You can put your dissection kits away, kids. Japanese researchers have developed a method that results in extremely detailed images of the insides of individual organs and even entire animals. The incredible new technique is set to dramatically improve our understanding of how biological systems work.

This biotechnological feat was performed by scientists at the Riken Institute in Japan, the same team responsible for a chemical that makes organs transparent. But now, instead of working on individual organs, the researchers have expanded and refined their method such that an entire animal — in this case a mouse — was made to be practically invisible.

Clear Advantages

Working with transparent animals post mortem has its advantages. Scientists can now study how genes are expressed or view the structure of organs without having to slice into them; it offers a "bigger picture" view of the problems they're working on.

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Ideally, they'll be able to use the new method for 3D pathology, anatomical studies, and immunohistochemistry of entire organisms. It could be used to study how embryos form, or how cancer and autoimmune diseases develop at the cellular level, say the scientists.

From there it could lead to a richer understanding of various diseases and new therapeutic strategies. It could also lead to one of the holy grails of science: organism-level systems biology based on whole-body imaging at single cell resolution.

Taking a Look Inside

To do it, the researchers used a method, called CUBIC (Clear, Unobstructed Brain Imaging Cocktails and Computational Analysis), that practically removes all color from tissue. The process was used to take images of mouse brains, hearts, lungs, kidneys, and livers.

Mouse kidneys, liver, and pancreas imaged after treatment with a variety of protocols: a saline solution, Scale, SeeDB, CUBIC, and CB-Perfusion (which was used in this study). Credit: Riken.

Incredibly, the researchers found that the same technique could be used on the whole bodies of infant and adult mice to produce clear tissues.

The work, which also involved the University of Tokyo and the Japan Science and Technology Agency, focused on a compound called heme — the constituent that gives blood its red color and is found in most body tissue. Saline solution was pumped through the dead mouse's heart to push the blood out of its circulatory system. A reagent was then introduced, which separated the heme from the hemoglobin that remained in the animal's organs.

For the final process, the mouse was skinned and soaked in the reagent for two weeks. Then, in a process called light-sheet fluorescent microscopy, a sheet of laser light was used to penetrate specific levels, building a complete image of the body, much like the way a 3D printer creates physical objects in an additive, layered process.

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"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 two-week clearing protocol," noted lead author Kazuki Tainaka. "It allowed us to see cellular networks inside tissues, which is one of the fundamental challenges in biology and medicine."

To test the practicability of the method, the researchers examined the pancreases of diabetic and non-diabetic mice to find discernible differences in the isles of Langerhans (no, that's not a nice place to visit — it's the structure in the pancreas that produces insulin).

Looking ahead, the researchers would like to improve the technique even further for more rapid imaging, and to study larger samples such as human brains.

As noted, the technique isn't used on living things. That said, nature has produced its own semi-transparent creatures, including this otherworldly frog and its transparent underbelly, and this barrel eye fish with a transparent head:

Credit: Monterey Bay Aquarium Research Institute.

Read the entire study at Cell: "Whole-Body Imaging with Single-Cell Resolution by Tissue Decolorization". Supplementary information via Riken and Japan Times.

Images: Tainaka et al./Cell

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