Generating complex patterns with limited signals: Three mechanisms by which <italic>wingless</italic> and <italic>decapentaplegic</italic> establish spatial complexity in the <italic>Drosophila</italic> embryo.

Patterning during embryogenesis occurs at several levels, including the establishment and elaboration of gene expression patterns, the specification and positioning of specialized cell types, and the organization of the overall body plan. wg and dpp have emerged as principle players in each of these levels of patterning in every region of the embryo, raising the question of how two signaling molecules can specifically affect so many diverse events. This thesis describes results of experiments in which the patterns of these genes were altered, revealing three mechanisms by which the patterns of wg and dpp organize spatial complexity within the Drosophila embryo. The expression patterns of wg and dpp are dynamic, and transition from early, relatively broad patterns, into later, more restricted patterns. It is shown here that each of these unique patterns of wg and dpp provides unique positional information, and that they are, in combination, sufficient to uniquely define the region of heart specification. Thus one way that wg and dpp determine complex spatial effects is by virtue of their own complex temporal-spatial expression patterns. wg and dpp determine complex patterns of cell specification not only in the mesoderm, but throughout the embryo. The expression of a different region-specific gene in each region would provide the type of spatial information required to ensure that each region can respond in a different way to wg and dpp. Evidence is provided that tinman, a mesoderm-specific homeodomain gene, provides such mesoderm-specific spatial information, and suggests that wg and dpp add further complexity by interacting with region-specific genes. Finally, experiments described here show that wg and dpp play a role in generating left-right asymmetry in the Drosophila hindgut. Importantly, there is first a bend and then a twist in the hindgut tube, resulting in the re-positioning of the anterior-posterior and dorsal-ventral axes of the hindgut along the left-right axis of the embryo. Thus a morphogenetic event re-positions the wg- and dpp-dependent asymmetries of the hindgut axes along the left-right axis of the embryo, and provides a third mechanism by which the same signaling molecules contribute to the spatial complexity of the Drosophila embryo.PhDBiological SciencesGeneticsUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/132301/2/9963738.pd