Cell lineage in retinal development of mice studied in experimental chimaeras

Abstract

IN vertebrate embryos, the optic cups develop as lateral outgrowths of the diencephalon, the rudiments of which are first recognised at the antero-lateral margins of the neural plate. Evidence accumulating from extensive studies with vital dyes^1–4, excision and transplantation experiments^5–7 in amphibian embryos have shown that the cell boundaries of the different areas of the central nervous system are already fixed at the early neurula stage when the presumptive retinal cells are located in the antero-median border of the neural plate. It has remained unresolved whether the two retinal primordia and the layers thereof are determined in a single or separate group of cells. It seems to us that the problem is one of cell lineage and can be analysed with genetic mosaics. The retinal pigment epithelium (RPE) is derived from the outer layer of the embryonic optic cup. In chimaeric mice, produced by aggregating morulae from albino and pigmented strains, the presence of two types of cells in the RPE has been reported^8–10. Deol and Whitten¹¹ first noted that RPE of the two eyes of such chimaeras showed similar proportions of cells. It was recently observed that there is a close correlation in occurrence of chimaerism in the RPE and in the neural retina and between the two eyes of the individuals^12,17. Here we present quantitative data on the relative proportion and spatial distribution of cells from the two donor genotypes in the RPE and compare them with the relative proportion of cells in the neighbouring melanocyte population of the choroidal layer of the eye. The results show that there is a marked similarity in the proportion of the cells of the RPE from the two eyes of the individual chimaeras suggesting a lineage relationship between the two retinal primordia.