The goal of this proposal is to apply a multi-scale analysis of the mechanics of convergent extension, identifying biomechanical mechanisms that regulate cell shape and drive mediolateral cell behaviors, establish passive tissue properties such as stiffness as well as active processes that generate forces of extension, and how passive mechanics and active force generating processes are coordinated within the frog embryo. We will use an established toolkit consisting of three elements: 1) the aquatic frog Xenopus laevis for direct modulation of protein function and gene expression;2) high resolution confocal microscopy to visualize cell behaviors, cytoskeletal dynamics, and tissue architecture;and 3) biophysical methods for applying strains, measuring tissue stiffness and force production. Studies outlined in this proposal will answer: 1) How do embryonic cells use actomyosin to physically generate force, change shape, and direct movement during convergent extension? To understand how movements are physically controlled we will take a """"""""bottom-up"""""""" analysis of F-actin in the cortex of mesodermal cells as these cells initiate cell shape changes and adopt mediolateral intercalation behaviors. 2) What are the cell and molecular mechanisms underlying bulk tissue stiffness and tissue elongation forces during convergent extension? Our characterization of stiffness of embryonic tissues during gastrulation and axis extension has revealed both broad regulation of stiffness as the embryo ages as well as precise control over stiffness from one germ layer to the next. We propose to test the role of the physical state of the F-actin cytoskeleton in regulating of tissue stiffness and force-production as dorsal tissues converge and extend. 3) What are the physical mechanisms coordinating cell intercalation and stiffness during convergent extension? We hypothesize that gastrulation relies on a proper balance of forces from the elongating dorsal axis and resistance from surrounding tissues. To test this we propose to construct finite element based models to investigate these interactions and test qualitative predictions of our working models. These models will serve to both demonstrate the plausibility of simple mechanical feed-back mechanisms as well as predict the outcome of experimental manipulations. This work will complement ongoing efforts to identify the molecular regulators of morphogenesis by providing underlying biophysical principles for new hypotheses and bioengineering tools to test them. The significance of our work extends beyond defining the mechanical conditions and forces that convert mediolateral cell intercalation into large-scale convergent extension to allow a more complete understanding of the contribution of tissue mechanics to birth defects, to understand the role of tissue mechanics in oncogenesis, and to provide fundamental physical principles for future tissue engineers.
The goal of this proposal is to understand the physical mechanisms by which actomyosin dynamics drive cell shape changes, generate traction forces, establish passive tissue properties such as stiffness, active force production by convergence and extension, and how passive mechanics and active forces shape a vertebrate embryo. The significance of our work extends beyond defining the mechanical conditions and their role in early development to provide fundamental physical principles for future tissue engineers, allow a more complete understanding of the contribution of tissue mechanics to birth defects, and to understand the role of tissue mechanics in oncogenesis.
|Shook, David R; Kasprowicz, Eric M; Davidson, Lance A et al. (2018) Large, long range tensile forces drive convergence during Xenopus blastopore closure and body axis elongation. Elife 7:|
|Shawky, Joseph H; Balakrishnan, Uma L; Stuckenholz, Carsten et al. (2018) Multiscale analysis of architecture, cell size and the cell cortex reveals cortical F-actin density and composition are major contributors to mechanical properties during convergent extension. Development 145:|
|López-Escobar, Beatriz; Caro-Vega, José Manuel; Vijayraghavan, Deepthi S et al. (2018) The non-canonical Wnt-PCP pathway shapes the mouse caudal neural plate. Development 145:|
|Davidson, Lance A (2017) Mechanical design in embryos: mechanical signalling, robustness and developmental defects. Philos Trans R Soc Lond B Biol Sci 372:|
|Jackson, Timothy R; Kim, Hye Young; Balakrishnan, Uma L et al. (2017) Spatiotemporally Controlled Mechanical Cues Drive Progenitor Mesenchymal-to-Epithelial Transition Enabling Proper Heart Formation and Function. Curr Biol 27:1326-1335|
|Stooke-Vaughan, Georgina A; Davidson, Lance A; Woolner, Sarah (2017) Xenopus as a model for studies in mechanical stress and cell division. Genesis 55:|
|Chanet, Soline; Miller, Callie J; Vaishnav, Eeshit Dhaval et al. (2017) Actomyosin meshwork mechanosensing enables tissue shape to orient cell force. Nat Commun 8:15014|
|Kim, Hye Young; Jackson, Timothy R; Davidson, Lance A (2017) On the role of mechanics in driving mesenchymal-to-epithelial transitions. Semin Cell Dev Biol 67:113-122|
|Holt, Brian D; Shawky, Joseph H; Dahl, Kris Noel et al. (2016) Developing Xenopus embryos recover by compacting and expelling single wall carbon nanotubes. J Appl Toxicol 36:579-85|
|Holt, Brian D; Shawky, Joseph H; Dahl, Kris Noel et al. (2016) Distribution of single wall carbon nanotubes in the Xenopus laevis embryo after microinjection. J Appl Toxicol 36:568-78|
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