When tasked with discovering a better way to obtain images of biological tissues, Japanese researchers came up with an interesting solution: make them transparent. In studies involving mice, the scientists at the RIKEN Brain Science Institute succeeded in doing so using a new chemical reagent known as Scale. Soaking mouse brains and embryos in the solution for two weeks made them clear enough to be transparent. The technique, however, preserved artifacts that enable detection by fluorescence imaging. According to an abstract describing the research, a mouse brain treated with the reagent allowed visualization to be carried out at an unprecedented depth in millimeter-scale three-dimensional networks and at subcellular resolution.
The breakthrough could lead to advances in mapping the brain’s cellular architecture, according to the scientists. “Our current experiments are focused on the mouse brain, but applications are neither limited to mice nor to the brain,” explains Atsushi Miyawaki, of the RIKEN Brain Science Institute, in a press release. “We envision using Scale on other organs such as the heart, muscles, and kidneys and on tissues from primate and human biopsy samples.” Miyawaki hopes that the reagent could eventually be used to learn more about primate (including human) tissues. Miyawaki reports that a milder reagent is now being explored that “would allow [the researchers] to study live tissue in the same way, at somewhat lower levels of transparency. This would open the door to experiments that have simply never been possible before.”
For those of you interested, the Scale reagent is composed of urea, glycerol, and a detergent known as Triton-X.
Check out the press release:
Our understanding of biological organisms and how they function is intrinsically tied to the limits of what we can actually see. Even today’s most promising techniques for visualizing biological tissue face this limitation: mechanical methods require that samples be sectioned into smaller pieces for visualization, while optical methods are prevented by the scattering property of light from probing deeper than 1mm into tissue. Either way, the full scope and detail of the biological sample is lost.
The new reagent, referred to as Scale and developed by Atsushi Miyawaki and his team at the RIKEN Brain Science Institute (BSI), gets around these problems by doing two things together that no earlier technique has managed to do. The first is to render biological tissue transparent. Scale does this significantly better than other clearing reagents and without altering the overall shape or proportions of the sample. The second is to avoid decreasing the intensity of signals emitted by genetically-encoded fluorescent proteins in the tissue, which are used as markers to label specific cell types.
This combination makes possible a revolution in optical imaging, enabling researchers to visualize fluorescently-labeled brain samples at a depth of several millimeters and reconstruct neural networks at sub-cellular resolution. Already, Miyawaki and his team have used Scale to study neurons in the mouse brain at an unprecedented depth and level of resolution, shedding light onto the intricate networks of the cerebral cortex, hippocampus and white matter. Initial experiments exploit Scale’s unique properties to visualize the axons connecting left and right hemispheres and blood vessels in the postnatal hippocampus in greater detail than ever before.
Press release: New chemical reagent turns mouse brain transparent
Abstract in Nature Neuroscience: Scale: a chemical approach for fluorescence imaging and reconstruction of transparent mouse brain
