Assessing the critical period for Rho kinase activity during Drosophila ventral furrow formation

Abstract

Background: Drosophila ventral furrow formation (VFF), which is the first morphogenetic event during embryo development, serves as a model for epithelial sheet folding. VFF can be subdivided into five cell shape changes: apical membrane flattening, apicobasal nuclear migration, apicobasal cell shortening, random apical constriction, and concerted apical constriction. These processes are generally believed to be driven by Rho kinase (Rok) activation of myosin II to stimulate the constriction of the apical actomyosin network. To test the role of Rok and its downstream target myosin II in VFF, timed injections of the Rok inhibitor, Y-27632, were performed. Results: Embryos injected with Y-27632 before the concerted apical constriction phase of VFF were able to execute apicobasal nuclear migration and random apical constriction, but were unable to enter the concerted apical constriction phase. Embryos injected with Y-27632 during concerted apical constriction reverted to the transition point between random apical constriction and concerted apical constriction. Finally, embryos injected with Y-27632 upon the initiation of furrow ingression were able to complete VFF. Conclusions: Together these results suggest a critical period for Rok activity and presumably myosin II activation during the initiation of the concerted apical constriction phase of VFF.

Mechanical feedback and robustness of apical constrictions inDrosophilaembryo ventral furrow formation

“…Specifically, the cells in already formed constriction chains continued to constrict, causing the others to expand. A similar behavior can be seen in images of embryos with delayed or failed VFF due to injection of Rho kinase inhibitor [39]. The 3.0 mW laser beam hinders constrictions in the affected zone almost entirely (Fig 13A-D).…”

Crumbs is an essential regulator of cytoskeletal dynamics and cell-cell adhesion during dorsal closure in Drosophila

“…Moreover, Rho1 1B hemizygosity effectively suppresses the DC defects of foscrb Y10A embryos ( Figure 7A , 14 th bar vs. 1 st black bars, 79.2 vs. 98.3%). In contrast, foscrb Y10A embryos hemi- or homozygous for rok 2 show no suppression of the DC phenotypes ( Figure 7A , 15 th vs. 3 rd bars), which suggests that rok deficiency may be deleterious in the foscrb Y10A background and that other morphological processes dependent on Rok could be affected ( Simões et al, 2010 ; Krajcovic and Minden, 2012 ; Mason et al, 2013 ; Bertet et al, 2004 ). Similarly, over-expression of dominant-negative Rac1 (Rac1 N17 ) in the AS of foscrb Y10A embryos does not suppress the DC phenotype ( Figure 7A , 16 th vs. 5 th bars) and even appears to increase the proportion of embryos with open cuticles ( Figure 7—figure supplement 1 , 5 th vs. 16 th black bars, from 52.7% to 72.9%).…”

An energy landscape approach to understanding variety and robustness in tissue morphogenesis

“…For example, during furrow formation in early Drosophila embryos, in which constriction drives tissue invagination, the qualitatively different tissue morphologies arise from the timing of inhibition of cell constriction. While inhibition of cell constriction at the early formation stage resulted in the failure of invagination, the tissue invaginated even with the inhibition in the late stage (Royou et al 2004;Krajcovic and Minden 2012). This difference in the tissue morphologies can be explained based on the energy landscape illustrated in this study.…”

“…To elucidate the concept of an energy landscape approach, we investigated variety and robustness of morphogenesis using an idealized model of curved sheet-like tissue. Despite the idealized model, we believe that this model realistically captures essential behaviors of sheet-like tissue morphogenesis with cell proliferation and constriction, such as during furrow formation in Drosophila (Royou et al 2004;Krajcovic and Minden 2012), neurulation in Chick and Xenopus (Nishimura et al 2012;Butler and Wallingford 2018), and optic-cup formation in Zebrafish (Nicolas-Perez et al 2016;Martinez-Morales et al 2017). We constructed a finite element (FE) model of an idealized circular sheet-like tissue that had an initial curvature ( Fig.…”

“…Despite its potential of variation, morphogenesis is a surprisingly robust process, in which qualitatively similar morphologies are reproducibly formed even under spatiotemporal fluctuations caused by multicellular activities (Goodwin 1 3 et al 1993;Conte et al 2009;Davidson 2017). For example, even when the constriction driving tissue deformation is fluctuated at a particular stage, morphogenesis proceeds normally (Royou et al 2004;Eiraku et al 2011;Krajcovic and Minden 2012). Different spatiotemporal activities induce different morphologies, but these morphogenetic processes remain robust in spite of their fluctuations.…”