The structure and development of the pigmented retinal clone

Abstract

Cytological changes during growth and differentiation of chick pigmented epithelial cells in clonal culture are described at the light microscope level. Initially the cells are squamous and unpigmented. By 3 weeks, cells in the center of the colonies are highly differentiated, i.e. they are polygonal in shape and densely pigmented. During differentiation, cells in the center of the colony pass through a series of morphological stages comparable to those seen from the edge to the center of a 3-week-old clone. Cells in the inner two zones of a differentiated colony resemble stages found during differentiation in vivo. Those in the outer two zones appear to have no morphological counterparts in the intact animal.Extracellular materials are abundant in the stratified zone of the colony. These exhibit staining properties similar to those of acid mucopolysaccharides found in the developing retina. Vacuoles containing a flocculent material appear within the differentiated cells of colonies older than 2.5 weeks. Later, some of these vacuoles disappear and flocculent material is found between the cells and the plate. The possible significance of these observations is discussed.