Shroom family proteins regulate γ-tubulin distribution and microtubule architecture during epithelial cell shape change

Abstract

Cell shape changes require the coordination of actin and microtubule cytoskeletons. The molecular mechanisms by which such coordination is achieved remain obscure, particularly in the context of epithelial cells within developing vertebrate embryos. We have identified a novel role for the actin-binding protein Shroom3 as a regulator of the microtubule cytoskeleton during epithelial morphogenesis. We show that Shroom3 is sufficient and also necessary to induce a redistribution of the microtubule regulator ␥-tubulin. Moreover, this change in ␥-tubulin distribution underlies the assembly of aligned arrays of microtubules that drive apicobasal cell elongation. Finally, experiments with the related protein, Shroom1, demonstrate that ␥-tubulin regulation is a conserved feature of this protein family. Together, the data demonstrate that Shroom family proteins govern epithelial cell behaviors by coordinating the assembly of both microtubule and actin cytoskeletons.

Neogenin and RGMa Control Neural Tube Closure and Neuroepithelial Morphology by Regulating Cell Polarity

“…Moreover, while some degree of apical constriction had occurred in these superficial cells, they were significantly less wedge-shaped and less elongated than those on the wild-type side. Also, while ␤-tubulin had accumulated under the apical surface in the morphant superficial cells, long apicobasally directed MT filaments originating from the apical region (Karfunkel, 1971;Burnside, 1973;Lee et al, 2007) were only seen in wild-type cells (Fig. 5, compare G,H ).…”

“…These cells had undergone some degree of apical constriction as a high concentration of tubulin was localized under the apical membrane (Karfunkel, 1971;Burnside, 1973;Lee et al, 2007) and obvious hinge-points were generated in the mutants, indicating that apical constriction had occurred, albeit less efficiently. Since Xneog and Xrgma are not expressed in the superficial layer, this disruption is non-cell-autonomous and secondary to the disruption of the deep cell layer.…”

“…Instead, NF elevation and neural plate bending are the primary forces driving anterior neurulation. Neural plate bending is generated by the constriction of actin filaments under the apical surface of the neuroectodermal cells (apical constriction) leading to the formation of hingepoints on either side of the dorsal midline (Haigo et al, 2003;Lee et al, 2007). Inability to undergo apical constriction results in failure of anterior neural tube closure (anencephaly) (Hildebrand and Soriano, 1999;Haigo et al, 2003).…”

Comparative analysis of neurulation: First impressions do not count

“…Following NT closure, proliferation becomes more uniform, however, a gradient of cell differentiation is now observed, with a greater number of differentiated cells in the ventral NT. Disruption of the proliferation/ differentiation balance in mouse mutants in which cell division is either up-or downregulated causes exencephaly (Ishibashi et al, 1995;Sah et al, 1995;Gowen et al, 1996;Zhong et al, 2000;Kim et al, 2007;Lee et al, 2007). While the underlying cause for these NT defects is not understood, it has been speculated that the premature differentiation of the neuroepithelium in some mutants might render the neural plate mechanically inflexible and prevent dorsolateral bending or inhibit the adhesion process that is necessary for neural fold fusion (Copp et al, 2003).…”

“…3C,C.1; Schroeder, 1971;Haigo et al, 2003). As in mice, this process is mediated by the actinbinding protein Shroom and disruption of Shroom function results in a specific failure of hinge point formation and brain NTDs (Haigo et al, 2003;Martin, 2004;Wallingford, 2005;Lee et al, 2007). Further shaping and closure of the NT involves a number of complex cell movements.…”