Pattern formation: from theoretical models to molecular biology.

The field of pattern formation in biological systems is viewed, taking into consideration the major theoretical and experimental information. The basic idea which has emerged from the different theoretical models is that short range cell-to-cell interactions could manifest the hierarchy of patterns. These interactions could actually be governed by simple signals in the cell surface. In the second part the experimental evidence is examined, namely, the genes that control pattern formation in Drosophila. The products of these genes display a variety of characteristics ranging from being molecules at the cell surface to regulatory proteins in the nucleus. The hypothesis is presented that molecules in the cytoplasm could connect the two parts. According to this, signals at the cell surface and subsequent cell-to-cell interactions should be of primary importance in the mechanisms that underlie morphogenesis.