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Résumé |
A key morphogenetic process during animal development is convergent extension
(CE). From a physics perspective, tissues undergoing CE can be described as
oriented active materials. However, active matter physics predicts that such
materials are inherently unstable, raising the question of how CE can be robust
during development. We show that the presence of a signaling gradient can
stabilize CE, but only if it acts to actively extend the tissue along the gradient
direction. Conversely, tissues are unstable if they tend to actively contract
along the gradient direction. Intriguingly, developing tissues seem to exclusively
use the gradient-extensile and not the unstable gradient-contractile coupling.
This suggests that the active matter instability acts as an evolutionary selection
criterion. In other words, our work points to a new principle of multi-cellular
development that is directly rooted in active matter physics.
We further discuss oriented flows in the context of body axis formation. Most
animals display one or more body axes (e.g. head-to-tail, dorsal-ventral, left-
right). In our work, we demonstrate that the formation of the primary, head-to-
tail, axis can be promoted by large-scale tissue flows. Specifically, we study
aggregates of mouse embryonic stem cells, called gastruloids, which are initially
spherically symmetric, but later form an axis defined by the polarized expression
of the transcription factor T/Brachyury. We show that advection of cells with
tissue flows contribute substantially to the overall polarization, and that these
flows are driven by effective interface and surface tension differences. |
