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Young neurons in the adult brain are key to some types of learning and memory. They integrate in the dentate gyrus (DG) of the hippocampus contributing to such cognitive processes following timely developmental events. While experimentally impairing GABAergic transmission through the blockade or elimination of the ionic cotransporter NKCC1 leads to alterations in the proper maturation of young neurons, it is still unknown if the in vivo administration of common use diuretic drugs that block the cotransporter, alters the development of young hippocampal neurons and affects DG-related functions. In this study, we delivered chronically and intracerebroventricularly the NKCC1 blocker bumetanide to young-adult rats. We analyzed doublecortin density and development parameters (apical dendrite length and angle and dendritic arbor length) in doublecortin positive neurons from different subregions in the DG and evaluated the performance of animals in contextual fear learning and memory. Our results show that in bumetanide-treated subjects, doublecortin density is diminished in the infra and suprapyramidal blades of the DG; the length of primary dendrites is shortened in the infrapyramidal blade and; the growth angle of primary dendrites in the infrapyramidal blade is different from control animals. Behaviorally, treated animals showed the typical learning curve in a contextual fear task, and freezing-time displayed during contextual fear memory was not different from controls. Thus, in vivo icv delivery of bumetanide negatively alters DCX density associated to young neurons and its proper development but not to the extent of affecting a DG dependent task as aversive context learning and memory.
Adult neurogenesis is regulated by stem cell niche-derived extrinsic factors and cell-intrinsic regulators, yet the mechanisms by which niche signals impinge on the activity of intrinsic neurogenic transcription factors remain poorly defined. Here, we report that MEIS2, an essential regulator of adult SVZ neurogenesis, is subject to posttranslational regulation in the SVZ olfactory bulb neurogenic system. Nuclear accumulation of MEIS2 in adult SVZ-derived progenitor cells follows downregulation of EGFR signaling and is modulated by methylation of MEIS2 on a conserved arginine, which lies in close proximity to nested binding sites for the nuclear export receptor CRM1 and the MEIS dimerization partner PBX1. Methylation impairs interaction with CRM1 without affecting PBX1 dimerization and thereby allows MEIS2 nuclear accumulation, a prerequisite for neuronal differentiation. Our results describe a form of posttranscriptional modulation of adult SVZ neurogenesis whereby an extrinsic signal fine-tunes neurogenesis through posttranslational modification of a transcriptional regulator of cell fate.