Pumilio2regulates synaptic plasticity via translational repression of synaptic receptors in mice

Abstract

PUMILIO 2 (PUM2) is a member of Pumilio and FBF (PUF) family, an RNA binding protein family with phylogenetically conserved roles in germ cell development. The Drosophila Pumilio homolog is also required for dendrite morphogenesis and synaptic function via translational control of synaptic proteins, such as glutamate receptors, and recent mammalian studies demonstrated a similar role in neuronal culture with associated motor and memory abnormalities in vivo. Importantly, transgenic mice with PUM2 knockout show prominent epileptiform activity, and patients with intractable temporal lobe epilepsy and mice with pilocarpine-induced seizures have decreased neuronal PUM2, possibly leading to further seizure susceptibility. However, how PUM2 influences synaptic function in vivo and, subsequently, seizures is not known. We found that PUM2 is highly expressed in the brain, especially in the temporal lobe, and knockout of Pum2 (Pum2–/–) resulted in significantly increased pyramidal cell dendrite spine and synapse density. In addition, multiple proteins associated with excitatory synaptic function, including glutamate receptor 2 (GLUR2), are up-regulated in Pum2–/– mice. The expression of GLUR2 protein but not mRNA is increased in the Pum2–/– mutant hippocampus, Glur2 transcripts are increased in mutant polysome fractions, and overexpression of PUM2 led to repression of reporter expression containing the 3′Untranslated Region (3′UTR) of Glur2, suggesting translation of GLUR2 was increased in the absence of Pum2. Overall, these studies provide a molecular mechanism for the increased temporal lobe excitability observed with PUM2 loss and suggest PUM2 might contribute to intractable temporal lobe epilepsy.

Pumilio2 and Staufen2 selectively balance the synaptic proteome

“…As outlined above, Pum2 and Stau2 exert distinct roles in this process. It was shown that Pum2 represses expression of sodium channels, such as Na v 1.6 (Driscoll et al, 2013), as well as the AMPA receptor subunit Gria2 in the hippocampus (Dong et al, 2018), thereby dampening neuronal excitation. In our study, we do not observe Gria2 being regulated by Pum2.…”

Principles of mRNA control by human PUM proteins elucidated from multimodal experiments and integrative data analysis

“…Human PUM1 and PUM2 are expressed across tissues and their expression is highly overlapping [5,16] suggesting that they likely act redundantly. Mammalian PUM proteins have been implicated in spermatogenesis [17,18], neuronal development and function [19][20][21][22][23][24], immune function [25,26], and cancer [27][28][29][30]. PUM1 missense and deletion mutants lead to adult-onset ataxia (Pumilio1-related cerebellar ataxia, PRCA) and loss of one copy leads to developmental delay and seizures (Pumilio1-associated developmental disability, ataxia, and seizure; PADDAS) [31].…”

Targeting neuronal homeostasis to prevent seizures

“…Inset shows an example Western Blot. ** = p < 0 .01, *** = p < 0.001 Validated Pum-dependent regulated transcripts, in mammals, include Nav1.1 (SCN1A), Nav1.6 (SCN8A) and GLUR2 (aka GLUR-A, AMPA receptor) 2,8,21 . Bioinformatic analysis of expressed mRNAs also identifies a putative PRE motif in NaV1.2 (SCN2A), indicative that this channel variant is also regulated by Pum 12 .…”

“…However, Pum requires additional co-factors (including Nanos and Brain-tumor) and the actual effect of Pum is likely dictated by both the number and proximity of these additional binding elements, in addition to the number of PREs 6,7 . In mammals, regulated transcripts that have potential to influence neuron activity include Na v 1.6 (SCN8A) 2 and GLUR2 (AMPA receptor) 8 . Pum-dependent homeostatic translational repression of Na v 1.6, in rat cortical pyramidal neurons, reduces the amplitude of expressed voltage-gated Na + current (I Na ) and lowers action potential firing frequency 2 .…”