Abstract
Purpose:
Damage to the optic nerve in mammals results in permanent loss of retinal ganglion cells (RGC) and their axons. In contrast, zebrafish and other teleost fish are able to fully regenerate and reconnect RGCs and axons after injury. Previous studies of optic nerve regeneration in zebrafish have relied on invasive retro- and anterograde labeling of RGC axons and cell bodies. The purpose of this study was to identify and utilize a transgenic zebrafish model to study RGC regeneration.
Methods:
Fluorescent confocal imaging of retinal sections and flat mounts was used evaluate for RGC specific expression in the Tg(isl2b-GFP) zebrafish line. Optic nerve crush and transection injury were done in one eye of adult Tg(isl2b-GFP) fish with sham surgery done on the opposite eye. Fluorescent confocal imaging of retinal flat mounts and of sections through the visual tectum were done at one week and three weeks after injury.
Results:
The Tg(isl2b-GFP) line was identified to have strong RGC specific expression into adulthood, both within the cell bodies and axons. One week after optic nerve crush injury there was a mild decline in fluorescent signal within the visual tectum as compared to control. No difference was observed in retinal flat mount imaging. By three weeks post crush injury, no difference in fluorescent signal was observed as compared to control in either the retina or the visual tectum. After optic nerve transection, a large decrease in signal was observed after one week with partial recovery observed three weeks after injury in both the retina and in the visual tectum.
Conclusions:
The isl2b promoter was identified to have robust and specific RGC expression in the adult zebrafish. Optic nerve injury experiments have demonstrated its utility to study RGC injury response and axon regeneration. Future studies will utilize this promoter to study RGC regeneration and axon retargeting in vivo.