The role of Dachsous and Fat in regulating planar cell polarity across the embryonic epidermis. Kynan Lawlor, Stephen DiNardo. Department of Cell and Developmental Biology, Perelman School of Medicine, University of Pennsylvania, Philadelphia, PA.

   Directional cues are necessary to orient and coordinate tissue morphogenesis and patterning during development. The polarization of cells along the plane of a tissue, termed planar cell polarity, is one way in which these directional cues may be specified. Two groups of genes, the Dachsous (Ds) and Frizzled (Fz) systems, play key roles in the establishment, maintenance and propagation of planar cell polarity. While progress has been made in understanding the function of these two systems, unanswered questions remain. We have been studying the elaboration of polarity within the larval ventral epidermis to address several of these questions. Previously we showed that dachsous and frizzled contribute independently to polarity, and that they do so over spatially distinct domains. Here we examine how the atypical cadherins Dachsous and Fat regulate planar polarity across the denticle field within each segment of the epidermis. In this tissue, f-actin becomes enriched specifically on the posterior edge of aligned columns of cells. In dachsous mutants, sites of f-actin enrichment are not correctly positioned, with defects observed at a greater frequency within specific columns of each denticle field. Furthermore, over-activation of the pathway, by ectopic expression of extracellular Dachsous is able to re-orient f-actin positioning in adjacent cells. Using these assays, both in fixed tissue and in live-imaging, we will report on the role of key components of the Dachsous/Fat system in regulating planar cell polarity.