Cellular morphogenesis is an essential part of animal development and growth. During this process, cellscoordinately change shape, migrate, and may fuse. These processes are executed by molecules called"effectors". Such effectors have been identified in several model systems and include the cytoskeleton anddeterminants of cell polarity. The sex-, tissue-, position-, and time-specificity of morphogenesis is determinedby "regulators", such as transcription factors. How transcriptional regulators are linked to the effectors in agene network (GN) for morphogenesis is not well understood in nearly any system, but such knowledge isrequired to predict how perturbations could lead to morphogenetic changes during development, cancer, andthe evolution of form. Elucidating this GN would also impact our understanding of wound healing andregeneration. Our long-term goal is to completely delineate the GN architecture governing the morphogenesisof a novel, simple and sexually dimorphic model structure, the tail tip of Caenorhabditis elegans. The tail tip iscomposed of four cells which-in males only-radically alter their shape and position at the end of larvaldevelopment. Previous studies identified a "master regulator" for tail tip morphogenesis (TTM), thetranscription factor DMD-3 (homologous to DMRT1 in humans, which specifies male fates). Without DMD-3,TTM completely fails. Also, DMD-3 is sufficient to cause TTM when ectopically expressed in hermaphrodites.Here, we will test how DMD-3 is linked to the effectors of TTM. Specific Aim 1 will test this hypothesis by aseries of pairwise molecular epistasis experiments with DMD-3 and a set of key effectors of TTM which theFitch lab previously identified in a postembryonic-RNAi screen. In these experiments, a gene X (e.g. DMD-3)will be knocked down and the effect on the transcription, translation or subcellular localization of a geneproduct Y will be analyzed. Network analysis will be used to identify auto-regulatory, feedback, feed-forward, orother system controls important for the GN. Specific Aim 2 addresses the question of which other genes aredownstream of DMD-3 and what contributes to the sufficiency of DMD-3 for TTM. Tail-tip-specifictranscriptome analyses will be performed on samples from wild-type males and hermaphrodites, malesdeficient for DMD-3, and hermaphrodites misexpressing DMD-3. The expected outcome is a framework for theGN architecture downstream of DMD-3 and an understanding of how it governs the localization or expressionof key effectors of cell shape change. This GN will lay the requisite foundation for future studies on themolecular mechanisms underlying these interactions and how they affect cell-biological modules. These resultsare expected to have a positive impact on medicine, as they could identify key conserved genes that controlmorphogenesis, thus providing new targets for drugs to mitigate the effects of morphogenetic defects orcancer, or to aid wound healing.