A loss of function allele for murine Staufen1 leads to impairment of dendritic Staufen1-RNP delivery and dendritic spine morphogenesis

Abstract

The dsRNA-binding protein Staufen was the first RNA-binding protein proven to play a role in RNA localization in Drosophila. A mammalian homolog, Staufen1 (Stau1), has been implicated in dendritic RNA localization in neurons, translational control, and mRNA decay. However, the precise mechanisms by which it fulfills these specific roles are only partially understood. To determine its physiological functions, the murine Stau1 gene was disrupted by homologous recombination. Homozygous stau1 tm1Apa mutant mice express a truncated Stau1 protein lacking the functional RNA-binding domain 3. The level of the truncated protein is significantly reduced. Cultured hippocampal neurons derived from stau1 tm1Apa homozygous mice display deficits in dendritic delivery of Stau1-EYFP and ␤-actin mRNA-containing ribonucleoprotein particles (RNPs). Furthermore, these neurons have a significantly reduced dendritic tree and develop fewer synapses. Homozygous stau1 tm1Apa mutant mice are viable and show no obvious deficits in development, fertility, health, overall brain morphology, and a variety of behavioral assays, e.g., hippocampus-dependent learning. However, we did detect deficits in locomotor activity. Our data suggest that Stau1 is crucial for synapse development in vitro but not critical for normal behavioral function.dendrite ͉ RNA transport ͉ ribonucleoprotein particles ͉ double-stranded RNA-binding protein

Staufen1 senses overall transcript secondary structure to regulate translation

“…Like many RNA-binding factors, the Drosophila and mammalian Staufen proteins have been implicated in multiple post-transcriptional processes including alternative splicing 13 , RNA localization 4,6,[30][31][32] , translational activation 7 and translation-dependent mRNA decay [8][9][10][11]14,20,33,34 . Which activity is observed depends on the cellular context, the identity of the bound RNA and the location of the binding site on the target RNA.…”

“…FMRP, however, is a negative regulator of translation. Whereas deletion of either FMRP or Stau1 causes neurological defects, the phenotypes are opposite: absence of FMRP leads to dendritic spine overgrowth 46 , whereas absence of Stau1 results in fewer spines 14 . Thus it is possible that FMRP and Stau1 have opposing roles in synaptic protein production, with FMRP inhibiting translation and Stau1 promoting it.…”

“…In mammals, Stau1 has been implicated in mRNA transport to neuronal dendrites 6 , regulation of translation via physical interaction with the ribosome 7 , a form of translation-dependent mRNA degradation known as Staufen-mediated decay (SMD) [8][9][10][11] , regulation of stress-granule homeostasis 12 , alternative splicing, nuclear export and translation of a gene containing 3′-UTR CUG-repeat expansions 13 . Although Stau1 is not essential for mammalian development, neurons lacking Stau1 have dendritic spinemorphogenesis defects in vitro, and knockout mice have locomotor-activity deficits 14 .…”

Dendritically Localized Transcripts Are Sorted into Distinct Ribonucleoprotein Particles That Display Fast Directional Motility along Dendrites of Hippocampal Neurons

“…Single detection was performed as described previously (Vessey et al, 2008). For the simultaneous detection of two transcripts, differentially labeled RNA probes (DIG and fluorescein) are allowed to hybridize together to their targets at 65°C overnight.…”

Genomic analysis of RNA localization

“…55,76 Expression of a dominant negative form of staufen results in inhibition of RNA transport to dendrites, 77 and neurons from knockout mice are deficient in dendritic delivery of RNPs while the mice themselves show defects in locomotor activity. 78 Mammalian staufen has four double-stranded RNA binding domains, although not all of them have strong doublestranded RNA binding activity. 54 Besides a preference for double-stranded RNA, staufen has long been thought to be relatively nonspecific in its RNA binding, but recent work has demonstrated that staufen may in fact prefer distinct double-stranded structures.…”