Structure And Function Of Unconventional Myosins

内质网(ER)向浦肯野神经元(PNS)树突棘的延伸是小脑突触可塑性所必需的，在编码肌球蛋白-VA1-3的Myo5a基因零突变的动物中，内质网(ER)的伸展被破坏。虽然有人提出动物V类肌球蛋白通过将细胞器拴在肌动蛋白细胞骨架4-7上来定位细胞器，但我们在这里证明了肌球蛋白-Va作为点到点的细胞器转运体将ER作为货物拉到PN脊柱中。具体地说，当细胞器移动到脊柱中时，肌球蛋白在内质网末端积累，而肌球蛋白水解三磷酸腺苷的能力是脊柱ER靶向所必需的。此外，肌球蛋白-Va负责绝大多数脊柱ER插入事件。最后，肌球蛋白沿肌动蛋白细丝移动的能力减弱，降低了内质网进入脊柱的最大速度，为肌球蛋白-Va驱动内质网运动提供了直接证据。因此，我们建立了基于肌动蛋白的马达在动物细胞内移动ER的机制，并揭示了将ER定位到PN脊椎的机制，这是突触可塑性的先决条件。

Extension of the endoplasmic reticulum (ER) into dendritic spines of Purkinje neurons (PNs) is required for cerebellar synaptic plasticity and is disrupted in animals with null mutations in Myo5a, the gene encoding myosin-Va1-3. While it has been proposed that animal class V myosins localize organelles by tethering them to the actin cytoskeleton4-7, we demonstrate here that myosin-Va acts as a point-to-point organelle transporter to pull ER as cargo into PN spines. Specifically, the myosin accumulates at the ER tip as the organelle moves into spines, and the myosins ability to hydrolyze ATP is required for spine ER targeting. Moreover, myosin-Va is responsible for the vast majority of spine ER insertional events. Finally, attenuation of the myosins ability to move along actin filaments reduces the maximum velocity of ER movement into spines, providing direct evidence that myosin-Va drives ER motility. Thus, we establish that an actin-based motor moves ER within animal cells, and we uncover the mechanism that mediates ER localization to PN spines, a prerequisite for synaptic plasticity.