A Novel Single Vector Intersectional AAV Strategy for Interrogating Cellular Diversity and Brain Function
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ABSTRACT: As the discovery of cellular diversity in the brain accelerates, so does the need for functional tools that target cells based on multiple features, such as gene expression and projection target. By selectively driving recombinase expression in a feature-specific manner, one can utilize intersectional strategies to conditionally promote payload expression only where multiple features overlap. We developed Conditional Viral Expression by Ribozyme Guided Degradation (ConVERGD), a single-construct intersectional targeting strategy that combines a self-cleaving ribozyme with traditional FLEx switches. ConVERGD offers benefits over existing platforms, such as expanded intersectionality, the ability to accommodate larger and more complex payloads, and a vector design that is easily modified to better facilitate rapid toolkit expansion. To demonstrate its utility for interrogating neural circuitry, we employed ConVERGD to target an unexplored subpopulation of norepinephrine (NE)-producing neurons within the rodent locus coeruleus (LC) identified via single-cell transcriptomic profiling to co-express the stress-related endogenous opioid gene prodynorphin (Pdyn). These studies showcase ConVERGD as a versatile tool for targeting diverse cell types and reveal Pdyn-expressing NE+ LC neurons as a small neuronal subpopulation capable of driving anxiogenic behavioral responses in rodents.
Project description:Central norepinephrine (NE) neurons, mainly located in the Locus coeruleus (LC), play roles in a wide range of behavioral and physiological processes. How the human LC-NE neurons develop and what roles they play in the pathophysiology of human diseases is poorly understood, partly due to the unavailability of functional human LC-NE neurons. Here we established a technology for efficient generation of LC-NE neurons from human pluripotent stem cells by identifying a novel role of ACTIVIN A in regulating the LC-NE transcription factors in the dorsal rhombomere 1 (r1) progenitors. The in vitro generated human LC-NE neurons not only display extensive axonal arborization and release/uptake NE, but also exhibit the pacemaker activity, calcium oscillation, and in particular chemoreceptor activity in response to CO2. Multiple timepoint single nucleus RNA-Seq (snRNA-Seq) analysis captured the dynamic NE differentiation process, confirmed the NE cell population and revealed the differentiation trajectory from hindbrain progenitors to NE neurons via ASCL1 expressing precursor stage. The LC-NE neurons engineered with a NE sensor reliably reported the extracellular NE level. The availability of functional human LC-NE neurons enables investigation of their roles in the pathogenesis of and development of therapeutics for neural psychiatric and degenerative diseases.
Project description:Estrogen receptor a (ERa) signaling in the ventromedial hypothalamus (VMH) contributes to energy homeostasis by modulating physical activity and thermogenesis. However, the precise neuronal populations involved remain undefined. Using single-cell RNA transcriptomics and in situ hybridization, we describe six neuronal populations in the mouse VMH. ERa is enriched in populations showing sex biased expression of reprimo (Rprm), tachykinin 1 (Tac1), and prodynorphin (Pdyn). Female biased expression of Tac1 and Rprm is patterned by ERa-dependent repression during male development, whereas male biased expression of Pdyn is maintained by circulating testicular hormone in adulthood. Chemogenetic activation of ERa+ VMH neurons stimulates heat generation and movement in both sexes. However, silencing Rprm gene function increases core temperature selectively in females and ectopic Rprm expression in males is associated with reduced core temperature. Together these findings reveal a role for Rprm in temperature regulation and ERa in the masculinization of neuron populations that underlie energy expenditure.
Project description:Purpose: The locus coeruleus (LC) is a small nucleus in the pons, with norepinephrine (NE) as its major transmitter. It plays key roles in wakefulness and is associated with disorders like depression. The study aims to analyze single-cell RNA-seq data to subdivide neurons in the LC and chart their neuropeptide, co-transmitter, and receptor profiles. It also seeks to build a precise map of galanin and its receptors in the mouse LC, and understand the role of neuropeptide expression and signaling. Results: The study identified 24 clusters in total, with 3 NE, 17 glutamate, and 5 GABA subtypes. NE neurons expressed at least 19 neuropeptide transcripts, mainly galanin (Gal) but not Npy, and >30 neuropeptide receptors. Among galanin receptors, Galr1 was expressed in ~19% of NE neurons, and highly expressed in GABA neurons surrounding the NE ensemble. Patch-clamp electrophysiology and cell-type-specific Ca2+-imaging using GCaMP6s revealed that a GalR1 agonist inhibits no more than ~35% of NE neurons, with the effect being direct and not relying on feed-forward GABA inhibition. Conclusions: The results define a role for the galanin system in NE functions and provide a conceptual framework for the action of many other peptides and their receptors. The study found that most NE neurons express mRNA transcripts for galanin, at least 19 neuropeptides (but not Npy), and >30 neuropeptide receptors, including Galr1 at low levels. Selective activation of GalR1 inhibited the spontaneous activity of a subset of NE neurons possibly through the activation of Kv currents. These findings offer new insights into the role of neuropeptide expression and signaling in mouse LC.
Project description:Addiction to psychostimulants is associated with neuroadaptive changes in various brain regions. In this experiment we use a model of methamphetamine self-administration during which we use footshocks as adverse consequences to divide rats into animals that continue to press an active lever to get the drug (shock-resistant) whereas other rats stop or significantly reduce pressing the lever (shock-sensitive) in the presence of these adverse consequences. To investigate potential molecular bases for the divergent phenotype, we performed a whole rat transcriptome study using Affymetrix rat arrays that cover more than 24,000 coding transcripts. The array experiments revealed that there were 24 differentially expressed genes between the resistant and sensitive rats, with 15 up- and 9 downregulated transcripts. Ingenuity pathway analysis revealed that these transcripts belong in a network of genes involved in nervous system development and function, cell signaling, behavior, and disorders of the basal ganglia. These genes included proenkephalin (PENK) and prodynorphin (PDYN), among others. Because PDYN and PENK are expressed in dopamine D1- and D2-containing NAc neurons, respectively, these findings suggest that mechanisms that impact both cell types may play a role in the regulation of compulsive methamphetamine taking by rats.
Project description:As the primary source of norepinephrine (NE) in the brain, the locus coeruleus (LC) regulates both arousal and stress responses, but how neuromodulatory inputs contribute to LC modulation remains incompletely understood. In this study, we isolated a network of transcriptionally diverse inhibitory pericoerulear (peri-LC) GABAergic neurons that integrate distant stimuli and modulate modes of LC firing. To define the peri-LC anatomy, we used viral tracing, single-nuclei and high-resolution spatial RNA transcriptomics to molecularly characterize both LC and peri-LC cell types. We complemented this approach with techniques in electrophysiology, photometry, optogenetics, and chemogenetics to probe the function of peri-LC neurons in behaving mice. These findings indicate that LC and peri-LC neurons comprise transcriptionally heterogenous neuronal groups which integrate diverse inputs to influence behavioral arousal states and avoidance. We used snRNAseq to characterize the peri-LC and LC brain regions. Our dataset contains 30,838 cells, of which 12,278 are neurons.
Project description:As the primary source of norepinephrine (NE) in the brain, the locus coeruleus (LC) regulates both arousal and stress responses1,2. However, how local neuromodulatory inputs contribute to LC function remains unresolved. Here we identify a network of transcriptionally and functionally diverse GABAergic neurons in the LC dendritic field that integrate distant inputs and modulate modes of LC firing to control arousal. We define peri-LC anatomy using viral tracing and combine single-cell RNA sequencing and spatial transcriptomics to molecularly define both LC and peri-LC cell types. We identify several cell types which underlie peri-LC functional diversity using a series of complementary approaches in behaving mice. Our findings indicate that LC and peri-LC neurons comprise transcriptionally and functionally heterogenous neuronal populations, alongside anatomically segregated features which coordinate specific influences on behavioral arousal and avoidance states. Defining the molecular, cellular and functional diversity in the LC provides a road map for understanding the neurobiological basis of arousal alongside hyperarousal-related neuropsychiatric phenotypes.
Project description:Conventional reverse genetic approaches for study of Plasmodium malaria parasite gene function are limited, or not applicable. Hence, new inducible systems are needed. Here we describe a method to control P. falciparum gene expression in which target genes bearing a glmS ribozyme in the 3M-bM-^@M-2 untranslated region (3M-bM-^@M-2-UTR) are efficiently knocked down in transgenic P. falciparum parasites in response to exogenous glucosamine (GlcN) inducer. Using reporter genes, we show that the glmS ribozyme cleaves reporter mRNA in vivo leading to reduction in mRNA expression following GlcN treatment. GlcN-induced ribozyme activation also led to efficient reduction of reporter protein, which could be rapidly reversed by removing the inducer. The glmS ribozyme was validated as a reverse-genetic tool by integration into the essential gene and antifolate drug target dihydrofolate reductase-thymidylate synthase (PfDHFR-TS). GlcN treatment of transgenic parasites led to rapid and efficient knockdown of PfDHFR-TS mRNA and protein. PfDHFR-TS knockdown led to a growth/arrest mutant phenotype and hypersensitivity to pyrimethamine. The glmS ribozyme is thus an important tool for study of P. falciparum essential genes and anti-malarial drug discovery. mRNA profiles were generated from 3D7 wild-type and DHFR-TS-GFP_glmS integrant parasites in untreated and treated with 10 mM Glucosamine conditions in duplicate.
Project description:After injury, mammalian spinal cords develop scars to confine the lesion and prevent further damage. However, excessive scarring can hinder neural regeneration and functional recovery. These competing actions underscore the importance of developing therapeutic strategies to dynamically modulate scar progression. Previous research on scarring has primarily focused on astrocytes, but recent evidence has suggested that ependymal cells also participate. Ependymal cells normally form the epithelial layer encasing the central canal, but they undergo massive proliferation and differentiation into astroglia following certain injuries, becoming a core scar component. However, the mechanisms regulating ependymal proliferation in vivo remain unclear. Here we uncover an endogenous κ-opioid signalling pathway that controls ependymal proliferation. Specifically, we detect expression of the κ-opioid receptor, OPRK1, in a functionally under-characterized cell type known as cerebrospinal fluid-contacting neuron (CSF-cN). We also discover a neighbouring cell population that expresses the cognate ligand prodynorphin (PDYN). Whereas κ-opioids are typically considered inhibitory, they excite CSF-cNs to inhibit ependymal proliferation. Systemic administration of a κ-antagonist enhances ependymal proliferation in uninjured spinal cords in a CSF-cN-dependent manner. Moreover, a κ-agonist impairs ependymal proliferation, scar formation and motor function following injury. Together, our data suggest a paracrine signalling pathway in which PDYN+ cells tonically release κ-opioids to stimulate CSF-cNs and suppress ependymal proliferation, revealing an endogenous mechanism and potential pharmacological strategy for modulating scarring after spinal cord injury.
Project description:Prodynorphine-expressing neurons were targeted by eGFP-RPL10a, a transgene that is expressed under the control of the Pdyn promoter in a BAC containing the Pdyn backbone. Trangenic mice were made with FvB embryos via pro-nuclear injection. Transgene-positive progenies were bred to C57BL/6J for more than five generations before being used in the current experiment. Triplicates of 6-8 hypothalami were collected per sample from wild-type and ob/ob adult mice. Polysomal IP RNA and total Input RNA were purified from each sample. Affymetrix GeneChip Mouse 430 2.0 arrays (900495) were used to identify transcripts that are specifically expressed in Pdyn neurons with a fold change (IP vs. Input) of >=2 in wild-type mice. The same microarrays were also used to identify Pdyn-specific transcripts that are differentially regulated transcriptionally by leptin deficiency with a fold change (ob IP vs. wt IP) of >=1.5.
Project description:Resistance to 2nd generation androgen receptor (AR) signaling inhibitors (ARSi) occurs in a subset of metastatic castration-resistant prostate cancer (mCRPC) patients with the emergence of a neuroendocrine (NE) phenotype. This NE phenotype is typically accompanied by loss of AR expression coupled with mutations/deletions in PTEN, TP53, and/or RB1, in addition to overexpression of DNMTs, EZH2, and/or SOX2. A combination of cell and molecular biology analyses of 29 prostate cancer patient-derived xenografts (PDXs) recapitulating the full spectrum of proposed genetic alterations driving NE differentiation, in addition to CRISPR-Cas9 AR-knockout cells were utilized. These analyses document that: 1) ARSi-resistance in mCRPC cells that lack AR expression in the context of a TP53 mutation and PTEN deletion does not necessitate acquiring a NE phenotype, but alternatively can occur via emergence of an AR-/NE- double negative (DN) cancer; 2) NE cancers lack AR expression due to transcriptional silencing via promoter hypermethylation; and 3) in contrast, the lack of AR expression in DN cancers is not due to promoter hypermethylation-dependent silencing. Regardless of their cell of origin, the prevalence of both AR-/NE- DN and AR-/NE+ ARSi-resistant cancers is increasing clinically, highlighting the urgent need to develop therapies that target vulnerabilities beyond AR pathway inhibition.