Evidence for two distinct mechanisms of neurogenesis and cellular pattern formation in regenerated goldfish retinas

Abstract

After its destruction by intraocular injection of ouabain, the goldfish retina regenerates, but little is known about the histogenesis of the new tissue, including the structure and formation of regenerated cell mosaic patterns. In an effort to determine how retinal cells are generated and spatially organized within retina regenerated after ouabain injection, in situ hybridization and immunocytochemical techniques were combined with computational analyses of two-dimensional spatial patterns of identified neurons. Labeling with specific opsin riboprobes revealed two distinct cone patterns in the ouabain-injected eyes, each of which was different from the relatively orderly cone patterns of native retina. Central, regenerated regions had sparse aggregates of cones, and a relatively lower density of each cone type. Peripheral regions of experimental retina, likely derived from the circumferential germinal zone, had high densities of all cone types, each of which tended to be distributed randomly. The spatial patterns of inner retinal neurons in experimental eyes were also disorganized with respect to native retina. These results indicate that although some aspects of retinal regeneration resemble normal retinal development and growth, ouabain-induced regeneration does not produce well-organized mosaics of neurons, indicating a failure of the developmental interactions needed for proper pattern formation, which in turn could compromise visual recovery. Furthermore, the distinct cone patterns in different regions of experimental retina support the hypothesis that new goldfish retina arises via two spatially and cellularly distinct mechanisms after exposure to ouabain.

Retinal stem cells and regeneration

“…However, the regenerated tissue from the CMZ after neurotoxic lesions in adult goldfish lacks the proper organization of cells seen in normal retina (Stenkamp et al, 2001). …”

Neurogenesis in the Fish Retina

“…The CGZ most certainly contains stem cells that meet the criteria above, although they continuously generate new retinal tissue and their activities are not dependent upon injury. Under conditions of injury, neurogenesis at the CGZ is accelerated, but has been shown not to contribute to retinal cell replacement in regions beyond the retinal periphery (i.e., cells derived from the CGZ do not migrate within the retina to replace cells at a distance) Stenkamp et al, 2001).…”

Control of Cellular Pattern Formation in the Vertebrate Inner Retina by Homotypic Regulation of Cell-Fate Decisions

“…The details, statistical utility, and application of these techniques, including their application to empirical-and model-derived cellular patterns in the retina, have been described previously (Cameron andCarney, 2000, 2004;Stenkamp et al, 2001). Briefly, NND analysis provides a measure of local pattern regularity or nonregularity.…”

“…The observation that cells in the vertebrate retina are arranged nonrandomly across twodimensional space was originally reported by Hannover (1840), and a large number of subsequent investigations have confirmed this cellular attribute of the vertebrate retina (Eigenmann and Mean NND values and recovered cell densities from the DRP analysis are indicated; in the DRP plots, the recovered cell density is indicated graphically by the horizontal dotted line, and the effective radius is indicated by the vertical dashed line. The quadrat functions, which mostly lie below the central demarcated field of each plot, indicate cellular patterns that exhibit long-range regularity (rather than aggregation or randomness) (Grieg-Smith, 1964;Stenkamp et al, 2001;Cameron and Carney, 2004). Note the overall similarity between the in vivo and model-derived patterns (see Results) (Tables 1, 2).…”

“…Note the overall similarity between the in vivo and model-derived patterns (see Results) (Tables 1, 2). Shafer, 1900;Lyall, 1957;Engström, 1963;Marc and Sperling, 1976;Williams, 1988;Wikler and Rakic, 1990;Wässle and Boycott, 1991;Cameron and Easter, 1993;Vaney, 1994;Cook, 1996;Cameron andCarney, 2000, 2004;Cook and Chalupa, 2000;Galli-Resta, 2000;Rockhill et al, 2000;Stenkamp et al, 2001).…”