Abstract
We investigate the mechanisms of planar cell polarity (PCP) in the larval epidermis of Drosophila. Measurements of the amount of Dachsous across the segment find a peak located near the rear of the anterior compartment. Localisation of Dachs and orientation of ectopic denticles reveal the polarity of every cell in the segment. We discuss how well these findings evidence a zigzag gradient model of Dachsous activity. Several groups have proposed that Dachsous and Fat fix the direction of PCP via oriented microtubules that transport PCP proteins to one side of the cell. We test this proposition in the larval cells and find that most microtubules grow perpendicularly to the axis of PCP. We find no significant bias in the polarity of those microtubules aligned close to that axis. We also reexamine published data from the pupal abdomen and fail to find evidence supporting the hypothesis that microtubular orientation draws the arrow of PCP.