We describe a strategy for developing hydrophilic chemical cocktails for tissue delipidation, decoloring, refractive index (RI) matching, and decalcification, based on comprehensive chemical profiling. More than 1,600 chemicals were screened by a high-throughput evaluation system for each chemical process. The chemical profiling revealed important chemical factors: salt-free amine with high octanol/water partition-coefficient (logP) for delipidation, N-alkylimidazole for decoloring, aromatic amide for RI matching, and protonation of phosphate ion for decalcification. The strategic integration of optimal chemical cocktails provided a series of CUBIC (clear, unobstructed brain/body imaging cocktails and computational analysis) protocols, which efficiently clear mouse organs, mouse body including bone, and even large primate and human tissues. The updated CUBIC protocols are scalable and reproducible, and they enable three-dimensional imaging of the mammalian body and large primate and human tissues. This strategy represents a future paradigm for the rational design of hydrophilic clearing cocktails that can be used for large tissues.

Mammalian bodies have more than a billion cells per cubic centimeter, which makes whole-body cell (WBC) profiling of an organism one of the ultimate challenges in biology and medicine. Recent advances in tissue-clearing technology have enabled rapid and comprehensive cellular analyses in whole organs and in the whole body by a combination of state-of-the-art technologies of optical imaging and image informatics. In this review, we focus mainly on the chemical principles in currently available techniques for tissue clearing and staining to facilitate our understanding of their underlying mechanisms. Tissue clearing is usually conducted by the following steps: (a) fixation, (b) permeabilization, (c) decolorizing, and (d) refractive index (RI) matching. To phenotype individual cells after tissue clearing, it is important to visualize genetically encoded fluorescent reporters and/or to stain tissues with fluorescent dyes, fluorescent labeled antibodies, or nucleic acid probes. Although some technical challenges remain, the chemical principles in tissue clearing and staining for WBC profiling will enable various applications, such as identifying cellular circuits across multiple organs and measuring their dynamics in stochastic and proliferative cellular processes, for example, autoimmune and malignant neoplastic diseases.

The forfeiting of photosynthetic capabilities has occurred independently many times throughout eukaryotic evolution. But almost all non-photosynthetic plants and algae still retain a colorless plastid and an associated genome, which performs fundamental processes apart from photosynthesis. Unfortunately, little is known about the forces leading to photosynthetic loss; this is largely because there is a lack of data from transitional species. Here, we compare the plastid genomes of two “transitional” green algae: the photosynthetic, mixotrophicAuxenochlorella protothecoidesand the non-photosynthetic, obligate heterotrophPrototheca wickerhamii. Remarkably, the plastid genome ofA. protothecoidesis only slightly larger than that ofP. wickerhamii, making it among the smallest plastid genomes yet observed from photosynthetic green algae. Even more surprising, both algae have almost identical plastid genomic architectures and gene compositions (with the exception of genes involved in photosynthesis), implying that they are closely related. This close relationship was further supported by phylogenetic and substitution rate analyses, which suggest that the lineages giving rise toA. protothecoidesandP. wickerhamiidiverged from one another around six million years ago.

SUMMARY: The advent of three-dimensional histological methods has advanced studies of cellular-resolution anatomy of the brain. The use of whole-mount staining and tissue clearing has advanced systems-level identification of cells underlying brain functions in mouse models. However, application of these methods to studies of human brains has been difficult due to their structural variability and the lack of standardized quantitative metrics. Here we report a rapid and scalable staining/imaging technique, termed mFISH3D, that enables single-cell-resolution imaging of mRNAs of more than ten genes in a large mammalian brain. To apply mFISH3D to postmortem human cerebral cortex, we have reconstructed morphogenic tracks of cortical growth, and used the tracks to provide a framework for quantitative assessment of cytoarchitecture. The workflow enabled the objective quantification of biological heterogeneity among cortical regions. We propose these techniques for standardization of 3D histology of the human cortex to provide reproducible measurements of cell-type-specific neuroanatomy.

Fluorescence imaging enables visualization of the specific molecules of interest with high contrast, and the use of multiple fluorophores in a single tissue sample allows visualization of complex relationships between biological molecules, cell types, and anatomy. The utility of fluorescence imaging in human tissue has been limited by endogenous pigments that can block the light path or emit an autofluorescence, thereby interfering with the specific imaging of target molecules. Although photobleachers have been developed to quench endogenous pigments, the lack of customizability limits their utility for a broad range of applications. Here, we present a high luminous-intensity photobleacher that is based on rigorous simulations of illumination patterns, along with the framework to maximize bleaching efficiency. This open-source project is designed to help scientists customize and scale the device according to their research goals. The photobleacher is applicable to both thin tissue slices and large-volume cleared tissue samples to enable serial three-dimensional imaging of postmortem human brain using multiplexed antibody or oligonucleotide probes.