AUTONOMY AND NON-AUTONOMY IN DROSOPHILA MESODERM DETERMINATION AND MORPHOGENESIS

The mesoderm in Drosophila invaginates by a series of characteristic c ell shape changes. Mosaics of wild-type cells in an environment of mut ant cells incapable of making mesodermal invaginations show that this morphogenetic behaviourdoes not require interactions between large num bers of cells but that small patches of cells can invaginate independe nt of their neighbours' behaviour. While the initiation of cell shape change is locally autonomous, the shapes the cells assume are partly d etermined by the individual cell's environment. Cytoplasmic transplant ation experiments show that areas of cells expressing mesodermal genes ectopically at any position in the egg form an invagination. We propo se that ventral furrow formation is the consequence of all prospective mesodermal cells independently following their developmental program. Gene expressionat the border of the mesoderm is induced by the apposi tion of mesodermal and non-mesodermal cells.