Dendrites of Mammalian Neurons Contain Specialized P-Body-Like Structures That Respond to Neuronal Activation

Abstract

Intracellular mRNA transport and local translation play a key role in neuronal physiology. Translationally repressed mRNAs are transported as a part of ribonucleoprotein (RNP) particles to distant dendritic sites, but the properties of different RNP particles and mechanisms of their repression and transport remain largely unknown. Here, we describe a new class of RNP-particles, the dendritic P-bodylike structures (dlPbodies), which are present in the soma and dendrites of mammalian neurons and have both similarities and differences to P-bodies of non-neuronal cells. These structures stain positively for a number of P-body and microRNP components, a microRNA-repressed mRNA and some translational repressors. They appear more heterogeneous than P-bodies of HeLa cells, and they rarely contain the exonuclease Xrn1 but are positive for rRNA. These particles show motorized movements along dendrites and relocalize to distant sites in response to synaptic activation. Furthermore, Dcp1a is stably associated with dlP-bodies in unstimulated cells, but exchanges rapidly on neuronal activation, concomitantly with the loss of Ago2 from dlP-bodies. Thus, dlP-bodies may regulate local translation by storing repressed mRNPs in unstimulated cells, and releasing them on synaptic activation.

Genetic Modifiers ofdFMR1Encode RNA Granule Components in Drosophila

“…Remarkably, four out of the five proteins colocalized, albeit at different levels, with a YFP-labeled dFMR1 granules in neurites of cultured Drosophila motor neurons ( Figure 2; Barbee et al 2006). No specific antibody was available to test the presence of Dco/Dbt in neuronal granules but studies from Saccharomyces cerevisiae have shown that a homologous protein is present on P bodies (D. Muhlrad and R. Parker, unpublished observations), which contain many of the components found in neuronal granules (Barbee et al 2006;Cougot et al 2008;Miller et al 2009). Thus, we conclude that at least PABP, Orb2, Rm62, and SmD3 are components of FMRP-containing RNA granules found in neuronal processes.…”

BDNF-induced local protein synthesis and synaptic plasticity

“…Furthermore, BDNF was shown to induce the translocation of dendritic P-body-like structures toward the distal regions of dendrites in hypothalamic neurons (Cougot et al, 2008). These P-body-like structures often contained ZBP1 and FMRP, well described RNA-binding proteins involved in mRNA transport (Cougot et al, 2008). These findings, together with the emerging roles of miRNAs in the regulation of local mRNAs, suggest a close interplay between P-bodies and RNA transport granules.…”

“…It was recently shown that BDNF treatment increased the formation of dendritic and somatic P-bodies that contain untranslated RNA targeted for repression or degradation (Huang et al, 2012). Furthermore, BDNF was shown to induce the translocation of dendritic P-body-like structures toward the distal regions of dendrites in hypothalamic neurons (Cougot et al, 2008). These P-body-like structures often contained ZBP1 and FMRP, well described RNA-binding proteins involved in mRNA transport (Cougot et al, 2008).…”

EGFP-FMRP Granules Are Proto-Granules That Can Be Shunted to Stress Granules During a Stress Response

“…Heterologously expressed EGFP-FMRP has been used as a surrogate marker for endogenous FMRP by several laboratories in a wide variety of studies (Antar et al, 2005;Castren et al, 2001;Cougot et al, 2008;Darnell et al, 2005;Davidovic et al, 2004;De Diego Otero et al, 2002;Dictenberg et al, 2008;Levenga et al, 2009;Pfeiffer and Huber, 2007). Like endogenous FMRP, EGFP-FMRP was found to co-sediment with polyribosomes in cultured neurons (Darnell et al, 2005).…”

“…In contradistinction to endogenous FMRP granules, which are small, and while pervasive in cultured cells not particularly prevalent, (Cougot et al, 2008;Dolzhanskaya et al, 2006a;Dolzhanskaya et al, 2006b) EGFP-FMRP granules are large, and amorphous. In fact, they tend to be larger and more non-uniformly round than stress granules, Table 2.…”