A novel medical method makes tissue transparent, substantially simplifying research

A simple and universal technique

“This is a simple and universal tissue-clearing technique for studies of large body parts or even entire animals,” said study senior author Li Ye, Ph.D., assistant professor of neuroscience at Scripps Research.

The research has started 15 years ago and is still in development. Initially, it was conceived mainly for the purpose of tracing nerve connections within whole brains.

Unfortunately, it only worked well for brains and not on other body parts. This is because the methods used until now employed either organic or water-based solvents that came with many complications.

The first diminished the fluorescent signals that marked the active genes or other molecules of interest in lab animals while the latter were impractically weak for clearing non-brain tissue. To make matters more complicated, both methods saw the use of burdensome, labor-intensive procedures, often using hazardous chemicals.

To be used in an ordinary lab

“An ordinary lab generally can’t use these methods routinely and at scale,” said Yu Wang, a graduate student in the Ye laboratory who was the co-first author of the paper.

The new method devised by Scripps Research scientists bypasses these issues by employing water-based hydrogels to protect those molecules within the tissue that need to be preserved. Using this new technique, the researchers have already managed to image SARS-CoV-2-infected cells in the whole chests of mice for the first time ever.

“In many cases, you can just put the whole thing in a jar and keep it in a shaker on your benchtop until it’s done,” said co-first author Victoria Nudell, a research assistant in the Ye lab. “This makes it practical and scalable enough for routine use.”

The study was published in the journal Nature Methods.

Study abstract:

The recent development of solvent- and polymer-based brain-clearing techniques has advanced our ability to visualize the mammalian nervous system in three dimensions. However, it remains challenging to image the mammalian body en bloc. Here we developed HYBRiD (hydrogel-based reinforcement of three-dimensional imaging solvent-cleared organs (DISCO)), by recombining components of organic- and polymer-based clearing pipelines. We achieved high transparency and protein retention, as well as compatibility with direct fluorescent imaging and immunostaining in cleared mammalian bodies. Using parvalbumin- and somatostatin-Cre models, we demonstrated the utility of HYBRiD for whole-body imaging of genetically encoded fluorescent reporters without antibody enhancement of signals in newborn and juvenile mice. Using K18-hACE2 transgenic mice, HYBRiD enabled perfusion-free clearing and visualization of SARS-CoV-2 infection in a whole mouse chest, revealing macroscopic and microscopic features of viral pathology in the same sample. HYBRiD offers a simple and universal solution to visualize large heterogeneous body parts or entire animals for basic and translational research.