Conserved signals orchestrate self-organization and symmetry breaking of bi-layered epithelia during development and regeneration

Abstract

Organ development relies on complex molecular mechanisms that guide initially homogeneous populations of stem cells to differentiate into specialized cell types within defined spatial patterns. While stable during homeostasis, the proper spatial organization of cell types must be re-established in case of tissue injury for successful regeneration of organ shape and function. How cells commit to a differentiation path is a central question in stem cell research; however, the coordination between tissue geometry and cell fate specification remains enigmatic. To elucidate the molecular mechanisms instructing self-organization and symmetry breaking of epithelial stem cells, we developed a multi-faceted approach combining in vitro organoids, ex vivo embryonic tissue explants, and single-cell quantitative imaging to investigate the dynamic acquisition of cell fate in four bi-layered epithelia, during embryonic development but also in regeneration. Our findings indicate that tissue architecture is the primary determinant of cell fate decisions in these tissues. Upon the initial cell internalization event, the homogeneous population of stem cell break symmetry. Through genetic and pharmacological perturbations, we have demonstrated that a tightly coordinated interplay between Hippo/YAP and Notch signaling is essential for conveying information from tissue architecture to functional cell differentiation and stem cell potency restriction. Globally, this study uncovers the inherent capacity of stem cells to self-organize into multicellular structures, where the precise position of each differentiated cell is critical to instruct their differentiation choices during embryonic development and regeneration.