Understanding how the Reissner fiber in the cerebrospinal fluid contributes to shape the posterior axis of the body – FIBERSHAPE

One major question in the study of animal development is to understand how cell signaling and tissue shape are precisely coordinated while the organism grows towards its final form. The cerebrospinal fluid (CSF) is a protein rich solution filling the brain and spinal cord cavities. It has recently emerged as an important signaling path for neurogenesis and for the morphogenesis of specific subsets of cells in the nervous system. However, whether this fluid could influence morphogenesis outside the nervous system, and possibly body shape, remains poorly understood. In vertebrate species, the CSF contains the Reissner fiber, an extracellular thread conserved in vertebrates formed by the aggregation of the SCO-spondin protein. We discovered that this fiber, described more than 150 years ago by the anatomist Ernst Reissner, controls the axial morphogenesis in the embryonic zebrafish. Indeed, zebrafish scospondin mutants lacking the Reissner fiber develop a ventral curvature of the posterior axis of the body. At the juvenile stage, scospondin mutants develop as well a misalignment of the spine, reminiscent of human adolescent idiopathic scoliosis. This highlights the idea that the Reissner fiber influences body geometry throughout life. Yet, the mechanisms underlying this control remain poorly understood. Here, the FIBERSHAPE project will uncover the signaling pathways contributing to shape the geometry of the body at embryonic and post-embryonic stage. By combining state-of-the-art in vivo imaging in zebrafish with genetics, we will first identifying the cellular and molecular signaling cascade involving the Reissner fiber that contributes to shape the embryo. Second, we will uncover how the temporal stability of this polymer is controlled and adjusted during the post-embryonic and juvenile life to ensure a proper alignment of the spine. The dissection of the signaling steps identified here will allow understand better how a polymer bathing in the CSF facilitates a long-range signaling to tune the geometry of the trunk in a developing vertebrate, but also pave the avenue to better understand the mechanisms involved in idiopathic scoliosis.