Cell Reports

Insufficient insulin secretion relative to insulin demand is a key feature of type 2 diabetes (T2D). While the defects of insulin-producing {beta}-cells in T2D are well defined, little is known about how {beta}-cells progress from the functionally normal state to the decompensated state during the natural history of this disease. Here, we provide evidence that workload-induced {beta}-cell overstimulation precipitates {beta}-cell failure in T2D. We employ scRNA-seq to define workload-induced changes to {beta}-cell transcriptional states, identifying a novel compensating state that is distinct from the stressed state of decompensated {beta}-cells. We demonstrate a key role for the chromatin-modifying enzyme Lysine-specific demethylase 1 (Lsd1) in restraining workload-induced {beta}-cell state transitions, indicating epigenomic control of {beta}-cell state. Experimental manipulations that promote the compensating state accelerate {beta}-cell failure in mouse models of diabetes. Altogether, these findings show that the compensatory response of the {beta}-cell to increased workload becomes maladaptive over time and contributes to the pathogenesis of T2D.

The preBotzinger Complex (preBotC) within the medulla oblongata contains neuronal circuits critical for generating the mammalian respiratory rhythm, but the functional connectivity among its core excitatory and inhibitory populations remains debated. Defining this connectivity requires disentangling synaptic interactions of functionally identified excitatory and inhibitory preBotC neurons with various electrophysiological phenotypes. We applied a novel synaptic conductance inference method to whole-cell recordings from genetically specified VgluT2-expressing (excitatory) and VGAT-expressing (inhibitory) preBotC neurons active in the rhythmic medullary slice in vitro, which contains core inhibitory-excitatory circuitry with an excitatory rhythmogenic kernel. We found that this circuitry consists of a self-exciting inspiratory VgluT2 population coupled to inspiratory and expiratory VGAT populations that interact reciprocally through inhibition. The functional inhibitory connectome is more complex than previously understood. However, compared with functional synaptic interactions inferred from recordings in the preBotC in situ, the neuronal synaptic conductance profiles in the rhythmic slice reveal a functionally reduced inhibitory connectome, characterized by prominent tonic expiratory inhibition and phasic inspiratory inhibition, without the characteristic multiphasic structure in situ. These results indicate that the functional excitatory and inhibitory circuit interactions within the preBotC isolated in vitro, although reduced relative to more intact states in situ, are intrinsically designed to generate coordinated inspiratory and expiratory population activity. Tonic expiratory phase inhibition together with inspiratory phasic inhibition serves to regulate excitability and phase transitions of the excitatory rhythmogenic kernel.

Rapid termination of odor responses is essential for accurate olfactory coding in insects, where odorant receptors function as ligand-gated ion channels rather than G protein-coupled receptors. However, the mechanisms that restore olfactory receptor neuron (ORN) excitability after stimulation remain poorly understood. Here, we identify DmTMEM16O (CG6938), an arthropod-specific member of the TMEM16 (Anoctamin) family, as a key regulator of ORN response termination in Drosophila melanogaster. DmTMEM16O is highly enriched in Orco-positive ORNs in both larval and adult olfactory organs. Loss of DmTMEM16O prolongs odor-evoked neuronal activity, increasing decay time constants and causing persistent depolarization. DmTMEM16O mutant ORNs fail to resolve repeated odor stimulation and show impaired temporal coding, accompanied by reduced behavioral responses to both attractive and aversive odorants. Cell-specific rescue demonstrates that DmTMEM16O acts within ORNs to accelerate response termination. Although DmTMEM16O does not exhibit detectable Ca2+-activated chloride channel activity in heterologous cells, our results support a model in which it increases membrane conductance during the decay phase of the response, thereby shortening the membrane time constant and promoting rapid repolarization. This function is consistent with a role for chloride influx in insect ORNs, in contrast to mammalian systems where TMEM16B-mediated chloride efflux amplifies depolarization. Together, our findings identify DmTMEM16O as a lineage-specific regulator of ORN dynamics that enables precise temporal coding in insect olfaction.

An immune engram is a recently described phenomenon in which neuronal populations encode functional aspects of an immune challenge. Here we investigate an immune engram arising from respiratory infection with influenza A virus, demonstrating a molecular mechanism with differential influence over behavioral and immunological aspects of the engram. We first define a cellular response to acute non-neurotropic influenza A/Puerto Rico/8/1934 (PR8) infection by mapping cFos+ cells and microglia morphology across brain regions. In the posterior insula, this response has an early peak at 3 days post infection. Using a cre-dependent excitatory chemogenetic system in TRAP2 mice, we capture an engram at this same region and infection timepoint. Activation of this PR8 engram results in anxiety behavior and increased transcriptional expression of cytokines in lung tissue but not spleen tissue. We further explore how pulmonary signals contribute to this PR8 engram. Using tissue-specific, cre-dependent expression of diphtheria toxin fragment in Calcacre mice, we ablate Calca-expressing cells including pulmonary neuroendocrine cells in respiratory tissue. Loss of Calca-expressing cells prevents changes in synaptic engulfment by microglia in the insula during PR8 infection without altering the cellular response to infection in pulmonary tissue. Signaling of calcitonin gene related peptide (CGRP), a peptide encoded by Calca, can be blocked with the small molecule CGRP receptor antagonist rimegepant. Using rimegepant during acute PR8 infection we again demonstrate that loss of Calca signaling prevents the cellular response to PR8 infection in the insula. Finally, applying rimegepant alongside the chemogenetic system in TRAP2 mice we show that CGRP receptor antagonism during engram formation prevents anxiety behavior but not peripheral gene expression changes resulting from PR8 engram activation.

Age-related diseases arise from prolonged exposure to genetic and/or environmental factors, ultimately leading to cumulative and irreversible degeneration of tissues and the organism as a whole. We previously reported that accumulation of mitochondrially-generated aldehydes (i.e., 4-hydroxynonenal and acetaldehyde) causes mitochondrial dysfunction and accelerates the progression of age-related diseases. However, the contribution of mitochondrial aldehyde metabolism to aging (via aldehyde dehydrogenase 2, ALDH2) remains elusive. Here, we provide a comprehensive analysis of aldehyde metabolism and mitochondrial bioenergetics across different tissues in aging mice. We also address how mitochondrial function is influenced by the highly prevalent human inactivating ALDH2 E504K point mutation (ALDH2E504K) during aging. The liver metabolism was relatively resilient to aging, showing enhanced ALDH2 activity and improved mitochondrial coupling. Strikingly, aging-associated liver resilience was lost in ALDH2E504K mice. Aged hearts exhibited mixed outcomes including impaired mitochondrial basal respiration, improved ADP-driven respiration, and decreased ALDH2 detox capacity. The ALDH2E504K mutation exacerbated the already impaired cardiac ALDH2 detox capacity in aging. Strikingly, aging brain displayed pronounced vulnerability, with decreased ALDH2 activity, impaired mitochondrial bioenergetics and defective ALDH2 detox capacity. These changes were paralleled by impaired cognitive and behavioral functions in aged mice. As proof of concept, either the presence of ALDH2E504K mutation or acute ethanol challenge worsened cognitive and behavioral dysfunction in aging mice. Finally, we assessed in vitro efficacy of pharmacological ALDH2 activation in aging tissues. Collectively, these findings unravel the contribution of ALDH2E504K mutation to mitochondrial metabolism during aging; highlighting the detrimental synergy between genetic ALDH2 deficiency and aging in brain metabolism and physiology.

The neurotransmitter dopamine (DA) is central to synaptic regulation that support diverse behavioral functions, including both learning and forgetting. This multi-functional role of DA is due to receptor specific signaling in specific subcellular environments that remain uncharacterized. Here we utilized proximity labelling proteomics in human cells to characterize the proximal environments of two Drosophila D1-like DA receptors (Dop1R1 and Dop1R2) in basal and DA activation environments. While DA drives both receptors to recruit Beta-Arrestin 2, Dop1R1 alone showed ligand driven recruitment of G-protein Receptor Kinase 2/3, proximity to clathrin mediated endocytosis, and WASH complex mediated endosomal trafficking. Additionally, we show evidence that Dop1R1 and Dop1R2 reside in distinct domains at the cell surface. In vivo disruption of Drosophila orthologs of Dop1R proximal proteins revealed three trafficking proteins, Sec24AB, Krz, and CG13887, that regulate R1-mediated learning, starvation induced attraction to odors, and DA-mediated cAMP responses in memory circuits. In addition to revealing DA receptor trafficking proteins that support learning, our comparative characterization of the cellular environments D1-like receptors offers insights into how DA differentially regulates diverse behavioral and synaptic functions. For TOC only O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=110 SRC="FIGDIR/small/728438v1_ufig1.gif" ALT="Figure 1"> View larger version (29K): org.highwire.dtl.DTLVardef@656e56org.highwire.dtl.DTLVardef@12f0084org.highwire.dtl.DTLVardef@cb05cdorg.highwire.dtl.DTLVardef@e9d623_HPS_FORMAT_FIGEXP M_FIG C_FIG

Postpartum mammary gland involution is a coordinated process of cell death and remodeling that returns the tissue to a near pre-pregnant state following lactation and weaning. In models of postpartum breast cancer, defined as breast cancer diagnosed in women under age 45 and within 10 years of recent childbirth, involution induces durable phenotypes in breast tumor cells that promote progression and are associated with increased risk for therapeutic resistance, metastasis, and death in patients. SRY-Box Transcription Factor 9 (SOX9), a known regulator of mammary stem and progenitor cells, also promotes resistance to therapy and metastasis in breast cancers. Yet the contribution of SOX9 to the involution process is not well understood. We utilized single-cell RNA sequencing of mouse mammary glands during involution to delineate Sox9-expressing cell populations during lactation and involution. We found that Sox9 mRNA is primarily expressed in luminal progenitor cells that are largely absent during lactation and present during early involution. We also reveal that Sox9 is involved in a shift in cell state from lactational to non-lactational and is expressed in the surviving cells during involution. Prior work revealed that Semaphorin-7a (SEMA7A) also promotes cancer stem cell and pro-survival phenotypes in luminal progenitor cells during involution, and we observe a population of luminal progenitor cells that co-expresses Sox9 and Sema7a during involution. Mechanistically, we demonstrate that knockdown of Sox9 in cultured mammary epithelial cells results in increased SEMA7A expression, mesenchymal phenotypes, and loss of lactogenic differentiation capacity, identifying a potential regulatory axis where SOX9 balances SEMA7A expression in normal mammary epithelium and that disruption of this balance results in a dedifferentiated state that resembles mesenchymal cells. We validated a spatial relationship between SOX9 and SEMA7A proteins in a unique set of breast tissue samples from healthy human donors to show co-expression during early involution. In breast cancer datasets, we observe elevated expression of SOX9 and SEMA7A in triple-negative breast cancers, as well as in the mesenchymal subtype of triple-negative breast cancers, suggesting disruption of this regulatory axis in breast cancer. Finally, we observe that co-expression increases metastatic risk in both estrogen receptor-negative and -positive breast cancers. Collectively, these findings define a novel SOX9-SEMA7A relationship in healthy mammary tissues and illustrate how studies of normal progenitor cell phenotypes can delineate cellular mechanisms that contribute to breast tumor progression.

Protein S-palmitoylation is a reversible lipid modification that regulates protein trafficking, membrane association, and synaptic signaling, yet its role in learning-induced hippocampal plasticity remains incompletely understood. Here, we investigated how spatial learning remodels the hippocampal palmitoylome in rats trained in a Morris water maze using short-term training (1 session, 15 trials; test at 1 h, STT) or long-term training (4 sessions over 4 days; 4 trials/session; test at 24 h, LTT). Palmitoylated proteins were profiled using acyl-biotin exchange followed by tandem mass tag labeling and LC-MS/MS. In total, 5,260 proteins were identified, including 763 palmitoylated species. Spatial learning induced robust and time-dependent remodeling of protein S-palmitoylation, with pronounced differences between STT and LTT. Comparison of trained and yoked controls revealed 186 differentially palmitoylated proteins (DPPs) in STT and 62 in LTT, indicating stronger early molecular reorganization. Notably, yoked animals also displayed substantial palmitoylation changes versus cage controls, indicating that locomotor activity and mild stress independently reshape the hippocampal palmitoylome. DPPs were broadly distributed across cellular compartments, with enrichment of synaptic proteins at both stages. STT preferentially engaged functional enrichment in synaptic vesicle cycling, GTPase signaling, cytoskeletal remodeling, mitochondrial metabolism, and secretory pathways, whereas LTT was associated with protein translation, synaptic membrane organization, and structural plasticity, consistent with consolidation processes. Protein-protein interaction and KEGG analyses supported a transition from widespread early network remodeling toward more selective regulation of synaptic and translational machinery. Site-specific analysis further identified previously unreported palmitoylation sites in rat hippocampal proteins. Together, these data demonstrate that spatial learning dynamically reshapes the hippocampal palmitoylome in a temporally structured manner, suggesting a key role for S-palmitoylation in coordinating metabolic and synaptic adaptations underlying memory formation.

Astrocytes are increasingly recognized as dynamic modulators of brain circuit function, memory processing, and behavior. Emerging evidence suggests that astrocytic G-protein-coupled receptors (GPCRs) are key regulators of these processes through their influence on intracellular signaling and neuron-glia interactions. Here, we show that the repertoire of functionally expressed GPCRs in cortical astrocytes is broader than previously appreciated. Yet, how distinct GPCR pathways contribute to behavioral regulation remains unknown for most brain areas and behavioral contexts. We therefore investigated the role of astrocytic GPCR signaling in the temporal cortex, a region that integrates multimodal sensory information and learned fear associations. Using chemogenetic tools to selectively activate distinct GPCR pathways in astrocytes, we demonstrate that Gi-coupled GPCR signaling, but not Gs- or Gq-coupled signaling, enhances fear memory retrieval. In vivo fiber photometry revealed that temporal cortex astrocytes exhibit robust Ca2+ transients to neutral, conditioned auditory and aversive sensory stimuli. Notably, astrocytic Gi-GPCR activation attenuated cue-evoked Ca2+ transients during memory retrieval. Together, these findings identify astrocytic GPCR signaling as a pathway-specific regulator of fear memory retrieval and suggest that astrocytic Gi-GPCR signaling modulates the processing of sensory cues to drive defensive behavior.

Elucidating the mechanisms that control the formation of the mammalian neocortex is crucial for understanding brain functions. Synaptic activity of thalamocortical axons (TCAs), mediated by glutamate, exerts a major extrinsic influence on the maturation of their target layer 4 neurons in postnatal primary sensory cortex. However, TCAs reach the sensory cortex during mid-embryonic stages in mice, when neurons of future superficial layers, including layer 4, are still being generated from radial glia (RGs) or intermediate progenitor cells (IPCs), well before the formation of direct synapses. We previously showed that TCAs are required for the production and specification of the proper number of layer 4 neurons in sensory areas, and that part of these area-specific roles is played by the thalamus-derived molecule VGF. However, the role of TCA-derived glutamate prior to synapse formation has remained unclear. In this study, we used mutant mice lacking vGluT2, a vesicular glutamate transporter expressed in the embryonic thalamus, and found that vesicular release of thalamus-derived glutamate is required for the proper production and specification of layer 4 neurons in the sensory cortex by the neonatal stage, through mechanism distinct from those involving VGF. Our findings reveal that multiple molecular cues produced by incoming TCAs play distinct roles in the production and specification of layer 4 neurons in the sensory cortex.

In type 1 diabetes (T1D), insulin-producing {beta} cells are destroyed by an autoimmune response driven by pro-inflammatory cytokines, including interferons. {beta}-cell cytokine signaling is mediated in part by post-translational modifications, such as phosphorylation and acetylation. However, the role of other post-translational modifications in {beta}-cell cytokine signaling represents an important knowledge gap. In the context of autoimmune diseases, lysine carbamylation has gained attention for its role in pathogenesis. Here, we investigate the role of carbamylation in T1D. We found that pancreatic islet cells from the T1D model, non-obese diabetic (NOD) mice, exhibit 11% carbamylation-positive cells, whereas non-diabetic CD1 mice have only 5%. Proteomics analysis of the MIN6 insulin-producing cell line treated with a cocktail of three pro-inflammatory cytokines IFN{gamma} + IL-1{beta} + TNF identified 284 carbamylated peptides from 222 proteins impacted by the cytokine treatment. Integration of carbamylation and acetylation provided a deep view of the cytokine-regulated PTMs and potential points of interplay. A functional-enrichment analysis revealed that carbamylation was enriched in pathways related to autoimmune diseases, metabolism, DNA replication, and protein translation. Moreover, functional testing demonstrated that carbamylation inhibits the glycolytic enzyme aldolase A and the insulin-processing enzyme carboxypeptidase E, identifying a possible role for cytokine-induced {beta}-cell dysfunction. In summary, protein carbamylation is elevated in islets from NOD mice, and pro-inflammatory cytokine treatment regulates protein carbamylation in MIN6 cells. These data identify carbamylation as a potential regulatory mechanism for {beta}-cell metabolism and insulin production in the context of islet inflammation.

Type 1 diabetes (T1D) is characterized by the autoimmune destruction of pancreatic beta cells. While most beta cells are lost, a subset of beta cells persists years and even decades after disease onset. Studying these surviving cells is challenging, and thus how they escape immune killing remains poorly understood. Here, we applied a gene regulatory network inference-based clustering approach on existing islet scRNAseq data from cadaveric donors with T1D, autoantibody positive donors at risk for T1D, and non-diabetic donors to analyze beta cells from patients with established T1D. This approach identified a novel beta cell subtype enriched in T1D donors defined by the activity of several transcription factors which have well-characterized roles in beta cell survival, most notably IRF1. We found increased expression of immunomodulatory genes (e.g. SOCS1/3, HLA-E) as well as decreased expression of autoantigens and secretory genes, suggesting dedifferentiation. We identified inflammatory cytokines as a driver of this phenotype by reanalyzing public data from primary human beta cells stimulated with inflammatory cytokines in vitro. We additionally find a similar transcriptional program active in a subset of alpha cells, consistent with cell-extrinsic inflammatory cytokine signaling in vivo. Overall, we propose that this population represents a resilient beta cell phenotype, and that the transcriptional program active in these cells may identify targets for T1D prevention and reversal.

Organisms need to be able to adapt to a changing environment in order to survive. The adaptive response invoked by a low dose of a stressor resulting in resistance to high levels of that stressor is known as hormesis and can even lead to lifespan extension of organisms. The exact mechanisms underlying stress-induced hormesis are unknown, although multiple studies pose mitochondria-derived Reactive Oxygen Species (ROS, e.g. H2O2) as an important contributor. Here we used chemo-genetic H2O2 production as a model to study ROS-dependent adaptive responses in a localization-dependent manner. We found that brief, sublethal H2O2 production at the nucleosomes provides p53-dependent resistance to a subsequent high dose of H2O2, whereas mitochondrial H2O2 production, surprisingly, does not. A multi-omics approach revealed that p53-induced hormesis is accompanied by metabolic rewiring that boosts reductive capacity, and that the increased stress resistance can mostly be attributed to its downstream target p21. Importantly, brief p53 stabilization also mounted protection against chemotherapy-induced DNA damage, suggesting that p53-dependent hormesis could be exploited to selectively protect healthy, p53-wildtype tissue from chemotherapy in the treatment of patients with p53 mutant tumors.

Basal ganglia models commonly propose that relative imbalances between direct and indirect pathway output shapes movement, but how such imbalances are expressed during behavior remains unclear. We simultaneously imaged identified direct-pathway and indirect-pathway spiny projection neurons (dSPNs and iSPNs) in dorsal striatum as mice locomoted through virtual visual environments for reward. Individual dSPNs and iSPNs encoded discrete locations within specific visual environments and, in a distance-based task, encoded distance traveled or elapsed time, revealing structured representations of goal-directed trajectories. At the population level, both pathways were broadly co-active and similarly correlated with locomotor speed, but their relative activity shifted systematically across learned trajectories: dSPNs dominated during early accelerating segments, and iSPNs dominated during later slowing segments. These imbalances were selectively expressed within ensembles tuned to spatial location or distance/time, depending on task structure, but were absent during comparable spontaneous locomotion outside the task context and during initial exposure to a novel environment. A computational model demonstrated that opponent plasticity driven by kinematics-linked teaching signals can reproduce the observed task-dependent imbalances through cell-type-specific plasticity of discrete trajectory-related inputs and can progressively organize locomotor kinematics over learning. Our findings indicate that direct/indirect pathway imbalances are not a general reflection of motor output, but are dynamic, state-dependent features of striatal activity that link structured trajectory representations to associated changes in behavioral vigor along repeated, goal-directed locomotor paths through learning.

Most of our mechanistic understanding of threat responding and defensive fear behaviors is based on exposure to aversive stimuli in the environment. However, unpleasant, within-the body interoceptive signals can also regulate threat and emotion although underlying cell-circuit mechanisms are not well understood. Abnormal interoceptive sensitivity is associated with fear-associated psychiatric conditions such as panic disorder and PTSD. The ventromedial infralimbic (IL) subdivision of the prefrontal cortex plays a key role in threat appraisal and fear, however, IL engagement in interoceptive threat response and contributory afferent mechanisms are not known. Here, using an interoceptive clinical panicogen, carbon dioxide (CO2) inhalation, we report IL-mediated regulation of fear in mice via afferents from the subfornical organ (SFO), a key viscero-humoral circumventricular organ lacking a traditional blood brain barrier. Chemogenetic inhibition of SFO-to-IL (but not SFO-to-BNST) projections regulated defensive behaviors during CO2 inhalation and associative contextual fear. Notably, the SFO-IL circuit also modulated delayed CO2 effects on contextual fear conditioning-extinction, but not startle, neuroendocrine response or motivated behaviors. We also established more specifically that SFO angiotensin II receptor type-1 (AT-1R)+ve neuronal afferents to the IL regulate CO2-associated fear and long-term deficits in contextual fear extinction. CO2 inhalation reduced neuronal activation within the IL and optogenetic activation of SFO neurons activated inhibitory parvalbumin (PV) (but not somatostatin (SST)) interneurons in the IL. Collectively, these data reveal that aversive interoceptive signals can be directly conveyed to the IL via the SFO, a sensory hub for systemic perturbations, to regulate spontaneous and long-term fear. Our findings provide important mechanistic insights into fear-associated disorders with abnormal interoceptive threat sensitivity such as panic disorder and PTSD.

The medial preoptic area (MPOA) is a central hub for maternal behavior, integrating hormonal and sensory signals to coordinate adaptive postpartum responses. Although melanin-concentrating hormone (MCH) neurons are well characterized in the lateral hypothalamus, their identity and functional engagement within MPOA circuits remain poorly defined. Here, through integrative reanalysis of a publicly available single-cell RNA sequencing dataset of the mouse MPOA (GSE295610), we identify two transcriptionally distinct Pmch-expressing neuronal populations. Both populations are GABAergic and emerge prominently during mid to late lactation. Lactation is characterized by significant upregulation of Pmch and coordinated enrichment of neuropeptidergic and hormone-responsive genes, including islet amyloid polypeptide (Iapp), prodynorphin (Pdyn), and prolactin receptor (Prlr). Independent single-cell gene expression profiling of FACS-isolated GAD67-GFP neurons from the MPOA further corroborated these findings, confirming the selective emergence of Pmch expression during lactation and its co-expression with neuropeptidergic and hormone-responsive genes. NeuroEstimator-based activity inference demonstrates increased predicted neuronal activity in lactating females, while pseudotime reconstruction reveals a lactation-associated transcriptional shift toward later trajectory states. hdWGCNA analysis identified gene co-expression modules significantly enriched during lactation. Regulatory network inference using SCENIC further revealed activation of activity-dependent transcriptional regulons, including cyclic AMP-responsive element-binding protein 3-like 1 (Creb3l1), early growth response 1 (Egr1), and FBJ osteosarcoma oncogene (Fos). These transcriptional programs converge on gene networks associated with synaptic plasticity, regulation of neurogenesis, and broader mechanisms of neuronal plasticity. Notably, these Pmch populations were not annotated in the original study, underscoring the power of systems-level reanalysis to uncover previously unrecognized components of maternal circuitry. Together, our findings provide single-cell evidence that MCH-expressing neurons in the MPOA undergo state-dependent transcriptional reorganization during lactation, suggesting a dynamic role for MCH signaling in postpartum neuroendocrine plasticity.

Granule cell precursors (GCPs) drive the major postnatal expansion of the cerebellum and are the cells of origin of sonic hedgehog medulloblastoma (SHH MB). Although GCPs are often treated as a uniform population, increasing evidence suggests they are heterogeneous, and whether specific subpopulations show distinct tumorigenic competence remains unclear. Here, we identified a rare Nestin-expressing GCP subpopulation in the normal early postnatal cerebellum and showed that it is spatially restricted, molecularly distinct and highly competent to form tumors. These cells are enriched in the posterior external granule layer and co-express Atoh1. Using different SHH MB mouse models, we showed that when this rare subpopulation of GCPs is targeted they can give rise to SHH MB with an efficiency comparable to targeting a larger number of Atoh1-expressing GCPs and that tumors derived from Nestin-expressing GCPs arise in the posterior-lateral cerebellum. Single cell RNA sequencing revealed that Nestin-expressing GCP have a transcriptome indicating reduced neuronal differentiation and enrichment for stem cell genes compared to bulk GCPs and more closely align with SHH MB cells. Together, our findings reveal functionally important heterogeneity within the GCP lineage and suggest that SHH MB arises preferentially from a small subpopulation of GCPs that express Nestin.

Understanding how the nervous system regulates immune responses requires insight into how individual neurons respond to infection. In Caenorhabditis elegans, sensory neurons such as ASH play important roles in modulating innate immunity; however, the molecular mechanisms operating within these neurons remain poorly defined. Previous transcriptomic studies have relied on whole-animal RNA sequencing, which lacks the cellular resolution needed to detect neuron-specific signaling programs. Here, we performed single-type neuron transcriptomic profiling to characterize gene expression in ASH neurons from infected and uninfected animals. We found that ASH neurons undergo extensive transcriptional remodeling in response to pathogen exposure, with enrichment of genes associated with G protein-coupled receptor signaling, neuropeptide activity, and sensory transduction. Notably, we identified genes, including zig-3 and F36F2.8, that are strongly induced in ASH neurons but are not detected in whole-animal transcriptomic datasets. Functional analysis using ASH-specific RNA interference demonstrated that knockdown of either gene significantly reduces survival during Pseudomonas aeruginosa infection, whereas whole-animal RNAi produces no detectable phenotype. Together, these findings reveal that cell-type-resolved transcriptomics can uncover functionally important regulators of host defense that are masked in bulk analyses and provide new insight into neuron-intrinsic mechanisms of neuroimmune regulation.

Small heat-shock proteins (sHSPs) are an ancient and diverse class of molecular chaperones, acting as a first line of defense against proteotoxic stresses. While the canonical sHSPs prevent uncontrollable aggregation of a broad range of non-native substrates, a subset of sHSPs do not exhibit this broad activity in vitro, and their functions in vivo are poorly understood. Interestingly, several such sHSPs are selectively expressed in muscle tissues, including by myogenic programs, indicating likely functional roles. We examined in vivo function of C. elegans HSP-12.6, which possesses no chaperone activity in vitro but regulates lifespan, and is developmentally induced in the muscles of long-lived dauer animals. We found that HSP-12.6 exhibits exceptional selectivity in protecting the muscle function against folding or assembly mutations in thick filament proteins, but not in thin filament or non-filament proteins. This reflected its exclusive chaperone-like binding to the healthy myosin-containing thick filaments, and to their aggregates. HSP-12.6 did not bind other muscle structures or aggregates, including those of thin filaments, and retained its selectivity to either healthy thick filaments or their aggregates when challenged with a toxic aggregation-prone polyQ protein. Our data establish HSP-12.6 as a highly-selective myoprotective chaperone, with client spectrum distinct from other sHSPs.

Local protein synthesis in neurons occurs in both axons and dendrites and plays a central role in synaptic function. High-throughput-based sequencing and imaging studies have demonstrated the presence and translation of synaptically localised mRNAs. However, quantification of activity-dependent translation dynamics at synapses at the transcriptome-wide scale remains limited. Here, we apply ribosome profiling to synapse-enriched fractions (synaptoneurosomes) derived from rat cortical tissue following stimulation with the group 1 mGluR agonist DHPG. DHPG stimulation induced translation of mRNAs involved in synaptic processes, including synaptic vesicle exocytosis and axo-dendritic transport. Notably, translation of ribosomal protein mRNAs was upregulated upon mGluR activation, consistent with the expected increase in de novo protein synthesis. Together, these results demonstrate the use of ribosome profiling to capture changes in local mRNA translation from isolated preparations.