Eggshell shape differs substantially among different species of drosophilids, with particularly obvious variation in the number of dorsal appendages. In Drosophila melanogaster for example, two patches of follicle cells are specified to an appendage fate, resulting in two dorsal appendages. In contrast, the follicular epithelium of Scaptodrosophila lebanonenesis (or S. pattersoni) contains only one patch of appendage-fated cells, but this patch gives rise to 4-8 separate dorsal appendages. Previous work has shown that these appendages are formed by the elongation of an alternating set of cell-cell edges within the linear floor cell domain. In other words, there is an alternating left/right pattern, so if a given floor cell lengthens on its left edge, its neighboring floor cells lengthen on their right edges. This study reveals a major molecular mechanism underlying this alternating cell polarity. A series of candidate approaches led to the identification of several molecules that localize specifically to the elongating subset of floor-floor edges; these molecules include Bazooka/Par-3, atypical protein kinase C (aPKC), F-actin, and phosphatidylinositol-4-phosphate (PI4P). In vitro treatment of Scaptodrosophila egg chambers with a panel of phosphatidylinositol kinase or phosphatase inhibitors revealed that PIK93 potently abolishes alternating localization of both PI4P and F-actin and also abolishes dorsal appendage formation. Based on the known selectivity of PIK93, this strongly suggests a role for a type-III PI4 Kinase, namely PI4KIIIbeta/Fwd or PI4KIIIalpha, in this process. Additionally, in vitro treatment of Scaptodrosophila egg chambers with Latrunculin abolishes the alternating localization of both F-actin and PI4P. The apparent requirement of F-actin and PI4P for each other's localization suggests that a positive feedback loop involving these components is important for selecting the subset of floor-floor edges that will elongate. Current work is focused on developing genetic tools in Scaptodrosophila to further examine this unexpected example of planar polarity.