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Fig. 8. Shrm is required for proper myosin IIB distribution during neural tube closure. (A-D) Cryosections of wild type (A and B) or shrm mutant (C and D) e9.25 mouse embryos were stained to detect non-muscle myosin II-B (green, A'-D') and ß-catenin (red). Panels A and C show sections through the cranial neural folds while B and D are sections through the trunk neural tube. Scale bar equals 15 µm, ap, apical surface. (E) Model of Shrm function in neural tube closure. Shown are schematics of the neural tube in both cranial and trunk regions indicating the presence of bending (a) and non-bending (b) regions of the cranial and trunk neural tube. Cells in both types of regions contain contractile rings (c) in the AJC that provide force around the circumference of the cell to mediate either apical constriction or provide tension. (d) Shrm is recruited to the AJC via either F-actin that is already localized there or another protein in the AJC (double head arrows). Once in the AJC complex, the C-terminal domain of Shrm facilitates the assembly of a contractile actomyosin complex (green actin and myosin). The C-terminus of Shrm could act directly or through a second cellular protein (?) to facilitate formation of the complex. It is predicted that Rock could be needed in parallel to maintain a population of active myosin II.
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