Considerable progress has been made understanding the effects of microRNAs on neuronal development, but microRNAs are also expressed in mature neurons where they have been proposed to control synaptic plasticity. This is an appealing concept because local regulation of protein translation is essential for this process and microRNAs can regulate dendritic growth and spine formation, properties that underlie plasticity. The idea that microRNAs contribute to axonal growth has received less attention, in part because the existence of polyribosomes in this compartment has been controversial. We argue in this proposal that microRNA regulation of axonal growth does not necessarily require translation to occur within the axon and that palmitoylation enzymes, regulated by microRNAs elsewhere in the neuron, can direct trafficking of key signaling molecules to axonal membranes. This proposal focuses on miR-134, a microRNA initially characterized by virtue of its "activity-dependence" and ability to regulate dendritic spine size. Using a set of ratiometric microRNA sensors, we found, unexpectedly, that miR-134 activity in mature cortical neurons was limited to inhibitory somatostatin (SST)-producing interneurons, contradicting a widely held view of miR-134 function. The mechanisms responsible for restricting miR-134 expression to SST-interneurons are unknown, and we propose that this is accomplished via cell-specific processing of the miR-134 precursor. We will establish whether the ability of neurons to generate mature, functional miR-134 is due to transcriptional or post-transcriptional mechanisms, identify RNA-binding proteins that interact with the precursor, and test whether these factors affect processing of the miR-134 precursor in a cell- specific manner using miR-Glo, a novel fluorescence assay. Using a new method termed RISC-trap designed to capture microRNA-mRNA interactions prior to mRNA degradation, we discovered that miR-134 targets the palmitoylation enzyme, DHHC9, which controls Ras trafficking to the cell membrane. We will test whether the miR-134 regulation of DHHC9 in inhibitory SST interneurons, and the consequent palmitoylation of Ras, controls Ras trafficking to axonal growth cones and, consequently, axon morphology in SST interneurons. We hypothesize that activity-regulation of miR- 134 negatively influences axon growth and is related to the unique axonal branching pattern characteristic of these cells. The ability of microRNAs such as miR-134 to regulate palmitoylation enzymes, and thereby membrane trafficking of signaling molecules like Ras, could be an important component of synaptic plasticity, particularly in relation to axonal growth.

Public Health Relevance

This proposal focuses on miR-134, a microRNA initially characterized by virtue of its activity- dependence and ability to regulate dendritic spine size. Using a set of ratiometric microRNA sensors, we found, unexpectedly, that miR-134 activity in mature cortical neurons was limited to inhibitory somatostatin (SST)-producing interneurons, contradicting a widely held view of miR-134 function. We will determine how this specificity occurs, explore a novel target of miR-134 action, and elucidate how the regulation of this target contributes to the unique axonal characteristics of SST interneurons.)

Agency
National Institute of Health (NIH)
Institute
National Institute of Mental Health (NIMH)
Type
Research Project (R01)
Project #
1R01MH099099-01
Application #
8416571
Study Section
Synapses, Cytoskeleton and Trafficking Study Section (SYN)
Program Officer
Beckel-Mitchener, Andrea C
Project Start
2012-12-24
Project End
2017-11-30
Budget Start
2012-12-24
Budget End
2013-11-30
Support Year
1
Fiscal Year
2013
Total Cost
$385,000
Indirect Cost
$135,000
Name
Oregon Health and Science University
Department
Neurosciences
Type
Schools of Medicine
DUNS #
096997515
City
Portland
State
OR
Country
United States
Zip Code
97239
Chai, Sunghee; Cambronne, Xiaolu A; Eichhorn, Stephen W et al. (2013) MicroRNA-134 activity in somatostatin interneurons regulates H-Ras localization by repressing the palmitoylation enzyme, DHHC9. Proc Natl Acad Sci U S A 110:17898-903