Science Concentrates BIOTECHNOLOGY
Making bone transparent Researchers adapt tissue-clarifying technique to clear minerals from bone too
A transparent mouse femur shows fluorescently labeled bone stem cells in red.
Scientists have developed a biochemical process that renders bones transparent and then used it to visualize the bone-cell-proliferating action of a new osteoporosis drug (Sci. Transl. Med. 2017, DOI: 10.1126/scitranslmed.aah6518). In addition to enabling the study of drug effects on bone cells, the feat could provide an unprecedented view of the processes in bone cell growth and death. The team, led by Caltech biology and biological engineering professor Viviana Gradinaru, based its bone-clearing strategy on a soft-tissue-clarifying method, called Clarity, that Gradinaru helped develop as a postdoc in Karl Deisseroth’s lab at Stanford University. In recent years, numerous scientists have made significant progress in being
the group genetically engineered mice so that their bone stem cells, known as osteoprogenitors, glowed red. Drug company Amgen provided the team with a new osteoporosis drug to investigate. Gradinaru’s team compared the bones of mice who had received the drug with those who hadn’t. They saw a clear proliferation of osteoprogenitors in the vertebrae of mice who had been given the drug. Sean Morrison, director of the Children’s Medical Center Research Institute at the University of Texas Southwestern says “improving our understanding of the localization of osteoprogenitors in the bone marrow is an important goal that will enhance our understanding of the mechanisms that regulate the maintenance of the adult skeleton.”—ELIZABETH WILSON
able to remove light-scattering lipids from brains and other soft-tissue constructs. The ability to visualize clear, intact soft tissue has great advantages over examining tissue slices because the structures and cells within remain connected and undisturbed. Bones, however, have been tougher to render transparent than soft tissues because they are impregnated with minerals, which are difficult to wash away while maintaining bone structure. To clear the calcium from bones, Gradinaru’s lab used ethylenediaminetetraacetic acid (EDTA). Then, as in the original version of Clarity, the researchers infused the bone with acrylamide monomers to form a stabilizing hydrogel mesh and finally washed out lipids with a detergent. To see cells inside the transparent bone,
MICROSCOPY The researchers integrated the chip with a standard optical microscope equipped with either a 20X or a 60X objective lens. With the 60X objective, the spatial resoluChip-based illumination enables superresolution tion was better than 50 nm. With the 20X objective, the spatial resolution was only microscopy with a wide field of view 138 nm, but the field of view was an extraorSuperresolution microscopy techniques to convert it into an optical nanoscope.” dinarily large 0.5 mm x 0.5 mm. They used allow researchers to observe objects tens The waveguide chips direct laser light the system to image structures in liver cells. of nanometers in size on or inside cells. to the sample. Because the waveguides are So far, the chips are limited to total inBut the methods can only keep an eye on made of high-refractive-index materials, ternal reflectance fluorescence, or TIRF, patches 100 µm or less on a side at a time, the chips generate an intense evanescent excitation. “This limits the use to imaging making it difficult to image multiple cells field strong enough for the superresolution structures up to 150–200 nm away from the simultaneously. microscopy method called direct STORM waveguide surface,” Ahluwalia says. But Now, by coupling a photonic chip with a (dSTORM). that’s also a benefit, he says, because TIRF standard optical microscope, illumination allows researchresearchers have achieved suers to look at thin slices with perresolution fluorescence mivery little background. croscopy with a simpler set-up Suliana Manley, a superand a wider field of view than resolution imaging expert at conventional methods (Nat. the Swiss Federal Institute of Photonics 2017, DOI: 10.1038/ Technology, Lausanne, says the nphoton.2017.55). work “represents a significant “You just need a basic microadvance in making TIRF miscope,” says Balpreet S. Ahlucroscopy more accessible, since walia of the Arctic University it doesn’t require an expensive of Norway, who co-led the reTIRF objective.” For superressearch with Mark Schüttpelz of A direct STORM image acquired with chip-based illumination olution imaging, membrane Bielefeld. “Our photonic chip shows the interaction between actin (magenta) and the biologists are most likely to technology can be retrofitted membrane (green) in liver sinusoidal endothelial cells. The inset benefit from the technology, with any standard microscope shows the presence of actin between neighboring pores. she says.—CELIA ARNAUD
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C&EN | CEN.ACS.ORG | MAY 1, 2017
CREDIT: SCI. TRANSL. MED. (BONE); NAT U RE ( STO R M)
Getting a bigger picture
