SUMMARY
Understanding the structure-function relationships at cellular, circuit, and organ-wide scale requires 3D anatomical and phenotypical maps, currently unavailable for many organs across species. At the root of this knowledge gap is the absence of a method that enables whole-organ imaging. Herein we present techniques for tissue clearing in which whole organs and bodies are rendered macromolecule-permeable and optically-transparent, thereby exposing their cellular structure with intact connectivity. We describe PACT, a protocol for passive tissue clearing and immunostaining of intact organs; RIMS, a refractive index matching media for imaging thick tissue; and PARS, a method for whole-body clearing and immunolabeling. We show that in rodents PACT, RIMS, and PARS are compatible with endogenous-fluorescence, immunohistochemistry, RNA single-molecule FISH, long-term storage, and microscopy with cellular and subcellular resolution. These methods are applicable for high-resolution, high-content mapping and phenotyping of normal and pathological elements within intact organs and bodies.
Plunging into a domain of silence
Female mammals have two X chromosomes. One must be silenced to “balance” gene dosage with male XY cells. The Xist long noncoding RNA coats the inactive X chromosome in female mammalian cells. Chen
et al.
show that the Xist RNA helps recruit the X chromosome to the internal rim of the cell nucleus, a region where gene expression is silenced. Xist is recruited to the domain through an interaction with the Lamin B receptor. This recruitment allows the Xist RNA to spread across the future inactive X chromosome, shutting down gene expression.
Science
, this issue p.
468
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