The study of complex nanoarchitectures in biological specimens has been hindered by the physical accessibility of labels to the biomolecules of interest. Biomolecular structures in cells and tissues are often too crowded to view with conventional microscopy and antibody labeling. A method described in Nature Biomedical Engineering uses a novel chemistry to preserve and decrowd biomolecular structures in intact tissue, resulting in improved imaging to a resolution of around 20 nm. Called ‘expansion revealing’, the method involves anchoring proteins to a gel followed by two rounds of expansion with swellable hydrogels to prepare cells and tissue for imaging. “We find that more antibodies bind when applied after expansion. Invisible molecules, which are unlabeled when stained pre-expansion because they are so densely packed, become visible after expansion when labels have room to bind,” says Edward Boyden, corresponding author of this study.
The researchers tested the ability of their expansion method in brain tissue containing somatosensory cortex from mouse. They observed that seven synaptic proteins, chosen for their role in neural architecture and transmission, exhibited well-defined images when stained after expansion. The technology revealed that presynaptic calcium channels aligned, with nanoscale precision, with postsynaptic scaffolding proteins. Applying this expansion method to a mouse model of Alzheimer’s disease uncovered previously undescribed periodic amyloid nanoclusters containing ion channel proteins. “This approach may open up new frontiers on an intractable disease,” says Boyden.
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