A special vector system was developed to monitor the in vitro and in vivo endogenous level of a primary transcript of miR124a during neuronal differentiation The upstream regions of miR124a were fused with luciferase (Gluc) and their activity was measured. During neurogenesis of P19 cells, the primary transcript level of miR124a was increased 1.5-times compared to the undifferentiated P19 cells. P19 cells grafted to nude mice exhibited the same pattern of luciferase activity in vivo as they did in vitro. The expression of primary miR124a during neurogenesis was successfully imaged by in vitro and in vivo luciferase reporter gene-based method.