Claudins Regulate Cellular Events that Occur at the Apical Cell Surface during Neural Tube Closure

Amanda Baumholtz*1,3, Annie Simard3 and Aimee K. Ryan1,2,3

Departments of 1. Human Genetics and 2. Pediatrics, McGill University, Montreal, Quebec, Canada; 3. RI-MUHC

*Corresponding author. Address: Research Institute of the McGill University Health Centre, 1001 Decarie Blvd, Block E, Lab # ES14374, Montreal, Quebec, Canada. H4A 3J1

Neurulation is a critical developmental process that converts the flat neural plate into a closed neural tube. Throughout this process the neural plate epithelium undergoes extensive remodeling that requires the coordinated activity of ROCK signaling to regulate actin-myosin contractility that drives apical constriction of midline neural ectoderm cells and the planar cell polarity (PCP) pathway to direct polarized cell rearrangements that drive convergent extension. We investigated the role of the claudin family of tight junction proteins in coordinating these two pathways in chick neural tube morphogenesis. Removal of claudin-3, -4, and -8 from tight junctions of the chick ectoderm using the C-terminal domain of Clostridium perfringens enterotoxin (C-CPE) resulted in folate-resistant neural tube defects in 100% of treated embryos that are caused by defective apical constriction and convergent extension. We showed that apical constriction defects are due to defective ROCK signaling: RhoA, which acts upstream of ROCK, and pMLC, which is downstream of ROCK, showed reduced apical accumulation in the neural ectoderm of C-CPE-treated embryos. Vangl2, a core PCP protein, also showed reduced apical accumulation in the neural ectoderm of C-CPE-treated embryos indicating that defective PCP signaling is responsible for the convergent extension defects observed in these embryos. We sequenced six claudins in 94 patients with neural tube defects and identified 7 missense variants that are predicted to be deleterious by in silico prediction tools in 16 patients. 6 of these variants have not been reported in dbSNP, the 1000 Genome Project, the Exome Aggregation Consortium (ExAC) Browser or the Exome Variant Server (EVS). These findings support a conserved role for claudins in regulating the morphogenetic movements that drive neural tube closure.