Neuronal activity-related transcription is blunted in immature compared to mature dentate granule cells

Immature dentate granule cells (DGCs) generated in the hippocampus during adulthood are believed to play a unique role in dentate gyrus function. Although immature DGCs have hyperexcitable membrane properties in vitro, the consequences of this hyperexcitability in vivo remain unclear. In particular, the relationship between experiences that activate the dentate gyrus, such as exploration of a novel environment (NE), and downstream molecular processes that modify dentate gyrus circuitry in response to cellular activation are unknown in this cell population. We first performed quantification of immediate early gene proteins in immature (5-week-old) and mature (13-week-old) DGCs from mice exposed to a NE. Paradoxically, we observed lower immediate early gene protein expression in hyperexcitable immature DGCs. We then isolated nuclei from active and inactive immature DGCs and performed single nuclei RNA-Sequencing. Compared to mature nuclei collected from the same animal, immature DGC nuclei showed less activity-induced transcriptional change, even though they were classified as active based on expression of ARC protein. These results demonstrate that the coupling of spatial exploration, cellular activation, and transcriptional change differs between immature and mature DGCs, with blunted activity-induced changes in immature cells. Single-nucleus RNA-seq of mouse dentate granule neurons (PROX1+CTIP2+) collected after the mouse was exposed to a novel environment. Cells are either immature (approximately 5 weeks of age) or mature and either active (ARC protein detected at sort) or inactive (ARC protein not detected). Two time points after the novel environment exposure are included, either 1hr or 4hr.