The Reissner fiber under tension in vivo shows dynamic interaction with ciliated cells contacting the cerebrospinal fluid

The Reissner fiber (RF) is an acellular thread positioned in the midline of the central canal that forms together with cerebrospinal fluid (CSF)-contacting neurons (CSF-cNs) an axial sensory system detecting curvature in the spinal cord. How these components interact is unknown. Using in vivo imaging in larval zebrafish, we show that RF is under tension and resonates dorsoventrally. Focal RF ablations trigger retraction and relaxation of the fiber cut ends, with larger retraction speeds for rostral ablations. We built a mechanical model that estimates RF stress diffusion coefficient at 10 mm2/s and reveals that tension builds up rostrally along the fiber. After RF ablation, CSF-cN spontaneous activity decreased and ciliary motility changed, suggesting physical interactions between RF and cilia projecting into the central canal. We observed that motile cilia were caudally-tilted and frequently interacted with RF. We propose that the numerous ependymal motile monocilia contribute to RF he..., ,