The calcium-regulated protein phosphatase Calcineurin (CaN) participates in synaptic plasticity and the regulation of transcription factors, including Nuclear Factor of Activated T cells (NFAT). To understand how CaN contributes to neuronal circuit development, whole-cell mEPSC recordings and multiphoton imaging were performed in the visual system of living Xenopus laevis tadpoles electroporated to express either a CaN phosphatase inhibitor or N-VIVIT, a nuclear localization sequence-tagged VIVIT peptide that blocks the binding of CaN to select substrates including NFAT. Both strategies increased mEPSC frequency and dendritic arbor complexity in tectal neurons over 3 days. Expression of either of two constitutively active Xenopus NFATs (CA-NFATs) restored normal synaptic properties in neurons expressing N-VIVIT. However, the morphological phenotype was only rescued by a CA-NFAT bearing an intact regulatory domain, implying that transcriptional control of morphological and electrophysiological properties of neurons is mediated by distinct NFAT interactions.
