Models of Biological Pattern Formation and Their Application to the Early Development of Drosophila
The complexity of a higher organism indicates that very many pattern forming reactions are at work that are coupled to each other in such a way that the final pattern can be generated with a high degree of reproducibility. Investigations of early development in Drosophila have provided us with much information about the molecular machinery on which development is based. About ten years ago, I proposed a model for pattern formation in early insect embryogenesis (Meinhardt, 1977). This model was based on a single morphogen gradient with a high point at the posterior pole of the egg. The gradient was assumed to be generated by short range auto catalysis and long range inhibition (Gierer and Meinhardt, 1972). This model was able to account for most of the experimental observations available at that time. More recently, this model of positional information has been complemented by a model for the hierarchical activation of gap-, pair rule and segment polarity genes (Meinhardt, 1985, 1986). In the meantime many additional genetic and molecular data have become available for Drosophila. Much of this new data supports the basic stipulations of these models, while some of it suggests modifications of these models. In this paper I will mention very briefly the basic ingredients of the models with reference to the Drosophila system and show of how these elements can be linked to obtain a reproducible pattern formation. This paper will be partially based on arguments previously put forward (Meinhardt, 1985,1986) and more recently updated (Meinhardt, 1988).
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