Solute transporting epithelial cells build arrays of microvilli on their apical surface to increase membrane scaffolding capacity and enhance function potential. In epithelial tissues such as the kidney and gut, microvilli are length-matched and assembled into tightly packed “brush borders,” which are organized by ∼50-nm thread-like links that form between the distal tips of adjacent protrusions. Composed of protocadherins CDHR2 and CDHR5, adhesion links are stabilized at the tips by a cytoplasmic tripartite module containing the scaffolds USH1C and ANKS4B and the actin-based motor MYO7B. Because several questions about the formation and function of this “intermicrovillar adhesion complex” remain open, we devised a system that allows one to study individual binary interactions between specific complex components and MYO7B. Our approach employs a chimeric myosin consisting of the MYO10 motor domain fused to the MYO7B cargo-binding tail domain. When expressed in HeLa cells, which do not normally produce adhesion complex proteins, this chimera trafficked to the tips of filopodia and was also able to transport individual complex components to these sites. Unexpectedly, the MYO10–MYO7B chimera was able to deliver CDHR2 and CDHR5 to distal tips in the absence of USH1C or ANKS4B. Cells engineered to localize high levels of CDHR2 at filopodial tips acquired interfilopodial adhesion and exhibited a striking dynamic length-matching activity that aligned distal tips over time. These findings deepen our understanding of mechanisms that promote the distal tip accumulation of intermicrovillar adhesion complex components and also offer insight on how epithelial cells minimize microvillar length variability.

中文翻译：

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异源细胞内测定研究微绒毛间黏附复合物相互作用揭示了一种新颖的突出长度匹配机制

溶质运输的上皮细胞在其顶表面上形成微绒毛阵列，以增加膜支架能力并增强功能潜能。在肾和肠等上皮组织中，微绒毛长度匹配，并组装成紧密堆积的“刷状边界”，其由在相邻突起的远端之间形成的〜50 nm线状链节组织。由原钙粘着蛋白CDHR2和CDHR5组成，通过包含支架USH1C和ANKS4B以及基于肌动蛋白的运动型MYO7B的细胞质三方组件，可以使尖端的粘附连接稳定。由于有关“微绒毛间黏附复合物”的形成和功能的几个问题仍然存在，我们设计了一种系统，可以研究特定的复杂成分与MYO7B之间的二元相互作用。我们的方法采用了一种嵌合肌球蛋白，该肌球蛋白由MYO10电机域和MYO7B货物结合尾域融合而成。当在通常不产生粘附复合蛋白的HeLa细胞中表达时，这种嵌合体转运到丝状伪足的尖端，并且还能够将单个复合物转运到这些部位。出乎意料的是，在没有USH1C或ANKS4B的情况下，MYO10–MYO7B嵌合体能够将CDHR2和CDHR5递送至远端。经过工程改造以将高水平的CDHR2定位在丝足末端的细胞获得了丝囊间的粘附，并表现出惊人的动态长度匹配活性，该活性随着时间的推移使远端末端对齐。