Department of Neuroscience, Yale University School of Medicine, New Haven, CT 06510.
Department of Cell Biology, Yale University School of Medicine, New Haven, CT 06510.
Proc Natl Acad Sci U S A. 2022 Oct 18;119(42):e2203750119. doi: 10.1073/pnas.2203750119. Epub 2022 Oct 10.
The spine apparatus is a specialized compartment of the neuronal smooth endoplasmic reticulum (ER) located in a subset of dendritic spines. It consists of stacks of ER cisterns that are interconnected by an unknown dense matrix and are continuous with each other and with the ER of the dendritic shaft. While this organelle was first observed over 60 y ago, its molecular organization remains a mystery. Here, we performed in vivo proximity proteomics to gain some insight into its molecular components. To do so, we used the only known spine apparatus-specific protein, synaptopodin, to target a biotinylating enzyme to this organelle. We validated the specific localization in dendritic spines of a small subset of proteins identified by this approach, and we further showed their colocalization with synaptopodin when expressed in nonneuronal cells. One such protein is Pdlim7, an actin binding protein not previously identified in spines. Pdlim7, which we found to interact with synaptopodin through multiple domains, also colocalizes with synaptopodin on the cisternal organelle, a peculiar stack of ER cisterns resembling the spine apparatus and found at axon initial segments of a subset of neurons. Moreover, Pdlim7 has an expression pattern similar to that of synaptopodin in the brain, highlighting a functional partnership between the two proteins. The components of the spine apparatus identified in this work will help elucidate mechanisms in the biogenesis and maintenance of this enigmatic structure with implications for the function of dendritic spines in physiology and disease.
脊椎器官是神经元平滑内质网（ER）的一个特殊隔室，位于树突棘的一部分中。它由 ER 潴泡的堆叠组成，这些堆叠通过未知的致密基质相互连接，并且与树突干的 ER 连续。尽管这个细胞器早在 60 多年前就被首次观察到，但它的分子组织仍然是一个谜。在这里，我们进行了体内邻近蛋白质组学研究，以深入了解其分子成分。为此，我们使用了唯一已知的脊椎器官特异性蛋白 synaptopodin 将生物素化酶靶向该细胞器。我们验证了这种方法鉴定的一小部分蛋白质在树突棘中的特异性定位，并且当在非神经元细胞中表达时，我们进一步显示它们与 synaptopodin 的共定位。这样的一种蛋白质是 Pdlim7，一种以前在棘突中未被识别的肌动蛋白结合蛋白。Pdlim7 通过多个结构域与 synaptopodin 相互作用，也与 synaptopodin 在 cisternal 细胞器上共定位，cisternal 细胞器是一种类似于脊椎器官的 ER 潴泡的特殊堆叠，存在于神经元的一部分轴突起始段。此外，Pdlim7 在大脑中的表达模式与 synaptopodin 相似，突出了这两种蛋白质之间的功能伙伴关系。这项工作中鉴定的脊椎器官成分将有助于阐明这种神秘结构的生物发生和维持机制，对树突棘在生理和疾病中的功能具有重要意义。
