Figure 1.

Physiological all-trans retinoic acid (RA) determines different cell fate decisions in normal and aberrant mammary epithelial cells. Blueprint of the three-module mechanism that integrates physiological RA and two RA receptor alpha (RARA) functions (center). In the course of normal human mammary epithelial cell morphogenesis (left scheme), physiological RA acts as the ancient two-faced Janus Bifrons god that regulates—in a spatiotemporal fashion—cell life (red) and cell death (green). Genetic factors affecting the RA-RARA mechanism induce 3D aberrant mammary morphogenesis (right scheme) [88].