Evaluation of different procedures for the dissociation of retinal pigmented epithelium into single viable cells

Retinal pigmented epithelium (RPE) from 7-day-old chicken embryos (stages 29 to 31) was isolated and dissociated into single cells using different procedures. The results were assessed in two ways. (1) The yield of single RPE cells per embryo was determined, and their ability to form pigmented colonies in clonal culture was tested. The most efficient and gentle procedure included isolation of the RPE in EDTA solution, trypsinization at low temperature and low enzyme concentration in the presence of EDTA, followed by incubation in culture medium for up to 4 hr. The completely dissociated cells thus obtained had a much higher plating efficiency and more uniform pattern of colony growth and differentiation than those obtained under any other conditions tested. (2) The effects of different treatments on cell junctions and morphological integrity of the cells were determined by transmission electron microscopy. EDTA solution yielded excellent separation of the epithelial sheet from the mesenchyme by dissociating it from Bruch's membrane, but had little effect on the junctions between adjacent RPE cells. Trypsinization of the epithelium under various conditions separated the basal lateral cell borders and caused loss of gap junctions, but left many cells still joined by apical tight junctions. Final disruption of the tight junctions occurred during recovery of the trypsinized cells in culture medium and was accompanied by dedifferentiation of the RPE cells.