Volume conservation principle involved in cell lengthening and nucleus movement during tissue morphogenesis

Abstract

Tissue morphogenesis is the process in which coordinated movements and shape changes of large numbers of cells form tissues, organs, and the internal body structure. Understanding morphogenetic movements requires precise measurements of whole-cell shape changes over time. Tissue folding and invagination are thought to be facilitated by apical constriction, but the mechanism by which changes near the apical cell surface affect changes along the entire apical-basal axis of the cell remains elusive. Here, we developed Embryo Development Geometry Explorer, an approach for quantifying rapid whole-cell shape changes over time, and we combined it with deep-tissue time-lapse imaging based on fast two-photon microscopy to study Drosophila ventral furrow formation. We found that both the cell lengthening along the apical-basal axis and the movement of the nucleus to the basal side proceeded stepwise and were correlated with apical constriction. Moreover, cell volume lost apically due to constriction largely balanced the volume gained basally by cell lengthening. The volume above the nucleus was conserved during its basal movement. Both apical volume loss and cell lengthening were absent in mutants showing deficits in the contractile cytoskeleton underlying apical constriction. We conclude that a single mechanical mechanism involving volume conservation and apical constriction-induced basal movement of cytoplasm accounts quantitatively for the cell shape changes and the nucleus movement in Drosophila ventral furrow formation. Our study provides a comprehensive quantitative analysis of the fast dynamics of whole-cell shape changes during tissue folding and points to a simplified model for Drosophila gastrulation.two-photon imaging | 4D reconstruction | segmentation

Apical constriction: themes and variations on a cellular mechanism driving morphogenesis

“…In addition, the microtubule cytoskeleton is likely to play important roles in regulating cell morphology during apical constriction, having been implicated in apical-basal lengthening downstream of Shroom3, regulation of actin-myosin contractility through interactions with PDZ-RhoGEF, and control of cell-cell adhesion (Rogers et al, 2004;Lee and Harland, 2007;Suzuki et al, 2010). Finally, how cytoplasm, the nucleus and other organelles are influenced by apical constriction and vice versa is not well understood (Gelbart et al, 2012;Jayasinghe et al, 2013). Advances in microscopy and the increasing availability of molecular and biophysical tools to perturb gene/protein function and probe the mechanics of developing organisms means that we are likely to see progress and new surprises in years to come.…”

Downregulation of basal myosin‐ II is required for cell shape changes and tissue invagination

“…Image preprocessing was done using Fiji. Image segmentation and cell tracking was done using Embryo Development Geometry Explorer (EDGE) software (Gelbart et al , 2012) provided via GitHub (https://github.com/mgelbart/embryo-development-geometry-explorer). …”

Actomyosin-based tissue folding requires a multicellular myosin gradient

“…All live and immunostained images were then segmented using an existing MATLAB package, Embryo Development Geometry Explorer (EDGE) (Gelbart et al, 2012). Membrane signal (Gap43::mCherry) or cortical actin ( phalloidin) were used to detect cell boundaries and track cells in time for live images.…”