Quantitative Analysis of Developing Tissues

Both the number of cells and their diversity increase dra- matically during the progression from a fertilized egg to an adult organism. The increase in the number of cells requires control of cell proliferation and death, while the increase in cell diversity requires control of cell differentiation. The elaborate architectures of living tissues depend on tight spatiotemporal regulation of these processes. From molecular studies of de- velopment,6 tissue- and organogenesis emerge as control sys- tems with levels of regulation that range from a few nucleotides in the sequence of a gene to hundreds of cells in a three- dimensional tissue. At this level of complexity, quantitative approaches are critical for interpreting the rapidly accumulat- ing data and for design of new experiments. Today, quantita- tive analysis of embryonic development is becoming feasible due to the advances in developmental genetics that enable direct tests of quantitative models. As the confidence in these models increases, they can be used to guide the design of man-made tissues.