Rapid, biochemical tagging of cellular activity history in vivo.

A new enzyme-based method called CaST (Ca2+-activated Split-TurboID) biochemically tags cells with elevated calcium levels in living animals within 10 minutes, without requiring implants or light delivery. The signal increases with calcium concentration and labeling time, acting as a time-gated integrator of calcium activity. Unlike transcriptional reporters that take hours, CaST allows immediate read-out after activity labeling. The approach 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

Intracellular calcium (Ca2+) is ubiquitous to cell signaling across all biology. While existing fluorescent sensors and reporters can detect activated cells with elevated Ca2+ 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 Ca2+ in vivo. Ca2+-activated Split-TurboID (CaST) labels activated cells within 10 minutes with an exogenously-delivered biotin molecule. The enzymatic signal increases with Ca2+ concentration and biotin labeling time, demonstrating that CaST is a time-gated integrator of total Ca2+ activity. Furthermore, the CaST read-out 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.