Actin and Myosin Synthesis During Differentiation of Neuroblastoma Cells

Abstract: The levels and rates of synthesis of actin and myosin in murine neuroblastoma S20 cells have been examined during neurite formation in the absence of serum. Two forms of actin (β, ‐γ) have been identified in these cells; they have isoelectric points of about 5.43 and 5.45, respectively, which differ from that of murine skeletal muscle actin (5.41). Although the neuroblastoma actins have the same molecular weight as skeletal muscle actin, they can be clearly distinguished from this protein by peptide maps. Actin comprises about 7% of the total protein in these cells and neither the level nor the proportion of the two isoelectric forms change during neurite extension (β: γ:60: 40). Myosin ATPase activity is also similar in morphologically differentiated and undifferentiated cells. The rates of synthesis of actin and myosin relative to total protein synthesis undergo small changes during differentiation. Actin synthesis increases about 30% in the 1st day of induction and falls off to the undifferentiated level by day 4. Myosin synthesis increases by about 30% within 2 days of induction and remains at that level for at least 2 days. In contrast, no change in the relative synthesis of tubulin occurs over 4 days of neurite induction. Thus, neurite extension by these cells is not accompanied by large changes in either the level or rates of synthesis of actin and/or myosin.