Biology subjects

Kasza, K. E.

Publications and source records attributed to Kasza, K. E..

3 recordsLinked to original sources

bioRxiv2021

Optogenetic dissection of the roles of actomyosin in the mechanics underlying tissue fluidity

Rapid epithelial tissue flows are essential to building and shaping developing embryos. However, it is not well understood how the mechanical properties of tissues and the forces driving them to flow are jointly regulated to accommodate rapid tissue remodeling. To dissect the roles of actomyosin in the mechanics of epithelial tissue flows, here we use two optogenetic tools, optoGEF and optoGAP, to manipulate Rho/Rho-kinase signaling and actomyosin contractility in the germband epithelium, which flows via convergent extension movements during Drosophila body axis elongation. The ability to perturb actomyosin in the tissue allows us to analyze the effects of actomyosin on cell rearrangements, tissue tensions, and tissue mechanical properties. We find that either optogenetic activation or deactivation of Rho1 signaling and actomyosin contractility at the apical surface of the germband disrupts cell rearrangements and tissue-level flows. Rho1 activation leads to poorly oriented rearrangements that are associated with a redistribution of myosin II from the junctional to the medial-apical domain, whereas Rho1 deactivation leads to fewer, slower cell rearrangements that are associated with decreased junctional and medial myosin. By probing mechanical tensions in the tissue using laser ablation and inferring tissue mechanical properties from cell packings, we find that actomyosin influences both the anisotropic forces that drive tissue flow and the mechanical properties of the tissue that resist flow, leading to complex relationships between actomyosin activity and tissue fluidity. Moreover, our results link the subcellular distribution of myosin II to tissue tension and cell packings, revealing how junctional and medial myosin have differential roles in promoting and orienting cell rearrangements during tissue flow.

developmental biology↗

bioRxiv2021

Using optogenetics to link myosin patterns to contractile cell behaviors during convergent extension

Distinct spatiotemporal patterns of actomyosin contractility are often associated with particular epithelial tissue shape changes during development. For example, a planar polarized pattern of myosin II localization regulated by Rho1 signaling during Drosophila body axis elongation is thought to drive the cell behaviors that contribute to convergent extension. However, it is not well understood how specific aspects of a myosin localization pattern influence the multiple cell behaviors--including cell intercalation, cell shape changes, and apical cell area fluctuations--that simultaneously occur within a tissue during morphogenesis. Here, we use optogenetic activation (optoGEF) and deactivation (optoGAP) of Rho1 signaling to perturb the myosin pattern in the germband epithelium during Drosophila axis elongation and analyze the effects on contractile cell behaviors within the tissue. We find that uniform photoactivation of optoGEF or optoGAP is sufficient to rapidly override the endogenous myosin pattern, abolishing myosin planar polarity and reducing cell intercalation and convergent extension. However, these two perturbations have distinct effects on junctional and medial myosin localization, apical cell area fluctuations, and cell packings within the germband. Activation of Rho1 signaling in optoGEF embryos increases myosin accumulation in the medial-apical domain of germband cells, leading to increased amplitudes of apical cell area fluctuations. This enhanced contractility is translated into heterogeneous reductions in apical cell areas across the tissue, disrupting cellular packings within the germband. Conversely, inactivation of Rho1 signaling in optoGAP embryos decreases both medial and junctional myosin accumulation, leading to a dramatic reduction in cell area fluctuations. These results demonstrate that the level of Rho1 activity and the balance between junctional and medial myosin regulate apical cell area fluctuations and cellular packings in the germband, which have been proposed to influence the biophysics of cell rearrangements and tissue fluidity. STATEMENT OF SIGNIFICANCETissues are shaped by forces produced by dynamic patterns of actomyosin contractility. However, the mechanisms underlying these myosin patterns and their translation into cell behavior and tissue-level movements are not understood. Here, we show that optogenetic tools designed to control upstream regulators of myosin II can be used to rapidly manipulate myosin patterns and analyze the effects on cell behaviors during tissue morphogenesis. Combining optogenetics with live imaging in the developing fruit fly embryo, we show that acute perturbations to upstream myosin regulators are sufficient to rapidly perturb existing myosin patterns and alter cell movements and shapes during axis elongation, resulting in abnormalities in embryo shape. These results directly link myosin contractility patterns to cell behaviors that shape tissues, providing new insights into the mechanisms that generate functional tissues.

developmental biology↗

bioRxiv2019

Anisotropy links cell shapes to a solid-to-fluid transition during convergent extension

Within developing embryos, tissues flow and reorganize dramatically on timescales as short as minutes. This includes epithelial tissues, which often narrow and elongate in convergent extension movements due to anisotropies in external forces or in internal cell-generated forces. However, the mechanisms that allow or prevent tissue reorganization, especially in the presence of strongly anisotropic forces, remain unclear. We study this question in the converging and extending Drosophila germband epithelium, which displays planar polarized myosin II and experiences anisotropic forces from neighboring tissues, and we show that in contrast to isotropic tissues, cell shape alone is not sufficient to predict the onset of rapid cell rearrangement. From theoretical considerations and vertex model simulations, we predict that in anisotropic tissues two experimentally accessible metrics of cell patterns--the cell shape index and a cell alignment index--are required to determine whether an anisotropic tissue is in a solid-like or fluid-like state. We show that changes in cell shape and alignment over time in the Drosophila germband indicate a solid-to-fluid transition that corresponds to the onset of cell rearrangement and convergent extension in wild-type embryos and are also consistent with more solid-like behavior in bnt mutant embryos. Thus, the onset of cell rearrangement in the germband can be predicted by a combination of cell shape and alignment. These findings suggest that convergent extension is associated with a transition to more fluid-like tissue behavior, which may help accommodate tissue shape changes during rapid developmental events.

developmental biology↗