For instance, activity-regulated cytoskeleton-associated protein (Arc) is an IEG that encodes a postsynaptically localized protein that directly

influences synaptic function ( Lyford et al., 1995). Fos, Arc, and other IEGs have been frequently used as markers for neurons that were active during a short period prior to sacrifice. Although no single IEG is a perfect surrogate for neuronal activity, throughout this paper, we Selleck Apoptosis Compound Library use “activity” loosely to refer to IEG expression. Activity-dependent IEG expression has been exploited in a number of methods for studying neural circuits. With these methods, it is possible to identify cells that express IEGs in response to multiple learn more stimuli separated in time (Guzowski et al., 1999), visualize active neurons in fixed or live tissue from transgenic animals (Barth et al., 2004; Smeyne et al., 1992; Wang et al., 2006),

and manipulate the activities of IEG-expressing populations (Garner et al., 2012; Koya et al., 2009; Liu et al., 2012; Reijmers et al., 2007). Although these strategies have been useful for addressing many biological questions, they suffer from a number of limitations, including poor temporal resolution, transience of effector protein expression, and low signal-to-noise ratio. Here, we describe an approach using genetically engineered mice to obtain permanent genetic access to distributed neuronal populations that are activated by experiences within a limited time window. This approach, called targeted recombination

in active populations (TRAP), offers several advantages over currently available technologies and, when combined with genetically encoded effectors for visualizing and manipulating neurons, has the potential to greatly facilitate experimental dissection of neural circuit function. TRAP utilizes two genetic components: (1) a transgene that takes advantage of IEG regulatory elements in order to express a drug-dependent recombinase, such as the tamoxifen (TM)-dependent Cre recombinase CreERT2 (Feil et al., 1997), in an activity-dependent manner and (2) a transgene or virus that expresses an effector protein in a recombination-dependent manner (Figure 1A). For the first component, we generated knockin MYO10 mice in which CreERT2 is expressed from the endogenous Fos and Arc loci ( Figure 1B and Figure S1 available online). These knockins retain all sequences 5′ to the translational start site but replace the endogenous 3′ untranslated regions (3′UTRs), which contribute to messenger RNA (mRNA) destabilization and Arc mRNA dendritic trafficking (see Supplemental Experimental Procedures), with an exogenous SV40 polyadenylation signal to promote high-level expression. The introns and coding regions are also displaced ( Figures 1B and S1).