动物的三个身体轴是在发育过程中依次形成的——先是前-后轴和背-腹轴，然后是左-右非对称性，但后者是怎样源自前者的却不清楚。现在，Yingzi Yang及其同事发现，属于“planar cell polarity”家族的两个小鼠基因(Vangl1 和 Vangl2) 是纤毛在身体后部沉积所必需的，后者又决定穿过后部脊索的左向“节流动”。

这项工作表明，平面细胞极性是一个在演化过程中保留下来的机制，它传输预先确定的前-后位置信息，并将其转换成胚胎中第一个打破侧向对称的事件。

原文出处：

Nature doi:10.1038/nature09129

Planar cell polarity breaks bilateral symmetry by controlling ciliary positioning
Hai Song Jianxin Hu Wen Chen Gene Elliott Philipp Andre Bo Gao Yingzi Yang

Defining the three body axes is a central event of vertebrate morphogenesis. Establishment of left–right (L–R) asymmetry in development follows the determination of dorsal–ventral and anterior–posterior (A–P) body axes1, 2, although the molecular mechanism underlying precise L–R symmetry breaking in reference to the other two axes is still poorly understood. Here, by removing both Vangl1 and Vangl2, the two mouse homologues of a Drosophila core planar cell polarity (PCP) gene Van?Gogh (Vang), we reveal a previously unrecognized function of PCP in the initial breaking of lateral symmetry. The leftward nodal flow across the posterior notochord (PNC) has been identified as the earliest event in the de novo formation of L–R asymmetry3, 4. We show that PCP is essential in interpreting the A–P patterning information and linking it to L–R asymmetry. In the absence of Vangl1 and Vangl2, cilia are positioned randomly around the centre of the PNC cells and nodal flow is turbulent, which results in disrupted L–R asymmetry. PCP in mouse, unlike what has been implicated in other vertebrate species, is not required for ciliogenesis, cilium motility, Sonic hedgehog (Shh) signalling or apical docking of basal bodies in ciliated tracheal epithelial cells. Our data suggest that PCP acts earlier than the unidirectional nodal flow during bilateral symmetry breaking in vertebrates and provide insight into the functional mechanism of PCP in organizing the vertebrate tissues in development.