Biology subjects

Doubrovinski, K.

Publications and source records attributed to Doubrovinski, K..

6 recordsLinked to original sources

bioRxiv2023

A scaling law for epithelial tissue rheology

Epithelial morphogenesis is a process through which simple cellular sheets are shaped into complex tissues and organs in a developing animal. From a physics perspective, understanding any shape change requires knowing the active forces driving its dynamics, as well as the material properties, i.e. the rheology, of the material that is undergoing the deformation. Despite a long-standing effort, rheological properties of embryonic tissues have remained elusive. Here, we develop a minimal theory providing a comprehensive explanation of rheological measurements characterizing the mechanics of epithelia in the early fly embryo. Our theory explains a key experimental observation: when subjected to concentrated pulling force, the embryonic epithelium of the fruit fly Drosophila melanogaster deforms following a power law with an exponent of 1/2. All dimensional parameters of our theory are constrained by direct measurements and have allowed us to estimate the spring constant of an individual cellular edge. We show that stress relaxation (attributable to actin turnover), stretching elasticity of individual cellular edges, and the floppy topology of the cellular network are the sole physical properties governing tissue rheology on the developmentally relevant time scale of 1-10 minutes.

biophysics↗

bioRxiv2022

Tissue recoil in the early Drosophila embryo is a passive not active process

Understanding tissue morphogenesis is impossible without knowing the mechanical properties of the tissue being shaped. Although techniques for measuring tissue material properties are continually being developed, methods for determining how individual proteins contribute to mechanical properties are very limited. Here, we developed two complementary techniques for the acute inactivation of sqh (the Drosophila myosin regulatory light chain), one based on the recently introduced AID2 system, and the other based on a novel method for conditional protein aggregation. Combining these techniques with rheological measurements, we show that passive material properties of the cellularization-stage Drosophila embryo are essentially unaffected by myosin activity. The significance of this study is two-fold. We introduce a system for the nearly instantaneous inactivation of proteins in a variety of systems. Additionally, we demonstrate a method to distinguish between active and passive contributions to effective tissue elasticity. SummaryTechniques to examine the contribution of specific proteins to tissue mechanical properties are extremely limited. Here, Goldner et al. develop two complementary techniques for rapid protein depletion combined with mechanical measurements, and show that myosin activity is dispensable for tissue elasticity.

cell biology↗

bioRxiv2022

Cantilever-based in vivo measurements in the early Drosophila embryo reveal adiabatic elastic response on developmentally relevant time scales

In order to understand morphogenesis, it is necessary to know the material properties or forces shaping the living tissue. In spite of this need, very few in vivo measurements are currently available. Here, using the early Drosophila embryo as a model, we describe a novel cantilever-based technique which allows for the simultaneous quantification of applied force and tissue displacement in a living embryo. By analyzing data from a series of experiments in which embryonic epithelium is subjected to developmentally relevant perturbations, we conclude that the response to applied force is adiabatic and is dominated by elastic forces and geometric constraints, or system size effects. Crucially, computational modeling of the experimental data indicated that the apical surface of the epithelium must be softer than the basal surface, a result which we confirmed experimentally. Further, we used the combination of experimental data and comprehensive computational model to estimate the elastic modulus of the apical surface and set a lower bound on the elastic modulus of the basal surface. More generally, our investigations revealed important general features that we believe should be more widely addressed when quantitatively modeling tissue mechanics in any system. Specifically, different compartments of the same cell can have very different mechanical properties; when they do, they can contribute differently to different mechanical stimuli and cannot be merely averaged together. Additionally, tissue geometry can play a substantial role in mechanical response, and cannot be neglected.

biophysics↗

bioRxiv2022

Feedback in the β-catenin destruction complex imparts bistability and cellular memory

Wnt ligands are considered classical morphogens, for which the strength of the cellular response is proportional to the concentration of the ligand. Herein, we show an emergent property of bistability arising from feedback among the Wnt destruction complex proteins that target the key transcriptional co-activator {beta}-catenin for degradation. Using biochemical reconstitution, we identified positive feedback between the scaffold protein Axin and the kinase GSK3. Theoretical modeling of this feedback between Axin and GSK3 predicted that the activity of the destruction complex exhibits bistable behavior. We experimentally confirmed these predictions by demonstrating that cellular cytoplasmic {beta}-catenin concentrations exhibit an "all-or-none" response with sustained memory (hysteresis) of the signaling input. This bistable behavior was transformed into a graded response and memory was lost through inhibition of GSK3. These findings provide a mechanism for establishing decisive, switch-like cellular response and memory upon Wnt pathway stimulation. One Sentence SummaryPositive feedback within the {beta}-catenin destruction complex gives rise to bistability and memory in response to Wnt stimulation, imparting signal transduction accuracy and insulation.

cell biology↗

bioRxiv2021

What basal membranes can tell us about viscous forces in Drosophila ventral furrow formation

Ventral furrow (VF) formation in Drosophila melanogaster is an important model of epithelial folding. Previous models of VF formation require cell volume conservation to convert apically localized constriction forces into lateral cell elongation and tissue folding. Here, we investigated embryonic morphogenesis in anillin knockdown (scra RNAi) embryos, where basal cell membranes fail to form and therefore cells can lose cytoplasmic volume through their basal side. Surprisingly, the mesoderm elongation and subsequent folding that comprise VF formation occurred essentially normally. We hypothesized that the effects of viscous shear may be sufficient to drive membrane elongation, providing effective volume conservation, and thus driving tissue folding. Since this hypothesis may not be possible to test experimentally, we turned to a computational approach. A minimal model of VF formation accounting for fluid dynamics indicated that shear forces can indeed explain our experimental observation. However, this conclusion depended on specific values of the model parameters. To test whether viscous shear is a dominant force for morphogenesis in vivo, we developed a highly realistic computational model incorporating both accurate cell and tissue geometry and experimentally measured material parameters. Results from this model demonstrate that viscous shear generates sufficient force to drive cell elongation and tissue folding in vivo.

developmental biology↗

bioRxiv2017

Cortical elasticity determines the geometry of prospective mesoderm constriction in Drosophila melanogaster

1An animal embryo begins its life as a ball of epithelial cells. In the course of development, invariably, this cellular ball will undergo a process of gastrulation to form a multilayered structure with the different germ layers designated to form organs with different shapes and functions. In the fruit fly Drosophia melanogaster, gastrulation begins with the constriction of mesodermal cells that make up a rectangular domain in the ventral part of the embryo. A remarkable aspect of this morphogenetic event is its anisotropy - the mesoderm constricts much more along one axis than along the other. In this paper we propose an explanation of this observed anisotropy. Specifically, we show that tissue contraction must be anisotropic, provided that the tissue is elastic and that the contractile domain is elongated (e.g. rectangular as opposed to square). This conclusion is generic in the sense that it does not depend on the specific values of model parameters. Since our recent study demonstrated that embryonic tissue is elastic on a developmentally relevant time-scale, it appears likely that the anisotropy of mesoderm contraction is an elastic effect. Our model makes a number of specific predictions that appear in close agreement with the available data.

developmental biology↗