The Caenorhabditis elegans ASPP homolog APE-1 is a junctional protein phosphatase 1 modulator

How serine/threonine phosphatases are spatially and temporally tuned by regulatory subunits is a fundamental question in cell biology. Ankyrin repeat, SH3 domain, proline-rich-region-containing proteins are protein phosphatase 1 catalytic subunit binding partners associated with cardiocutaneous diseases. Ankyrin repeat, SH3 domain, proline-rich-region-containing proteins localize protein phosphatase 1 catalytic subunit to cell-cell junctions, but how ankyrin repeat, SH3 domain, proline-rich-region-containing proteins localize and whether they regulate protein phosphatase 1 catalytic subunit activity in vivo is unclear. Through a Caenorhabditis elegans genetic screen, we find that loss of the ankyrin repeat, SH3 domain, proline-rich-region-containing protein homolog, APE-1, suppresses a pathology called "jowls," providing us with an in vivo assay for APE-1 activity. Using immunoprecipitations and mass spectrometry, we find that APE-1 binds the protein phosphatase 1 catalytic subunit called GSP-2. Through structure-function analysis, we discover that APE-1's N-terminal half directs the APE-1-GSP-2 complex to intercellular junctions. Additionally, we isolated mutations in highly conserved residues of APE-1's ankyrin repeats that suppress jowls yet do not preclude GSP-2 binding, implying APE-1 does more than simply localize GSP-2. Indeed, in vivo reconstitution of APE-1 suggests the ankyrin repeats modulate phosphatase output, a function we find to be conserved among vertebrate homologs.

Structural basis of an endocytic checkpoint that primes the AP2 clathrin adaptor for cargo internalization

Clathrin-mediated endocytosis (CME) is the main route of internalization from the plasma membrane. It is known that the heterotetrameric AP2 clathrin adaptor must open to simultaneously engage membrane and endocytic cargo, yet it is unclear how transmembrane cargos are captured to catalyze CME. Using cryogenic-electron microscopy, we discover a new way in which mouse AP2 can reorganize to expose membrane- and cargo-binding pockets, which is not observed in clathrin-coated structures. Instead, it is stimulated by endocytic pioneer proteins called muniscins, which do not enter vesicles. Muniscin-engaged AP2 is primed to rearrange into the vesicle-competent conformation on binding the tyrosine cargo internalization motif (YxxΦ). We propose adaptor priming as a checkpoint to ensure cargo internalization.

A structural mechanism for phosphorylation-dependent inactivation of the AP2 complex

Endocytosis of transmembrane proteins is orchestrated by the AP2 clathrin adaptor complex. AP2 dwells in a closed, inactive state in the cytosol, but adopts an open, active conformation on the plasma membrane. Membrane-activated complexes are also phosphorylated, but the significance of this mark is debated. We recently proposed that NECAP negatively regulates AP2 by binding open and phosphorylated complexes (Beacham et al., 2018). Here, we report high-resolution cryo-EM structures of NECAP bound to phosphorylated AP2. The site of AP2 phosphorylation is directly coordinated by residues of the NECAP PHear domain that are predicted from genetic screens in C. elegans. Using membrane mimetics to generate conformationally open AP2, we find that a second domain of NECAP binds these complexes and cryo-EM reveals both domains of NECAP engaging closed, inactive AP2. Assays in vitro and in vivo confirm these domains cooperate to inactivate AP2. We propose that phosphorylation marks adaptors for inactivation.

Conformational regulation of AP1 and AP2 clathrin adaptor complexes

Heterotetrameric clathrin adaptor protein complexes (APs) orchestrate the formation of coated vesicles for transport among organelles of the cell periphery. AP1 binds membranes enriched for phosphatidylinositol 4-phosphate, such as the trans Golgi network, while AP2 associates with phosphatidylinositol 4,5-bisphosphate of the plasma membrane. At their respective membranes, AP1 and AP2 bind the cytoplasmic tails of transmembrane protein cargo and clathrin triskelions, thereby coupling cargo recruitment to coat polymerization. Structural, biochemical and genetic studies have revealed that APs undergo conformational rearrangements and reversible phosphorylation to cycle between different activity states. While membrane, cargo and clathrin have been demonstrated to promote AP activation, growing evidence supports that membrane-associated proteins such as Arf1 and FCHo also stimulate this transition. APs may be returned to the inactive state via a regulated process involving phosphorylation and a protein called NECAP. Finally, because antiviral mechanisms often rely on appropriate trafficking of membrane proteins, viruses have evolved novel strategies to evade host defenses by influencing the conformation of APs. This review will cover recent advances in our understanding of the molecular inputs that stimulate AP1 and AP2 to adopt structurally and functionally distinct configurations.

NECAPs are negative regulators of the AP2 clathrin adaptor complex

Eukaryotic cells internalize transmembrane receptors via clathrin-mediated endocytosis, but it remains unclear how the machinery underpinning this process is regulated. We recently discovered that membrane-associated muniscin proteins such as FCHo and SGIP initiate endocytosis by converting the AP2 clathrin adaptor complex to an open, active conformation that is then phosphorylated (Hollopeter et al., 2014). Here we report that loss of ncap-1, the sole C. elegans gene encoding an adaptiN Ear-binding Coat-Associated Protein (NECAP), bypasses the requirement for FCHO-1. Biochemical analyses reveal AP2 accumulates in an open, phosphorylated state in ncap-1 mutant worms, suggesting NECAPs promote the closed, inactive conformation of AP2. Consistent with this model, NECAPs preferentially bind open and phosphorylated forms of AP2 in vitro and localize with constitutively open AP2 mutants in vivo. NECAPs do not associate with phosphorylation-defective AP2 mutants, implying that phosphorylation precedes NECAP recruitment. We propose NECAPs function late in endocytosis to inactivate AP2.

The membrane-associated proteins FCHo and SGIP are allosteric activators of the AP2 clathrin adaptor complex

The AP2 clathrin adaptor complex links protein cargo to the endocytic machinery but it is unclear how AP2 is activated on the plasma membrane. Here we demonstrate that the membrane-associated proteins FCHo and SGIP1 convert AP2 into an open, active conformation. We screened for Caenorhabditis elegans mutants that phenocopy the loss of AP2 subunits and found that AP2 remains inactive in fcho-1 mutants. A subsequent screen for bypass suppressors of fcho-1 nulls identified 71 compensatory mutations in all four AP2 subunits. Using a protease-sensitivity assay we show that these mutations restore the open conformation in vivo. The domain of FCHo that induces this rearrangement is not the F-BAR domain or the µ-homology domain, but rather is an uncharacterized 90 amino acid motif, found in both FCHo and SGIP proteins, that directly binds AP2. Thus, these proteins stabilize nascent endocytic pits by exposing membrane and cargo binding sites on AP2.

Ultrafast endocytosis at Caenorhabditis elegans neuromuscular junctions

Synaptic vesicles can be released at extremely high rates, which places an extraordinary demand on the recycling machinery. Previous ultrastructural studies of vesicle recycling were conducted in dissected preparations using an intense stimulation to maximize the probability of release. Here, a single light stimulus was applied to motor neurons in intact Caenorhabditis elegans nematodes expressing channelrhodopsin, and the animals rapidly frozen. We found that docked vesicles fuse along a broad active zone in response to a single stimulus, and are replenished with a time constant of about 2 s. Endocytosis occurs within 50 ms adjacent to the dense projection and after 1 s adjacent to adherens junctions. These studies suggest that synaptic vesicle endocytosis may occur on a millisecond time scale following a single physiological stimulus in the intact nervous system and is unlikely to conform to current models of endocytosis. DOI:http://dx.doi.org/10.7554/eLife.00723.001.

AP2 hemicomplexes contribute independently to synaptic vesicle endocytosis

The clathrin adaptor complex AP2 is thought to be an obligate heterotetramer. We identify null mutations in the α subunit of AP2 in the nematode Caenorhabditis elegans. α-adaptin mutants are viable and the remaining μ2/β hemicomplex retains some function. Conversely, in μ2 mutants, the alpha/sigma2 hemicomplex is localized and is partially functional. α-μ2 double mutants disrupt both halves of the complex and are lethal. The lethality can be rescued by expression of AP2 components in the skin, which allowed us to evaluate the requirement for AP2 subunits at synapses. Mutations in either α or μ2 subunits alone reduce the number of synaptic vesicles by about 30%; however, simultaneous loss of both α and μ2 subunits leads to a 70% reduction in synaptic vesicles and the presence of large vacuoles. These data suggest that AP2 may function as two partially independent hemicomplexes. DOI:http://dx.doi.org/10.7554/eLife.00190.001.

Nano-fEM: protein localization using photo-activated localization microscopy and electron microscopy

Mapping the distribution of proteins is essential for understanding the function of proteins in a cell. Fluorescence microscopy is extensively used for protein localization, but subcellular context is often absent in fluorescence images. Immuno-electron microscopy, on the other hand, can localize proteins, but the technique is limited by a lack of compatible antibodies, poor preservation of morphology and because most antigens are not exposed to the specimen surface. Correlative approaches can acquire the fluorescence image from a whole cell first, either from immuno-fluorescence or genetically tagged proteins. The sample is then fixed and embedded for electron microscopy, and the images are correlated (1-3). However, the low-resolution fluorescence image and the lack of fiducial markers preclude the precise localization of proteins. Alternatively, fluorescence imaging can be done after preserving the specimen in plastic. In this approach, the block is sectioned, and fluorescence images and electron micrographs of the same section are correlated (4-7). However, the diffraction limit of light in the correlated image obscures the locations of individual molecules, and the fluorescence often extends beyond the boundary of the cell. Nano-resolution fluorescence electron microscopy (nano-fEM) is designed to localize proteins at nano-scale by imaging the same sections using photo-activated localization microscopy (PALM) and electron microscopy. PALM overcomes the diffraction limit by imaging individual fluorescent proteins and subsequently mapping the centroid of each fluorescent spot (8-10). We outline the nano-fEM technique in five steps. First, the sample is fixed and embedded using conditions that preserve the fluorescence of tagged proteins. Second, the resin blocks are sectioned into ultrathin segments (70-80 nm) that are mounted on a cover glass. Third, fluorescence is imaged in these sections using the Zeiss PALM microscope. Fourth, electron dense structures are imaged in these same sections using a scanning electron microscope. Fifth, the fluorescence and electron micrographs are aligned using gold particles as fiducial markers. In summary, the subcellular localization of fluorescently tagged proteins can be determined at nanometer resolution in approximately one week.

Membrane tension regulates motility by controlling lamellipodium organization

Many cell movements proceed via a crawling mechanism, where polymerization of the cytoskeletal protein actin pushes out the leading edge membrane. In this model, membrane tension has been seen as an impediment to filament growth and cell motility. Here we use a simple model of cell motility, the Caenorhabditis elegans sperm cell, to test how membrane tension affects movement and cytoskeleton dynamics. To enable these analyses, we create transgenic worm strains carrying sperm with a fluorescently labeled cytoskeleton. Via osmotic shock and deoxycholate treatments, we relax or tense the cell membrane and quantify apparent membrane tension changes by the membrane tether technique. Surprisingly, we find that membrane tension reduction is correlated with a decrease in cell displacement speed, whereas an increase in membrane tension enhances motility. We further demonstrate that apparent polymerization rates follow the same trends. We observe that membrane tension reduction leads to an unorganized, rough lamellipodium, composed of short filaments angled away from the direction of movement. On the other hand, an increase in tension reduces lateral membrane protrusions in the lamellipodium, and filaments are longer and more oriented toward the direction of movement. Overall we propose that membrane tension optimizes motility by streamlining polymerization in the direction of movement, thus adding a layer of complexity to our current understanding of how membrane tension enters into the motility equation.

Protein localization in electron micrographs using fluorescence nanoscopy

A complete portrait of a cell requires a detailed description of its molecular topography: proteins must be linked to particular organelles. Immunocytochemical electron microscopy can reveal locations of proteins with nanometer resolution but is limited by the quality of fixation, the paucity of antibodies and the inaccessibility of antigens. Here we describe correlative fluorescence electron microscopy for the nanoscopic localization of proteins in electron micrographs. We tagged proteins with the fluorescent proteins Citrine or tdEos and expressed them in Caenorhabditis elegans, fixed the worms and embedded them in plastic. We imaged the tagged proteins from ultrathin sections using stimulated emission depletion (STED) microscopy or photoactivated localization microscopy (PALM). Fluorescence correlated with organelles imaged in electron micrographs from the same sections. We used these methods to localize histones, a mitochondrial protein and a presynaptic dense projection protein in electron micrographs.

Targeted gene deletions in C. elegans using transposon excision

We have developed a method, MosDel, to generate targeted knock-outs of genes in C. elegans. We make use of the Mos1 transposase to excise a Mos1 transposon adjacent to the region to be deleted. The double-strand break is repaired using injected DNA as a template. Repair can delete up to 25 kb of DNA and simultaneously insert a positive selection marker.

The P2Y12 receptor regulates microglial activation by extracellular nucleotides

Microglia are primary immune sentinels of the CNS. Following injury, these cells migrate or extend processes toward sites of tissue damage. CNS injury is accompanied by release of nucleotides, serving as signals for microglial activation or chemotaxis. Microglia express several purinoceptors, including a G(i)-coupled subtype that has been implicated in ATP- and ADP-mediated migration in vitro. Here we show that microglia from mice lacking G(i)-coupled P2Y(12) receptors exhibit normal baseline motility but are unable to polarize, migrate or extend processes toward nucleotides in vitro or in vivo. Microglia in P2ry(12)(-/-) mice show significantly diminished directional branch extension toward sites of cortical damage in the living mouse. Moreover, P2Y(12) expression is robust in the 'resting' state, but dramatically reduced after microglial activation. These results imply that P2Y(12) is a primary site at which nucleotides act to induce microglial chemotaxis at early stages of the response to local CNS injury.

Identification of the platelet ADP receptor targeted by antithrombotic drugs

Platelets have a crucial role in the maintenance of normal haemostasis, and perturbations of this system can lead to pathological thrombus formation and vascular occlusion, resulting in stroke, myocardial infarction and unstable angina. ADP released from damaged vessels and red blood cells induces platelet aggregation through activation of the integrin GPIIb-IIIa and subsequent binding of fibrinogen. ADP is also secreted from platelets on activation, providing positive feedback that potentiates the actions of many platelet activators. ADP mediates platelet aggregation through its action on two G-protein-coupled receptor subtypes. The P2Y1 receptor couples to Gq and mobilizes intracellular calcium ions to mediate platelet shape change and aggregation. The second ADP receptor required for aggregation (variously called P2Y(ADP), P2Y(AC), P2Ycyc or P2T(AC)) is coupled to the inhibition of adenylyl cyclase through Gi. The molecular identity of the Gi-linked receptor is still elusive, even though it is the target of efficacious antithrombotic agents, such as ticlopidine and clopidogrel and AR-C66096 (ref. 9). Here we describe the cloning of this receptor, designated P2Y12, and provide evidence that a patient with a bleeding disorder has a defect in this gene. Cloning of the P2Y12 receptor should facilitate the development of better antiplatelet agents to treat cardiovascular diseases.

Role of the Y5 neuropeptide Y receptor in limbic seizures

Neuropeptide Y (NPY) is an inhibitory neuromodulator expressed abundantly in the central nervous system that is suspected of being an endogenous antiepileptic agent that can control propagation of limbic seizures. Electrophysiological and pharmacological data suggest that these actions of NPY are mediated by G protein-coupled NPY Y2 and NPY Y5 receptors. To determine whether the NPY Y5 receptor (Y5R) is required for normal control of limbic seizures, we examined hippocampal function and responsiveness to kainic acid-induced seizures in Y5R-deficient (Y5R-/-) mice. We report that Y5R-/- mice do not exhibit spontaneous seizure-like activity; however, they are more sensitive to kainic acid-induced seizures. Electrophysiological examination of hippocampal slices from mutant mice revealed normal function, but the antiepileptic effects of exogenously applied NPY were absent. These data demonstrate that Y5R has an important role in mediating NPY's inhibitory actions in the mouse hippocampus and suggest a role for Y5R in the control of limbic seizures.

Response of melanocortin-4 receptor-deficient mice to anorectic and orexigenic peptides

Mutations reducing the functional activity of leptin, the leptin receptor, alpha-melanocyte stimulating hormones (alpha-MSH) and the melanocortin-4 receptor (Mc4r) all lead to obesity in mammals. Moreover, mutant mice that ectopically express either agouti (Ay/a mice) or agouti-related protein (Agrp), antagonists of melanocortin signalling, become obese. These data suggest that alpha-MSH signalling transduced by Mc4r tonically inhibits feeding; however, it is not known to what extent this pathway mediates leptin signalling. We show here that Mc4r-deficient (Mc4r-/-) mice do not respond to the anorectic actions of MTII, an MSH-like agonist, suggesting that alpha-MSH inhibits feeding primarily by activating Mc4r. Obese Mc4r-/-mice do not respond significantly to the inhibitory effects of leptin on feeding, whereas non-obese Mc4r-/- mice do. These data demonstrate that melanocortin signalling transduced by Mc4r is not an exclusive target of leptin action and that factors resulting from obesity contribute to leptin resistance. Leptin resistance of obese Mc4r-/- mice does not prevent their response to the anorectic actions of ciliary neurotrophic factor (CNTF), corticotropin releasing factor (CRF), or urocortin; or the orexigenic actions of neuropeptide Y (NPY) or peptide YY (PYY), indicating that these neuromodulators act independently or downstream of Mc4r signalling.

Life without neuropeptide Y

Neuropeptide Y (NPY), a 36 amino acid neuromodulator that is secreted by neurons throughout the peripheral and central nervous system, has been implicated in the control of many physiological processes. We have begun to examine its role in regulation of appetite, behavior, and excitotoxicity by examining mice that are unable to produce NPY as a consequence of gene inactivation. These mutant mice are remarkably normal when reared under standard vivarium conditions. Despite considerable evidence that NPY plays a central role in stimulating appetite, NPY-deficient mice eat normally, grow normally, and refeed after a fast normally. Furthermore, all of their endocrine responses to fasting are normal. The response of NPY-null mice to diet-induced obesity, chemically induced obesity (monosodium glutamate and gold thioglucose), and genetic-based obesity (lethal yellow agouti, Ay; uncoupling protein-diphtheria toxin transgenics, UCP-DT) were all normal. However, NPY deficiency does partially ameliorate the obesity and all of the adverse endocrine effects of leptin deficiency in ob/ob mice. NPY-null mice as well as mice deficient in both NPY and leptin are more sensitive to leptin, suggesting that NPY may normally have a tonic inhibitory action on leptin-mediated satiety signals. NPY-null mice display the normal voracious feeding response to injected NPY. Thus, the only condition where we have observed a role for NPY in body-weight regulation is in the context of complete leptin deficiency--where absence of NPY is beneficial. The activity and general behavior of NPY-null mice are normal. They appear to have normal spatial and contextual learning ability; however, they manifest more anxiety under some conditions. NPY-null mice occasionally display spontaneous, seizure-like events. They also are less able to terminate seizures induced by GABA receptor antagonists or glutamate receptor agonists. These observations are consistent with previous data suggesting that NPY plays an important role in dampening excitotoxicity.

Response of neuropeptide Y-deficient mice to feeding effectors

Neuropeptide Y (NPY) is thought to be an important central regulator of feeding behavior and body weight. However, mice lacking NPY due to targeted genetic deletion do not display abnormalities in food intake or body weight with ad libitum access to food or in response to fasting. In this study, we investigate the response of NPY-deficient (NPY-/-) mice to anorexic and orexigenic treatments. The dose-dependent stimulation of food intake by central NPY administration was unaltered in NPY-/- mice. Peripheral administration of various doses of leptin for 2 days elicited a two-fold greater inhibition of food intake in NPY-/- mice than in wildtype (NPY+/+) mice. In addition, lateral ventricular administration of leptin (1 microg) suppressed refeeding in NPY-/- mice after a 24 h fast, but had little effect in NPY+/+ mice. However, the response to other feeding inhibitors such as corticotrophin releasing factor (CRF), dexfenfluramine, and a melanocortin 4 receptor (MC4R) agonist, MTII, was unaltered in NPY-/- mice. These results indicate that the appetite-suppressant action of exogenous leptin is uniquely amplified in NPY-/- mice, and suggest that NPY may tonically antagonize leptin action.

Role of the Y5 neuropeptide Y receptor in feeding and obesity

Neuropeptide Y (NPY), a 36-amino-acid neuromodulator abundantly expressed in the brain, has been implicated in the regulation of food intake and body weight. Pharmacological data suggest that NPY's stimulatory effect on appetite is transduced by the G-protein-coupled NPY Y5 receptor (Y5R). We have inactivated the Y5R gene in mice and report that younger Y5R-null mice feed and grow normally; however, they develop mild late-onset obesity characterized by increased body weight, food intake and adiposity. Fasting-induced refeeding is unchanged in younger Y5R-null mice and they exhibit normal sensitivity to leptin. Their response to intracerebroventricular (i.c.v.) administration of NPY and related peptides is either reduced or absent. NPY deficiency attenuates the obesity syndrome of mice deficient for leptin (ob/ob), but these effects are not mediated by NPY signaling through the Y5R because Y5R-null ob/ob mice are equally obese. These results demonstrate that the Y5R contributes to feeding induced by centrally administered NPY and its analogs, but is not a critical physiological feeding receptor in mice.

Role of neuropeptide Y in diet-, chemical- and genetic-induced obesity of mice

OBJECTIVE

The goal of this study was to ascertain whether neuropeptide Y (NPY) is required in mice for the development of obesity induced by a high-fat diet (HFD), chemical lesions of the hypothalamus caused by monosodium glutamate (MSG) or gold thioglucose (GTG), impaired brown adipose tissue (BAT) due to a diphtheria toxin transgene driven by the uncoupling protein 1 promoter (UCP-DTA) or the lethal yellow agouti mutation (Ay).

BACKGROUND

The obesity syndrome of the leptin-deficient (ob/ob) mouse can be partially reversed by the genetic removal of NPY. In the murine models of obesity examined in this study, the animals become obese despite increased serum leptin levels, indicating that they are resistant to the weight-limiting actions of leptin. The role of NPY in these obesity models with elevated leptin levels is unknown.

EXPERIMENTAL DESIGN

Mice lacking NPY due to genetic disruption of the gene and wildtype littermates were made obese by allowing them access to a highly palatable HFD, by treatment with MSG, or GTG, or by inheriting the dominant UCP-DTA or Ay alleles. Food consumption, body weight and dissectable fat pad weights were measured and compared to values obtained from non-obese littermates.

RESULTS

In each model of obesity tested, NPY-deficient mice achieved the same food intake, body weight and fat content as wildtype littermates.

CONCLUSION

NPY is not necessary for the progressive development of obesity exhibited by multiple murine models with leptin resistance.

Knock-out mice reveal a critical antiepileptic role for neuropeptide Y

Neuropeptide Y (NPY) inhibits excitatory synaptic transmission in the hippocampus and is implicated in control of limbic seizures. In the present study, we examined hippocampal function and the response to pharmacologically induced seizures in mutant mice lacking this peptide. In slice electrophysiology studies, no change in normal hippocampal function was observed in NPY-deficient mice compared with normal wild-type littermates. Kainic acid (KA) produced limbic seizures at a comparable latency and concentration in NPY-deficient mice compared with littermates. However, KA-induced seizures progressed uncontrollably and ultimately produced death in 93% of NPY-deficient mice, whereas death was rarely observed in wild-type littermates. Intracerebroventricular NPY infusion, before KA administration, prevented death in NPY-deficient mice. These results suggest a critical role for endogenous NPY in seizure control.

Endocrine function of neuropeptide Y knockout mice

Among its many proposed functions, neuropeptide Y (NPY) is thought to modulate the hypothalamic-pituitary axis. Specifically, increased hypothalamic NPY signaling may be critical in mediating the neuroendocrine response to fasting. To determine the consequences of NPY deficiency on endocrine physiology, multiple hormones were quantitated in wildtype and NPY-knockout mice under fed and fasted conditions. Serum concentrations of leptin, corticosterone, thyroxine, and testosterone were normal in NPY-knockout males fed ad libitum. A 48-hour fast resulted in a 50% reduction in leptin, a 60% reduction in thyroxine, a 75% reduction in testosterone, and a 12-fold increase in corticosterone in both wildtype and NPY-knockout mice. Fasting also increased the estrous cycle length by 3 days in both wildtype and NPY-deficient female mice. We conclude that NPY is not essential for appropriate function of the gonadotropic, thyrotropic, or corticotropic axes under ad lib fed conditions or in response to acute fasting.

Disruption of the metallothionein-III gene in mice: analysis of brain zinc, behavior, and neuron vulnerability to metals, aging, and seizures

Metallothionein-III (MT-III), a brain-specific member of the metallothionein family of metal-binding proteins, is abundant in glutamatergic neurons that release zinc from their synaptic terminals, such as hippocampal pyramidal neurons and dentate granule cells. MT-III may be an important regulator of zinc in the nervous system, and its absence has been implicated in the development of Alzheimer's disease. However, the roles of MT-III in brain physiology and pathophysiology have not been elucidated. Mice lacking MT-III because of targeted gene inactivation were generated to evaluate the neurobiological significance of MT-III. MT-III-deficient mice had decreased concentrations of zinc in several brain regions, including hippocampus, but the pool of histochemically reactive zinc was not disturbed. Mutant mice exhibited normal spatial learning in the Morris water maze and were not sensitive to systemic zinc or cadmium exposure. No neuropathology or behavioral deficits were detected in 2-year-old MT-III-deficient mice, but the age-related increase in glial fibrillary acidic protein expression was more pronounced in mutant brain. MT-III-deficient mice were more susceptible to seizures induced by kainic acid and subsequently exhibited greater neuron injury in the CA3 field of hippocampus. Conversely, transgenic mice containing elevated levels of MT-III were more resistant to CA3 neuron injury induced by seizures. These observations suggest a potential role for MT-III in zinc regulation during neural stimulation.

Attenuation of the obesity syndrome of ob/ob mice by the loss of neuropeptide Y

The obesity syndrome of ob/ob mice results from lack of leptin, a hormone released by fat cells that acts in the brain to suppress feeding and stimulate metabolism. Neuropeptide Y (NPY) is a neuromodulator implicated in the control of energy balance and is overproduced in the hypothalamus of ob/ob mice. To determine the role of NPY in the response to leptin deficiency, ob/ob mice deficient for NPY were generated. In the absence of NPY, ob/ob mice are less obese because of reduced food intake and increased energy expenditure, and are less severely affected by diabetes, sterility, and somatotropic defects. These results suggest that NPY is a central effector of leptin deficiency.