Cellular proliferation and neurogenesis in the injured retina of adult zebrafish

The retinas of adult teleost fish can regenerate neurons following a chemic al or mechanical injury. Previous studies have demonstrated that mechanical excision of fish retina induces a hyperplasia within the retinal sheet, in cluding the formation of a proliferative blastema from whence new retinal c ells are produced to fill the excision site. The current study was designed to address two issues regarding injury-induced retinal hyperplasia: (1) Re tinas of adult zebrafish can regenerate following a surgical excision, but compared to other fish they contain very few proliferative cells: Might ret inal injury in adult zebrafish therefore induce minimal, or perhaps no, hyp erplasia? (2) The fate of injury-induced, proliferative retinal cells outsi de surgical excision sites has yet to be determined. Do such cells produce retinal neurons? Evidence is presented that mechanical injury to the adult zebrafish retina induces a dramatic increase in the number of proliferative cells both within and external to the lesion site, and some of these cells apparently migrate within the radial dimension of the retina. Evidence is also presented that injury-induced proliferative cells outside a lesion sit e can produce retinal neurons-including cone photoreceptors, interplexiform cells, and amacrine cells-that are incorporated into the extant retina. Th e results suggest that the adult zebrafish retina contains a latent populat ion of cells that is induced to proliferate following retinal injury, and t hat these cells might represent a novel avenue for pluripotent neurogenesis within the intact adult teleost retina.