNA levels increased by 10 days, peaked at 20 days at around 5.5- to 6.5-fold over normal, and although they dropped slightly thereafter, they remained elevated at around 5-fold over normal for at least 115 days. When axons regenerated to the ipsilateral tectal lobe as a result of a left tectal lobe removal and left eye removal surgery the expression pattern of gefiltin mRNA paralleled that of the ONC group. It was also found that the abundance of gefiltin subunits in the retina was elevated at 30 days of regeneration in ONC and ETR animals, and that levels in the nerve were reconstituted to 80% of normal by 30 days. These results demonstrate that increases in gefiltin mRNA and protein levels during optic nerve regeneration are independent of the tectum, whereas the downregulation of gefiltin mRNA levels is entirely dependent upon the tectum. (Abstract shortened by UMI.