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Séminaires MSC
"Matière et Systèmes Complexes"

                      

Lundi 15 février 2010 à 11h30
Bâtiment Condorcet, 4ème étage, salle 454 A.


Rachele Allena
(MSSMat Laboratory, Ecole Centrale Paris)


Concurrent simulation of morphogenetic movements in Drosophila embryo


Gastrulation is one of the most complex phase during Drosophila embryo development. It involves a sequence of morphogenetic movements responsible for important shape changes.
The elementary cell deformations triggering the embryo evolution are controlled by the sonamed "patterning genes". The influence of the patterning genes on the mechanical constraints has been observed for a long time, however only lately the inverse process has been detected. Actually, recent works [1] have shown that a local pressure at the anterior pole of the embryo may induce the expression of the twist, a gene normally expressed only at the ventral region. Therefore, mechanotransduction takes place by which a mechanical stimulus is transformed into a chemical activity.
For the present work, three successive morphogenetic movements have been studied: ventral furrow invagination, cephalic furrow formation and germ band extension. An apico-basal elongation and an apical constriction characterize the first two events, triggered by the recruitment of the actin-myosin protein at the apical end of the cells. While the third one is accompanied by a convergent-extension movement coupled with cell rearrangement. A 3D finite elements model of the embryo is described [2]. Large strains of the mesoderm are considered using a deformation gradient decomposition method where the total deformation of a cell is decomposed into a non-stress-generating deformation (active deformation), relative to the reference configuration, and a stressgenerating elastic deformation (passive deformation), due to the deformation incompatibility between adjacent cells. In reality, the active deformations are activated by chemical signals internal to the cell. Then, we introduce a morphogen concentration which is coupled with the evolution of the active deformation intensity by a simple linear relationship. Additionally, the required yolk pressure and the unilateral contact condition with the surrounding stiff vitelline membrane are here taken into account. Both individual and concurrent simulations of the biological events are presented. Results are very similar to experimental observations and allow to confirm important hypotheses pointed out by the biologists. From a quantitative point of view, we have been able to estimate the induced pressures whose amplitude is in the order of the ones applied to cells in culture and liable to many cellular processes.

[1] E. Farge, Mechanical Induction of Twist in the Drosophila Fore-Gut/Stomodeal Primordium , Current Biology, 13 : 1365-1377, 2003.
[2] R. Allena, A.-S. Mouronval and D. Aubry, Simulation of multiple morphogenetic movements in the Drosophila embryo by a single 3D finite element model, JMBBM,
doi:10.1016/j.jmbbm.2010.01.001, 2010.