Magnified analysis of proteome (MAP) technique allows researchers to examine the brain in unprecedented detail.
A team of engineers recently developed a new technique that allows them to image brain tissue at unprecedented size scales. The technique, called magnified analysis of proteome (MAP), offers a way to examine both local molecules within cells as well as long-range neuron connections within the brain.
MAPping the Brain
Imagine a magnifying glass that, instead of bending light to make an object appear bigger, actually caused it to grow in size. That’s kind of how MAP works – it causes entire organs to expand, while still preserving their overall architecture and three-dimensional proteome organization. The word ‘proteome’ simply refers to the set of proteins in a given type of cell or organism at a specific time.
This expansion is achieved by first flooding the brain tissue with acrylamide polymers, forming a dense gel. The proteins inside the cells are attached to the gel using formaldehyde, which enables researchers to denature and dissociate the proteins without compromising the tissue’s structural integrity. After this process, the gel expands the tissue sample up to five times its original size.
“It is reversible and you can do it many times,” said Kwanghun Chung, assistant professor of medical engineering and one of the authors on the paper. “You can then use off-the-shelf molecular markers like antibodies to label and visualize the distribution of all these preserved biomolecules.”
The researchers conducted their study on a mouse brain and conducted multiple rounds of immunolabeling (a process used to detect and localize antigens, proteins that serve as the “key” to an antibody’s “lock”) and imaging of the tissue’s magnified proteome. The researchers found that of 122 antibodies tested, 100 were compatible with MAP-processed samples and 43 of 51 target molecules were successfully labeled.
Pushing the Limits of Tissue Imaging
These high success rates indicate a minimal degradation of antibody structure due to protein denaturation from the technique. This demonstrates the ability to use off-the-shelf-antibodies without modification, meaning the technique should be easy for other researchers to adapt.
“We can use these antibodies to visualize any target structures or molecules,” explained Chung. “We can visualize different neuron types and their projections to see their connectivity. We can also visualize signalling molecules or functionally important proteins.”
Researchers can use conventional microscopes to obtain high-resolution images of the expanded tissue. The 60-nm resolution obtainable with the MAP technique is around four times as high as the usual limit of light microscopes, and the technique can be applied to relatively large tissue samples up to 2 mm thick.
“This is, as far as I know, the first demonstration of super-resolution proteomic imaging of millimeter-scale samples,” said Chung.
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