From Molecular Patterns to Morphogenesis--The Lessons from Studies on the Fruit Fly Drosophila (Nobel Lecture)

摘要

During development, cells in an embryo face two major tasks. First, they must be programmed to form specific parts of the body, and second, they must realize those fates by altering their shape, position, and patterns of gene expression. Both the determination of cell fate and the corresponding alterations in form occur progressively during development. The organism that results from this process contains a wide variety of different cell types and functions, arranged in a complex spatial pattern. Inthe fruit fly Droxopliila this final pattern is achieved about 20 hours after fertilization, when the embryo has formed a larva of 40000 cells. The most obvious external feature of this larva is a segmentally repeated pattern of hairs and denticles secreted by the underlying epidermis. Beneath these hypodermal cells is a complex array of muscles also arranged in a segmentally repeated fashion. Internal to this somatic musculature are other meso-dermal ddrivatives. as well as equally complex structuresand organs of enclodermal origin. By following the development of individual cells, it has been possible to trace the precursors for each structure in the differentiated larva back to the earliest cellular stages in the embryo. In Dnisophila this stage (the blastoderm) consists of an oblong embryo about half a millimeter in length, with about 100 cells along the future anterior posterior axis and 40 cells along the dorsal ventral axis. The epidermis is formed by ceils on the lateral side of the embryo,the muscles and other mesodermal derivatives are formed from a stripe of cells on the ventral side of the blastoderm, and the endodermal cells arise from two groups of precursors at the anterior and posterior ends of the embryo.