Guidance of regenerative axons in optic nerve regeneration in Bcl-2 overexpressing mice

Abstract

To determine whether optic nerve can regenerate after optic nerve crush and weather the regenerating axon reaches the target in the brain in Bcl-2 overexpressing mice. Left eye optic nerve crush was performed in wild-type (C57Bl/6J) and Bcl-2 transgenic mouse pups at 3 days after birth (P3), followed immediately by the opposite eyeball enucleated. Mouse pups were killed at 4 days post-surgery. Optic nerve regeneration was assessed at the sections of optic nerve and the brain. An anterograde tracer, cholera toxin B subunit conjugated with fluorescein (CTB-F), was applied intraocularly, immediately after optic nerve crush to label retinal ganglion cell axons. Immunofluorescence staining with anti-GAP-43 was carried out to reveal regenerating axons in optic nerve sections. In wild-type mice, severed optic nerves failed to regenerate. In contrast, in all of the Bcl-2 transgenic mice examined, optic nerves regenerated robustly over long distances, but the regenerating fibers were found to deviate from the optic pathway and grew into the forebrain to form aberrant projection. When the opposite eyeball is removed in P3 Bcl-2 overexpressing mice with optic nerve was crushed in one side, the guidance from the normal optic pathway is lost, the optic nerve could regenerate and reach the brain, but the regenerating axons could not reach both side of target in the midbrain, they grow into aberrant place of forebrain.