Expansion Microscopy for Brain Mapping

Abstract

More than one billion people in the world suffer from brain disorders. To address this, more than one trillion US dollars are spent to develop the drugs, but ~92% fail to receive clinical approval. Among many potential reasons why treating brain disorders has been strikingly difficult, one reason could be that the complexity of neural circuitry and molecular composition of the brain have been poorly understood. For this reason, there needs to be new innovations in brain mapping pursuits, and expansion microscopy (ExM) is proposed throughout this thesis as a potential candidate for most effectively meeting the needs of the efforts. First introduced in 2015, ExM allows for nanometer scale resolution to be achieved on a conventional microscope. By constructing an expanding polymer network inside the biological specimen, conjugating the biomolecules of interest to the matrix, and letting it expand after getting rid of everything else we are not interested in imaging, the physical distance between the biomolecules anchored to the polymer matrix increases, effectively overcoming the diffraction-limit of the conventional confocal microscope and thereby increasing the effective resolution of the microscope down to nanometer scale. Over the course of my graduate studies, I worked on three improvements to this modality: (1) applying ExM iteratively to the specimen and increase the effective resolution exponentially, (2) developing intercalating lipid probes for visualizing lipid membranes in the context of ExM, and (3) devising a ExM-compatible approach to visualize extracellular space of a whole larval zebrafish. In addition to these, in an effort to understand what type of infrastructural help is needed to map the brain within our foreseeable future, I summarized an overview of current practices pursued by governments, industry, and academia to achieve scientific discoveries towards the end of this thesis.