Brush border microvilli enable functions that are critical for epithelial homeostasis, including solute uptake and host defense. However, mechanisms that regulate the assembly and morphology of these protrusions are poorly understood. The parallel actin bundles that support microvilli have their pointed-end rootlets anchored in a filamentous meshwork referred to as the “terminal web.” Although classic EM studies revealed complex ultrastructure, the composition and function of the terminal web remains unclear. Here we identify non-muscle myosin-2C (NM2C) as a component of the terminal web. NM2C is found in a dense, isotropic layer of puncta across the sub-apical domain, which transects the rootlets of microvillar actin bundles. Puncta are separated by ∼210 nm, the expected size of filaments formed by NM2C. In intestinal organoid cultures, the terminal web NM2C network is highly dynamic and exhibits continuous remodeling. Using pharmacological and genetic perturbations in cultured intestinal epithelial cells, we found that NM2C controls the length of growing microvilli by regulating actin turnover in a manner that requires a fully active motor domain. Our findings answer a decades old question on the function of terminal web myosin and hold broad implications for understanding apical morphogenesis in diverse epithelial systems.

刷状缘微绒毛具有对上皮稳态至关重要的功能，包括溶质摄取和宿主防御。然而，人们对调节这些突起的组装和形态的机制知之甚少。支持微绒毛的平行肌动蛋白束的尖端细根锚定在被称为“末端网”的丝状网状结构中。尽管经典的电镜研究揭示了复杂的超微结构，但末端网络的组成和功能仍不清楚。在这里，我们将非肌肉肌球蛋白-2C (NM2C) 确定为终端网络的一个组成部分。NM2C 存在于横跨亚顶端域的致密、各向同性的斑点层中，该斑点横断微绒毛肌动蛋白束的细根。点状结构的间隔约为 210 nm，这是 NM2C 形成的细丝的预期尺寸。在肠道类器官培养中，末端网络 NM2C 网络高度动态并表现出持续重塑。利用培养的肠上皮细胞中的药理学和遗传扰动，我们发现 NM2C 通过以需要完全活跃的运动域的方式调节肌动蛋白周转来控制微绒毛生长的长度。我们的研究结果回答了关于末端网状肌球蛋白功能的几十年前的问题，并对理解不同上皮系统中的顶端形态发生具有广泛的意义。