Morphogenesis, plasticity and irreversibility.

The dynamical systems theory of morphogenesis is surveyed, in which positional information is generated through intracellular reaction dynamics and cell-cell interaction. Cells differentiate because of these dynamics. In addition, these differentiated cells form an ordered spatial pattern, which further stabilizes the cellular states, leading to robust morphogenesis and irreversibility in the differentiation. Induction, community effect, gastrulation and activin-controlled artificial tissue-genesis are discussed from the perspective of this theory and the relevance of dynamics of cellular plasticity is stressed.