A DNA nanodevice for mapping sodium at single-organelle resolution

Area of Science:

• Cell Biology
• Physiology
• Biochemistry

Background:

• Cellular sodium ion (Na+) homeostasis is crucial for organismal physiology.
• Current understanding of Na+ homeostasis primarily focuses on plasma membrane transport.
• The role of organelles in Na+ homeostasis and the direction of Na+ flow across organelle membranes remain largely unknown due to imaging limitations.

Purpose of the Study:

• To develop a novel method for imaging lumenal Na+ within organelles.
• To investigate the dynamics of organelle Na+ levels in the endolysosomal pathway.
• To explore the role of organellar Na+ in cellular responses to salt stress.

Main Methods:

• Development of a pH-independent, organelle-targetable, ratiometric probe using a DNA nanodevice.
• The nanodevice incorporates a Na+-sensitive fluorophore, a reference dye, and an organelle-targeting domain.
• Imaging of lumenal Na+ at single endosome resolution in mammalian cells and Caenorhabditis elegans.

Main Results:

• Lumenal Na+ levels in all stages of the endolysosomal pathway were found to be higher than cytosolic levels.
• Organelle Na+ levels decrease progressively as endosomes mature.
• Lysosomal Na+ levels in nematodes are regulated by the Na+/H+ exchanger NHX-5 during salt stress.

Conclusions:

• The developed probe enables visualization of subcellular Na+ concentrations, overcoming previous imaging limitations.
• Organelles, particularly the endolysosomal pathway, play a significant role in cellular Na+ homeostasis.
• This technology opens new avenues for detailed investigation into the mechanisms governing Na+ regulation within cells.