From seq-ing to modeling: towards a molecular understanding of special properties of immature neurons in the human hippocampus

2 32 New neurons arising from adult neurogenesis represent a striking manifestation of neural 33 cell plasticity that persists throughout adulthood 1 .These immature dentate granule cells 34 (imGCs) exhibit distinct cellular and physiological properties compared to their mature 35 counterparts and execute the function of adult neurogenesis, making them an important 36 focus for analysis 1 .They play pivotal roles in modulating learning and memory, affective 37 behaviors, and cognition, whereas dysregulation of imGCs has been associated with 38 various human neurological disorders 1 .These intrinsic adult-born neurons offer potential 39 for developing new strategies to alleviate brain disorders, stroke and injury 1 .However, our 40 understanding of imGCs is largely based on studies involving mouse models 2 .The 41 molecular features and regulatory mechanisms of imGCs in humans and non-human 42 primates (NHPs) remain elusive, and their existence in adult humans was debated 2-4 .This 43 is largely attributed to the common assumption that imGCs in different species share vast 44 similarities.There is a lack of cross-species comparative studies and human cell-based 45 modeling for mechanistic investigation to directly examine human imGCs.Therefore, the 46 lack of a consistent method for identifying human and NHP imGCs and elucidating their 47 human-specific features impedes molecular targeting and therapeutic applications of 48 immature neurons in the human hippocampus. 49Recent efforts have utilized single-cell and single-nucleus RNA sequencing (scRNA-50 seq) to explore cell heterogeneity in the hippocampus of humans and NHPs (summarized 51 in references [ [5][6][7]).However, the DCX + PROX1 + imGCs are interspersed among other cells 52 within the dentate granule cell (GC) cluster using unsupervised clustering, even during 53 perinatal stages 5 .Consequently, these studies have yielded inconsistent cell-typing 54 outcomes of imGCs.Most studies have relied on prior knowledge from mouse models and 55 have adopted study-specific criteria for cell definition, such as using various combinationsPage 3 of 11 https://mc.manuscriptcentral.com/lifemed