Revealing intact neuronal circuitry in centimeter-sized formalin-fixed paraffin-embedded brain

Abstract

Current tissue clearing and labeling approaches require freshly prepared samples to avoid problems related to over-fixation, such as loss of antigenicity or difficulty of tissue clearing. Thus, the predicament of specimens with long-term preservation limits the application of state-of-art technology to archived human brain tissues. Here, we present the development and validation of multiplex labeling of centimeter-sized archived tissue (MOCAT), a formalin-fixed paraffin-embedding (FFPE) based sample preservation and delipidation technique for centimeter-level tissue clearing and immunolabeling. We demonstrate that MOCAT sufficiently delipidates whole mouse brain and human brain blocks and is superior to 10% formalin for long-term antigenicity preservation; moreover, the spatial information of biomarkers offered by MOCAT-processed intact mouse brains is identical to that offered by freshly prepared SDS-delipidated intact mouse brains. MOCAT not only satisfies the need for long-term tissue storage before performing volumetric multiplex imaging for research purposes but also has the potential to be used in human clinical examination.