Obtaining high-resolution information from a complex system, while maintaining the global perspective needed to understand system function, represents a key challenge in biology. Here we address this challenge with a method (termed CLARITY) for the transformation of intact tissue into a nanoporous hydrogel-hybridized form (crosslinked to a three-dimensional network of hydrophilic polymers) that is fully assembled but optically transparent and macromolecule-permeable. Using mouse brains, we show intact-tissue imaging of long-range projections, local circuit wiring, cellular relationships, subcellular structures, protein complexes, nucleic acids and neurotransmitters. CLARITY also enables intact-tissue in situ hybridization, immunohistochemistry with multiple rounds of staining and de-staining in non-sectioned tissue, and antibody labelling throughout the intact adult mouse brain. Finally, we show that CLARITY enables fine structural analysis of clinical samples, including non-sectioned human tissue from a neuropsychiatric-disease setting, establishing a path for the transmutation of human tissue into a stable, intact and accessible form suitable for probing structural and molecular underpinnings of physiological function and disease. High-resolution imaging has traditionally required thin sectioning, a process that disrupts long-range connectivity in the case of brains: here, intact mouse brains and human brain samples have been made fully transparent and macromolecule permeable using a new method termed CLARITY, which allows for intact-tissue imaging as well as repeated antibody labelling and in situ hybridization of non-sectioned tissue. High-resolution imaging of biological tissue has traditionally required sectioning, which for tissues like the brain means the loss of long-range connectivity. Now Karl Deisseroth and colleagues have developed a way of making full, intact organs optically transparent and macromolecule-permeable by building a hydrogel-based infrastructure from within the tissue that allows subsequent removal of light-scattering lipids, resulting in a transparent brain. The method, termed CLARITY, also allows repeated antibody labelling of proteins, and in situ hybridization of nucleic acids in non-sectioned tissue, such as full mouse brains or human clinical samples stored in formalin for many years.

Structural and molecular interrogation of intact biological systems