A bimodal bioluminescent Ca2+ indicator toward spatiotemporally-scalable imaging

Abstract

For decades, genetically encoded Ca2+ indicators (GECIs), have been under development for the purpose of visualizing intracellular Ca2+ dynamics. Fluorescent GECIs are limited for the purpose of deep tissue long-term whole-body imaging due to their requirement for external illumination. Bioluminescent GECIs overcome these restraints but are somewhat compromised in terms of spatiotemporal resolution compared to fluorescent probes. To address this, we developed a bimodal Ca2+ indicator by combining a single fluorescent protein based Ca2+ indicator and a split luciferase. The novel design of this bimodal indicator enables Ca2+ imaging in the same specimen in both fluorescent and bioluminescent mode. The ability to switch between fluorescent and bioluminescent modes with a single indicator should benefit applications where micro and macro scale observation of cells or tissues is desirable. Use of such a probe enables trans-scale imaging, where macro scale imaging of a group of cells or tissue can be combined with fluorescent imaging of single cells.