We created a transgenic mouse line using the Cre-loxp system, allowing these mice to release fluorescent exosomes muscle-specifically by tagging turboGFP to CD63. Specific green fluorescence was observed in the muscle tissues through IVIS imaging and confocal microscopy. However, we were unable to detect the same fluorescence in the serum of these mice. We also tried to isolate the exosomes from the supernatant of cultured muscle samples, but only very faint fluorescence was found by nanoflow.
I'm confused about why muscle-derived exosomes can't enter circulation or why the fluorescence of exosomes fades away. Any suggestions or discussions on this topic would be greatly appreciated. Thank you!
Hi Nanxi, sorry I'm late to respond, but I just saw your post. In general, GFP is a poor in vivo imaging reagent because green light doesn't penetrate through tissue very well. I'm attaching a graphic that shows the problems you may encounter at the wavelengths that GFP emits (low tissue penetration, interference from oxyhemoglobin absorption, and high tissue autofluorescence).
For the serum results, it could be that the concentration of circulating exosomes is just very very low.
I wonder how much of the fluorescence you're seeing in the muscle is really GFP and how much is just tissue autofluorescence. I'm assuming you used negative control mice (no GFP expression) and have some comparison data. I'm happy to connect you with an application scientist if you want to talk through the imaging results. -Jess
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