Symmetry breaking is a fundamental biological principle that converts initially homogeneous systems into spatially and functionally organized structures, forming the basis of tissue complexity. Studying symmetry breaking in skin appendages offers a unique opportunity to understand how fundamental patterning principles operate within a highly accessible and experimentally tractable organ system. In mammals, hair follicles, sweat glands, and sebaceous glands exhibit remarkable diversity in morphology and regenerative capacity, yet all originate from a common epithelial framework through precisely coordinated symmetry-breaking events. Symmetry breaking is governed not only by intrinsic determinants such as morphogen gradients and mechanical forces within tissues, but also by extrinsic cues from the surrounding microenvironment, including extracellular matrix architecture and systemic hormonal or inflammatory signals. These factors interact through mechanisms such as reaction-diffusion dynamics and mechanochemical feedback to direct spatial patterning and cell fate specification. By using skin appendages as a paradigm, this review highlights the central role of symmetry breaking in linking developmental pattern formation, stem cell regulation during regeneration, and structural alterations in disease, offering insights that are broadly applicable across organ systems.
Zhou et al. (Sun,) studied this question.