SCO-spondin knockout mice exhibit small brain ventricles and mild spine deformation

Abstract

Reissner’s fiber (RF) is an extracellular polymer comprising the large monomeric protein SCO-spondin (SSPO) secreted by the subcommissural organ (SCO) that extends through cerebrospinal fluid (CSF)-filled ventricles into the central canal of the spinal cord. In zebrafish, RF and CSF-contacting neurons (CSF-cNs) form an axial sensory system that detects spinal curvature, instructs morphogenesis of the body axis, and enables proper alignment of the spine. In mammalian models, RF has been implicated in CSF circulation. However, challenges in manipulatingSspo, an exceptionally large gene of 15,719 nucleotides, with traditional approaches has limited progress. Here, we generated aSspoknockout mouse model using CRISPR/Cas9-mediated genome-editing.Sspoknockout mice lacked RF-positive material in the SCO and fibrillar condensates in the brain ventricles. Remarkably,Sspoknockout brain ventricle sizes were reduced compared to littermate controls. Minor defects in thoracic spine curvature were detected inSspoknockouts, which did not alter basic motor behaviors tested. Altogether, our work in mouse demonstrates that SSPO and RF regulate ventricle size during development but only moderately impact spine geometry.