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.