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Subcellular and regional localization of mRNA translation in midbrain dopamine neurons

ABSTRACT: Local translation within excitatory and inhibitory neurons is known to be involved in neuronal development and synaptic plasticity. Despite the extensive dendritic and axonal arborizations of monoaminergic neurons, the subcellular localization of protein synthesis has not been well-characterized in these populations. Here, we investigated mRNA localization in midbrain dopaminergic (mDA) neurons, cells with enormous axonal and dendritic projections, both of which can release dopamine (DA). Using highly-sensitive sequencing and imaging approaches in mDA axons, we found no evidence for axonal mRNA localization or translation. In contrast, we found that mDA neuronal dendritic projections into the substantia nigra reticulata (SNr) contain ribosomes and mRNAs encoding the DA synthesis, release, and reuptake machinery. Surprisingly, we found dendritic localization of mRNAs encoding synaptic vesicular release proteins in mDA neurons. Our results are consistent with a role for local translation in the regulation of DA transmission from dendrites, but not striatal axons. Finally, we defined a molecular signature of sparse mDA neurons in the SNr, including enrichment of an ER calcium pump previously undescribed in mDA neurons.

ORGANISM(S): Mus musculus

PROVIDER: GSE180913 | GEO | 2021/07/27

REPOSITORIES: GEO

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Project description:While microRNAs (miRNAs) have recently emerged as critical post-transcriptional modulators of gene expression in neuronal development, very little is known regarding the roles of miRNA-mediated regulation in the specification of cell-type specific dendritic complexity. The dendritic arborization (da) sensory neurons of the Drosophila PNS offer an excellent model system for elucidating the molecular mechanisms governing class specific dendrite morphogenesis and for exploring miRNA-mediated control of this process. To facilitate functional analyses of miRNA regulation in da neurons, we have conducted whole-genome miRNA expression profiling as well as mRNA expression profiling of three distinct classes of da neurons, thereby generating a comprehensive molecular gene expression signature within these individual subclasses of da neurons. To further validate the role of these expressed miRNAs in directing dendritic architecture, we conducted a genome-wide UAS-miRNA phenotypic screen using live-image confocal microscopy followed by semi-automated neurometric quantification, to directly assess the effect of over/mis-expression of individual and clustered miRNAs on neurons of varying dendritic complexity. Through this approach, we have identified numerous miRNAs with previously unknown functions in dendritic development. Gain-of-function and loss-of-function analyses revealed an endogenous role miR-2b and miR-13b (members of the K-box family) and miR-12/283/304 in dendritic patterning in da neuron subclasses. Moreover, using an integrative bioinformatic analysis approach involving inverse correlation between miRNA and mRNA expression profiling data in combination with existing target prediction algorithms, we have identified putative target of these miRNAs in regulating da neuron dendritic development. Validation of these predicted miRNA-target relationships via phenotypic analyses as well as QPCR, revealed the regulatory effect of these molecules in restricting dendritic branching in da neurons.

Project description:Induced pluripotent stem cells (iPSCs) hold great promise for in vitro disease modeling and cell replacement therapy for Parkinson’s disease (PD). Both applications crucially require an in-depth profiling of the disease-relevant, iPSC-derived cell type. Midbrain dopaminergic (mDA) neurons derived from pluripotent stem cells are of substantial interest because of their instrumental value for PD therapy. IPSC-derived mDA neuron-like cells have been generated, however, detailed genetic and epigenetic characterization of strictly purified in vitro generated DA neurons has so far lagged behind. We generated mouse Pitx3gfp/+ iPSC-derived DA neurons that, after fluorescent activated cell sorting (FACS) allowed comprehensive comparison to mesodiencephalic dopaminergic (mdDA) neurons from Fac-sorted Pitx3gfp/+ ventral midbrains. We performed detailed analysis of global gene expression and genome-scale DNA methylation of CpG islands (CGIs) by reduced representation bisulfite sequencing. The reprogramming pathway from fibroblasts to iPSCs left parental cell footprints for both gene expression and DNA methylation. However, most gene expression patterns of iPSC-derived DA neurons closely resembled that of primary mdDA neurons with the strongest correlations for mdDA specific genes. Also, for DNA methylation patterns, high similarities were found for the vast majority of CGIs when comparing primary mdDA neurons with iPSC-derived DA neurons. Additionally, we found de novo DNA methylation during in vitro differentiation for hundreds of genes specifically in lineage-committed neural precursors that persisted in iPSC-derived DA neurons. Our study provides novel detailed characteristics of iPSC-derived DA neurons in comparison to the primary cell type. These findings add important information to our knowledge about these biomedically highly valuable, in vitro generated neurons. Microarray expression study comparing 3 samples of facs-sorted, Pitx3-gfp positive cells from each experimental group to a common reference consisting of adult mouse midbrain RNA. Each sample was analysed in normal and opposite dye orientation.

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Subcellular and regional localization of mRNA translation in midbrain dopamine neurons

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