Transcription profiling of dopaminergic neurons of the substantia nigra pars compacta (SNc) and the ventral tegmental area from normal rats
ABSTRACT: The cardinal clinical features of Parkinson's disease result from selective loss of midbrain dopaminergic neurons. The goal of this experiment is to determine the gene expression profiles of these neurons by studying untreated rat substantia nigra pars compacta (SNc) and ventral tegmental area (VTA) dopaminergic neurons using laser capture microscopy to obtain region-specific neuronal mRNA.
Project description:RNA-SEQ profiling of dopaminergic neurons from the substantia nigra pars compacta and ventral tegmental area regions of the mouse mid-brain Murine midbrain dopaminergic neurons from the SNpc and VTA regions
Project description:Pitx3 is a transcription factor that is expressed in all midbrain dopaminergic (mDA) neurons during early development, but later becomes restricted in dopaminergic subsets of substantia nigra compacta (SNc) and of the ventral tegmental are (VTA) that are vulnerable to neurodegenerative stress (MPTP, 6-OHDA, rotenone, Parkinson's disease). Overall, in mice, Pitx3 is required for developmental survival of ventral SNc neurons and for postnatal survival of VTA neurons (after postnatal day 40). With the aim of determining the gene networks that distinguish Pitx3-vulnerable (Pitx3-positive) from Pitx3-resistant (Pitx3-negative) subsets of SNc and VTA, we performed a comparison at the transcriptome level between FAC-sorted mDA neurons of SNc and VTA that were obtained from wild-type and Pitx3-/- newborn mice. The latter mice have already lost the majority of their TH+Calb1- mDA neurons of ventral SNc (Pitx3-dependent), but their TH+Calb1+ neurons of dorsal SNc (Pitx3-independent), including all of VTA neurons (50% are Pitx3-dependent and 50% Pitx3-independent), are unaffected by Pitx3 deletion. At postnatal day 40, Pitx3-/- mice display a marked loss of dopaminergic subsets of VTA that normally co-express Pitx3 and Calb1 (Pitx3-dependent neurons of VTA). Overall design: Ventral midbrains were dissected from Pitx3+/+;TH-EGFP+/- and Pitx3-/-;TH-EGFP+/- mouse pups (P1-P4). SNc and VTA were separated for both mouse genotypes (4 sample types: VTA WT, VTA KO, SNc WT and SNc KO) and then tissues were digested in papain solution. Propidium-iodide (PI) was then added to the single cell suspensions and EGFP+/PI- mDA neurons were sorted by flow cytometry into RNAlater solution (3000 cells per 30uL). Batches of EGFP+ cells in RNAlater were stored at -80°C until the necessary number of cells had been accumulated for enough total RNA (100ng) per sample type, as recommended by Affymetrix and Nugen companies. Prior to purification of total RNA, corresponding batches of cells were thawed from -80°C and pooled together in order to achieve the required amount of total RNA for each sample type (VTA WT, VTA KO, SNc WT and SNc KO) in duplicate (8 samples in total).
Project description:The cardinal clinical features of Parkinson's disease (PD) (rigidity, rest tremor, bradykinesia, and postural instability) result from selective loss of midbrain dopaminergic neurons. More specifically, dopaminergic neurons in the substantia nigra pars compacta (SNc) are much more susceptible to damage than the adjacent dopaminergic neurons in the ventral tegmental area (VTA). This dichotomy is not only seen in human Parkinson's disease, but also in many animal models of PD, including administration of the mitochondrial toxin rotenone to rats, which replicates many of the behavioral and neuropathological features of PD. The factors underlying this selective vulnerability are unknown, but could be related to differences in neuronal circuitry, differences in glial support, or intrinsic differences between the neuronal populations of the two regions. Elucidation of these factors may lead to a greater understanding of the pathogenesis and treatment of Parkinson's disease. We will determine gene expression profiles of untreated rat SNc and VTA dopaminergic neurons using laser capture microscopy to obtain region-specific neuronal mRNA. There are intrinsic differences in gene expression between dopaminergic neurons in the rat SNc and VTA that result in greater susceptibility of SNc neurons to degeneration in experimental parkinsonism. These differences may be related to dopamine metabolism, oxidative metabolism and stress, protein aggregation, or other unforseen pathways. We will compare gene expression profiles between SNc and VTA dopaminergic neurons in normal rats. No treatment or time points will be studied in this experiment. Animals will be anesthetized, sacrificed by decapitation, and brains frozen on dry ice. Frozen sections will be collected onto glass microscope slides and rapidly immunostained for tyrosine hydroxylase to identify dopaminergic neurons. SNc and VTA neurons (approx. 200 per sample) will be isolated using laser capture microscopy. Total RNA will be extracted and poly-A RNA will be amplified using a modified Eberwine protocol. aRNA will be sent to the centers for labeling and hybridization to Affymetrix rat U34A arrays. We have confirmed with the center that our aRNA protocol is compatible with the centers amplification protocols; in fact, it is essentially identical. We will be providing a two-round amplification product to the center for labeling and hybridization. We recognize that using RNA after three rounds of amplification may decrease sensitivity for low copy number transcripts, but favor this approach versus pooling our samples (which are inherently paired) at this point. We have discussed this point in detail with the center. SNc and VTA samples from eight animals (16 samples total) will be provided to mitigate differences specific to individual animals. With the assisatnce of the center, paired t-tests will be used to determine differential expression between the two regions. Permutational t-test analysis and/or Benjamini and Hochberg analysis of expression ratios will be used to protect against multiple comparisons. Selected differentially expressed genes will be validated on separate tissue samples using quantitative RT-PCR or in situ hybridization.
Project description:WNT1/beta-catenin signaling plays a crucial role in the generation of mesodiencephalic dopaminergic (mdDA) neurons including the Substantia nigra pars compacta (SNc) subpopulation, whose degeneration is a hallmark of Parkinson’s Disease (PD). However, the precise functions of WNT/beta-catenin signaling in this context remain unknown. Using mutant mice, primary ventral midbrain (VM) cells and pluripotent stem cells (mouse embryonic stem cells and induced pluripotent stem cells), we show that Dickkopf 3 (DKK3), a secreted glycoprotein that modulates WNT/beta-catenin signaling, is specifically required for the correct differentiation of a rostrolateral mdDA precursor subset into SNc DA neurons. Dkk3 transcription in the murine VM coincides with the onset of mdDA neurogenesis and is required for the maintenance of LMX1A and consequently PITX3 expression in rostrolateral mdDA precursors, without affecting the proliferation or specification of their progenitors. Treatment of primary VM cells or differentiating pluripotent stem cells with recombinant WNT1 and/or DKK3 proteins consistently increases the proportion of mdDA cells with SNc DA neuron identity and promotes their survival in vitro. The SNc DA pro-differentiation and pro-survival properties of DKK3, together with its known anti-tumorigenic effect, therefore make it an ideal candidate for the improvement of regenerative and neuroprotective strategies in the treatment of PD. We performed gene expression microarray analysis on iPSC-derived and FACS-sorted GFP-positive Pitx3GFP/+ mdDA neurons, differentiated in the presence or absence of recombinant human WNT1 and recombinant human DKK3. In addition, we analysed primary and FACS-sorted GFP-positive Pitx3+/GFP mdDA neurons isolated from the E13.5 and E14.5 ventral midbrain of Pitx3+/GFP embryos
Project description:Substantia nigra pars compacta (SNpc) is highly sensitive to normal aging and selectively degenerates in Parkinson's disease. However, ventral tegmental area (VTA), a region adjacent to SNpc, is less affected in PD. Until now, molecular mechanisms behind VTA aging have not been fully investigated using high throughput techniques. Here, aging-associated early changes in transcriptome of VTA were investigated comparing late middle-aged (18 months old) to young (2 months old) mice. Three age groups of C57 wild type mice were used in microarray analysis: young (2 months old), middle aged (10 months old), and late-middle aged (18 months old) mice. Four replicates were included in each age group and each replicate was pooled from 5 mice (5 mice/replicate x 4 replicates x 3 age groups). Total RNA was isolated from VTA for hybridization on Affymetrix microarrays.
Project description:Certain neuron types fire spontaneously at high rates, an ability that is crucial for their function in brain circuits. The spontaneously active GABAergic neurons of the substantia nigra pars reticulata (SNr), a major output of the basal ganglia, provide tonic inhibition of downstream brain areas. A depolarizing "leak" current supports this firing pattern, but its molecular basis remains poorly understood. To understand how SNr neurons maintain tonic activity, we used single-cell RNA sequencing to determine the transcriptome of individual SNr neurons. We discovered that SNr neurons express the sodium leak current, NaLCN and that SNr neurons lacking NaLCN have impaired spontaneous firing. RNA sequencing profiles from 87 GFP-positive GABAergic SNr neurons and 9 GFP-negative SNr cells were carried out. However only 80 samples that passed initial quality control and that were included in the data processing are represented in this record.
Project description:We compared the proteome from a vulnerable region (Substantia nigra pars compacta, SNc) of wild-type and Parkinsonian mice to that of an adjacent, less vulnerable, region (Ventral tegmental area, VTA) and identified several proteins which exhibited both spatiotemporal- and genotype-restricted changes.
Project description:Midbrain dopamine neurons project to numerous targets throughout the brain to modulate various behaviors and brain states. Within this small population of neurons exists significant heterogeneity based on physiology, circuitry, and disease susceptibility. Recent studies have shown that dopamine neurons can be subdivided based on gene expression; however, the extent to which genetic markers represent functionally relevant dopaminergic subpopulations has not been fully explored. Here we performed single-cell RNA-sequencing of mouse dopamine neurons and validated studies showing that Neurod6 and Grp are selective markers for dopaminergic subpopulations. Using a combination of multiplex fluorescent in situ hybridization, retrograde labeling, and electrophysiology in mice of both sexes, we defined the anatomy, projection targets, physiological properties, and disease vulnerability of dopamine neurons based on Grp and/or Neurod6 expression. We found that the combinatorial expression of Grp and Neurod6 defines dopaminergic subpopulations with unique features. Grp/Neurod6 dopamine neurons reside in the ventromedial VTA, send projections to the medial shell of the nucleus accumbens, and have noncanonical physiological properties. Grp/Neurod6- DA neurons are found in the VTA as well as in the ventromedial portion of the SNc, where they project selectively to the dorsomedial striatum. Grp-/Neurod6 DA neurons represent a smaller VTA subpopulation, which is preferentially spared in a 6-OHDA model of Parkinson’s disease. Together, our work provides detailed characterization of Neurod6 and Grp expression in the midbrain and generates new insights into how these markers define functionally relevant dopaminergic subpopulations with distinct projection patterns, physiology, and disease vulnerability. Overall design: We collected a total of 384 neurons from 8 different p26-p34 DAT-Cre::Ai9 mice (6 male 2 female) to isolate DA neurons. RNA was captured from each samples neurons on separate fluidigm chips then all samples were pooled before sequencing.
Project description:Adult male Sprague Dawley rats (5 month-old at the beginning of the study) were subcutaneously exposed to 0.5 mg.kg/d rotenone or the corresponding solvent (PEG/DMSO, 1/1) for 28 days. At the end of the experiment, animals were sacrificed by decapitation and brains were rapidly taken out within 30-40 s. Total RNA was prepared from laser-capture microdissected rat substantia nigra pars compacta (Snpc). Changes in transcript abundance within SNpc were analyzed on samples from solvent and rotenone-exposed groups (n = 3 per group) using CodeLink™ Rat Whole Genome bioarrays containing 34,000 transcripts and EST probes (GE Healthcare, Amersham, Saclay, France). Overall design: Two groups of rats were exposed either to rotenone (CR rats) or to solvents (CS rats) in order to analyse pesticides impact on gene expression.