Overexpression of miR-137 leads to altered neuronal maturation of new neurons in vivo. (A): Illustration showing the stage-specific neuronal markers that can be used to identify the maturation state of developing dentate gyrus (DG) granule neurons. (B, C): Confocal images showing two representative eGFP-expressing neurons in the DG: a relatively immature eGFP neuron (B) expressed DCX (immature marker) but not NeuN (mature neuron) and a relatively mature eGFP+ neuron (C) expressed NeuN but not DCX. (D): The miR-137-overexpressing neuron population had decreased proportions of NeuN+ only (blue) mature neurons and of DCX+/NeuN+ (yellow) transitioning neurons, but increased proportion of DCX+ only (red) immature neurons compared with control (*p < .05). Abbreviations: DCX, doublecortin; eGFP, enchanced green fluorescent protein; NeuN, neuronal nuclear antigen.