Cytoskeletal regulation of normal rat glioblasts differentiated by glia maturation factor

The morphological differentiation of normal rat glioblasts induced by glia maturation factor (GMF) was investigated with regard to the reorganization of the cytoskeletal structures by the use of indirect immunofluorescence staining methods. The microfilaments were reorganized from a stress fiber form to a plasmalemmal undercoat structure by GMF, and to a network-like structure by dBcAMP. The GMF- or dBcAMP-induced morphological differentiation was enhanced by cytochalasin D (over 2 ?M) and conversely inhibited by colchicine (over 1 ?M). Phalloidin, an F-actin stabilizer, inhibited more strongly the morphological differentiation induced by dBcAMP than that induced by GMF. Both glia filaments and microtubules existing as a network in control glioblasts assembled after GMF or dBcAMP stimulation to form thick filamentous structures, not only in the cell bodies but also in the processes. The bundle formation of glia filaments was inhibited by colchicine. These findings suggest that glial differentiation depends on both stress fiber disintegration and microtubule assembly, which are closely related to the bundle formation of glia filaments. The GMF- or dBcAMP-induced differentiation was promoted by 25 ?M W-7 and inhibited by 1 mM CaCl(2) plus 4 ?M A23187. At a higher concentration (50?M) W-7 promoted the differentiation even in the presence of CaCl(2) and A23187 at the same concentrations. These findings suggest that the suppression of the calmodulin function is important for morphological differentiation of glioblasts.