Biomedical Neuroscience Institute (BNI), Faculty of Medicine, Universidad de Chile, Santiago, Chile.
PLoS One. 2012;7(8):e44168. doi: 10.1371/journal.pone.0044168. Epub 2012 Aug 27.
In neuronal cells the intracellular trafficking machinery controls the availability of neurotransmitter receptors at the plasma membrane, which is a critical determinant of synaptic strength. Metabotropic γ amino-butyric acid (GABA) type B receptors (GABA(B)Rs) are neurotransmitter receptors that modulate synaptic transmission by mediating the slow and prolonged responses to GABA. GABA(B)Rs are obligatory heteromers constituted by two subunits, GABA(B)R1 and GABA(B)R2. GABA(B)R1a and GABA(B)R1b are the most abundant subunit variants. GABA(B)R1b is located in the somatodendritic domain whereas GABA(B)R1a is additionally targeted to the axon. Sushi domains located at the N-terminus of GABA(B)R1a constitute the only difference between both variants and are necessary and sufficient for axonal targeting. The precise targeting machinery and the organelles involved in sorting and transport have not been described. Here we demonstrate that GABA(B)Rs require the Golgi apparatus for plasma membrane delivery but that axonal sorting and targeting of GABA(B)R1a operate in a pre-Golgi compartment. In the axon GABA(B)R1a subunits are enriched in the endoplasmic reticulum (ER), and their dynamic behavior and colocalization with other secretory organelles like the ER-to-Golgi intermediate compartment (ERGIC) suggest that they employ a local secretory route. The transport of axonal GABA(B)R1a is microtubule-dependent and kinesin-1, a molecular motor of the kinesin family, determines axonal localization. Considering that progression of GABA(B)Rs through the secretory pathway is regulated by an ER retention motif our data contribute to understand the role of the axonal ER in non-canonical sorting and targeting of neurotransmitter receptors.
在神经元细胞中，细胞内运输机制控制着神经递质受体在质膜上的可用性，这是突触强度的关键决定因素。代谢型 γ 氨基丁酸（GABA）B 型受体（GABA(B)Rs）是神经递质受体，通过介导 GABA 的缓慢和持久反应来调节突触传递。GABA(B)Rs 是由两个亚基组成的必需异源二聚体，GABA(B)R1 和 GABA(B)R2。GABA(B)R1a 和 GABA(B)R1b 是最丰富的亚基变体。GABA(B)R1b 位于体树突域，而 GABA(B)R1a 则另外靶向轴突。位于 GABA(B)R1a N 端的 Sushi 结构域构成了这两种变体之间的唯一差异，是轴突靶向所必需且充分的。精确的靶向机制和参与分拣和运输的细胞器尚未描述。在这里，我们证明 GABA(B)Rs 需要高尔基体才能将其递送到质膜，但 GABA(B)R1a 的轴突分拣和靶向作用发生在高尔基体前区室。在轴突中，GABA(B)R1a 亚基富含内质网（ER），其动态行为及其与其他分泌细胞器（如 ER 到高尔基体中间区室（ERGIC））的共定位表明它们采用了局部分泌途径。轴突 GABA(B)R1a 的运输依赖于微管，并且驱动蛋白家族的分子马达 kinesin-1 决定了轴突定位。考虑到 GABA(B)Rs 通过分泌途径的进展受到 ER 保留基序的调节，我们的数据有助于理解轴突 ER 在神经递质受体非典型分拣和靶向中的作用。
