Spatial Pattern Formation and Morphogenesis in Development: Recent Progress for Two Model Systems

The rapid growth in the number of identified molecular components that comprise signal transduction and gene control networks has focused attention on the difficult problem of understanding how networks of such components function and how they are controlled. In the context of developmental biology. the problem is to understand how the inherited genetic information in a fertilized egg is translated into a normal adult that may comprise several hundred different cell types arranged into numerous specialized tissues and organs. The complexity of the problem stems in part from one of the central facts of developmental biology, which is that the developmental fate of a cell in a multicellular system is determined not only by its genome, but also by its spatial position relative to other cells and the signals it receives from them. Intercellular communication, either through cell-cell contact or through release or presentation of signaling molecules, plays a significant role in determining what part of the genetic code is transcribed at a particular point in space and time in a multicellular system. While gene-sequencing has provided enormous detail concerning which genes are present in the genome of various organisms, much less is understood about the complex networks of regulatory interactions that control how genes are turned on or off at the appropriate time and place in a developing organism.