Bidirectional Regulation of Motor Circuits Using Magnetogenetic Gene Therapy

Here we report a novel suite of magnetogenetic tools, based on a single anti-ferritin nanobody-TRPV1 receptor fusion protein, which regulated neuronal activity when exposed to magnetic fields. AAV-mediated delivery of a floxed nanobody-TRPV1 into the striatum of adenosine 2a receptor-cre driver mice resulted in motor freezing when placed in an MRI or adjacent to a transcranial magnetic stimulation (TMS) device. Functional imaging and fiber photometry both confirmed activation of the target region in response to the magnetic fields. Expression of the same construct in the striatum of wild-type mice along with a second injection of an AAVretro expressing cre into the globus pallidus led to similar circuit specificity and motor responses. Finally, a mutation was generated to gate chloride and inhibit neuronal activity. Expression of this variant in subthalamic nucleus in PitX2-cre parkinsonian mice resulted in reduced local c-fos expression and motor rotational behavior. These data demonstrate that magnetogenetic constructs can bidirectionally regulate activity of specific neuronal circuits non-invasively in-vivo using clinically available devices.

Teaser

A novel magnetogenetics toolbox to regulate neural circuits in-vivo .

Drugs of abuse hijack a mesolimbic pathway that processes homeostatic need

Drugs of abuse are thought to promote addiction in part by "hijacking" brain reward systems, but the underlying mechanisms remain undefined. Using whole-brain FOS mapping and in vivo single-neuron calcium imaging, we found that drugs of abuse augment dopaminoceptive ensemble activity in the nucleus accumbens (NAc) and disorganize overlapping ensemble responses to natural rewards in a cell type-specific manner. Combining FOS-Seq, CRISPR-perturbation, and single-nucleus RNA sequencing, we identified Rheb as a molecular substrate that regulates cell type-specific signal transduction in NAc while enabling drugs to suppress natural reward consumption. Mapping NAc-projecting regions activated by drugs of abuse revealed input-specific effects on natural reward consumption. These findings characterize the dynamic, molecular and circuit basis of a common reward pathway, wherein drugs of abuse interfere with the fulfillment of innate needs.

Seeking satiety: From signals to solutions

Remedies for the treatment of obesity date to Hippocrates, when patients with obesity were directed to "reduce food and avoid drinking to fullness" and begin "running during the night." Similar recommendations have been repeated ever since, despite the fact that they are largely ineffective. Recently, highly effective therapeutics were developed that may soon enable physicians to manage body weight in patients with obesity in a manner similar to the way that blood pressure is controlled in patients with hypertension. These medicines have grown out of a revolution in our understanding of the molecular and neural control of appetite and body weight, reviewed here.

Drugs of abuse hijack a mesolimbic pathway that processes homeostatic need

Addiction prioritizes drug use over innate needs by "hijacking" brain circuits that direct motivation, but how this develops remains unclear. Using whole-brain FOS mapping and in vivo single-neuron calcium imaging, we find that drugs of abuse augment ensemble activity in the nucleus accumbens (NAc) and disorganize overlapping ensemble responses to natural rewards in a cell-type-specific manner. Combining "FOS-Seq", CRISPR-perturbations, and snRNA-seq, we identify Rheb as a shared molecular substrate that regulates cell-type-specific signal transductions in NAc while enabling drugs to suppress natural reward responses. Retrograde circuit mapping pinpoints orbitofrontal cortex which, upon activation, mirrors drug effects on innate needs. These findings deconstruct the dynamic, molecular, and circuit basis of a common reward circuit, wherein drug value is scaled to promote drug-seeking over other, normative goals.

FGF21 counteracts alcohol intoxication by activating the noradrenergic nervous system

Animals that consume fermenting fruit and nectar are at risk of exposure to ethanol and the detrimental effects of inebriation. In this report, we show that the hormone FGF21, which is strongly induced by ethanol in murine and human liver, stimulates arousal from intoxication without changing ethanol catabolism. Mice lacking FGF21 take longer than wild-type littermates to recover their righting reflex and balance following ethanol exposure. Conversely, pharmacologic FGF21 administration reduces the time needed for mice to recover from ethanol-induced unconsciousness and ataxia. FGF21 did not counteract sedation caused by ketamine, diazepam, or pentobarbital, indicating specificity for ethanol. FGF21 mediates its anti-intoxicant effects by directly activating noradrenergic neurons in the locus coeruleus region, which regulates arousal and alertness. These results suggest that this FGF21 liver-brain pathway evolved to protect against ethanol-induced intoxication and that it might be targeted pharmaceutically for treating acute alcohol poisoning.

Pharmacological targeting of glutamatergic neurons within the brainstem for weight reduction

Food intake and body weight are tightly regulated by neurons within specific brain regions, including the brainstem, where acute activation of dorsal raphe nucleus (DRN) glutamatergic neurons expressing the glutamate transporter Vglut3 (DRN^Vglut3) drive a robust suppression of food intake and enhance locomotion. Activating Vglut3 neurons in DRN suppresses food intake and increases locomotion, suggesting that modulating the activity of these neurons might alter body weight. Here, we show that DRN^Vglut3 neurons project to the lateral hypothalamus (LHA), a canonical feeding center that also reduces food intake. Moreover, chronic DRN^Vglut3 activation reduces weight in both leptin-deficient (ob/ob) and leptin-resistant diet-induced obese (DIO) male mice. Molecular profiling revealed that the orexin 1 receptor (Hcrtr1) is highly enriched in DRN Vglut3 neurons, with limited expression elsewhere in the brain. Finally, an orally bioavailable, highly selective Hcrtr1 antagonist (CVN45502) significantly reduces feeding and body weight in DIO. Hcrtr1 is also co-expressed with Vglut3 in the human DRN, suggesting that there might be a similar effect in human. These results identify a potential therapy for obesity by targeting DRN^Vglut3 neurons while also establishing a general strategy for developing drugs for central nervous system disorders.

Higher-Order Inputs Involved in Appetite Control

The understanding of the neural control of appetite sheds light on the pathogenesis of eating disorders such as anorexia nervosa and obesity. Both diseases are a result of maladaptive eating behaviors (overeating or undereating) and are associated with life-threatening health problems. The fine regulation of appetite involves genetic, physiological, and environmental factors, which are detected and integrated in the brain by specific neuronal populations. For centuries, the hypothalamus has been the center of attention in the scientific community as a key regulator of appetite. The hypothalamus receives and sends axonal projections to several other brain regions that are important for the integration of sensory and emotional information. These connections ensure that appropriate behavioral decisions are made depending on the individual's emotional state and environment. Thus, the mechanisms by which higher-order brain regions integrate exteroceptive information to coordinate feeding is of great importance. In this review, we will focus on the functional and anatomical projections connecting the hypothalamus to the limbic system and higher-order brain centers in the cortex. We will also address the mechanisms by which specific neuronal populations located in higher-order centers regulate appetite and how maladaptive eating behaviors might arise from altered connections among cortical and subcortical areas with the hypothalamus.

Functional analysis of distinct populations of subthalamic nucleus neurons on Parkinson's disease and OCD-like behaviors in mice

The subthalamic nucleus (STN) is a component of the basal ganglia and plays a key role to control movement and limbic-associative functions. STN modulation with deep brain stimulation (DBS) improves the symptoms of Parkinson's disease (PD) and obsessive-compulsive disorder (OCD) patients. However, DBS does not allow for cell-type-specific modulation of the STN. While extensive work has focused on elucidating STN functionality, the understanding of the role of specific cell types is limited. Here, we first performed an anatomical characterization of molecular markers for specific STN neurons. These studies revealed that most STN neurons express Pitx2, and that different overlapping subsets express Gabrr3, Ndnf, or Nos1. Next, we used optogenetics to define their roles in regulating locomotor and limbic functions in mice. Specifically, we showed that optogenetic photoactivation of STN neurons in Pitx2-Cre mice or of the Gabrr3-expressing subpopulation induces locomotor changes, and improves locomotion in a PD mouse model. In addition, photoactivation of Pitx2 and Gabrr3 cells induced repetitive grooming, a phenotype associated with OCD. Repeated stimulation prompted a persistent increase in grooming that could be reversed by fluoxetine treatment, a first-line drug therapy for OCD. Conversely, repeated inhibition of STN^Gabrr3 neurons suppressed grooming in Sapap3 KO mice, a model for OCD. Finally, circuit and functional mapping of STN^Gabrr3 neurons showed that these effects are mediated via projections to the globus pallidus/entopeduncular nucleus and substantia nigra reticulata. Altogether, these data identify Gabrr3 neurons as a key population in mediating the beneficial effects of STN modulation thus providing potential cellular targets for PD and OCD drug discovery.

Melanocortin 4 receptor stimulation prevents anti-depressant-associated weight gain in mice caused by long-term fluoxetine exposure

Contrasting with the predicted anorexigenic effect of increasing brain serotonin signaling, long-term use of selective serotonin reuptake inhibitors (SSRIs) antidepressants correlates with body weight gain. This adverse outcome increases the risk of transitioning to obesity and interferes with treatment compliance. Here we show that orally administered fluoxetine (Flx), a widely prescribed SSRI, increased body weight by enhancing food intake in healthy mice at two different time points and through two distinct mechanisms. Within hours, Flx decreased the activity of a subset of brainstem serotonergic neurons by triggering autoinhibitory signaling through the Htr1a receptor. Upon longer treatment Flx blunted Htr2c expression/signaling, decreased the phosphorylation of Creb and Stat3 and dampened the production of POMC/α-MSH in hypothalamic neurons, thereby increasing food intake. Accordingly, exogenous stimulation of the melanocortin 4 receptor (MC4R) by co-treating mice with Flx and lipocalin-2, an anorexigenic hormone signaling through this receptor, normalized feeding and body weight. Flx and other SSRIs also inhibit CREB/STAT3 phosphorylation in a human neuronal cell line suggesting that these non-canonical effects could also occur in long-term users of SSRIs. By defining the molecular basis of the long-term SSRIs-associated weight gain this study proposes a therapeutic strategy to counter it.

How the discovery of microbial opsins led to the development of optogenetics

This year's Lasker Award recognizes Dieter Oesterhelt, Peter Hegemann, and Karl Deisseroth for their discovery of microbial opsins as light-activated ion conductors and the development of optogenetics using these proteins to regulate neural activity in awake, behaving animals. Optogenetics has revolutionized neuroscience and transformed our understanding of brain function.

Top-down control of conditioned overconsumption is mediated by insular cortex Nos1 neurons

Associative learning allows animals to adapt their behavior in response to environmental cues. For example, sensory cues associated with food availability can trigger overconsumption even in sated animals. However, the neural mechanisms mediating cue-driven non-homeostatic feeding are poorly understood. To study this, we recently developed a behavioral task in which contextual cues increase feeding even in sated mice. Here, we show that an insular cortex to central amygdala circuit is necessary for conditioned overconsumption, but not for homeostatic feeding. This projection is marked by a population of glutamatergic nitric oxide synthase-1 (Nos1)-expressing neurons, which are specifically active during feeding bouts. Finally, we show that activation of insular cortex Nos1 neurons suppresses satiety signals in the central amygdala. The data, thus, indicate that the insular cortex provides top-down control of homeostatic circuits to promote overconsumption in response to learned cues.

Critical roles of transcriptional coactivator MED1 in the formation and function of mouse adipose tissues

In this study, Ito et al. sought to understand the precise roles of MED1, and its various domains, at various stages of adipogenesis and in adipose tissue. Using multiple genetic approaches to assess requirements for MED1 in adipocyte formation and function in mice, they show that MED1 is indeed essential for the differentiation and/or function of both brown and white adipocytes, as its absence in these cells leads to, respectively, defective brown fat function and lipodystrophy.

The MED1 subunit has been shown to mediate ligand-dependent binding of the Mediator coactivator complex to multiple nuclear receptors, including the adipogenic PPARγ, and to play an essential role in ectopic PPARγ-induced adipogenesis of mouse embryonic fibroblasts. However, the precise roles of MED1, and its various domains, at various stages of adipogenesis and in adipose tissue have been unclear. Here, after establishing requirements for MED1, including specific domains, for differentiation of 3T3L1 cells and both primary white and brown preadipocytes, we used multiple genetic approaches to assess requirements for MED1 in adipocyte formation, maintenance, and function in mice. We show that MED1 is indeed essential for the differentiation and/or function of both brown and white adipocytes, as its absence in these cells leads to, respectively, defective brown fat function and lipodystrophy. This work establishes MED1 as an essential transcriptional coactivator that ensures homeostatic functions of adipocytes.

Gut-to-brain signals in feeding control

Interoceptive signals from gut and adipose tissue and sensory cues from the environment are integrated by hubs in the brain to regulate feeding behavior and maintain homeostatic control of body weight. In vivo neural recordings have revealed that these signals control the activity of multiple layers of hunger neurons and eating is not only the result of feedback correction to a set point, but can also be under the influence of anticipatory regulations. A series of recent technical developments have revealed how peripheral and sensory signals, in particular, from the gut are conveyed to the brain to integrate neural circuits. Here, we describe the mechanisms involved in gastrointestinal stimulation by nutrients and how these signals act on the hindbrain to generate motivated behaviors. We also consider the organization of multidirectional intra- and extrahypothalamic circuits and how this has created a framework for understanding neural control of feeding.

A limbic circuit selectively links active escape to food suppression

Stress has pleiotropic physiologic effects, but the neural circuits linking stress to these responses are not well understood. Here, we describe a novel population of lateral septum neurons expressing neurotensin (LS^Nts) in mice that are selectively tuned to specific types of stress. LS^Nts neurons increase their activity during active escape, responding to stress when flight is a viable option, but not when associated with freezing or immobility. Chemogenetic activation of LS^Nts neurons decreases food intake and body weight, without altering locomotion and anxiety. LS^Nts neurons co-express several molecules including Glp1r (glucagon-like peptide one receptor) and manipulations of Glp1r signaling in the LS recapitulates the behavioral effects of LS^Nts activation. Activation of LS^Nts terminals in the lateral hypothalamus (LH) also decreases food intake. These results show that LS^Nts neurons are selectively tuned to active escape stress and can reduce food consumption via effects on hypothalamic pathways.

Selection of a Full Agonist Combinatorial Antibody that Rescues Leptin Deficiency In Vivo

Growth factor deficiency in adulthood constitutes a distinct clinical syndrome with significant morbidities including abnormal body composition, reduced energy, affective disturbances, dyslipidemia, and increased cardiovascular risk. Protein replacement therapies using recombinant proteins or enzymes represent the only approved treatment. Combinatorial antibodies have shown great promise as a new class of therapeutic molecules because they act as "mechanism-based antibodies" with both agonist and antagonist activities. Using leptin, a key hormone in energy metabolism, as an example, a function-guided approach is developed to select combinatorial antibodies with high potency and full agonist activity that substitute natural growth factors in vivo. The identified antibody shows identical biochemical properties and cellular profiles as leptin, and rescues leptin-deficiency in ob/ob mice. Remarkably, the antibody activates leptin receptors that are otherwise nonfunctional because of mutations (L372A and A409E). Combinatorial antibodies have significant advantages over recombinant proteins for chronical usage in terms of immunological tolerance and biological stability.

Limitation of adipose tissue by the number of embryonic progenitor cells

Adipogenesis in adulthood replaces fat cells that turn over and can contribute to the development of obesity. However, the proliferative potential of adipocyte progenitors in vivo is unknown (Faust et al., 1976; Faust et al., 1977; Hirsch and Han, 1969; Johnson and Hirsch, 1972). We addressed this by injecting labeled wild-type embryonic stem cells into blastocysts derived from lipodystrophic A-ZIP transgenic mice, which have a genetic block in adipogenesis. In the resulting chimeric animals, wild-type ES cells are the only source of mature adipocytes. We found that when chimeric animals were fed a high-fat-diet, animals with low levels of chimerism showed a significantly lower adipose tissue mass than animals with high levels of chimerism. The difference in adipose tissue mass was attributed to variability in the amount of subcutaneous adipose tissue as the amount of visceral fat was independent of the level of chimerism. Our findings thus suggest that proliferative potential of adipocyte precursors is limited and can restrain the development of obesity.

Control of non-homeostatic feeding in sated mice using associative learning of contextual food cues

Feeding is a complex motivated behavior controlled by a distributed neural network that processes sensory information to generate adaptive behavioral responses. Accordingly, studies using appetitive Pavlovian conditioning confirm that environmental cues that are associated with food availability can induce feeding even in satiated subjects. However, in mice, appetitive conditioning generally requires intensive training and thus can impede molecular studies that often require large numbers of animals. To address this, we developed and validated a simple and rapid context-induced feeding (Ctx-IF) task in which cues associated with food availability can later lead to increased food consumption in sated mice. We show that the associated increase in food consumption is driven by both positive and negative reinforcement and that spaced training is more effective than massed training. Ctx-IF can be completed in ~1 week and provides an opportunity to study the molecular mechanisms and circuitry underlying non-homeostatic eating. We have used this paradigm to map brain regions that are activated during Ctx-IF with cFos immunohistochemistry and found that the insular cortex, and other regions, are activated following exposure to cues denoting the availability of food. Finally, we show that inhibition of the insular cortex using GABA agonists impairs performance of the task. Our findings provide a novel assay in mice for defining the functional neuroanatomy of appetitive conditioning and identify specific brain regions that are activated during the development of learned behaviors that impact food consumption.

Leptin and the endocrine control of energy balance

The discovery of leptin changed the view of adipose tissue from that of a passive vessel that stores fat to that of a dynamic endocrine organ that actively regulates behaviour and metabolism. Secreted by adipose tissue, leptin functions as an afferent signal in a negative feedback loop, acting primarily on neurons in the hypothalamus and regulating feeding and many other functions. The leptin endocrine system serves a critical evolutionary function by maintaining the relative constancy of adipose tissue mass, thereby protecting individuals from the risks associated with being too thin (starvation and infertility) or too obese (predation). In this Review, the biology of leptin is summarized, and a conceptual framework is established for studying the pathogenesis of obesity, which, analogously to diabetes, can result from either leptin hyposecretion or leptin resistance. Herein, these two states are distinguished with the terms 'type 1 obesity' and 'type 2 obesity': type 1 obesity describes a subset of obese individuals with low endogenous plasma leptin levels who respond to leptin therapy, whereas type 2 obesity describes most obese individuals, who are leptin resistant but might respond to leptin therapy in combination with other drugs, such as leptin sensitizers.

Regulation of Energy Expenditure by Brainstem GABA Neurons

Homeostatic control of core body temperature is essential for survival. Temperature is sensed by specific neurons, in turn eliciting both behavioral (i.e., locomotion) and physiologic (i.e., thermogenesis, vasodilatation) responses. Here, we report that a population of GABAergic (Vgat-expressing) neurons in the dorsolateral portion of the dorsal raphe nucleus (DRN), hereafter DRN^Vgat neurons, are activated by ambient heat and bidirectionally regulate energy expenditure through changes in both thermogenesis and locomotion. We find that DRN^Vgat neurons innervate brown fat via a descending projection to the raphe pallidus (RPa). These neurons also densely innervate ascending targets implicated in the central regulation of energy expenditure, including the hypothalamus and extended amygdala. Optogenetic stimulation of different projection targets reveals that DRN^Vgat neurons are capable of regulating thermogenesis through both a "direct" descending pathway through the RPa and multiple "indirect" ascending pathways. This work establishes a key regulatory role for DRN^Vgat neurons in controlling energy expenditure.

Electromagnetic Regulation of Cell Activity

The ability to observe the effects of rapidly and reversibly regulating cell activity in targeted cell populations has provided numerous physiologic insights. Over the last decade, a wide range of technologies have emerged for regulating cellular activity using optical, chemical, and, more recently, electromagnetic modalities. Electromagnetic fields can freely penetrate cells and tissue and their energy can be absorbed by metal particles. When released, the absorbed energy can in turn gate endogenous or engineered receptors and ion channels to regulate cell activity. In this manner, electromagnetic fields acting on external nanoparticles have been used to exert mechanical forces on cell membranes and organelles to generate heat and interact with thermally activated proteins or to induce receptor aggregation and intracellular signaling. More recently, technologies using genetically encoded nanoparticles composed of the iron storage protein, ferritin, have been used for targeted, temporal control of cell activity in vitro and in vivo. These tools provide a means for noninvasively modulating gene expression, intracellular organelles, such as endosomes, and whole-cell activity both in vitro and in freely moving animals. The use of magnetic fields interacting with external or genetically encoded nanoparticles thus provides a rapid noninvasive means for regulating cell activity.

Dysregulation of a long noncoding RNA reduces leptin leading to a leptin-responsive form of obesity

Quantitative changes in leptin concentration lead to alterations in food intake and body weight, but the regulatory mechanisms that control leptin gene expression are poorly understood. Here we report that fat-specific and quantitative leptin expression is controlled by redundant cis elements and trans factors interacting with the proximal promoter together with a long noncoding RNA (lncOb). Diet-induced obese mice lacking lncOb show increased fat mass with reduced plasma leptin levels and lose weight after leptin treatment, whereas control mice do not. Consistent with this finding, large-scale genetic studies of humans reveal a significant association of single-nucleotide polymorphisms (SNPs) in the region of human lncOb with lower plasma leptin levels and obesity. These results show that reduced leptin gene expression can lead to a hypoleptinemic, leptin-responsive form of obesity and provide a framework for elucidating the pathogenic mechanism in the subset of obese patients with low endogenous leptin levels.

α1- and β3-Adrenergic Receptor-Mediated Mesolimbic Homeostatic Plasticity Confers Resilience to Social Stress in Susceptible Mice

BACKGROUND

Homeostatic plasticity in mesolimbic dopamine (DA) neurons plays an essential role in mediating resilience to social stress. Recent evidence implicates an association between stress resilience and projections from the locus coeruleus (LC) to the ventral tegmental area (VTA) (LC→VTA) DA system. However, the precise circuitry and molecular mechanisms of the homeostatic plasticity in mesolimbic DA neurons mediated by the LC→VTA circuitry, and its role in conferring resilience to social defeat stress, have not been described.

METHODS

In a well-established chronic social defeat stress model of depression, using projection-specific electrophysiological recordings and optogenetic, pharmacological, and molecular profiling techniques, we investigated the functional role and molecular basis of an LC→VTA circuit in conferring resilience to social defeat stress.

RESULTS

We found that LC neurons projecting to the VTA exhibit enhanced firing activity in resilient, but not susceptible, mice. Optogenetically mimicking this firing adaptation in susceptible mice reverses their depression-related behaviors, and induces reversal of cellular hyperactivity and homeostatic plasticity in VTA DA neurons projecting to the nucleus accumbens. Circuit-specific molecular profiling studies reveal that α₁- and β₃-adrenergic receptors are highly expressed in VTA→nucleus accumbens DA neurons. Pharmacologically activating these receptors induces similar proresilient effects at the ion channel and cellular and behavioral levels, whereas antagonizing these receptors blocks the proresilient effect of optogenetic activation of LC→VTA circuit neurons in susceptible mice.

CONCLUSIONS

These findings reveal a key role of the LC→VTA circuit in mediating homeostatic plasticity in stress resilience and reveal α₁- and β₃-adrenergic receptors as new molecular targets for therapeutically promoting resilience.

Assessing Shared Decision-Making Clinical Behaviors Among Genetic Counsellors

Shared decision-making (SDM) is a collaborative approach in which clinicians educate, support, and guide patients as they make informed, value-congruent decisions. SDM improves patients' health-related outcomes through increasing knowledge, reducing decisional conflict, and enhancing experience of care. We measured SDM in genetic counselling appointments with 27 pregnant women who were at increased risk to have a baby with a genetic abnormality. The eight experienced genetic counsellors who participated had no specific SDM training and were unaware that SDM was being assessed. Audio transcripts of appointments were scored using 'Observing Patient Involvement in Decision Making' (OPTION12). Patients' anxiety and decisional conflict were also assessed. The genetic counsellors' mean OPTION12 score was 42.4% (SD 9.0%; possible range 0-100%). Specific SDM behaviours that scored highest included introducing the concept of equipoise and listing all options with their pros and cons. Behaviours that scored lowest included eliciting patients' preferred approach to receiving information and desired degree of involvement in decision-making. Patients' levels of anxiety and decisional conflict were unassociated with genetic counsellors' OPTION12 scores. Some SDM behaviours were better demonstrated in this prenatal genetic counselling study than others. Formal training of genetic counsellors in SDM may enhance use of this approach in their professional practice.

Functional analysis reveals differential effects of glutamate and MCH neuropeptide in MCH neurons

OBJECTIVES

Melanin-concentrating hormone (MCH) neurons in the lateral hypothalamus (LH) regulate food intake and body weight, glucose metabolism and convey the reward value of sucrose. In this report, we set out to establish the respective roles of MCH and conventional neurotransmitters in these neurons.

METHODS

MCH neurons were profiled using Cre-dependent molecular profiling technologies (vTRAP). MCHCre mice crossed to Vglut2fl/flmice or to DTRfl/flwere used to identify the role of glutamate in MCH neurons. We assessed metabolic parameters such as body composition, glucose tolerance, or sucrose preference.

RESULTS

We found that nearly all MCH neurons in the LH are glutamatergic and that a loss of glutamatergic signaling from MCH neurons from a glutamate transporter (VGlut2) knockout leads to a reduced weight, hypophagia and hyperkinetic behavior with improved glucose tolerance and a loss of sucrose preference. These effects are indistinguishable from those seen after ablation of MCH neurons. These findings are in contrast to those seen in mice with a knockout of the MCH neuropeptide, which show normal glucose preference and do not have improved glucose tolerance.

CONCLUSIONS

Overall, these data show that the vast majority of MCH neurons are glutamatergic, and that glutamate and MCH signaling mediate partially overlapping functions by these neurons, presumably by activating partially overlapping postsynaptic populations. The diverse functional effects of MCH neurons are thus mediated by a composite of glutamate and MCH signaling.

Molecular and cellular characterization of nicotinic acetylcholine receptor subtypes in the arcuate nucleus of the mouse hypothalamus

Nicotine, acting through nicotinic acetylcholine receptors (nAChRs), increases the firing rate of both orexigenic agouti-related peptide (AgRP) and anorexigenic pro-opiomelanocortin (POMC) neurons in the arcuate nucleus of the hypothalamus (ARC), yet nicotine and other nAChR agonists decrease food intake in mice. Viral-mediated knockdown of the β4 nAChR subunit in all neuronal cell types in the ARC prevents the nicotinic agonist cytisine from decreasing food intake, but it is not known whether the β4 subunit is selectively expressed in anorexigenic neurons or how other nAChR subtypes are distributed in this nucleus. Using translating ribosome affinity purification (TRAP) on ARC tissue from mice with ribosomes tagged in either AgRP or POMC cells, we examined nAChR subunit mRNA levels using real-time PCR. Both AgRP and POMC cells express a comparable panel of nAChR subunits with differences in α7 mRNA levels and a trend for difference in α4 levels, but no differences in β4 expression. Immunoprecipitation of assembled nAChRs revealed that the β4 subunit forms assembled channels with α3, β2 and α4, but not other subunits found in the ARC. Finally, using cell type-selective, virally delivered small hairpin RNAs targeting either the β4 or α7 subunit, we examined the contribution of each subunit in either AgRP or POMC cells to the behavioural response to nicotine, refining the understanding of nicotinic regulation of this feeding circuit. These experiments identify a more complex set of nAChRs expressed in ARC than in other hypothalamic regions. Thus, the ARC appears to be a particular target of nicotinic modulation.

Rapid Molecular Profiling of Defined Cell Types Using Viral TRAP

Translational profiling methodologies enable the systematic characterization of cell types in complex tissues, such as the mammalian brain, where neuronal isolation is exceptionally difficult. Here, we report a versatile strategy for profiling CNS cell types in a spatiotemporally restricted fashion by engineering a Cre-dependent adeno-associated virus expressing an EGFP-tagged ribosomal protein (AAV-FLEX-EGFPL10a) to access translating mRNAs by translating ribosome affinity purification (TRAP). We demonstrate the utility of this AAV to target a variety of genetically and anatomically defined neural populations expressing Cre recombinase and illustrate the ability of this viral TRAP (vTRAP) approach to recapitulate the molecular profiles obtained by bacTRAP in corticothalamic neurons across multiple serotypes. Furthermore, spatially restricting adeno-associated virus (AAV) injections enabled the elucidation of regional differences in gene expression within this cell type. Altogether, these results establish the broad applicability of the vTRAP strategy for the molecular dissection of any CNS or peripheral cell type that can be engineered to express Cre.

Creation of an international registry to support discovery in schwannomatosis

Schwannomatosis is a tumor suppressor syndrome that causes multiple tumors along peripheral nerves. Formal diagnostic criteria were first published in 2005. Variability in clinical presentation and a relative lack of awareness of the syndrome have contributed to difficulty recognizing affected individuals and accurately describing the natural history of the disorder. Many critical questions such as the mutations underlying schwannomatosis, genotype-phenotype correlations, inheritance patterns, pathologic diagnosis of schwannomatosis-associated schwannomas, tumor burden in schwannomatosis, the incidence of malignancy, and the effectiveness of current, or new treatments remain unanswered. A well-curated registry of schwannomatosis patients is needed to facilitate research in field. An international consortium of clinicians and scientists across multiple disciplines with expertise in schwannomatosis was established and charged with the task of designing and populating a schwannomatosis patient registry. The International Schwannomatosis Registry (ISR) was built around key data points that allow confirmation of the diagnosis and identification of potential research subjects to advance research to further the knowledge base for schwannomatosis. A registry with 389 participants enrolled to date has been established. Twenty-three additional subjects are pending review. A formal process has been established for scientific investigators to propose research projects, identify eligible subjects, and seek collaborators from ISR sites. Research collaborations have been created using the information collected by the registry and are currently being conducted. The ISR is a platform from which multiple research endeavors can be launched, facilitating connections between affected individuals interested in participating in research and researchers actively investigating a variety of aspects of schwannomatosis. © 2016 Wiley Periodicals, Inc.

Debris Flow Occurrence and Sediment Persistence, Upper Colorado River Valley, CO

Debris flow magnitudes and frequencies are compared across the Upper Colorado River valley to assess influences on debris flow occurrence and to evaluate valley geometry effects on sediment persistence. Dendrochronology, field mapping, and aerial photographic analysis are used to evaluate whether a 19th century earthen, water-conveyance ditch has altered the regime of debris flow occurrence in the Colorado River headwaters. Identifying any shifts in disturbance processes or changes in magnitudes and frequencies of occurrence is fundamental to establishing the historical range of variability (HRV) at the site. We found no substantial difference in frequency of debris flows cataloged at eleven sites of deposition between the east (8) and west (11) sides of the Colorado River valley over the last century, but four of the five largest debris flows originated on the west side of the valley in association with the earthen ditch, while the fifth is on a steep hillslope of hydrothermally altered rock on the east side. These results suggest that the ditch has altered the regime of debris flow activity in the Colorado River headwaters as compared to HRV by increasing the frequency of debris flows large enough to reach the Colorado River valley. Valley confinement is a dominant control on response to debris flows, influencing volumes of aggradation and persistence of debris flow deposits. Large, frequent debris flows, exceeding HRV, create persistent effects due to valley geometry and geomorphic setting conducive to sediment storage that are easily delineated by valley confinement ratios which are useful to land managers.

Plasmonic activation of gold nanorods for remote stimulation of calcium signaling and protein expression in HEK 293T cells

Remote activation of specific cells of a heterogeneous population can provide a useful research tool for clinical and therapeutic applications. Here, we demonstrate that photostimulation of gold nanorods (AuNRs) using a tunable near-infrared (NIR) laser at specific longitudinal surface plasmon resonance wavelengths can induce the selective and temporal internalization of calcium in HEK 293T cells. Biotin-PEG-Au nanorods coated with streptavidin Alexa Fluor-633 and biotinylated anti-His antibodies were used to decorate cells genetically modified with His-tagged TRPV1 temperature-sensitive ion channel and AuNRs conjugated to biotinylated RGD peptide were used to decorate integrins in unmodified cells. Plasmonic activation can be stimulated at weak laser power (0.7-4.0 W/cm(2) ) without causing cell damage. Selective activation of TRPV1 channels could be controlled by laser power between 1.0 and 1.5 W/cm(2) . Integrin targeting robustly stimulated calcium signaling due to a dense cellular distribution of nanoparticles. Such an approach represents a functional tool for combinatorial activation of cell signaling in heterogeneous cell populations. Our results suggest that it is possible to induce cell activation via NIR-induced gold nanorod heating through the selective targeting of membrane proteins in unmodified cells to produce calcium signaling and downstream expression of specific genes with significant relevance for both in vitro and therapeutic applications. Biotechnol. Bioeng. 2016;113: 2228-2240. © 2016 Wiley Periodicals, Inc.

Molecular characterization of neuronal cell types based on patterns of projection with Retro-TRAP

Retro-TRAP (translating ribosome affinity purification) technology enables the synthesis of molecular and neuroanatomical information through the use of transgenic and viral approaches. In contrast to other methods that are used to profile neural circuits such as laser-capture microdissection and FACS, Retro-TRAP is a high-throughput methodology that requires minimal specialized instrumentation. Retro-TRAP uses an anti-GFP ribosomal tag (expressed virally or using transgenesis) to immunoprecipitate translating mRNAs from any population of neurons that express GFP. The protocol detailed here describes the rapid extraction of molecular information from neural circuits in mice using retrograde-tracing GFP-expressing viruses. This approach can be used to identify novel cell types, as well as to molecularly profile cell types for which Cre-driver lines are available, in defined presynaptic loci. The current protocol describes a method for extracting translating mRNA from any neural circuit accessible by stereotaxic injection and manual dissection, and it takes 2-4 weeks. Although it is not described here, this mRNA can then be used in downstream processing applications such as quantitative PCR (qPCR) and high-throughput RNA sequencing to obtain 'molecular connectomic' information.

Growth in neurofibromatosis 1 microdeletion patients

Microdeletions of the entire NF1 gene and surrounding genomic region occur in about 5% of patients with neurofibromatosis 1 (NF1). NF1 microdeletion patients usually have more cutaneous and plexiform neurofibromas and a higher risk of developing malignant peripheral nerve sheath tumors than other people with NF1. Somatic overgrowth has also been observed in NF1 microdeletion patients, an observation that is remarkable because most NF1 patients are smaller than average for age and sex. We studied longitudinal measurements of height, weight, and head circumference in 56 patients with NF1 microdeletions and 226 NF1 patients with other kinds of mutations. Although children with NF1 microdeletions were much taller than non-deletion NF1 patients at all ages after 2 years, the lengths of deletion and nondeletion NF1 patients were similar in early infancy. NF1 microdeletion patients tended to be heavier than other NF1 patients, but height or weight more than 3 standard deviations above the mean for age and sex was infrequent in children with NF1 microdeletions. Head circumference and age of puberty were similar in deletion and non-deletion NF1 patients. The pattern of growth differs substantially in deletion and non-deletion NF1 patients, but the pathogenic basis for this difference is unknown.

Epigenetic alterations and microRNA misexpression in cancer and autoimmune diseases: a critical review

Epigenetic markers such as DNA methylation and histone modifications around promoter regions modify chromatin structure and regulate expression of downstream genes. In fact, aberrant epigenetic modifications are common events in human disease including tumorigenesis and autoimmunity. Small non-coding RNAs named microRNAs (miRNAs) are modulators of gene expression and play critical roles in various cellular processes. Several miRNAs have been characterized as tumor suppressors or oncogenes in cancer, and recent reports implicate certain miRNAs in the pathogenesis of autoimmune diseases. Epigenetic investigations have shown that distinct miRNAs are directly regulated by DNA methylation and histone modifications at their promoters. Moreover, miRNAs themselves are key participants in regulating the chromatin modifying machinery. Chromatin-modifying drugs such as DNA methylation inhibitors and histone deacetylase inhibitors have shown efficacy in human malignancies and there is some evidence that these drugs may be useful in autoimmune disease. The benefits of these drugs are at least partially mediated by restoring expression of epigenetically silenced tumor suppressor genes, including miRNAs. The complex layers regulating gene expression have yet to be fully elucidated, but it is clear that epigenetic alterations and miRNA misexpression are essential events in pathologic processes, especially cancer and autoimmune disease, and represent promising therapeutic targets.

Nuclear Factor-Y is an adipogenic factor that regulates leptin gene expression

Objective

Leptin gene expression is highly correlated with cellular lipid content in adipocytes but the transcriptional mechanisms controlling leptin expression in vivo are poorly understood. In this report, we set out to identify cis- and trans-regulatory elements controlling leptin expression.

Methods

Leptin-BAC luciferase transgenic mice combining with other computational and molecular techniques were used to identify transcription regulatory elements including a CCAAT-binding protein Nuclear Factor Y (NF-Y). The function of NF-Y in adipocyte was studied in vitro with 3T3-L1 cells and in vivo with adipocyte-specific knockout of NF-Y.

Results

Using Leptin-BAC luciferase mice, we showed that DNA sequences between −22 kb and +8.8 kb can confer quantitative expression of a leptin reporter. Computational analysis of sequences and gel shift assays identified a 32 bp sequence (chr6: 28993820–2899385) consisting a CCAAT binding site for Nuclear Factor Y (NF-Y) and this was confirmed by a ChIP assay in vivo. A deletion of this 32 bp sequence in the −22 kb to +8.8 kb leptin-luciferase BAC reporter completely abrogates luciferase reporter activity in vivo. RNAi mediated knockdown of NF-Y interfered with adipogenesis in vitro and adipocyte-specific knockout of NF-Y in mice reduced expression of leptin and other fat specific genes in vivo. Further analyses of the fat specific NF-Y knockout revealed that these animals develop a moderately severe lipodystrophy that is remediable with leptin therapy.

Conclusions

These studies advance our understanding of leptin gene expression and show that NF-Y controls the expression of leptin and other adipocyte genes and identifies a new form of lipodystrophy.

Recurrent triploidy due to a failure to complete maternal meiosis II: whole-exome sequencing reveals candidate variants

Triploidy is a relatively common cause of miscarriage; however, recurrent triploidy has rarely been reported. A healthy 34-year-old woman was ascertained because of 18 consecutive miscarriages with triploidy found in all 5 karyotyped losses. Molecular results in a sixth loss were also consistent with triploidy. Genotyping of markers near the centromere on multiple chromosomes suggested that all six triploid conceptuses occurred as a result of failure to complete meiosis II (MII). The proband's mother had also experienced recurrent miscarriage, with a total of 18 miscarriages. Based on the hypothesis that an inherited autosomal-dominant maternal predisposition would explain the phenotype, whole-exome sequencing of the proband and her parents was undertaken to identify potential candidate variants. After filtering for quality and rarity, potentially damaging variants shared between the proband and her mother were identified in 47 genes. Variants in genes coding for proteins implicated in oocyte maturation, oocyte activation or polar body extrusion were then prioritized. Eight of the most promising candidate variants were confirmed by Sanger sequencing. These included a novel change in the PLCD4 gene, and a rare variant in the OSBPL5 gene, which have been implicated in oocyte activation upon fertilization and completion of MII. Several variants in genes coding proteins playing a role in oocyte maturation and early embryonic development were also identified. The genes identified may be candidates for the study in other women experiencing recurrent triploidy or recurrent IVF failure.

Clinical and scientific impact of human papillomavirus on head and neck cancer

Head and neck cancer (HNC) arises from the skull base to the clavicles and is the fifth most common cancer in the world by incidence. Historically, in the developed world HNC was associated with tobacco use and alcohol consumption, and the combination of the two produced a synergistic increase in risk. However, beginning in 1983, investigators have found a significant and growing proportion of HNC patients with human papillomavirus-positive (HPV) tumors who neither drank nor used tobacco. Since that time, there has been increased interest in the molecular biology of HPV-positive HNC. Multiple studies now show that HPV has shifted the epidemiological landscape and prognosis of head and neck squamous cell carcinoma (HNSCC). These studies provide strong evidence for improved survival outcomes in patients with HPV-positive HNSCC compared to those with HPV-negative HNSCC. In many reports, HPV status is the strongest predictor of locoregional control, disease specific survival and overall survival. In response to these findings, there has been significant interest in the best management of HPV-positive disease. Discussions within major cooperative groups consider new trials designed to maintain the current strong survival outcomes while reducing the long-term treatment-related toxicities. This review will highlight the epidemiological, clinical and molecular discoveries surrounding HPV-related HNSCC over the recent decades and we conclude by suggesting how these findings may guide future treatment approaches.

Ablation of AgRP neurons impairs adaption to restricted feeding

While the SCN controls the circadian clock, further evidence suggests the existence of a food-entrainable oscillator (FEO) that links behavior to changes in food availability such as during restricted feeding (RF). We found that the activity of AgRP/NPY neurons changed rhythmically during RF suggesting that these neurons are a component of the FEO. We next ablated AgRP/NPY neurons in neonates with diphtheria toxin resulting in the loss of ∼50% of AgRP/NPY neurons. Body weight and food intake were unchanged in adult animals after neonatal ablation, as were the responses to leptin treatment, leptin withdrawal, food deprivation and ghrelin treatment. However, ablated animals showed 30% mortality within 4 days of RF. Moreover, the recovery of body weight and food intake in surviving animals lagged behind controls with an absence of food anticipatory activity even after three days. These findings identify AgRP/NPY neurons as a key cellular component of the food-entrained oscillator.

A critical role for mTORC1 in erythropoiesis and anemia

Red blood cells (RBC) must coordinate their rate of growth and proliferation with the availability of nutrients, such as iron, but the signaling mechanisms that link the nutritional state to RBC growth are incompletely understood. We performed a screen for cell types that have high levels of signaling through mTORC1, a protein kinase that couples nutrient availability to cell growth. This screen revealed that reticulocytes show high levels of phosphorylated ribosomal protein S6, a downstream target of mTORC1. We found that mTORC1 activity in RBCs is regulated by dietary iron and that genetic activation or inhibition of mTORC1 results in macrocytic or microcytic anemia, respectively. Finally, ATP competitive mTOR inhibitors reduced RBC proliferation and were lethal after treatment with phenylhydrazine, an inducer of hemolysis. These results identify the mTORC1 pathway as a critical regulator of RBC growth and proliferation and establish that perturbations in this pathway result in anemia.

DOI:http://dx.doi.org/10.7554/eLife.01913.001

To multiply and grow, cells need to create more of the molecules—such as proteins—that make up their structure. This only happens if the cell has a good supply of the nutrients used to build the proteins.

Red blood cells are particularly sensitive to the supply of nutrients, especially iron, which is a key component of the hemoglobin molecules that enable the cells to transport oxygen around the body. A lack of iron can lead to a shortage of red blood cells and a condition called anemia. People with mild forms of anemia may feel tired or weak, but more severe forms of anemia can cause heart problems and even death.

A protein called mTOR forms part of a protein complex that helps alert the cells of many different organisms to the presence of nutrients. mTOR can add phosphate groups to ribosomes—the molecular machines that translate molecules of mRNA to build proteins. In 2012, researchers developed a technique called Phospho-Trap that can isolate these phosphorylated ribosomes from cells. Cells with an activated mTOR complex express more mTOR protein and in turn have more ribosomes that are modified. Examining the mRNA molecules associated with these ribosomes can reveal which proteins are produced in greater amounts in these cells.

Previous experiments using Phospho-Trap found the proteins that make up hemoglobin in unexpectedly high amounts in the mouse brain. Now, Knight et al.—and other researchers involved in the 2012 work—have established that the hemoglobin was not coming from the brain cells but from immature red blood cells circulating within the brain. These immature blood cells were found to have a highly active mTOR complex that promotes the production of hemoglobin and new blood cells.

Using genetic techniques in mice, Knight et al. found that the mTOR complex can cause anemia if it is underactive or overactive. Underactive mTOR complexes cause a type of anemia that produces small red blood cells and is usually triggered by a lack of iron. This made sense because mTOR is known to regulate both protein production and cell size. Boosting the activity of the mTOR complex leads to a type of anemia in which the cells are much larger than normal, and which is normally associated with inadequate amounts of folate and B12 vitamins.

When Knight et al. gave mice a drug that inhibits the mTOR protein, the mice developed anemia that resolved when the treatment stopped. However, mice that were given the mTOR inhibitor at the same time as a drug that destroys red blood cells, all died within days. Clinical trials are currently testing mTOR inhibitors as a possible cancer treatment; however, a common side effect of chemotherapy is that it stops new red blood cells being produced. Knight et al. suggest that the red blood cells of patients in these clinical trials must be closely monitored before deciding whether to continue the treatment further.

DOI:http://dx.doi.org/10.7554/eLife.01913.002

Molecular profiling of neurons based on connectivity

The complexity and cellular heterogeneity of neural circuitry presents a major challenge to understanding the role of discrete neural populations in controlling behavior. While neuroanatomical methods enable high-resolution mapping of neural circuitry, these approaches do not allow systematic molecular profiling of neurons based on their connectivity. Here, we report the development of an approach for molecularly profiling projective neurons. We show that ribosomes can be tagged with a camelid nanobody raised against GFP and that this system can be engineered to selectively capture translating mRNAs from neurons retrogradely labeled with GFP. Using this system, we profiled neurons projecting to the nucleus accumbens. We then used an AAV to selectively profile midbrain dopamine neurons projecting to the nucleus accumbens. By comparing the captured mRNAs from each experiment, we identified a number of markers specific to VTA dopaminergic projection neurons. The current method provides a means for profiling neurons based on their projections.

The reward value of sucrose in leptin-deficient obese mice

Leptin-deficient patients report higher "liking" ratings for food, and leptin replacement therapy normalizes these ratings even before weight loss is achieved. Since animals cannot report their ratings, we studied the relationship between leptin and food reward in leptin-deficient ob/ob mice using a optogenetic assay that quantifies the reward value of sucrose. In this assay, mice chose between one sipper dispensing the artificial sweetener sucralose coupled to optogenetic activation of dopaminergic (DA) neurons, and another sipper dispensing sucrose. We found that the reward value of sucrose was high under a state of leptin deficiency, as well as at a dose of leptin that does not suppress food intake (12.5 ng/h). Treatment with higher doses of leptin decreased the reward value of sucrose before weight loss was achieved (100 ng/h), as seen in leptin-deficient patients. These results phenocopy in mice the behavior of leptin-deficient patients.

Stress and CRF gate neural activation of BDNF in the mesolimbic reward pathway

Mechanisms controlling release of brain-derived neurotrophic factor (BDNF) in the mesolimbic dopamine reward pathway remain unknown. We report that phasic optogenetic activation of this pathway increases BDNF amounts in the nucleus accumbens (NAc) of socially stressed mice but not of stress-naive mice. This stress gating of BDNF signaling is mediated by corticotrophin-releasing factor (CRF) acting in the NAc. These results unravel a stress context-detecting function of the brain's mesolimbic circuit.

Hypothalamic melanin concentrating hormone neurons communicate the nutrient value of sugar

Sugars that contain glucose, such as sucrose, are generally preferred to artificial sweeteners owing to their post-ingestive rewarding effect, which elevates striatal dopamine (DA) release. While the post-ingestive rewarding effect, which artificial sweeteners do not have, signals the nutrient value of sugar and influences food preference, the neural circuitry that mediates the rewarding effect of glucose is unknown. In this study, we show that optogenetic activation of melanin-concentrating hormone (MCH) neurons during intake of the artificial sweetener sucralose increases striatal dopamine levels and inverts the normal preference for sucrose vs sucralose. Conversely, animals with ablation of MCH neurons no longer prefer sucrose to sucralose and show reduced striatal DA release upon sucrose ingestion. We further show that MCH neurons project to reward areas and are required for the post-ingestive rewarding effect of sucrose in sweet-blind Trpm5(-/-) mice. These studies identify an essential component of the neural pathways linking nutrient sensing and food reward. DOI: http://dx.doi.org/10.7554/eLife.01462.001.

Exome sequencing identifies mutations in KIF14 as a novel cause of an autosomal recessive lethal fetal ciliopathy phenotype

Gene discovery using massively parallel sequencing has focused on phenotypes diagnosed postnatally such as well-characterized syndromes or intellectual disability, but is rarely reported for fetal disorders. We used family-based whole-exome sequencing in order to identify causal variants for a recurrent pattern of an undescribed lethal fetal congenital anomaly syndrome. The clinical signs included intrauterine growth restriction (IUGR), severe microcephaly, renal cystic dysplasia/agenesis and complex brain and genitourinary malformations. The phenotype was compatible with a ciliopathy, but not diagnostic of any known condition. We hypothesized biallelic disruption of a gene leading to a defect related to the primary cilium. We identified novel autosomal recessive truncating mutations in KIF14 that segregated with the phenotype. Mice with autosomal recessive mutations in the same gene have recently been shown to have a strikingly similar phenotype. Genotype-phenotype correlations indicate that the function of KIF14 in cell division and cytokinesis can be linked to a role in primary cilia, supported by previous cellular and model organism studies of proteins that interact with KIF14. We describe the first human phenotype, a novel lethal ciliary disorder, associated with biallelic inactivating mutations in KIF14. KIF14 may also be considered a candidate gene for allelic viable ciliary and/or microcephaly phenotypes.

Obese locus in WNIN/obese rat maps on chromosome 5 upstream of leptin receptor

WNIN/Obese (WNIN/Ob) rat a new mutant model of metabolic syndrome was identified in 1996 from an inbred Wistar rat strain, WNIN. So far several papers are published on this model highlighting its physical, biochemical and metabolic traits. WNIN/Ob is leptin resistant with unaltered leptin or its receptor coding sequences - the two well-known candidate genes for obesity. Genotyping analysis of F₂ progeny (raised from WNIN/Ob × Fisher - 344) in the present study localized the mutation to a recombinant region of 14.15cM on chromosome 5. This was further corroborated by QTL analysis for body weight, which narrowed this region to 4.43 cM with flanking markers D5Rat256 & D5Wox37. Interval mapping of body weight QTL shows that the LOD score peak maps upstream of leptin receptor and shows an additive effect suggesting this as a novel mutation and signifying the model as a valuable resource for studies on obesity and metabolic syndrome.