Changing topography of the RPE resulting from experimentally induced rapid eye growth

The retinal pigment epithelium (RPE) of the quokka wallaby, Setonix brachyurus, grows and changes throughout life. To investigate factors that determine changes in the quokka RPE, we have examined topography of this tissue in experimentally enlarged eyes. Unilateral eyelid suture was conducted at the time of normal eye opening, postnatal day (P) 110, and animals were examined at 1 or 1 1/4 years of age. The numbers and densities of RPE cells and the extent of multinucleation were compared with those in normal animals. Eyelid suture resulted in a 9.8% and 17.4% increase in retinal area at 1 and 1 1/4 years, respectively; a significant degree of myopia was associated with this enlargement. Cell density topography in experimental eyes was not the same as in controls. Cells from central retina were disproportionately larger in the experimental than control eyes. However, the RPE cell topography in sutured eyes was not the same as that of aged retinae of a similar size. Notably, in sutured eyes there was no development of the high or highest cell densities seen in equatorial and temporal central RPE in aged retinae, respectively. Furthermore, the degree of cell enlargement in peripheral regions was slight compared with that observed in similar-sized, aged retinae. There was no increase in RPE cell number; rather, average cell area increased accompanied by no change or a slight decrease in RPE thickness. Consequently, overall volume of cells did not change significantly. The large number of multinucleate cells normally seen n aged animals was not observed in experimentally enlarged eyes, implying that an increase in cell volume may be the trigger for multinucleation

The primary visual system of adult lizards demonstrates that neurogenesis is not obligatorily linked to central nerve regeneration but may be a prerequisite for the restoration of maps in the brain

AbstractFollowing optic nerve crush in the adult lizard Ctenophorus ornatus, most retinal ganglion cells regrow their axons into visual brain centres: however, the regenerated projections lack retinotopic order and the animals are blind via the experimental eye. Here we have used 3H-thymidine autoradiography to demonstrate that cell division is no longer taking place in the retina of normal adult lizards. We conclude that the optic nerve can regenerate in lizard even though cells are no longer being added to the retina, However, continued retinal neurogenesis may be linked to the ability to restore topographic maps

Retinal pigment epithelium topography in the mature quokka, Setonix brachyurus

In this paper we describe cell topography of the retinal pigment epithelium (RPE) for the mature marsupial wallaby, the quokka, Setonix brachyurus. RPE topography was analysed in bleached and stained whole mounted retinae, sampling from the entire surface area. The mature adult quokka RPE has a distinct topography in terms of both cell density and the distribution of multinucleate cells. Peripheral RPE demonstrates the lowest cell density and the greatest proportion of multinucleate cells. In an annulus surrounding central retina, corresponding to equatorial retina, RPE cell density is relatively high and multinucleate cells are at the lowest frequency. Cell density is highest in central temporal retina, in the regions adjacent to some of the highest densities in the neural retina. Other regions of central retina exhibit moderate cell densities. A small proportion of central cells are multinucleate. The RPE topography may result from, or account for, regional differences in susceptibility of this tissue to environmental influences and stressors. Understanding of this topography may throw light on the marked localization of certain human retinal diseases inherent to this tissue

Development and ageing of the RPE in a marsupial, the quokka

We have previously shown that the mature adult quokka, aged between 8 and 15 years, has a distinct cell topography in the retinal pigment epithelium (RPE). We reported that the adult cell densities were high in central temporal retina and low in a peripheral band, adjacent to the ora serrata, a region with a concentration of multinucleate cells. In the present paper, we have studied the development of these features in order to understand how they mature, as well as to gain insight into regional specializations of the RPE. Retinal area, cell density and the extent of multinucleation were analysed using whole-mounted retinae from animals aged post-natal day (P) 2 to 15. The retina continues to grow in area throughout life, however, RPE cell number does not change. The features of the mature adult RPE develop at different times over the entire lifespan of the animal. In peripheral retina, cell density decreases throughout life and the band of low cell density becomes progressively wider and more distinct with age with an increasing proportion of multinucleate cells. By contrast, RPE cell density in equatorial retina remains, throughout life, at the level observed in 1-year-old animals. A specialization of high cell density in temporal central RPE was discernible in animals older than 2 years, with the cell density of this region increasing steadily beyond this age. Central regions of other quadrants demonstrate a constant and relatively uniform density with age. The RPE in the marsupial quokka is a dynamic tissue, demonstrating topographic changes throughout life

Retinal pigment epithelium and photoreceptor maturation in a wallaby, the Quokka

Cell generation and the early stages of maturation of the retinal pigment epithelium (RPE) and photoreceptors were examined in a marsupial, the quokka, Setonix brachyurus. Results are presented for animals aged up to postnatal day (P)250. RPE cell generation was studied by analysis of cell number from wholemounted retinae and by tritiated thymidine (3HThy) autoradiography in sectioned material. For 3HThy autoradiography, quokkas aged P1–P200 were injected with 3HThy and killed either 6–20 hours later (pulse-kill) or at P100 or P250 (pulse-leave). The extent of pigmentation of the RPE sheet was examined from sections of embryonic and early postnatal stages. Retinae from animals aged P5 to P160 were also examined at the electron microscope. By P100, RPE cell number is within the range found in adults. New RPE cells are generated in a peripheral band which moves outwards as cells leave the cell cycle in more central locations. RPE cells thus complete their last cell division in a centre-to-periphery wave centred about the optic nerve head. At any given retinal location, RPE cells complete their last cell division earlier than the overlying layers of the neural retina. Cells of the RPE rapidly develop a mature morphology. For example, melanin granules are observed at P5 and Verhoeff's membrane (the terminal bar complex) is evident by P25. By contrast, photoreceptor development in this species is protracted; cone inner segments are observed by P40, whilst the first rod inner segments are observed at P60. Despite being generated earlier, morphological maturation of the cones appears retarded and prolonged compared with that of the rods. The last stages of RPE cell maturation occur late in development, in synchrony with the generation of rods