Fat, Fat-like, and Dachsous family cadherins are giant proteins that regulate planar cell polarity (PCP) and cell adhesion in bilaterians. Their evolutionary origin can be traced back to prebilaterian species, but their ancestral function(s) are unknown. We identified Fat-like and Dachsous cadherins in Hydra, a member of phylum Cnidaria a sister group of bilaterian. We found Hydra does not possess a true Fat homolog, but has homologs of Fat-like (HyFatl) and Dachsous (HyDs) that localize at the apical membrane of ectodermal epithelial cells and are planar polarized perpendicular to the oral–aboral axis of the animal. Using a knockdown approach we found that HyFatl is involved in local cell alignment and cell–cell adhesion, and that reduction of HyFatl leads to defects in tissue organization in the body column. Overexpression and knockdown experiments indicate that the intracellular domain (ICD) of HyFatl affects actin organization through proline-rich repeats. Thus, planar polarization of Fat-like and Dachsous cadherins has ancient, prebilaterian origins, and Fat-like cadherins have ancient roles in cell adhesion, spindle orientation, and tissue organization.

脂肪，类脂肪和Dachsous家族钙粘着蛋白是巨大蛋白，可调节Bilaterians中的平面细胞极性（PCP）和细胞粘附。它们的进化起源可以追溯到前白垩纪物种，但是它们的祖先功能是未知的。我们在Hydra中发现了脂肪样和Dachsous钙粘着蛋白，Cindaria门是bilaterian的姐妹组。我们找到了九头蛇没有真正的脂肪同源物，但是具有类似脂肪样（HyFatl）和Dachsous（HyDs）的同源物，它们位于外胚层上皮细胞的顶膜上，并且垂直于动物的口腔-口腔轴呈平面极化。使用组合式方法，我们发现HyFatl参与局部细胞排列和细胞间粘附，而HyFatl的减少会导致机体柱组织的缺陷。过表达和敲低实验表明，HyFatl的细胞内结构域（ICD）通过富含脯氨酸的重复序列影响肌动蛋白的组织。因此，Fat-like和Dachsous cadherins的平面极化具有古老的前波利多人起源，而Fat-like cadherins在细胞粘附，纺锤体定向和组织组织方面具有古老的作用。