Clearing of fixed tissue: a review from a microscopist's perspective

Chemical clearing of fixed tissues is becoming a key instrument for the three-dimensional reconstruction of macroscopic tissue portions, including entire organs. Indeed, the growing interest in this field has both triggered and been stimulated by recent advances in high-throughput microscopy and data analysis methods, which allowed imaging and management of large samples. The strong entanglement between clearing methods and imaging technology is often overlooked, as typical classification of the former is based only on the chemicals used. Here, we review the recent literature in the field, proposing a taxonomy of clearing techniques based on their mating with the major high-throughput microscopies. We hope that this application-oriented classification can help researchers to find the protocol best suited to their experiment among the many present in the literature.