Nat. Biotechnol. (2016)

Current imaging techniques such as proteomic imaging and expansion microscopy enable the characterization of the fine subcellular architectures of individual cells. However, the processing steps, which require protease digestion and tissue sectioning, cause the loss of proteins and the loss of intercellular connectivity. Researchers in the US and South Korea now report a new processing method that allows multiscale proteomic imaging of intact biological systems.

Kwanghun Chung and colleagues at the Massachusetts Institute of Technology, Yonsei University and Harvard University describe a tissue expansion method that preserves the 3D proteome content and organization, and the connections between the cells within an organ. The method, called magnified analysis of the proteome (MAP), involves the use of high concentrations of acrylamide monomers during a hydrogel-tissue hybridization step. Acrylamide prevents reactive hydroxymethyls — formed from the reaction between amine-containing residues on the protein and formaldehyde — from reacting with amide groups within the same protein or with adjacent proteins to form methylene bridges. Intra- and interprotein crosslinking can prevent complete denaturation and dissociation of the proteins and limit subsequent tissue expansion. Using the MAP technique, a whole mouse brain can be expanded fourfold within 7 days without any protease treatment. The 3D proteome of the expanded tissues can be labelled using conventional antibodies for super-resolution imaging of the fine subcellular architectures. One limitation of the method is that expansion decreases signal intensity.