Shroom3 functions downstream of planar cell polarity to regulate myosin II distribution and cellular organization during neural tube closure

Abstract

Neural tube closure is a critical developmental event that relies on actomyosin contractility to facilitate specific processes such as apical constriction, tissue bending, and directional cell rearrangements. These complicated processes require the coordinated activities of Rho-Kinase (Rock), to regulate cytoskeletal dynamics and actomyosin contractility, and the Planar Cell Polarity (PCP) pathway, to direct the polarized cellular behaviors that drive convergent extension (CE) movements. Here we investigate the role of Shroom3 as a direct linker between PCP and actomyosin contractility during mouse neural tube morphogenesis. In embryos, simultaneous depletion of Shroom3 and the PCP components Vangl2 or Wnt5a results in an increased liability to NTDs and CE failure. We further show that these pathways intersect at Dishevelled, as Shroom3 and Dishevelled 2 co-distribute and form a physical complex in cells. We observed that multiple components of the Shroom3 pathway are planar polarized along mediolateral cell junctions in the neural plate of E8.5 embryos in a Shroom3 and PCPdependent manner. Finally, we demonstrate that Shroom3 mutant embryos exhibit defects in planar cell arrangement during neural tube closure, suggesting a role for Shroom3 activity in CE. These findings support a model in which the Shroom3 and PCP pathways interact to control CE and polarized bending of the neural plate and provide a clear illustration of the complex genetic basis of NTDs.

Planar cell polarity in moving cells: think globally, act locally

“…Dvl2 also exhibits a planar polarized distribution along mediolaterally oriented membranes (Fig. 2), being strongly recruited there by Celsr1 (McGreevy et al, 2015;Nishimura et al, 2012). Dvl2 asymmetry to posterior versus anterior membranes, if present in the neural plate, was not detectable in these studies.…”

“…Shroom3 is an apically enriched actin-binding protein that recruits Rho-associated kinase (Rock) to activate myosin II, driving apical constriction and neural tube closure (Nishimura and Takeichi, 2008). A recent report demonstrated that, in the mouse neural plate, Shroom3 and Rock become polarized to mediolaterally aligned membranes by Dvl2 (McGreevy et al, 2015). Daam1, which is a formin homology protein that directs nucleation and elongation of actin filaments, also functions as an adaptor linking Dvl to RhoA in multiple PCP processes (Habas et al, 2001).…”

Genetic and functional analysis of SHROOM1-4 in a Chinese neural tube defect cohort

“…SHROOM3 mediates the PCP pathway (McGreevy et al 2015) and plays an essential role in regulating cytoskeletal dynamics (Zalewski et al 2016), which are critically important during the closure of the neural tube. Recently, de novo LoF mutations in SHROOM3 were experimentally associated with the development of NTDs, suggesting that these variants may also contribute to the genetic etiology of severe human NTDs (Lemay et al 2015).…”

“…Previous animal models have demonstrated that homozygous Shroom3 mutant embryos exhibited exencephaly (Hildebrand and Soriano 1999). Shroom3 interacts genetically with the PCP components Vangl2 and Wnt5a, and depletion of Shroom3 and Vangl2 or Wnt5a can drastically increase the penetrance and severity of NTDs (McGreevy et al 2015). The PCP pathway is highly dosage sensitive, and over-or under-expression of PCP core genes in zebrafish and Xenopus embryos results in convergent extension defects (Roszko et al 2009; Wallingford 2005, 2013).…”

“…PCP-dependent convergent extension is crucial for NTC, and loss of function (LoF) alleles of Vangl2 (Greene et al 1998), Celsr1 (Curtin et al 2003), Frizzled3 ( Fz3 ) (Wang et al 2006), Frizzled6 ( Fz6 ) (Wang et al 2006), Dvl1 and Dvl2 (Etheridge et al 2008) cause craniorachischisis. Recently, SHROOM3 was demonstrated to function downstream of the PCP pathway to regulate myosin II distribution and cellular behavior to promote NTC in mouse models (McGreevy et al 2015). SHROOM3 is a cytoskeleton regulating protein that contains three evolutionarily conserved domains.…”