Expansion Microscopy for Brain Imaging

Abstract

Understanding the organ-wide molecular architecture of proteins is required to dissect the mechanisms of various diseases and answer many scientific questions. Accordingly, there is a significant need for an imaging methodology that is capable of imaging proteins at nanoscale resolution over whole organs. In 2015, a technique called expansion microscopy (ExM) was developed. This technique increases the resolution of conventional microscopy several-fold by physically expanding a specimen with a swellable polymer network. After expansion, specimens become transparent, enabling super-resolution imaging of relatively thick tissue slices without ultra-thin sectioning. Recently, multiple ExM variants which demonstrated expansion microscopy with conventional fluorophore-conjugated antibodies, super-resolution imaging of RNA in cells and tissue slices via expansion, multiplexed protein imaging via post-expansion antibody staining, and sub-20-nm resolution via expanding specimens more than 20-fold have been developed. This chapter presents the detailed molecular principles of ExM and its variants to understand the differences between various ExM-related techniques.