Myosin 18Aα is a myosin 2‐like protein containing unique N‐ and C‐terminal protein interaction domains that co‐assembles with myosin 2. One protein known to bind to myosin 18Aα is β‐Pix, a guanine nucleotide exchange factor (GEF) for Rac1 and Cdc42 that has been shown to promote dendritic spine maturation by activating the assembly of actin and myosin filaments in spines. Here, we show that myosin 18A⍺ concentrates in the spines of cerebellar Purkinje neurons via co‐assembly with myosin 2 and through an actin binding site in its N‐terminal extension. miRNA‐mediated knockdown of myosin 18A⍺ results in a significant defect in spine maturation that is rescued by an RNAi‐immune version of myosin 18A⍺. Importantly, β‐Pix co‐localizes with myosin 18A⍺ in spines, and its spine localization is lost upon myosin 18A⍺ knockdown or when its myosin 18A⍺ binding site is deleted. Finally, we show that the spines of myosin 18A⍺ knockdown Purkinje neurons contain significantly less F‐actin and myosin 2. Together, these data argue that mixed filaments of myosin 2 and myosin 18A⍺ form a complex with β‐Pix in Purkinje neuron spines that promotes spine maturation by enhancing the assembly of actin and myosin filaments downstream of β‐Pix's GEF activity.

中文翻译：

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肌球蛋白 18Aα 将鸟嘌呤核苷酸交换因子 β-Pix 靶向小脑浦肯野神经元的树突棘并促进脊柱成熟

肌球蛋白 18Aα 是一种肌球蛋白 2 样蛋白，含有独特的 N 端和 C 端蛋白相互作用结构域，与肌球蛋白 2 共同组装。已知与肌球蛋白 18Aα 结合的一种蛋白是 β-Pix，它是一种鸟嘌呤核苷酸交换因子 (GEF)，用于Rac1 和 Cdc42 已被证明通过激活棘中肌动蛋白和肌球蛋白丝的组装来促进树突棘成熟。在这里，我们展示了肌球蛋白 18A⍺ 通过与肌球蛋白 2 的共组装和通过其 N 端延伸部分的肌动蛋白结合位点集中在小脑浦肯野神经元的刺中。miRNA 介导的肌球蛋白 18A⍺ 敲低导致脊柱成熟的显着缺陷，而肌球蛋白 18A⍺ 的 RNAi 免疫版本挽救了这一缺陷。重要的是，β-Pix 与肌球蛋白 18A⍺ 共定位于刺中，并且在肌球蛋白 18A⍺ 敲低或当其肌球蛋白 18A⍺ 结合位点被删除时，其脊柱定位丢失。最后，我们表明肌球蛋白 18A⍺ 敲低浦肯野神经元的刺包含显着较少的 F-肌动蛋白和肌球蛋白 2。这些数据共同表明，肌球蛋白 2 和肌球蛋白 18A⍺ 的混合细丝与浦肯野神经元刺中的 β-Pix 形成复合物通过增强 β-Pix 的 GEF 活性下游的肌动蛋白和肌球蛋白丝的组装来促进脊柱成熟。