We investigate planar cell polarity (PCP) in the Drosophila larval epidermis. The intricate pattern of denticles depends on only one system of PCP, the Dachsous/Fat system. Dachsous molecules in one cell bind to Fat molecules in a neighbour cell to make intercellular bridges. The disposition and orientation of these Dachsous–Fat bridges allows each cell to compare two neighbours and point its denticles towards the neighbour with the most Dachsous. Measurements of the amount of Dachsous reveal a peak at the back of the anterior compartment of each segment. Localization of Dachs and orientation of ectopic denticles help reveal the polarity of every cell. We discuss whether these findings support our 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 meaningful bias in the polarity of microtubules aligned close to that axis. We also reexamine published data from the pupal abdomen and find no evidence supporting the hypothesis that microtubular orientation draws the arrow of PCP.

我们研究了果蝇中的平面细胞极性 (PCP)幼虫表皮。错综复杂的小齿图案仅依赖于一种 PCP 系统，即 Dachsous/Fat 系统。一个细胞中的 Dachsous 分子与相邻细胞中的脂肪分子结合，形成细胞间桥梁。这些 Dachsous-Fat 桥的布置和方向允许每个单元格比较两个邻居并将其小齿指向具有最多 Dachsous 的邻居。对 Dachsous 量的测量揭示了每个节段前隔室后部的峰值。Dachs 的定位和异位小齿的方向有助于揭示每个细胞的极性。我们讨论这些发现是否支持我们的 Dachsous 活动梯度模型。几个小组提出 Dachsous 和 Fat 通过定向微管将 PCP 蛋白运输到细胞的一侧来固定 PCP 的方向。我们在幼虫细胞中测试了这个命题，发现大多数微管垂直于 PCP 的轴生长。我们发现靠近该轴排列的微管的极性没有有意义的偏差。我们还重新检查了来自蛹腹部的已发表数据，没有发现任何证据支持微管方向绘制 PCP 箭头的假设。