Members of the superfamily of solute carrier (SLC) transmembrane proteins transport diverse substrates across distinct cellular membranes. Three SLC protein families transport distinct neurotransmitters into synaptic vesicles to enable synaptic transmission in the nervous system. Among them is the SLC17A6/7/8 family of vesicular glutamate transporters, which endows specific neuronal cell types with the ability to use glutamate as a neurotransmitter. The genome of the nematode Caenorhabditis elegans encodes three SLC17A6/7/8 family members, one of which, eat-4/VGLUT, has been shown to be involved in glutamatergic neurotransmission. Here, we describe our analysis of the two remaining, previously uncharacterized SLC17A6/7/8 family members, vglu-2 and vglu-3 These two genes directly neighbor one another and are the result of a recent gene duplication event in C. elegans, but not in other Caenorhabditis species. Compared to EAT-4, the VGLU-2 and VGLU-3 protein sequences display a more distant similarity to canonical, vertebrate VGLUT proteins. We tagged both genomic loci with gfp and detected no expression of vglu-3 at any stage of development in any cell type of both C. elegans sexes. In contrast, vglu-2::gfp is dynamically expressed in a restricted set of distinct cell types. Within the nervous system, vglu-2::gfp is exclusively expressed in a single interneuron class, AIA, where it localizes to vesicular structures in the soma, but not along the axon, suggesting that VGLU-2 may not be involved in synaptic transport of glutamate. Nevertheless, vglu-2 mutants are partly defective in the function of the AIA neuron in olfactory behavior. Outside the nervous system, VGLU-2 is expressed in collagen secreting skin cells where VGLU-2 most prominently localizes to early endosomes, and to a lesser degree to apical clathrin-coated pits, the trans-Golgi network, and late endosomes. On early endosomes, VGLU-2 colocalizes most strongly with the recycling promoting factor SNX-1, a retromer component. Loss of vglu-2 affects the permeability of the collagen-containing cuticle of the worm, and based on the function of a vertebrate VGLUT1 protein in osteoclasts, we speculate that vglu-2 may have a role in collagen trafficking in the skin. We conclude that C. elegans SLC17A6/7/8 family members have diverse functions within and outside the nervous system.

中文翻译：

---

线虫中的 SLC17A6/7/8 囊泡谷氨酸转运蛋白同系物。


溶质载体 (SLC) 跨膜蛋白超家族的成员跨不同的细胞膜转运不同的底物。三个 SLC 蛋白家族将不同的神经递质转运到突触小泡中，以实现神经系统中的突触传递。其中包括囊泡谷氨酸转运蛋白的 SLC17A6/7/8 家族，该家族赋予特定神经元细胞类型使用谷氨酸作为神经递质的能力。线虫秀丽隐杆线虫的基因组编码三个 SLC17A6/7/8 家族成员，其中之一eat-4 /VGLUT已被证明参与谷氨酸能神经传递。在这里，我们描述了对剩下的两个先前未表征的 SLC17A6/7/8 家族成员vglu-2和vglu-3的分析。这两个基因彼此直接相邻，是最近秀丽隐杆线虫中基因复制事件的结果，但在其他秀丽隐杆线虫属物种中则不然。与 EAT-4 相比，VGLU-2 和 VGLU-3 蛋白质序列与典型的脊椎动物 VGLUT 蛋白质具有更远的相似性。我们用gfp标记了两个基因组位点，并在秀丽隐杆线虫性别的任何细胞类型的任何发育阶段均未检测到vglu-3的表达。相比之下， vglu-2 :: gfp在一组有限的不同细胞类型中动态表达。在神经系统内， vglu-2 :: gfp仅在单个中间神经元类 AIA 中表达，它定位于体细胞中的囊泡结构，但不沿着轴突，表明 VGLU-2 可能不参与突触转运谷氨酸。 然而， vglu-2突变体的 AIA 神经元在嗅觉行为中的功能存在部分缺陷。在神经系统之外，VGLU-2 在分泌胶原蛋白的皮肤细胞中表达，其中 VGLU-2 最显着地定位于早期内体，并在较小程度上定位于顶端网格蛋白包被的小凹、反式高尔基体网络和晚期内体。在早期核内体上，VGLU-2 与回收促进因子 SNX-1（一种逆转录体成分）共定位最强。 vglu-2的缺失会影响线虫含有胶原蛋白的角质层的通透性，根据脊椎动物 VGLUT1 蛋白在破骨细胞中的功能，我们推测vglu-2可能在皮肤中的胶原蛋白运输中发挥作用。我们得出的结论是，线虫SLC17A6/7/8 家族成员在神经系统内外具有多种功能。