Abstract
Sensing a global directional cue to orient cell growth is crucial in tissue morphogenesis. An anterior-posterior gradient of Wnt signaling controls the helical growth of feather branches (barbs), and thus the formation of bilateral feathers. However, it remains unclear how the keratinocytes sense this gradient and orient barb growth. Here, we show that in chicken, owing to feather branching, the global Wnt gradient is subdivided into periodic barbs. Within each barb, the anterior barbule plate cells tilt before the posterior cells. The core planar cell polarity gene Prickle1 is involved, as knockdown of its expression resulted in no cell shape change and no barb tilting. Furthermore, perturbation of the Wnt gradient leads to diffusive Prickle1 expression and loss of barb orientation. Finally, the asymmetric distribution of Wnt6/Fzd10 is coordinated by the apical-basal polarity of the barbule plate keratinocytes, which is in turn regulated by the Par3/aPKC machinery. Our data elucidate a new mechanism through which the global Wnt signaling gradient is interpreted locally to construct complex spatial forms.