Differentiation in culture of myoblasts inhibited to fuse

The relationship between cell fusion and appearance of specific muscle proteins during myogenesis has been the object of widely different interpretations. The data reported by some authors are in agreement with the possibility that the cell fusion could play a regulatory role on the expression of several differentiative traits (SHAINBERGeL al., 1971; PATERSOaNn d STROIIMAN1,9 72; TURNEeRt al., 1974). Other evidences seem however to support the conclusion that myogenesis consists of a mosaic of independently regulated differentiative events, In order to approach this problem we used culture conditions which selectively impair cell fusion without affecting duplication and survival of myoblasts in culture (MOLINAROet al., 1975; ADAMOe t al., 1975). The culture medium non permissive for fusion (containing 5% horse serum and 3% embryo extract in Eagle based MEM) had a low Ca++ concentration (0.44 mM). In these conditions myotube differentiation in culture is completely prevented. The percentage of cell fusion sharply increases at a calcium concentration in the culture medium above 0.5 mM and reaches a plateau at 0.6 mM Ca++ (fig. 1). Calcium induced cell fusion does not require RNA or protein synthesis since it occurs in the presence of actinomycin D (0.06 pg/ml) or cycloheximide (10 pg/ml).