Subregion-specific rules govern the distribution of neuronal immediate-early gene induction

Abstract

The induction of immediate-early gene (IEG) expression in brain nuclei in response to an experience is necessary for the formation of long-term memories. Additionally, the rapid dynamics of IEG induction and decay motivates the common use of IEG expression as markers for identification of neuronal assemblies (“ensembles”) encoding recent experience. However, major gaps remain in understanding the rules governing the distribution of IEGs within neuronal assemblies. Thus, the extent of correlation between coexpressed IEGs, the cell specificity of IEG expression, and the spatial distribution of IEG expression have not been comprehensively studied. To address these gaps, we utilized quantitative multiplexed single-molecule fluorescence in situ hybridization (smFISH) and measured the expression of IEGs (Arc, Egr2, and Nr4a1) within spiny projection neurons (SPNs) in the dorsal striatum of mice following acute exposure to cocaine. Exploring the relevance of our observations to other brain structures and stimuli, we also analyzed data from a study of single-cell RNA sequencing of mouse cortical neurons. We found that while IEG expression is graded, the expression of multiple IEGs is tightly correlated at the level of individual neurons. Interestingly, we observed that region-specific rules govern the induction of IEGs in SPN subtypes within striatal subdomains. We further observed that IEG-expressing assemblies form spatially defined clusters within which the extent of IEG expression correlates with cluster size. Together, our results suggest the existence of IEG-expressing neuronal “superensembles,” which are associated in spatial clusters and characterized by coherent and robust expression of multiple IEGs.

Sleep loss drives brain region- and cell type-specific alterations in ribosome-associated transcripts involved in synaptic plasticity and cellular timekeeping

“…While IEGs are generally assumed to reflect specific patterns of recent neuronal activity (Tyssowski and Gray, 2019), there are brain region-and microcircuit-specific differences in IEG expression which reflect neurons' network connectivity patterns (Gonzalez et al, 2019;Tyssowski et al, 2018). Moreover, IEG expression in PV+ interneurons is regulated by distinct cellular pathways and is differentially gated by neuronal activation (Cohen et al, 2016).…”

Genes and environments, development and time

“…Gonzales et al (73) investigate the cellular distribution of IEG expression after an acute exposure to cocaine in mouse striatal neurons. The induction and decay of IEG expression is used as a marker to encode recent experience.…”

Egr2 induction in Drd1+ ensembles of the ventrolateral striatum supports the development of cocaine reward

“…Of these, the IEG whose expression contributes most towards classification of the recent experience of individual mice is Egr2 (Mukherjee et al, 2018). Egr2 is, furthermore, the gene most robustly induced by cocaine in the dorsal striatum [(Gonzales et al, 2020;Mukherjee et al, 2018); Supplementary file 4], and is a sensitive indicator of cocaine-engaged striatal cell assemblies Figure 1: Transcriptional profiling resolves the dynamics of cocaine-induced gene expression within major nodes of the reward circuitry. (A) Scheme describing the cocaine sensitization paradigm, and time points (0,1,2,4 hrs) at which samples were obtained for analysis of gene expression following acute (0 = cocaine naïve); repeated (5 th exposure to cocaine; 0 = 24 hrs following 4 th exposure); and challenge exposures (acute exposure following 21 days of abstinence from repeated exposure ; 0 = abstinent mice).…”

“…n= 3 mice in each group (***p < 0.0001, Mixed effects linear model; see Supplementary file 6). (Gonzales et al, 2020). Transgenic approaches based on IEG expression support genetic access to neuronal assemblies recruited by experience (Cruz et al, 2013;DeNardo and Luo, 2017;Hope, 2019;Minatohara et al, 2016;Sakaguchi and Hayashi, 2012;Tonegawa et al, 2015).…”