Artificial embryonic node elucidates the role of flow in left-right symmetry breaking in vertebrates

During the embryonic development of vertebrates, initially, symmetric embryos develop asymmetrically arranged organs. The asymmetry initiates with the formation of a small fluid-filled cavity on the embryo called the embryonic node, which contains motile cilia that generate specific flow patterns. The mechanism by which this nodal flow is sensed and causes asymmetry development has remained elusive despite major experimental and computational efforts. Existing hypotheses focus on either mechanical or chemical signaling processes. We report an experimental artificial embryonic node that, combined with numerical simulations, enables in-depth investigation of nodal flow and its role in left-right asymmetry development. Dissimilar fluid velocity profiles develop around primary cilia on the left and right nodal sides, producing distinct cilium bending. Also, the distribution of signaling particles with specific diffusivities exhibits spatial and temporal asymmetry. Together, our results support both mechanical and chemical sensing hypotheses and suggest a potential synergy between the two sensing mechanisms for the enhanced robustness of left-right asymmetry development.