The expression of the protein p68/70 within the Goldfish visual system suggests a role in both regeneration and neurogenesis

Abstract

Previous attempts to characterize the molecular events that support successful regeneration of axotomized goldfish retinal ganglion cells (RGCs) have led to the discovery of an acidic protein doublet in retina that displays an increased incorporation of 35S-methionine following axotomy, and is known to be axonally transported within the optic nerve. This protein is termed p68/70, reflecting its relative migration in 10% SDS-PAGE. In the present study, an affinity-purified polyclonal antibody to p68/70 (anti-p68/70) was developed and used to assess the species, tissue, and cellular distribution of p68/70. The antibody cross-reacted with homogenstes of brain and other tissues from goldfish and closely related fish species. While each goldfish tissue tested expressed p68/70, the levels varied over a 30-fold range, with the highest amounts in brain, egg, and ovary. Immunolabeling of goldfish retina revealed prominent staining of RGC somata, dendrites, and axons. During regeneration, the immunoreactivity of the RGC somata and axons increased dramatically. Intense immunolabeling was also observed in the germinal neuroeptthelial cells and rod precursors and in all retinal layers near the peripheral margin, in the region of recently differentiated neurons. In the tectum, the germinal zone was also highly labeled. The elevated expression of p68/70 in each of these areas known to mediate neuronal growth within the goldfish visual system suggests that p68/70 plays a role in axonal growth, regrowth, and possibly in neural development as well.