The Mef2c gene dose-dependently controls hippocampal neurogenesis and the expression of autism-like behaviors.

Mutations in the activity-dependent transcription factor MEF2C have been associated with several neuropsychiatric disorders. Among these, autism spectrum disorder (ASD)-related behavioral deficits are manifested. Multiple animal models that harbor mutations in Mef2c have provided compelling evidence that Mef2c is indeed an ASD gene. However, studies in mice with germline or global brain knockout of Mef2c are limited in their ability to identify the precise neural substrates and cell types that are required for the expression of Mef2c -mediated ASD behaviors. Given the role of hippocampal neurogenesis in cognitive and social behaviors, in this study we aimed to investigate the role of Mef2c in the structure and function of newly-generated dentate granule cells (DGCs) in the postnatal hippocampus, and to determine whether disrupted Mef2c function is responsible for manifesting ASD behaviors. Overexpression of Mef2c ( Mef2cOE ) arrested the transition of neurogenesis at progenitor stages, as indicated by sustained expression of Sox2+ in Mef2cOE DGCs. Conditional knockout of Mef2c ( Mef2ccko ) allowed neuronal commitment of Mef2ccko cells; however, Mef2ccko impaired not only dendritic arborization and spine formation, but also synaptic transmission onto Mef2ccko DGCs. Moreover, the abnormal structure and function of Mef2ccko DGCs led to deficits in social interaction and social novelty recognition, which are key characteristics of ASD behaviors. Thus, our study revealed a dose-dependent requirement of Mef2c in the control of distinct steps of neurogenesis, as well as a critical cell-autonomous function of Mef2c in newborn DGCs in the expression of proper social behavior in both sexes. Significance Statement Autism spectrum disorder (ASD) is a neurodevelopmental disorder causing significant social, communication and behavioral deficits in children worldwide. Genetic complexity and heterogeneity associated with ASD have hindered the filed from establishing any precise cellular substrate associated with ASD. Recent studies have implicated hippocampal neurogenesis as one of the key players in social behavior and ASD-like behaviors. Here, using conditional deletion of transcriptional factor Mef2c , in hippocampal newborn neurons or abDGCs, we have demonstrated how Mef2c impacts behavior by regulating the structural development, physiology, and function of abDGCs. Our results revealed the essential role of Mef2c in neurogenesis and identified hippocampal neurogenesis as a neural substrate necessary for social behaviors.