YAP1 and polycystic ovary syndrome: Mechanically, given the sensitivity of Hippo signaling to physical force, the effect of the fibrotic extracellular matrix (ECM) and the thickened and sclerosed cortex of the polycystic ovaries, which contains more F-actin and collagen, is to downregulate Hippo signaling, resulting in YAP1 over-activation, and thus leading to stromal hypertrophy and over-proliferation of theca cells.