Regulated expression of an actin-associated protein, synaptopodin, during long-term potentiation

We report NMDA receptor-dependent expression of synaptopodin mRNA in the dentate granule cells of the hippocampus following induction of long-term potentiation (LTP) in vivo. Synaptopodin did not belong to immediate-early genes, as de novo protein synthesis was required for the induction of synaptopodin gene transcription. An increased level of synaptopodin mRNA was observed at 75 min and 3.5 h after the onset of LTP. Importantly, there was correlation between the induction of mRNA expression and the persistence of LTP. Synaptopodin immunoreactivity was elevated specifically in synaptic layers, middle and outer molecular layers of dentate gyrus where LTP was induced. As synaptopodin is an actin-associated protein present in spine neck and implicated in the modulation of cell morphology, our results suggest that synaptopodin, by regulating the dynamics of the actin cytoskeleton, contributes to the morphological change in spine shape considered to be important for the maintenance of synaptic plasticity.