Fluid Dynamic Mechanism Responsible for Breaking the Left-Right Symmetry of the Human Body: The Nodal Flow

A left-right (LR) asymmetric body plan is crucial for the development of the human body. The past decade has seen rapid progress in our understanding of the LR symmetry-breaking process in vertebrate development. A series of experimental studies has demonstrated that leftward movement of fluid at the ventral node, designated nodal flow, is the central process in symmetry breaking. Nodal flow is autonomously generated by the posteriorly tilted rotation of cilia. The underlying fluid dynamic mechanism, especially the importance of viscous interactions between the cilia and the cell surface, has been clarified by theoretical analyses. Recent experiments have suggested how this leftward nodal flow can be interpreted to create LR asymmetry. Specifically, leftward transport of lipoprotein particles, called nodal vesicular parcels (NVPs), was uncovered. Nodal flow thus triggers left-specific signaling pathways by transporting signaling molecules to the left side using NVPs.