Ca²⁺ Indicators Show Their New Colors

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.”