A large‐scale functional screen identifies N ova1 and N coa3 as regulators of neuronal mi RNA function

Abstract

MicroRNAs (miRNAs) are important regulators of neuronal development, network connectivity, and synaptic plasticity. While many neuronal miRNAs were previously shown to modulate neuronal morphogenesis, little is known regarding the regulation of miRNA function. In a large-scale functional screen, we identified two novel regulators of neuronal miRNA function, Nova1 and Ncoa3. Both proteins are expressed in the nucleus and the cytoplasm of developing hippocampal neurons. We found that Nova1 and Ncoa3 stimulate miRNA function by different mechanisms that converge on Argonaute (Ago) proteins, core components of the miRNA-induced silencing complex (miRISC). While Nova1 physically interacts with Ago proteins, Ncoa3 selectively promotes the expression of Ago2 at the transcriptional level. We further show that Ncoa3 regulates dendritic complexity and dendritic spine maturation of hippocampal neurons in a miRNA-dependent fashion. Importantly, both the loss of miRNA activity and increased dendrite complexity upon Ncoa3 knockdown were rescued by Ago2 overexpression. Together, we uncovered two novel factors that control neuronal miRISC function at the level of Ago proteins, with possible implications for the regulation of synapse development and plasticity.

NMDAR ‐dependent Argonaute 2 phosphorylation regulates mi RNA activity and dendritic spine plasticity

“…Importantly, to confirm that the observed changes in reporter expression were miRNA‐dependent, we performed parallel experiments with reporter constructs carrying mutations in the miR‐134, miR‐138 or Let7 seed regions of LIMK1, APT1 or LIN41 3′UTRs, respectively, to prevent miRNA binding (Storchel et al , 2015; Fig EV3A–C; Appendix Fig S4A–C). Indeed, all translational control over the luciferase constructs was abolished by these mutations, supporting our conclusions that the observed changes are caused by altered miR‐134, miR‐138 and Let‐7 activity, respectively.…”

New Perspectives on Genomic Imprinting, an Essential and Multifaceted Mode of Epigenetic Control in the Developing and Adult Brain

“…Imprinted genes both promote and oppose these processes. Downregulation of the maternally biased Ago2 in the absence of the transcription cofactor NCOA3 results in abnormally high dendritogenesis (Störchel et al 2015). miR134 regulates the abundance of the pumilio2 RNA-binding protein, and its over- or underexpression reduces dendritogenesis (Fiore et al 2009).…”

miRNAs in synapse development and synaptic plasticity

“…Inactivation of Dicer1 in hippocampal excitatory neurons causes increases in dendritic spine length, neural excitability, and post-tetanic potentiation [24-26]. Lower RISC activity following knockdown of Ncoa3, a transcriptional co-activator promoting the transcription of Ago2 (a core component of RISC) results in decreases in the volume of dendritic spines and the amplitude of miniature excitatory postsynaptic currents (mEPSC) [27]. …”

“…Neurons need miRNAs to develop and maintain dendrites, axons and dendritic spines. In Ncoa3 knockdown neurons which have a low RISC activity, dendrites become more complex and bear smaller dendritic spines [27]. Deletion of Dicer1 in the adult mouse forebrain shifts dendritic arborization towards distal dendrites and elongates dendritic spines [25].…”