Abstract
During the developmental processes of embryos, cells undergo massive deformation and division that are regulated by mechanical cues. However, little is known about how embryonic cells change their mechanical properties during different cleavage stages. Here, using atomic force microscopy, we investigated the stiffness of cells in ascidian embryos from the fertilised egg to the stage before gastrulation. In both animal and vegetal hemispheres, we observed a Rho kinase (ROCK)-independent cell stiffening that the cell stiffness exhibited a remarkable increase at the timing of cell division where cortical actin filaments were organized. Furthermore, in the vegetal hemisphere, we observed another mechanical behaviour, i.e., a ROCK-associated cell stiffening, which was retained even after cell division or occurred without division and propagated sequentially toward adjacent cells, displaying a characteristic cell-to-cell mechanical variation. The results indicate that the mechanical properties of embryonic cells are regulated at the single cell level in different germ layers.
Highlights
During the developmental processes of embryos, cells undergo massive deformation and division that are regulated by mechanical cues
A similar relationship between actin filaments and microtubules has been observed in cells in vitro, so that single cells treated with NOC still accumulated cortical actomyosin and increased rounding force[34], and the actin filaments exhibited repeated polarisation[35]. We observed such a change in E of a NOC-treated embryo with inhibited cell division at later stages, such as the 32cell stage (Fig. 5d–f). These results suggested that the remodelling of cortical actin filaments in embryonic cells, which contributed to the cell stiffness measured by atomic force microscopy (AFM), was highly conserved during developing processes and less associated with the dynamics of microtubules that facilitate cytokinesis in cell division
The Y27632 treatment suppressed stiffening of A7.1 and A7.2 cells occurring without cell division at the 76-cell stage (Fig. 6i–k). These results indicated that the cell stiffening occurring without cell division in the interphase was strongly associated with myosin, which is regulated through the ROCK pathway, while the cell stiffening at the timing of cell division was associated with other pathways
Summary
During the developmental processes of embryos, cells undergo massive deformation and division that are regulated by mechanical cues. Using atomic force microscopy, we investigated the stiffness of cells in ascidian embryos from the fertilised egg to the stage before gastrulation In both animal and vegetal hemispheres, we observed a Rho kinase (ROCK)-independent cell stiffening that the cell stiffness exhibited a remarkable increase at the timing of cell division where cortical actin filaments were organized. Little is known about how individual cells temporarily change their mechanical properties in early embryogenesis after the embryo has divided into two hemispheres such as animal and vegetal poles To address this issue, we investigated the spatiotemporal change in single-cell mechanical properties of the ascidian embryo that exhibits mosaic development[19] using atomic force microscopy (AFM)[20] (Fig. 1a) providing a non-destructive measurement to simultaneously determine the topography and stiffness of embryonic cells (‘Methods’). The Y-27632 treatment experiments indicated that the cell stiffening occurring in the interphase was strongly associated with myosin, which is regulated through the ROCK pathway, while the cell stiffening at the timing of cell division was associated with other pathways
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
