The ventral epidermis in the Drosophila embryo is a prime model system to uncover rules by which pattern organizers work. Epidermal pattern is etched in the cuticle laid down by epithelial cells, and across each segment the pattern appears either smooth or decorated with denticles. Denticles are specializations of a process fundamental to all epithelial cells: actin-based apical protrusions that underlie brush border microvilli, sensory bristles and stereocilia. Unique to denticles, however, each actin protrusion is intricately shaped, and this shape is choreographed reproducibly for all denticles along every line of cells of the ventral denticle field. How denticle shaping and patterning is accomplished is unknown. While our earlier focus had been largely on Hedgehog and Wingless signaling and their impact on coarse-grained pattern, our more recent work has turned to fine-grained denticle pattern which provides a high-resolution readout for the cell biology of developmental signaling. We found that Hh and Wg subdivide segments into smaller territories. By studying these territories, each of which emit key signals, we have uncovered novel interactions between the Notch and EGF- Receptor pathways (Aim 1), and found evidence that these pathways control shaping of the actin protrusions (Aim 2). In addition, the positioning of the actin protrusions in cells reflects planar cell polarity within the denticle field, and our preliminary evidence points to novel use of Myosin II for this purpose (Aim 3). Our studies may reveal novel cellular processes that link developmental signaling to morphogenesis.
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