Global analysis of cell behavior and protein dynamics reveals region-specific roles for Shroom3 and N-cadherin during neural tube closure

Abstract

Failures of neural tube closure are common and serious birth defects, yet we have a poor understanding of the interaction of genetics and cell biology during neural tube closure. Additionally, mutations that cause neural tube defects (NTDs) tend to affect anterior or posterior regions of the neural tube but rarely both, indicating a regional specificity to NTD genetics. To better understand the regional specificity of cell behaviors during neural tube closure, we analyzed the dynamic localization of actin and N-cadherin via high-resolution tissue-level time-lapse microscopy during Xenopus neural tube closure. To investigate the regionality of gene function, we generated mosaic mutations in shroom3, a key regulator or neural tube closure. This new analytical approach elucidates several differences between cell behaviors during cranial/anterior and spinal/posterior neural tube closure, provides mechanistic insight into the function of shroom3 and demonstrates the ability of tissue-level imaging and analysis to generate cell-biological mechanistic insights into neural tube closure.

Distinct spatiotemporal contribution of morphogenetic events and mechanical tissue coupling during Xenopus neural tube closure

“…High-resolution imaging of NP morphogenesis revealed that the anterior and posterior regions of the NP display distinct morphogenetic behaviour. This is an agreement with a recent study that also detected distinct patterns of behaviour at the posterior and anterior NP (Baldwin et al, 2022). Specifically, here we show that whereas the NP narrows and elongates, the anterior part of the tissue displays a polarized anterior movement.…”

“…S6B,C). In agreement with our data, Crispr/Casmediated knock out of Shroom3 in Xenopus embryos leads to a mild effect on the polarity of T1 transitions, but does not affect the number of T1 transitions and CE-mediated tissue deformation (Baldwin et al, 2022). Altogether, our data show that NTC is clearly biphasic with an early CE-driven phase that is spatially restricted to the posterior NP, followed by a second phase driven by generalized AC across the entire NP (Fig.…”

Somitic mesoderm morphogenesis is necessary for neural tube closure during Xenopus development

“…The transformation of the flat neuroepithelium to the neural tube is primarily driven by forces generated by intrinsic morphogenetic events. Convergent extension and apical constriction are the two main morphogenetic movements taking place within the neuroepithelium during neural tube closure ( Keller et al, 1992 ; Davidson and Keller, 1999 ; Hildebrand and Soriano, 1999 ; Haigo et al, 2003 ; Nishimura et al, 2012 ; Zanardelli et al, 2013 ; Christodoulou and Skourides, 2015 ; Baldwin et al, 2022 ). In addition to neural plate generated forces, it has been suggested that extrinsic forces stemming from the adjacent surface ectoderm and the underlying somitic mesoderm actively contribute to neural tube closure ( Schroeder, 1970 ; Karfunkel, 1974 ; Jacobson and Gordon, 1976 ; Moury and Schoenwolf, 1995 ).…”

Synchronisation of apical constriction and cell cycle progression is a conserved behaviour of pseudostratified neuroepithelia informed by their tissue geometry

“…For example, formin homology domain-containing (Fhod)3 is selectively expressed in apically convex regions of the anterior neuroepithelium overlying the rhombomeres and its deletion prevents apical constriction, causing exencephaly in mice (Sulistomo et al, 2019). In Xenopus , simultaneous accumulation of F-actin and N-cadherin (CDH2) parallels apical constriction anteriorly, whereas N-cadherin does not increase in the constricting posterior neuroepithelium (Baldwin et al, 2022). Important differences between Xenopus and amniotes include the lack of a pseudostratified neuroepithelium and brevity of neural tube closure relative to cell cycle progression in the former (Nikolopoulou et al, 2017).…”

“…Both apicomedial and cell junction actomyosin can contribute to apical shrinkage. In the stratified neuroepithelium of Xenopus , apicomedial F-actin accumulation is associated with apical shrinkage in the presumptive brain, whereas both apicomedial and cortical accumulation can correlate with apical shrinkage in the spinal region (Baldwin et al, 2022).…”