ACTIN ISOFORM UTILIZATION DURING DIFFERENTIATION AND REMODELING OF BC3H1 MYOGENIC CELLS

Mouse BC3H1 myogenic cells and a bi-functional chemical cross linking reagent were utilized to investigate the polymerization of newly-synth esized vascular smooth muscle (alpha-actin) and non-muscle (beta- and gamma-actin) actin monomers into native F-actin filament structures du ring myogenesis. Two actin dimer species were identified by SDS-PACE a nalysis of phenylenebismaleimide-cross linked fractions of BC3H1 myobl asts and myocytes. P-dimer was derived from the F-actin-enriched, dete rgent-insoluble cytoskeleton. Pulse-chase analysis revealed that D-dim er initially was associated with the cytoskeleton but then accumulated in the soluble fraction of lysed muscle cells that contained a non-fi lamentous or aggregated actin pool. Immunoblot analysis indicated that non-muscle and smooth muscle actins were capable of forming both type s of dimer. However, induction of smooth muscle a-actin in developing myoblasts coincided with an increase in D-dimer level which may facili tate actin stress fiber assembly. Smooth muscle alpha-actin was rapidl y utilized in differentiating myoblasts to assemble extraction-resista nt F-actin filaments in the cytoskeleton whereas non-muscle beta-and g amma-actin filaments were more readily dissociated from the cytoskelet on by an extraction buffer containing ATP and EGTA. The data indicate that cytoarchitectural remodelling in developing BC3H1 myogenic cells is accompanied by selective actin isoform utilization that effectively segregates multiple isoactins into different sub-cellular domains and /or supramolecular entities. J. Cell. Biochem. 67:514-527, 1997. (C) 1 997 Wiley-Liss, Inc.