Wavelike isomorphic prepatterns in development.

The patterns generated by these mechanisms are usually wavelike spatial patterns in the distribution of the chemical components and/or physical properties of the organism or tissue being considered. In this paper the range of patterns generated by one of these mechanisms, namely the reaction-diffusion (RD) system (Turing, 1952), is reviewed and its potential to function as a source of isomorphic prepatterns for the regulation of development in a wide range of organisms is illustrated. Examples have been chosen to show the capacity of an RD system to generate a single stationary spatial prepattern, as well as a travelling wavelike spatial prepattern. However, the full potential of an RD system to regulate development stems from its capacity to spontaneously generate a temporal sequence of isomorphic stationary wavelike spatial prepatterns, rather than just a single isomorphic stationary spatial prepattern. To demonstrate this point the examples presented include the morphogenesis of the skin and some of its appendages, as well as the early decisions in the embryogenesis of Drosophila leading to segmentation. The mini-review begins by comparing the concepts of positional information and a temporal sequence of isomorphic prepatterns, which represent two quite different approaches to understanding the spatial and temporal regulation of cellular differentiation.