CFL1-dependent dynamicity of surface ectoderm filopodia-like protrusions enhances neurulation zippering speed in mice

Abstract

Progression of caudally-directed embryonic neural tube closure must exceed that of body axis elongation, otherwise closure is incomplete and neural tube defects arise. Genetic deletion and pharmacological antagonism studies establish the critical role of actomyosin regulation in this closure process in mice, but many models of impaired F-actin regulation are limited by early embryonic lethality, which precludes mechanistic insightin vivo. Here, we test the physiological functions of the F-actin severing protein CFL1 by selective deletion in various tissues of mouse embryos undergoing neural tube closure. Loss of CFL1 in the cranial neuroepithelium diminishes selective apical localisation of F-actin and produces dysmorphic, asymmetrical headfolds which fail to meet at the dorsal midline, causing exencephaly, with partial penetrance. During spinal neurulation, neuroepithelial CFL1 is dispensable, but its expression in the surface ectoderm enhances the dynamicity of filopodia-like protrusions involved in the zippering process of midline epithelial fusion. Compared with littermate controls, spinal zippering speed is decreased by 30% in embryos lacking surface ectoderm CFL1 and approximately 30% of embryos develop spina bifida. These findings suggest that molecular-level cytoskeletal regulation by CFL1 sets the cellular-level dynamicity of filopodial extensions which limit tissue- level zippering speed necessary to fully close the neural tube.