The researchers applied the CUBIC method to the brains, hearts, lungs, kidneys and livers of infant and adult mice.
Image credit: RIKEN
The collaborative team from the University of Tokyo and RIKEN Quantitative Biology Center were particularly interested in how to overcome the problem of "chromophores." Chromophores are molecular subunits that absorb light, preventing accurate imaging. One of these chromophores - heme - is present in most tissues in the body.
However, the team found that the amino alcohols present in a reagent they had previously experimented with can separate heme from hemoglobin, which makes the affected area "dramatically" more transparent.
RIKEN released details of this technique - called CUBIC (Clear, Unobstructed Brain Imaging Cocktails and Computational Analysis) - in April of this year. The technique was developed as a solution to achieve whole-brain imaging that would allow 3D analysis of neural circuits and gene expression profiles.
Although the initial research looked only at mouse and primate brains, team leader Hiroki Ueda commented, "In the near future, we would like to apply CUBIC technology to whole-body imaging at single-cell resolution."
In the new study, the researchers applied the CUBIC method to the brains, hearts, lungs, kidneys and livers of infant and adult mice. In all cases, the scientists were able to get clear tissue.
Using a technique called light-sheet fluorescent microscopy, the team was able to gain 3D images of "slices" of these transparent organs. Running a test of the technique on diabetic and non-diabetic mice, the researchers found that characteristic pancreatic differences between the two groups of mice were clearly visible in the images.
New method could allow 3D anatomical studies of entire organisms
"We were very surprised that the entire body of infant and adult mice could be made nearly transparent by a direct transcardial CUBIC perfusion coupled with a 2-week clearing protocol," says first author Kazuki Tainaka. "It allowed us to see cellular networks inside tissues, which is one of the fundamental challenges in biology and medicine."
Team leader Hiroki Ueda says that the new method could be used for 3D anatomical studies of entire organisms:
"For example, it could be used to study how embryos develop or how cancer and autoimmune diseases develop at the cellular level, leading to a deeper understanding of such diseases and perhaps to new therapeutic strategies. It could lead to the achievement of one of our great dreams, organism-level systems biology based on whole-body imaging at single-cell resolution."
However, the CUBIC technique cannot be applied to living organisms, as it requires the tissues to be "fixed" using reagents.
In August, Medical News Today reported on another "invisible mouse." A research team from the California Institute of Technology created see-through mice by removing the skin of the animals and clearing lipids from the tissue, which makes the tissue transparent.
As with the Japanese project, the intention of this research was to bring science closer to being able to image 3D maps of entire organs and bodies. Previously, techniques for making organs transparent had been limited to embryos and the brain.