Dishevelled is required in basal undifferentiated cells for organizing long-range ommatidial polarity signaling. J. Lim 1, K.-W. Choi 1,2,3. 1) Department of Molecular and Cellular Biology; 2) Program in Developmental Biology; 3) Department of Ophthalmology, Baylor College of Medicine, Houston, TX 77030.
The adult eye of Drosophila is comprised of approximately 800 ommatidia, each of which harbors eight photoreceptor cells arranged in an asymmetric trapezoidal pattern. Ommatidia in the dorsal and ventral domains of the eye show mirror-symmetric pattern of planar polarity. It has been shown that Frizzled (Fz) signaling in R3/4 cells is a key determinant for the polarity of each ommatidium. The Fz activation by a unknown polarity signal/ligand leads to the activation of Dishevelled (Dsh). Interestingly, Dsh functions in both autonomous and non-autonomous manners for determining the dorsoventral (DV) planar polarity. This raises the possibility that Dsh is important for not only reading out but also generating a polarity signal. To identify cell types responsible for long-range polarity signaling, we performed loss- and ectopic gain-of-function studies in the developing eye disc. An eye disc is partitioned into apical photoreceptor layer and basal undifferentiated cell layer. Here we show that Dsh has distinct roles in each cell layer in determining DV polarity. Dsh in the apical photoreceptor clusters is required for reading out a polarity signal in autonomous manner. In contrast, Dsh in basal undifferentiated cells are required for organizing long-range DV polarity signal. Loss of Dsh or ectopic expression of Dsh in the basal cells caused non-autonomous long-range DV polarity reversals in the neighboring wild-type ommatidia. Furthermore, similar non-autonomous long-range phenotypes were resulted from loss of Armadillo (Arm) or ectopic expression of Arm. Our data suggest that a canonical Wg signaling in the basal cells is essential for generating a DV polarity signal for the apical photoreceptor clusters.