An important challenge in biological research is the development of high-resolution optical methods to label and image cell populations in three dimensions deep in intact tissue. In the present study, we have developed a methodology for whole-organism clearing, building upon previous techniques. SUT (Scheme Update on tissue Transparency); a new tissue-clearing agent, can achieve fast and effective passive clearing of tissues with little protein loss. SUT was created by dissolving 250 g urea, 150 ml TritonX-100 and 80 g SDS in hot phosphate buffered saline (PBS) (0. 1M, pH = 7.40) to a total volume of 1 L. Via coronary perfusion, SUT can clear whole intact pig and mouse hearts, Further research found that SUT also has the potential to clear other parenchyma organs, such as lung, liver, kidney, brain and testis (Fig. 1). Compared to the other reagent, SUT can achieve higher transparency and less protein loss (Fig. 2). To test the compatibility of SUT with immunohistochemistry for identifying organ structures, we incubated SUT-treated tissues with antibodies and imaged them using light-sheet microscopy and single-photon confocal microscopy, our research suggests that SUT was compatible with immunohistochemistry, and small molecules were well retained after SUT clearing (Fig. 3). SUT techniques open a door for improving 3D imaging of molecular structures in intact tissues. In the future, a bank containing 3D microscopic information of human tissues could be built, and, together with macroscopic anatomy, this may present secrets of life directly and vividly before our eyes.
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