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Biological Chemistry

Ca2+ Indicators Show Their New Colors

by Lauren K. Wolf
September 12, 2011 | APPEARED IN VOLUME 89, ISSUE 37

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The Ca2+ indicators used to make this fluorescence image have been genetically coded for the nucleus (red), cytoplasm (green), and mitochondria (purple) of HeLa cells (20- to 30-µm diameter).
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The Ca2+ indicators used to make this fluorescence image have been genetically coded for the nucleus (red), cytoplasm (green), and mitochondria (purple) of HeLa cells (20- to 30-µm diameter).

Previously containing a single, lonely splotch of green, the palette of genetically encoded calcium-ion indicators for fluorescent cellular imaging has now expanded to other colors, thanks to researchers from Japan and Canada (Science, DOI: 10.1126/science.1208592). These indicator proteins are important tools, especially in neuroscience, for measuring Ca2+ concentrations in cells. Starting with a set of green-light-emitting indicators called GCaMPs, the researchers, led by Robert E. Campbell of the University of Alberta, screened genetic variants of these proteins in Escherichia coli’s periplasm—the space between the microbe’s inner and outer membranes. The team developed red- and blue-emitting indicators, an improved green indicator, and a version that emits blue light when Ca2+ is bound and green light when it is not. These sensors, which the research team dubbed GECOs to “bring to mind the colorful family of lizards,” Campbell says, enable scientists to simultaneously image Ca2+ concentrations in multiple locations within the same cell. He adds that his team will soon release the indicator genes to a public repository “to get them into the hands of as many end users as possible.”

Credit: Science
At the start of this video, histamine is added to HeLa cells (20- to 30-µm diameter), causing the release of calcium ions from their internal stores. The genetically encoded Ca2+ indicators labeling the nucleus (red), cytoplasm (green), and mitochondria (magenta) of the cells display a burst of fluorescence in response.
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