Valproic acid disrupts the biomechanics of late spinal neural tube closure in mouse embryos

Abstract

Failure of neural tube closure in the early embryo causes neural tube defects including spina bifida. Spina bifida lesions predominate in the distal spine, particularly after exposure to the anticonvulsant valproic acid (VPA). How VPA specifically disturbs late stages of neural tube closure is unclear, as neurulation is usually viewed as a uniform ‘zippering’ process along the spine. We recently identified a novel closure site (“Closure 5”) which forms at the caudal extremity of the mouse posterior neuropore (PNP) when completion of closure is imminent. Here we investigated whether distal spina bifida in VPA-exposed embryos involves disruption of Closure 5. Exposure of E8.5 mouse embryos to VPA in whole embryo culture had marked embryotoxic effects, whereas toxic effects were less pronounced in more developmentally advanced (E9) embryos. Only 33% of embryos exposed to VPA from E9 to E10.5 achieved PNP closure (control = 90%). Short-term (8 h) VPA treatment diminished supra-cellular F-actin cables which normally run along the lateral neural folds, and prevented caudal PNP narrowing normally characteristic of Closure 5 formation. Laser ablation of Closure 5 caused rapid neuropore widening. Equivalent ablations of the caudal PNP in VPA treated embryos resulted in significantly less widening, suggesting VPA prevents formation of Closure 5 as a biomechanically active structure. Thus, VPA exposure prevents morphological and biomechanical conversion of the caudal extreme of the PNP during late spinal closure. Closure 5 facilitates neural fold apposition when completion of closure is imminent, such that its disruption in VPA-exposed embryos may lead to distal spina bifida.

Rho kinase-dependent apical constriction counteracts M-phase apical expansion to enable mouse neural tube closure

“…To minimise the potential for secondary changes owing to prolonged culture, we first characterised the morphological changes caused by 8 h of Rock inhibition with the extensively used compound Y27632 in embryonic day (E)9–9.5 CD1 mouse embryos. This treatment period is sufficient to observe biologically meaningful differences in PNP dimensions (Hughes et al, 2018). After 8 h of Rock inhibition, we observed dose-dependent widening of the PNP, giving rise to PNPs that were more ‘diamond-shaped’ as opposed to the the elliptical structures characteristic of control embryos at late stages of closure (Fig.…”

The Secretory Pathway Calcium ATPase 1 (SPCA1) controls neural tube closure by regulating cytoskeletal dynamics

“…For instance, caffeine, the neuro-stimulating component in many popular beverages, stimulates the release of calcium from the Golgi apparatus by binding to ryanodine receptors (Lissandron et al, 2010) and has been shown to disrupt neural tube closure in rat, mouse and chicken embryos (Ma et al, 2012;Marret et al, 1997;Wilkinson and Pollard, 1994). Additionally, valproic acid, a drug used to treat depression and other mood disorders, affects calcium homeostasis (Ghodke-Puranik et al, 2013) and increases the incidence of neural tube defects (Hughes et al, 2018). Our results from the analysis of mouse Spca1 mutants, together with the growing body of evidence supporting a role for calcium in neurulation, urges additional epidemiological and clinical studies to examine how calcium homeostasis influences neural tube closure in humans, as well as whether counteracting dietary deficiencies in elemental calcium during early pregnancy could reduce the incidence of neural tube defects.…”

Embryo‐derived teratoma in vitro biological system reveals antitumor and embryotoxic activity of valproate

“…The FEBS Journal published by John Wiley & Sons Ltd on behalf of Federation of European Biochemical Societies development [61], basic research in various systems on the mechanisms of its teratogenicity is still necessary [62]. Important research on neural development is conducted in the gastrulating whole rat embryo (WEC) in vitro system that includes extraembryonic membranes and is of a shorter duration than this system [63], as well as in cultivated neuronal embryonic stem cells [58] first derived from the inner cell mass of the blastocyst. Transcriptomic evaluation of VPA activity across in vitro developmental models (WEC, cardiac, and neural embryonic stem cells) and nondevelopmental models has shown that developmental models were better for assessment of developmental-specific effects such as for neuronal differentiation [64].…”