Quantitative analysis of planar cell polarity. (a) Myosin II is planar polarized in the epidermis during elongation of the Drosophila embryo. Myosin II (red) localizes to vertical interfaces between anterior and posterior cells and Par3 (green) localizes to horizontal interfaces. Anterior is to the left and ventral is down in this image and in (b). (b) All cell interfaces in the image (red channel from (a)) were manually outlined in blue in order to quantify the orientation and mean fluorescence intensity of each interface.(c) The red channel in (a) and the blue lines in (b) were used to quantify the distribution of myosin II. Cell interfaces were grouped by orientation into 15° intervals. The absolute mean fluorescence intensity was quantified for each interval (left panel, sum of blue and red bars). Background was measured as the mean fluorescence intensity of the cytoplasm (left panel, red bars). Relative edge intensities were calculated using the raw data (center panel) or background correction (right panel). Values shown are relative to the mean fluorescence of horizontal interfaces (0-15°). The fold increase in myosin II at vertical interfaces (75-90°) in this example is 1.6 without background correction and 2.6 with background correction.

Planar cell polarity. (a) Epithelial tissues display apical-basal and planar polarity. Hair structures are generated at the apical (top) surface and are absent from the basal (bottom) surface, demonstrating asymmetry along the apical-basal axis. Planar polarity is evident from the fact that the hairs are placed at the distal (right) side of each cell's apical surface and point in a distal direction. (b) Generating planar polarity through asymmetric protein localization. Schematic depicting a bird's-eye or planar view of the apical surface of the wing. The proximal (left) and distal (right) sides of each cell are defined by specific Frizzled system proteins, depicted in purple and green, respectively. (c) Generating planar polarity through protein gradients. In the Drosophila wing, the cadherin Dachsous (blue) is expressed in a decreasing gradient from proximal to distal (left to right). As a result, the cadherin Fat, which is also present in cell membranes, is predicted to be more active at the distal cell surface (yellow asterisks), where it encounters less inhibitory Dachsous protein on the adjacent cell.