Differentiation of rat lens epithelial cells in tissue culture: II. Effects of cytochalasins B and D on actin organization and differentiation

Abstract

Cytochalasins B and D were used to investigate the involvement of microfilaments in the differentiation of rat lens epithelial cells in tissue culture. Two questions were asked: (1) Does the organization of microfilaments change upon morphological differentiation of the lens epithelial cell? (2) Is the change in the organization of microfilaments required for the production of the differentiation-specific protein, γ-crystallin? Cytochalasin B arborized differentiating lens epithelial cells and had no effect on the undifferentiated cells. Immunofluorescent staining of these two types of cells revealed significant differences in the organization of actin. Actin appeared as longitudinal filaments in the differentiating cells, while it appeared in a diffuse nonfibrillar form in the undifferentiated cells. This indicated changes in the organization of actin during differentiation. Cytochalasin B caused a decline in cell number at 10 −6–10 −5 M. However, only that concentration which caused arborization of cells and disruption of microfilaments (10 −5 M) inhibited morphological differentiation and production of γ-crystallin. Cytochalasin D (10 −7–10 −5 M) did not cause a dramatic decrease in cell number; nevertheless, it induced the arborization of cells and disruption of microfilaments at lower concentrations (10 −7–10 −6 M) and inhibited morphological differentiation and production of γ-crystallin at lower concentrations (10 −7–10 −6 M) than did cytochalasin B. Thus, only those concentrations of cytochalasins which disrupt microfilaments and prevent their organization into filamentous form seem to inhibit differentiation. This suggests that the organization of actin is required for the program of differentiation of the lens epithelial cells.