Adult chicken skeletal muscle cells express polypeptides that are antigenically related to ce-spectrin (Mr 240,000) and/3-spectrin (Mr 220,000-225,000), the major components of the erythrocyte membrane-skeleton, and to ankyrin (Mr 237,000; also termed goblin in chicken erythrocytes), which binds spectrin to the transmembrane anion transporter in erythrocytes. Comparative immunoblotting of SDS-solubilized extracts of presumptive myoblasts and fully differentiated myotubes cultured in vitro demonstrated that there is a dramatic accumulation of ankyrin and c~-and/3-spectrin during myogenesis and a concomitant switch in the subunit composition of spectrin from c~, to c~3. Analysis of early time points in myogenesis (12-96 h) revealed that these changes occur shortly after the main burst of cell fusion. To determine the temporal relationship between cell fusion and the accumulation of ankyrin and ~x-and B-spectrin, we treated presumptive myoblasts with 2 mM EGTA, which resulted in the complete inhibition of cell fusion. The incorporation of [35S]methionine into total protein and, specifically, into ~x-, 3,-, and/3-spectrin remained the same in EGTA-treated and control cells. Analysis by immunoblotting of the amounts of ankyrin and ce-and f3-spectrin in fusion-blocked cells revealed that there was no effect on accumulation for the first 19 h. However, there was then a dramatic cessation in their accumulation, and thereafter, the amount of each protein at steady state remained constant. Upon release from the EGTA block, the cells fused rapidly (< 11 h), and the accumulation of ankyrin and c~-and g3-spectrin was reinitiated after a lag period of 3-5 h at a rate similar to that in control cells. The inhibition in the accumulation of newly synthesized ankyrin, c~-spectrin, and B-spectrin in EGTA-treated myoblasts was not characteristic of all structural proteins, since the accumulation of the muscle-specific intermediate filament protein desmin was the same in control and fusionblocked cells. These results show that in myogenesis, the synthesis of ankyrin and c~-and Bspectrin and their accumulation as a complex, although concurrent, are not coupled events. We hypothesize that the extent of assembly of these components of the membrane-skeleton in muscle cells is determined by a control mechanism(s) operative at the posttranslational level that is triggered near the time of cell fusion and the onset of terminal differentiation.Adult chicken skeletal muscle cells express a class of proteins that are antigenically and structurally related to the major components of the erythrocyte membrane-skeleton. These proteins are a-spectrin (Mr 240,000; references 43 and 56), ~-spectrin (Mr 220,000-225,000; reference 43), and ankyrin (Mr 235,000; reference 46). In erythrocytes, a-and/3-spectrin form an (aj3)2 tetramer that binds actin oligomers (reviewed in references 2 and 10). Ankyrin (termed goblin in chicken erythrocytes; see references 38, 46, and 56) binds spectrin (4, 5; specifically the/3-spectrin subunit [33,40,65]) to ...