Congratulations to scientists at Seoul National University who have recently published their work in Cell Metabolism in their article “Mitochondrial fragmentation and donut formation enhance mitochondrial secretion to promote osteogenesis”! The authors characterized mitochondrial secretion by osteoblasts, and its role in regulating osteogenesis and bone regeneration¹.

Nanolive live cell imaging was used to capture the exact moment a mitochondrion was secreted by an osteoblast (see below). Thanks to the refractive index imaging of the platform, the group were able to image cellular components including the plasma membrane label-free, reducing the amount of harmful fluorescence that cells and mitochondria were exposed to. Author Professor Lee commented “Live cell imaging using Nanolive was useful for visualizing mitochondrial secretions because it can display plasma membranes without labeling.”

Mitochondria were imaged both by refractive index and fluorescence; refractive index images were taken every 20 seconds, and fluorescence images were taken every 2 minutes (to reduce phototoxicity) for a total of 2 hours. Six refractive index images were taken for each fluorescence image, to give a higher temporal resolution of the mitochondrial dynamics. Fluorescence was used to ensure that mitochondria were accurately detected, and the group created a mouse model where osteoblast mitochondria expressed green fluorescent protein to achieve this.

Figure 1. A single GFP-tagged mitochondrion (indicated by red arrow) was captured passing through the cell membrane (light gray, imaged by refractive index). EC indicates extracellular space, IC indicates intracellular space. Taken from Figure S2¹.

Nanolive’s live cell imaging is a go-to method for investigating mitochondrial dynamics for many research groups, thanks to its ability to image mitochondria, as well as other organelles without labels. See the full list of publications.

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