HOW TO BUILD A STRAIGHT BODY AXIS DURING EMBRYOGENESIS? EXPLORING THE CONTRIBUTION OF CILIARY BEATING TO OSCILLATIONS OF THE REISSNER FIBER IN ZEBRAFISH

The establishment of a straight anteroposterior body axis with left-right symmetry is important for animals to optimize behaviors such as posture control, predator avoidance, and foraging. In vertebrate species, this process requires to first form a straight body during embryogenesis and then to maintain this alignment throughout spine morphogenesis. The Reissner fiber, an acellular filament made by polymerization of SCO-spondin proteins that extends within the cerebrospinal fluid in the central canal, has been shown to play a key role for axis straightness across developmental stages. In zebrafish embryos and larvae, the fiber is maintained in vivo as a straight thread throughout the spinal cord while being subjected to heterogeneous tension and long-wavelength oscillatory motion along the dorsoventral axis, indicating the presence of mechanical forces whose physical origins are not yet understood. While motile cilia have been shown to contribute to central canal formation and Reissner fiber polymerization, the mechanisms responsible to build the fiber tension have not been investigated. We address this question here by perturbing ciliary beating within the central canal and investigating additional potential contributors to the fiber tension, including its anchoring sites and interactions with surrounding tissue. By analyzing Reissner fiber dynamics under perturbed ciliary motility, we aim to determine whether its oscillations are actively driven by cilia-generated fluid flows or can persist as an intrinsic, self-maintained mechanical force once the fiber is formed and anchored.