Fig. 7. Model of synergistic regulation of sarcomeric actin organization by Tmod, ADF/cofilin, AIP1 and profilin. A stable thin filament has CapZ at the barbed end, Tmod at the pointed end, and tropomyosin on the side (A). Dynamic behavior of Tmod at the pointed end transiently generates a free pointed end (B) and allows elongation (C). This tropomyosin-free region of the filament is subjected to severing by ADF/cofilin and AIP1 (D), and depolymerized actin is captured by profilin, which prevents elongation from the pointed end (E). When this machinery is impaired, excessively elongated filaments may become unstable and form aggregates (F).