A DNA nanodevice for mapping sodium at single organelle resolution - raw data

Cellular sodium ion (Na⁺) homeostasis is integral to organism physiology. Our current understanding of Na⁺ homeostasis is largely limited to Na⁺ transport at the plasma membrane. Organelles may also contribute to Na⁺ homeostasis, however, the direction of Na⁺ flow across organelle membranes is unknown because Na⁺ cannot be imaged. Here, we report a pH-independent, organelle-targetable, ratiometric probe that reports lumenal Na⁺. It is a DNA nanodevice containing a Na⁺-sensitive fluorophore, a reference dye and an organelle targeting domain. By measuring Na⁺ at single endosome resolution in mammalian cells and in <i>C. elegans</i>, we discover that lumenal<i> </i>Na⁺ levels in each stage of the endolysosomal pathway exceed cytosolic levels and decrease as endosomes mature. Further, we find that lysosomal Na⁺ levels in nematodes are modulated by the Na⁺/H⁺ exchanger NHX-5 in response to salt stress. The ability to image sub-cellular Na⁺ will unveil mechanisms of Na⁺ homeostasis at an increased level of cellular detail.

细胞内钠离子（Na⁺）稳态对于生物体生理活动具有核心作用。目前我们对于Na⁺稳态的认知，大多局限于质膜处的Na⁺转运过程。细胞器或许同样参与Na⁺稳态的调控，但由于无法对Na⁺进行成像，跨细胞器膜的Na⁺流动方向至今仍未明确。本研究报道了一种不依赖pH、可靶向细胞器的比率型探针（ratiometric probe），可用于检测细胞器腔室中的Na⁺。该探针为DNA纳米装置，包含Na⁺敏感型荧光团、参比染料与细胞器靶向结构域。我们通过单内体分辨率级别的检测，在哺乳动物细胞与秀丽隐杆线虫（C. elegans）中对Na⁺进行定量分析，发现内体-溶酶体通路各阶段的腔室Na⁺水平均高于胞质水平，且随内体成熟进程逐渐降低。此外，我们还发现，在线虫中，溶酶体Na⁺水平会受到钠氢交换体NHX-5的调控，以响应盐胁迫。能够对亚细胞水平的Na⁺进行成像的技术，将助力我们在更精细的细胞细节层面解析Na⁺稳态的调控机制。