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Résumé |
The development of multicellular organisms rests on highly intricate
genetic and molecular networks, whose behavior resists intuitive
interpretation and systematic analysis. The theory of dynamical systems
suggests that the essential features of this behavior can be
characterized geometrically, with much of the underlying molecular
architecture being abstracted away. Vulval development in the nematode C.
elegans is a classic example of the specification of different cell
identities by two molecular signals. A minimal geometric model explains
the effect of known mutations affecting these signals and predicts
strong, counter-intuitive interactions when mutations are combined. In
addition, it can be used to discriminate intrinsic and
extrinsic sources of variability in experiments where cell fates differ
among genetically identical individuals. This geometric approach, which
could readily be transposed to other systems, allows
the structure and evolution of developmental pathways to be approached on
the level of the phenotype (of observable traits), complementary to a
mechanistic description on the molecular level.
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