Formation of embryonic axes and organizing regions

Hans Meinhardt (Max-Planck-Institut fuer Entwicklungsbiologie,
              Tuebingen, Germany)

The formation of embryonic axes requires the formation of organizing
regions, i.e. of local concentration maxima of morphogenetic substances.
Corresponding models will be discussed. By ON-Line computer simulations
it will be shown that the models account for classical observations such
as regeneration. Recent molecular-genetic observations reported in the
literature have shown that pattern formation in more primitive (hydra)
and higher animals (vertebrates) share common elements that are
compatible with the theoretical predictions. Having a model for
generation of a co-ordinate system enables a modelling of the generation
of the fine structure. For instance, the generation of somites, the main
segmented structure of a vertebrate,  can be explained by a sequential
conversion of a periodic pattern in time into a periodic pattern in
space. The same type of reactions as required for insect segmentation
can also be used as an oscilator. Models for the initiation of
substructures in animals (legs and wings) and in plants (leaves) also
suggest a common base. Thus, models can provide a substantial help for
the understanding of the complex network of interactions on which
development is based.