Schematic illustration showing the evolution of the (myo)fibroblast phenotype. The myofibroblastic modulation of fibroblastic cells begins with the appearance of the proto-myofibroblast, whose stress fibers contain only β- and γ-cytoplasmic actins and evolves, but not necessarily always, into the appearance of the differentiated myofibroblast, the most common variant of this cell, with stress fibers containing α-smooth muscle actin. The myofibroblast may disappear by apoptosis; the deactivation leading to a quiescent phenotype has not been clearly demonstrated at least in vivo. TGF-β1: transforming growth factor-β1; ECM: extracellular matrix. Modified from .