Rapid, biochemical tagging of cellular activity history in vivo

A new technique called CaST (calcium-activated split-TurboID) uses an enzyme to rapidly tag cells that have elevated calcium levels in living animals, marking activated cells within 10 minutes. The tagging signal increases with both calcium concentration and labeling time, acting as a time-gated integrator of total calcium activity. Unlike transcriptional reporters that take hours to produce a signal, CaST provides readout immediately after activity labeling. The method was used to tag prefrontal cortex neurons activated by psilocybin in untethered mice, and the CaST signal correlated with psilocybin-induced head-twitch responses.

Study at a glance

Abstract

Abstract Intracellular calcium (Ca 2+ ) is ubiquitous to cell signaling across biology. While existing fluorescent sensors and reporters can detect activated cells with elevated Ca 2+ levels, these approaches require implants to deliver light to deep tissue, precluding their noninvasive use in freely behaving animals. Here we engineered an enzyme-catalyzed approach that rapidly and biochemically tags cells with elevated Ca 2+ in vivo. Ca 2+ -activated split-TurboID (CaST) labels activated cells within 10 min with an exogenously delivered biotin molecule. The enzymatic signal increases with Ca 2+ concentration and biotin labeling time, demonstrating that CaST is a time-gated integrator of total Ca 2+ activity. Furthermore, the CaST readout can be performed immediately after activity labeling, in contrast to transcriptional reporters that require hours to produce signal. These capabilities allowed us to apply CaST to tag prefrontal cortex neurons activated by psilocybin, and to correlate the CaST signal with psilocybin-induced head-twitch responses in untethered mice.