Changes in surface morphology of pigmented retinal cells during differentiation in clonal culture

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Abstract
The changes in surface morphology during the reexpression of differentiation of chick retinal pigmented epithelial cells (RPE) in clonal culture have been studied using the scanning electron microscope (SEM) and transmission electron microscope (TEM) and compared with those described in vivo. Three-week-old colonies demonstrated a gradual change in apical surface morphology along any colony radius. At the outer edge, the cell surfaces were either smooth with a few small filamentous protrusions or showed a varying number of large blebs. Toward the centre of the colony the surfaces demonstrated a gradual increase in filamentous protrusions. The apical surfaces of the most densely pigmented cells at the centre of the colony consisted mainly of small rounded protrusions. The changes in surface morphology of cells in the centre of younger colonies during redifferentiation were similar to those found along the radius of a 3-week-old colony. The results show that older colonies have all of the morphological stages of the redifferentiation process (and possibly the biochemical ones as well) arranged along any radius.The basal surfaces of all the colonies were covered by a thin acellular membrane that stained positively with periodic acid–Schiff (PAS) and which may contain fibronectins and appears to be involved in cellular attachment.