α-smooth muscle actin, encoded by ACTA2, is expressed in abundance in vascular smooth muscle, comprising 50–70% of total actin, with the remainder composed of β-cytoplasmic and γ-actins. Whereas Sα-smooth muscle expression is normally restricted to smooth muscle cells, it can also be expressed in nonmuscle cells, most notably myofibroblasts that use cell traction forces to remodel extracellular matrix.