DENDRITIC MRNAS

“Linking dendritic mRNA metabolism to neuronal functions and disorders”

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 Obiettivo del progetto (Objective)

'Synaptogenesis and synaptic plasticity rely on protein synthesis, in particular on localized translation within dendrites. The aim of my project will focus on investigating the multiple and overlapping molecular mechanisms that contribute to fine-tuning the expression of dendritic mRNA at synapses. In my previous work, I have identified a novel regulatory pathway that involves splicing and modulates the stability and expression of a subset of neuronal and dendritic mRNAs. Prominent amongst the mRNAs analyzed in my studies is Arc, encoding a protein essential for memory consolidation and maintenance of LTP. Several approaches will be undertaken to elucidate the molecular elements controlling Arc mRNA expression: 1) In vivo biochemical isolation and characterization of the ribonucleoprotein particle associated with Arc mRNA 3’UTR region. The procedure will be designed in order to identify trans-acting factors whose binding is connected to: i) synaptic activity ii) dendritic transport iii) splicing of the mRNA. 2) To unveil the role of the identified factors, assays will be carried out in vivo and in cultured neurons, and will include: silencing via lentiviral expression of siRNAs, microscopy, electrophysiology and expression of reporter Arc genes carrying specific modifications. 3) Involvement of miRNAs and of cis-acting elements in controlling synaptic Arc protein expression will also be tested. miRNAs-dependent regulation will be verified in cultured neurons and potential coupling with other pathways of translational and mRNA stability regulation will be tested. Overall, the in vivo biochemical and functional characterization of both cis- and trans-acting factors controlling the expression of Arc mRNA, will allow a better understanding of the mechanisms underlying its modulation, and likely shed light on the pathways controlling dendritic mRNA localized expression and synaptic plasticity.'

Introduzione (Teaser)

Neuronal synapses in the brain strengthen or weaken in intensity depending on the signal for information transmission. This synaptic plasticity is the underlying mechanism responsible for learning and memory consolidation.

Descrizione progetto (Article)

Arc mRNA is localised at activated synaptic sites and seems to be involved in the overproduction of beta amyloid, the hallmark of Alzheimer's disease. Understanding how Arc is regulated would shed light into the process of synaptic plasticity and may also serve as a therapeutic target in Alzheimer's disease.

To improve our understanding of synaptic plasticity, the EU-funded 'Linking dendritic mRNA metabolism to neuronal functions and disorders' (DENDRITIC MRNAS) project investigated the gene expression pattern at synapses with focus on the protein Arc.

Scientists of the DENDRITIC MRNAS project worked to unravel the factors controlling Arc expression upon synaptic activity. In this context, they placed the 3' untranslated region (3'UTR) of the Arc gene to drive expression of the firefly enzyme luciferase. Genetic manipulation of the 3'UTR showed which components were required for Arc expression.

Interestingly, differential splicing of Arc mRNA was responsible for the fine-tuning of Arc expression upon synaptic signalling. It either triggered mRNA decay, thereby limiting the time window in which this essential protein was made in response to stimuli, or it elicited translation. This paradox probably serves to achieve a rapid yet limited burst of Arc expression which goes hand in hand with the nature of synaptic plasticity.

Further experimental evidence indicated that Arc regulation also takes place at the translational level. Using specific inhibitors, project researchers identified eIF2 dephosphorylation and PKA activity as key steps in switching to long-term synaptic plasticity.

Overall, the work of the DENDRITIC MRNAS study provided evidence for a multi-parametric regulation of Arc expression. The project findings have important ramifications for comprehending how long term memories are established and how physiological responses get altered in neurodegenerative diseases.