The transcription factor ZFP64 facilitates climbing-fiber synapse elimination along signaling pathway mediated by P/Q-type voltage-dependent Ca2+ channel in the developing cerebellum

概要

Functional neural circuits are formed by eliminating early-formed redundant synapses and strengthening necessary ones in the developing nervous system. This process is known as synapse elimination and is widely thought to be fundamental for shaping functionally mature neural circuits during postnatal development. The climbing fiber to Purkinje cell synapse in the cerebellum provides an ideal model to study synapse elimination. In mice, Purkinje cells are innervated by multiple climbing fibers at birth, and then a single climbing fiber is selectively strengthened while the other climbing fibers are weakened and eventually eliminated by the end of the third postnatal week. Previous studies have demonstrated that the P/Q-type voltage-dependent Ca2+ channel (P/Q-VDCC) in Purkinje cells is essential for multiple phases of climbing fiber synapse elimination. To identify molecules that contribute to climbing fiber synapse elimination along the signaling pathway of P/QVDCC, I performed microarray analysis and detected molecules whose expression was significantly reduced in the cerebella of Purkinje cell-specific P/Q-VDCC knockout mice compared with those of their wild-type littermates. Utilizing RNAi-mediated knockdown of the candidate molecules in Purkinje cells in vivo during postnatal development and whole-cell recordings from Purkinje cells in cerebellar slices, I identified a transcription factor, ZFP64, as a novel molecule that is involved in climbing fiber synapse elimination after postnatal day 13. Morphological analyses of cerebellar slices with ZFP64 knockdown manifest that translocation of a single strengthened climbing fiber to the Purkinje cell dendrite and removal of climbing fiber synapses from the soma were both impaired in Purkinje cells with ZFP64 knockdown. Furthermore, ZFP64 knockdown in Purkinje cells enhanced synaptic responses from parallel fibers, the other excitatory inputs to Purkinje cells. By performing double knockdown of ZFP64 and P/Q-VDCC in Purkinje cells, I confirmed that ZFP64 acts functionally along the same pathway of P/Q-VDCC. These results suggest that ZFP64 in Purkinje cells contributes to climbing fiber synapse elimination along signaling pathway mediated by P/Q-VDCC by facilitating dendritic translocation of a single strongest climbing fiber and eliminating redundant climbing fiber synapses from the soma.