Rem2 interacts with CaMKII at synapses and restricts long-term potentiation in hippocampus

Synaptic plasticity, the process whereby neuronal connections are either strengthened or weakened in response to stereotyped forms of stimulation, is widely believed to represent the molecular mechanism that underlies learning and memory. The holoenzyme CaMKII plays a well-established and critical role in the induction of a variety of forms of synaptic plasticity such as long-term potentiation (LTP), long-term depression (LTD) and depotentiation. Previously, we identified the GTPase Rem2 as a potent, endogenous inhibitor of CaMKII. Here, we report that knock out of Rem2 enhances LTP at the Schaffer collateral to CA1 synapse in hippocampus, consistent with an inhibitory action of Rem2 on CaMKII in vivo. Further, re-expression of WT Rem2 rescues the enhanced LTP observed in slices obtained from Rem2 conditional knock out (cKO) mice, while expression of a mutant Rem2 construct that is unable to inhibit CaMKII in vitro fails to rescue increased LTP. In addition, we demonstrate that CaMKII and Rem2 interact in dendritic spines using a 2pFLIM-FRET approach. Taken together, our data lead us to propose that Rem2 serves as a brake on runaway synaptic potentiation via inhibition of CaMKII activity. Further, the enhanced LTP phenotype we observe in Rem2 cKO slices reveals a previously unknown role for Rem2 in the negative regulation of CaMKII function.

Plexin-B1 and Plexin-B2 play non-redundant roles in GABAergic synapse formation

Synapse formation in the mammalian brain is a complex and dynamic process requiring coordinated function of dozens of molecular families such as cell adhesion molecules (CAMs) and ligand-receptor pairs (Ephs/Ephrins, Neuroligins/Neurexins, Semaphorins/Plexins). Due to the large number of molecular players and possible functional redundancies within gene families, it is challenging to determine the precise synaptogenic roles of individual molecules, which is key to understanding the consequences of mutations in these genes for brain function. Furthermore, few molecules are known to exclusively regulate either GABAergic or glutamatergic synapses, and cell and molecular mechanisms underlying GABAergic synapse formation in particular are not thoroughly understood. We previously demonstrated that Semaphorin-4D (Sema4D) regulates GABAergic synapse development in the mammalian hippocampus while having no effect on glutamatergic synapse development, and this effect occurs through binding to its high affinity receptor, Plexin-B1. In addition, we demonstrated that RNAi-mediated Plexin-B2 knock-down decreases GABAergic synapse density suggesting that both receptors function in this process. Here, we perform a structure-function study of the Plexin-B1 and Plexin-B2 receptors to identify the protein domains in each receptor which are required for its synaptogenic function. Further, we examine whether Plexin-B2 is required in the presynaptic neuron, the postsynaptic neuron, or both to regulate GABAergic synapse formation. Our data reveal that Plexin-B1 and Plexin-B2 function non-redundantly to regulate GABAergic synapse formation and suggest that the transmembrane domain may underlie functional distinctions. We also provide evidence that Plexin-B2 expression in presynaptic GABAergic interneurons, as well as postsynaptic pyramidal cells, regulates GABAergic synapse formation in hippocampus. These findings lay the groundwork for future investigations into the precise signaling pathways required for synapse formation downstream of Plexin-B receptor signaling.

Plexin-B1 and Plexin-B2 play non-redundant roles in GABAergic synapse formation

Synapse formation in the mammalian brain is a complex and dynamic process requiring coordinated function of dozens of molecular families such as cell adhesion molecules (CAMs) and ligand-receptor pairs (Ephs/Ephrins, Neuroligins/Neurexins, Semaphorins/Plexins). Due to the large number of molecular players and possible functional redundancies within gene families, it is challenging to determine the precise synaptogenic roles of individual molecules, which is key to understanding the consequences of mutations in these genes for brain function. Furthermore, few molecules are known to exclusively regulate either GABAergic or glutamatergic synapses, and cell and molecular mechanisms underlying GABAergic synapse formation in particular are not thoroughly understood. However, we previously demonstrated that Semaphorin-4D (Sema4D) regulates GABAergic synapse development in the mammalian hippocampus while having no effect on glutamatergic synapse development, and this effect occurs through binding to its high affinity receptor, Plexin-B1. Furthermore, Plexin-B2 contributes to GABAergic synapse formation as well but is not required for GABAergic synapse formation induced by binding to Sema4D. Here, we perform a structure-function study of the Plexin-B1 and Plexin-B2 receptors to identify the protein domains in each receptor that are required for its synaptogenic function. We also provide evidence that Plexin-B2 expression in presynaptic parvalbumin-positive interneurons is required for formation of GABAergic synapses onto excitatory pyramidal neurons in CA1. Our data reveal that Plexin-B1 and Plexin-B2 function non-redundantly to regulate GABAergic synapse formation and suggest that the transmembrane domain may underlie these functional distinctions. These findings lay the groundwork for future investigations into the precise signaling pathways required for synapse formation downstream of Plexin-B receptor signaling.

Activity-dependent development of the body's touch receptors

We report a role for activity in the development of the primary sensory neurons that detect touch. Genetic deletion of Piezo2, the principal mechanosensitive ion channel in somatosensory neurons, caused profound changes in the formation of mechanosensory end organ structures and altered somatosensory neuron central targeting. Single cell RNA sequencing of Piezo2 conditional mutants revealed changes in gene expression in the sensory neurons activated by light mechanical forces, whereas other neuronal classes were less affected. To further test the role of activity in mechanosensory end organ development, we genetically deleted the voltage-gated sodium channel Nav1.6 (Scn8a) in somatosensory neurons throughout development and found that Scn8a mutants also have disrupted somatosensory neuron morphologies and altered electrophysiological responses to mechanical stimuli. Together, these findings indicate that mechanically evoked neuronal activity acts early in life to shape the maturation of the mechanosensory end organs that underlie our sense of gentle touch.

Semaphorin 4D induced inhibitory synaptogenesis decreases epileptiform activity and alters progression to Status Epilepticus in mice

Previously we demonstrated that intra-hippocampal infusion of purified, Semaphorin 4D (Sema4D) extracellular domain (ECD) into the mouse hippocampus rapidly promotes formation of GABAergic synapses and decreases seizure susceptibility in mice. Given the relatively fast action of Sema4D treatment revealed by these studies, we sought to determine the time course of Sema4D treatment on hippocampal network activity using an acute hippocampal slice preparation. We performed long-term extracellular recordings from area CA1 encompassing a 2-hour application of Sema4D and found that hippocampal excitation is suppressed for hours following treatment. We also asked if Sema4D treatment could ameliorate seizures in an acute seizure model: the kainic acid (KA) mouse model. We demonstrate that Sema4D treatment delays and suppresses ictal activity, delays the transition to Status Epilepticus (SE), and lessens the severity of SE. Lastly, we sought to explore alternative methods of Sema4D delivery to hippocampus and thus created an Adeno Associated Virus expressing the ECD of Sema4D. Our data reveal that virally delivered, chronically overexpressed Sema4D-ECD promotes GABAergic synapse formation and suppresses ictal activity and progression to SE. These results provide proof of concept that viral delivery of Sema4D is an efficacious and promising delivery method to abate epileptiform activity and progression to SE.

Assessing the impact of the global subsea telecommunications network on sedimentary organic carbon stocks

The sequestration of organic carbon in seafloor sediments plays a key role in regulating global climate; however, human activities can disturb previously-sequestered carbon stocks, potentially reducing the capacity of the ocean to store CO₂. Recent studies revealed profound seafloor impacts and sedimentary carbon loss due to fishing and shipping, yet most other human activities in the ocean have been overlooked. Here, we present an assessment of organic carbon disturbance related to the globally-extensive subsea telecommunications cable network. Up to 2.82-11.26 Mt of organic carbon worldwide has been disturbed as a result of cable burial, in water depths of up to 2000 m. While orders of magnitude lower than that disturbed by bottom fishing, it is a non-trivial amount that is absent from global budgets. Future offshore developments that disturb the seafloor should consider the safeguarding of carbon stocks, across the full spectrum of Blue Economy industries.

LADiBUG - A Communication Tool for Diagnostic Imaging

INTRODUCTION/BACKGROUND

As healthcare evolves, so should the way healthcare professionals deliver care to focus on the needs of patients and family members. One of the ways to provide patient and family centered care (PFCC) is through effective communication between the healthcare professional, patient, and family member.

METHOD

We have developed a new communication tool called LADiBUG that addresses many of the communication gaps identified by patient feedback from Diagnostic Imaging (DI). A pilot project was conducted at a rural site that involved establishing baseline patient feedback, providing education to staff about LADiBUG and the importance of PFCC, and follow-up with post-intervention patient feedback and staff feedback on the communication tool.

RESULTS/DISCUSSION

There were marked improvements in the areas such as patients being informed on how long the study would take (improved 61%), patients given direction about next steps and follow-up (improved 55%), and staff introducing themselves (improved 43%). Due to the success of the pilot project, LADiBUG has been approved for implementation within DI departments as an effective tool to provide PFCC. Reinforcement strategies such as staff meeting discussions and continued patient feedback surveys, will be important to ensure continued success of the communication tool. LADiBUG also has the potential to be used by any staff member and with any patient interaction.

CONCLUSION

The LADiBUG communication tool enables staff to provide more effective communication with patients, thereby improving the patient and family experience in DI. With continued staff education and department participation, LADiBUG will address communication gaps identified by patients and family members and further embed PFCC in DI.

TDP-43 dysfunction restricts dendritic complexity by inhibiting CREB activation and altering gene expression

Amyotrophic lateral sclerosis (ALS) and frontotemporal dementia (FTD) are two related neurodegenerative diseases that present with similar TDP-43 pathology in patient tissue. TDP-43 is an RNA-binding protein which forms aggregates in neurons of ALS and FTD patients as well as in a subset of patients diagnosed with other neurodegenerative diseases. Despite our understanding that TDP-43 is essential for many aspects of RNA metabolism, it remains obscure how TDP-43 dysfunction contributes to neurodegeneration. Interestingly, altered neuronal dendritic morphology is a common theme among several neurological disorders and is thought to precede neurodegeneration. We previously found that both TDP-43 overexpression (OE) and knockdown (KD) result in reduced dendritic branching of cortical neurons. In this study, we used TRIBE (targets of RNA-binding proteins identified by editing) as an approach to identify signaling pathways that regulate dendritic branching downstream of TDP-43. We found that TDP-43 RNA targets are enriched for pathways that signal to the CREB transcription factor. We further found that TDP-43 dysfunction inhibits CREB activation and CREB transcriptional output, and restoring CREB signaling rescues defects in dendritic branching. Finally, we demonstrate, using RNA sequencing, that TDP-43 OE and KD cause similar changes in the abundance of specific messenger RNAs, consistent with their ability to produce similar morphological defects. Our data therefore provide a mechanism by which TDP-43 dysfunction interferes with dendritic branching, and may define pathways for therapeutic intervention in neurodegenerative diseases.

The Metastasis Suppressor Protein Nme1 Is a Concentration-Dependent Modulator of Ca2+/Calmodulin-Dependent Protein Kinase II

Nucleoside diphosphate kinases (Nmes or NDPKs) have been implicated in a multitude of cellular processes, including an important role in metastasis suppression, and several enzymatic activities have been assigned to the Nme family. Nevertheless, for many of these processes, it has not been possible to establish a strong connection between Nme enzymatic activity and the relevant biological function. We hypothesized that, in addition to its known enzymatic functions, members of the Nme family might also regulate signaling cascades by acting on key signal transducers. Accordingly, here we show that Nme1 directly interacts with the calcium/calmodulin-dependent kinase II (CaMKII). Using purified proteins, we monitored the phosphorylation of a number of CaMKII substrates and determined that at nanomolar levels Nme1 enhances the phosphorylation of T-type substrates; this modulation shifts to inhibition at low micromolar concentrations. Specifically, the autophosphorylation of CaMKII at Thr286 is completely inhibited by 2 μM Nme1, a feature that distinguishes Nme1 from other known endogenous CaMKII inhibitors. Importantly, CaMKII inhibition does not require phosphotransfer activity by Nme1 because the kinase-dead Nme1 H118F mutant is as effective as the wild-type form of the enzyme. Our results provide a novel molecular mechanism whereby Nme1 could modulate diverse cellular processes in a manner that is independent of its known enzymatic activities.

Stable memory and computation in randomly rewiring neural networks

Our brains must maintain a representation of the world over a period of time much longer than the typical lifetime of the biological components producing that representation. For example, recent research suggests that dendritic spines in the adult mouse hippocampus are transient with an average lifetime of ~10 days. If this is true, and if turnover is equally likely for all spines, ~95% of excitatory synapses onto a particular neuron will turn over within 30 days; however, a neuron's receptive field can be relatively stable over this period. Here, we use computational modeling to ask how memories can persist in neural circuits such as the hippocampus and visual cortex in the face of synapse turnover. We demonstrate that Hebbian plasticity during replay of presynaptic activity patterns can integrate newly formed synapses into pre-existing memories. Furthermore, we find that Hebbian plasticity during replay is sufficient to stabilize the receptive fields of hippocampal place cells in a model of the grid-cell-to-place-cell transformation in CA1 and of orientation-selective cells in a model of the center-surround-to-simple-cell transformation in V1. Together, these data suggest that a simple plasticity rule, correlative Hebbian plasticity of synaptic strengths, is sufficient to preserve neural representations in the face of synapse turnover, even in the absence of activity-dependent structural plasticity. NEW & NOTEWORTHY Recent research suggests that synapses turn over rapidly in some brain structures; however, memories seem to persist for much longer. We show that Hebbian plasticity of synaptic strengths during reactivation events can preserve memory in computational models of hippocampal and cortical networks despite turnover of all synapses. Our results suggest that memory can be stored in the correlation structure of a network undergoing rapid synaptic remodeling.

Class 4 Semaphorins and Plexin-B receptors regulate GABAergic and glutamatergic synapse development in the mammalian hippocampus

To understand how proper circuit formation and function is established in the mammalian brain, it is necessary to define the genes and signaling pathways that instruct excitatory and inhibitory synapse development. We previously demonstrated that the ligand-receptor pair, Sema4D and Plexin-B1, regulates inhibitory synapse development on an unprecedentedly fast time-scale while having no effect on excitatory synapse development. Here, we report previously undescribed synaptogenic roles for Sema4A and Plexin-B2 and provide new insight into Sema4D and Plexin-B1 regulation of synapse development in rodent hippocampus. First, we show that Sema4a, Sema4d, Plxnb1, and Plxnb2 have distinct and overlapping expression patterns in neurons and glia in the developing hippocampus. Second, we describe a requirement for Plexin-B1 in both the presynaptic axon of inhibitory interneurons as well as the postsynaptic dendrites of excitatory neurons for Sema4D-dependent inhibitory synapse development. Third, we define a new synaptogenic activity for Sema4A in mediating inhibitory and excitatory synapse development. Specifically, we demonstrate that Sema4A signals through the same pathway as Sema4D, via the postsynaptic Plexin-B1 receptor, to promote inhibitory synapse development. However, Sema4A also signals through the Plexin-B2 receptor to promote excitatory synapse development. Our results shed new light on the molecular cues that promote the development of either inhibitory or excitatory synapses in the mammalian hippocampus.

The Ras-like GTPase Rem2 is a potent inhibitor of calcium/calmodulin-dependent kinase II activity

Ca²⁺/calmodulin-dependent protein kinase II (CaMKII) is a well-characterized, abundant protein kinase that regulates a diverse set of functions in a tissue-specific manner. For example, in heart muscle, CaMKII regulates Ca²⁺ homeostasis, whereas in neurons, CaMKII regulates activity-dependent dendritic remodeling and long-term potentiation (LTP), a neurobiological correlate of learning and memory. Previously, we identified the GTPase Rem2 as a critical regulator of dendrite branching and homeostatic plasticity in the vertebrate nervous system. Here, we report that Rem2 directly interacts with CaMKII and potently inhibits the activity of the intact holoenzyme, a previously unknown Rem2 function. Our results suggest that Rem2 inhibition involves interaction with both the CaMKII hub domain and substrate recognition domain. Moreover, we found that Rem2-mediated inhibition of CaMKII regulates dendritic branching in cultured hippocampal neurons. Lastly, we report that substitution of two key amino acid residues in the Rem2 N terminus (Arg-79 and Arg-80) completely abolishes its ability to inhibit CaMKII. We propose that our biochemical findings will enable further studies unraveling the functional significance of Rem2 inhibition of CaMKII in cells.

Rem2 stabilizes intrinsic excitability and spontaneous firing in visual circuits

Sensory experience plays an important role in shaping neural circuitry by affecting the synaptic connectivity and intrinsic properties of individual neurons. Identifying the molecular players responsible for converting external stimuli into altered neuronal output remains a crucial step in understanding experience-dependent plasticity and circuit function. Here, we investigate the role of the activity-regulated, non-canonical Ras-like GTPase Rem2 in visual circuit plasticity. We demonstrate that Rem2-/- mice fail to exhibit normal ocular dominance plasticity during the critical period. At the cellular level, our data establish a cell-autonomous role for Rem2 in regulating intrinsic excitability of layer 2/3 pyramidal neurons, prior to changes in synaptic function. Consistent with these findings, both in vitro and in vivo recordings reveal increased spontaneous firing rates in the absence of Rem2. Taken together, our data demonstrate that Rem2 is a key molecule that regulates neuronal excitability and circuit function in the context of changing sensory experience.

Semaphorin 4D promotes inhibitory synapse formation and suppresses seizures in vivo

OBJECTIVE

We previously discovered a role for the extracellular domain of the transmembrane protein semaphorin 4D (Sema4D) as a fast-acting, selective, and positive regulator of functional γ-aminobutyric acid (GABA)ergic synapse formation in hippocampal neuronal culture. We also demonstrated that Sema4D treatment increases inhibitory tone and suppresses hyperexcitability in an organotypic hippocampal slice culture model of epilepsy. Here, we investigate the ability of Sema4D to promote GABAergic synapse formation and suppress seizure activity in vivo in adult mice.

METHODS

We performed a 3-hour, intrahippocampal infusion of Sema4D or control protein into the CA1 region of adult mice. To quantify GABAergic presynaptic bouton density, we performed immunohistochemistry on hippocampal tissue sections isolated from these animals using an antibody that specifically recognizes the glutamic acid decarboxylase isoform 65 protein (GAD65), which is localized to presynaptic GABAergic boutons. To assess seizure activity, we employed 2 in vivo mouse models of epilepsy, intravenous (iv) pentylenetetrazol (PTZ) and hippocampal electrical kindling, in the presence or absence of Sema4D treatment. We monitored seizure activity by behavioral observation or electroencephalography (EEG). To assay the persistence of the Sema4D effect, we monitored seizure activity and measured the density of GAD65-positive presynaptic boutons 3 or 48 hours after Sema4D infusion.

RESULTS

Sema4D-treated mice displayed an elevated density of GABAergic presynaptic boutons juxtaposed to hippocampal pyramidal neuron cell bodies, consistent with the hypothesis that Sema4D promotes the formation of new inhibitory synapses in vivo. In addition, Sema4D acutely suppressed seizures in both the PTZ and electrical kindling models. When we introduced a 48-hour gap between Sema4D treatment and the seizure stimulus, seizure activity was indistinguishable from controls. Moreover, immunohistochemistry on brain sections or hippocampal slices isolated 3 hours, but not 48 hours, after Sema4D treatment displayed an increase in GABAergic bouton density, demonstrating temporal correlation between the effects of Sema4D on seizures and GABAergic synaptic components.

SIGNIFICANCE

Our findings suggest a novel approach to treating acute seizures: harnessing synaptogenic molecules to enhance connectivity in the inhibitory network.

TDP-43 misexpression causes defects in dendritic growth

Amyotrophic Lateral Sclerosis (ALS) and Frontotemporal Dementia (FTD) share overlapping genetic causes and disease symptoms, and are linked neuropathologically by the RNA binding protein TDP-43 (TAR DNA binding protein-43 kDa). TDP-43 regulates RNA metabolism, trafficking, and localization of thousands of target genes. However, the cellular and molecular mechanisms by which dysfunction of TDP-43 contributes to disease pathogenesis and progression remain unclear. Severe changes in the structure of neuronal dendritic arbors disrupt proper circuit connectivity, which in turn could contribute to neurodegenerative disease. Although aberrant dendritic morphology has been reported in non-TDP-43 mouse models of ALS and in human ALS patients, this phenotype is largely unexplored with regards to TDP-43. Here we have employed a primary rodent neuronal culture model to study the cellular effects of TDP-43 dysfunction in hippocampal and cortical neurons. We show that manipulation of TDP-43 expression levels causes significant defects in dendritic branching and outgrowth, without an immediate effect on cell viability. The effect on dendritic morphology is dependent on the RNA-binding ability of TDP-43. Thus, this model system will be useful in identifying pathways downstream of TDP-43 that mediate dendritic arborization, which may provide potential new avenues for therapeutic intervention in ALS/FTD.

Rem2 signaling affects neuronal structure and function in part by regulation of gene expression

The central nervous system has the remarkable ability to convert changes in the environment in the form of sensory experience into long-term alterations in synaptic connections and dendritic arborization, in part through changes in gene expression. Surprisingly, the molecular mechanisms that translate neuronal activity into changes in neuronal connectivity and morphology remain elusive. Rem2, a member of the Rad/Rem/Rem2/Gem/Kir (RGK) subfamily of small Ras-like GTPases, is a positive regulator of synapse formation and negative regulator of dendritic arborization. Here we identify that one output of Rem2 signaling is the regulation of gene expression. Specifically, we demonstrate that Rem2 signaling modulates the expression of genes required for a variety of cellular processes from neurite extension to synapse formation and synaptic function. Our results highlight Rem2 as a unique molecule that transduces changes in neuronal activity detected at the cell membrane to morphologically relevant changes in gene expression in the nucleus.

Preconception care among low-risk mothers in a French perinatal network: Frequency of utilization and factors associated

OBJECTIVE

Determine the frequency of preconception care use in France and factors impacting preconception visit.

MATERIALS AND METHODS

An epidemiological study was conducted from September 2015 to October 2015 in 5 maternity hospitals within the "Alpes-Isère" perinatal network, comprising of French-speaking women, with uncomplicated pregnancies, who delivered a healthy term baby (≥37 weeks of gestational age). Two groups were compared: patients with and without preconception care. Descriptive, univariate and multivariate analyses were performed for the sociodemographic, the environmental characteristics and the gynecologic obstetric history.

RESULTS

Among the 392 patients included in this study, only 62 (15.8% [12.0-20.0]) had used preconception care before their pregnancy. Multivariate analysis showed that the primiparous women (adjusted OR 2.47 [1.37-4.46]) and the women with a high socio-professional category (adjusted OR 2.32 [1.13-4.77]) were more likely to used preconception care.

CONCLUSION

Despite the positive effects on mother and baby's health, preconception care is insufficiently used in France. Every effort must be made to improve awareness of preconception care among health workers and patients.

[Skeletal muscle ischemia-reperfusion and ischemic conditioning pathophysiology-clinical applications for the vascular surgeon]

Ischemia-reperfusion, which is characterized by deficient oxygen supply and subsequent restoration of blood flow, can cause irreversible damage to tissue. The vascular surgeon is daily faced with ischemia-reperfusion situations. Indeed, arterial clamping induces ischemia, followed by reperfusion when declamping. Mechanisms underlying ischemia-reperfusion injury are complex and multifactorial. Increases in cellular calcium and reactive oxygen species, initiated during ischemia and then amplified upon reperfusion are thought to be the main mediators of reperfusion injury. Mitochondrial dysfunction also plays an important role. Extensive research has focused on increasing skeletal muscle tolerance to ischemia-reperfusion injury, especially through the use of ischemic conditioning strategies. The purpose of this review is to focus on the cellular responses associated with ischemia-reperfusion, as well as to discuss the effects of ischemic conditioning strategies. This would help the vascular surgeon in daily practice, in order to try to improve surgical outcome in the setting of ischemia-reperfusion.

Upregulation of μ3A Drives Homeostatic Plasticity by Rerouting AMPAR into the Recycling Endosomal Pathway

Synaptic scaling is a form of homeostatic plasticity driven by transcription-dependent changes in AMPA-type glutamate receptor (AMPAR) trafficking. To uncover the pathways involved, we performed a cell-type-specific screen for transcripts persistently altered during scaling, which identified the μ subunit (μ3A) of the adaptor protein complex AP-3A. Synaptic scaling increased μ3A (but not other AP-3 subunits) in pyramidal neurons and redistributed dendritic μ3A and AMPAR to recycling endosomes (REs). Knockdown of μ3A prevented synaptic scaling and this redistribution, while overexpression (OE) of full-length μ3A or a truncated μ3A that cannot interact with the AP-3A complex was sufficient to drive AMPAR to REs. Finally, OE of μ3A acted synergistically with GRIP1 to recruit AMPAR to the dendritic membrane. These data suggest that excess μ3A acts independently of the AP-3A complex to reroute AMPAR to RE, generating a reservoir of receptors essential for the regulated recruitment to the synaptic membrane during scaling up.

Electrically controllable extraordinary optical transmission in gold gratings on vanadium dioxide

Highly tunable optical transmission through one-dimensional gold gratings patterned on top of a film of the phase transition material, vanadium dioxide (VO2), is demonstrated. Dense electrical integration is enabled by grating features that also function as electrical contacts to the VO2. Extraordinary optical transmission is observed in the VO2 insulator phase, and the optical transmission is extinguished by up to about 6 dB in a 170 nm thick VO2 film. Measurements of gratings with varying duty cycles demonstrate the dependence of the optical transmission and tuning on the device geometry.

Wavelength-size hybrid Si-VO(2) waveguide electroabsorption optical switches and photodetectors

Ultra-compact waveguide electroabsorption optical switches and photodetectors with micron- and sub-micron lengths and compatible with silicon (Si) waveguides are demonstrated using the insulator-metal phase transition of vanadium dioxide (VO(2)). A 1 μm long hybrid Si-VO(2) device is shown to achieve a high extinction ratio of 12 dB and a competitive insertion loss of 5 dB over a broad bandwidth of 100 nm near λ = 1550 nm. The device, operated as a photodetector, can measure optical powers less than 1 μW with a responsivity in excess of 10 A/W. With volumes that are about 100 to 1000 times smaller than today's active Si photonic components, the hybrid Si-VO(2) devices show the feasibility of integrating transition metal oxides on Si photonic platforms for nanoscale electro-optic elements.

Molecular mechanisms of activity-dependent changes in dendritic morphology: role of RGK proteins

The nervous system has the amazing capacity to transform sensory experience from the environment into changes in neuronal activity that, in turn, cause long-lasting alterations in neuronal morphology. Recent findings indicate that, surprisingly, sensory experience concurrently activates molecular signaling pathways that both promote and inhibit dendritic complexity. Historically, a number of positive regulators of activity-dependent dendritic complexity have been described, whereas the list of identified negative regulators of this process is much shorter. In recent years, there has been an emerging appreciation of the importance of the Rad/Rem/Rem2/Gem/Kir (RGK) GTPases as mediators of activity-dependent structural plasticity. In the following review, we discuss the traditional view of RGK proteins, as well as our evolving understanding of the role of these proteins in instructing structural plasticity.

Enhanced potency of the metalloprotease inhibitor TAPI-2 by multivalent display

Metalloproteases regulate a vast array of critical cellular processes such as proliferation, migration, repair, and invasion/metastasis. In so doing, metalloproteases have been shown to play key roles in the pathogenesis of multiple disorders including arteriosclerosis, arthritis, cancer metastasis, and ischemic brain injury. Therefore, much work has focused on developing metalloprotease inhibitors to provide a potential therapeutic benefit against the progression of these and other diseases. In order to produce a more potent inhibitor of metalloproteases, we synthesized multivalent displays of a metalloprotease inhibitor derived from the ring-opening metathesis polymerization (ROMP). Specifically, multivalent ligands of a broad-spectrum metalloprotease inhibitor, TAPI-2, were generated upon conjugation of the amine-bearing inhibitor with the ROMP-derived N-hydroxysuccinimide ester polymer. By monitoring the metalloprotease dependent cleavage of the transmembrane protein Semaphorin4D (Sema4D), we demonstrated an enhancement of inhibition by multivalent TAPI-2 compared to monovalent TAPI-2. To further optimize the potency of the multivalent inhibitor, we systematically varied the polymer length and inhibitor ligand density (mole fraction, χ). We observed that while ligand density plays a modest role in the potency of inhibition caused by the multivalent TAPI-2 display, the length of the polymer produces a much greater effect on inhibitor potency, with the shortest polymer achieving the greatest level of inhibition. These findings validate the use of multivalent display to enhance the potency of metalloprotease inhibitors and further, suggest this may be a useful approach to enhance potency of other small molecule towards their targets.

One-step overall water splitting under visible light using multiband InGaN/GaN nanowire heterostructures

The conversion of solar energy into hydrogen via water splitting process is one of the key sustainable technologies for future clean, storable, and renewable source of energy. Therefore, development of visible light-responsive and efficient photocatalyst material has been of immense interest, but with limited success. Here, we show that overall water splitting under visible-light irradiation can be achieved using a single photocatalyst material. Multiband InGaN/GaN nanowire heterostructures, decorated with rhodium (Rh)/chromium-oxide (Cr2O3) core-shell nanoparticles can lead to stable hydrogen production from pure (pH ∼ 7.0) water splitting under ultraviolet, blue and green-light irradiation (up to ∼560 nm), the longest wavelength ever reported. At ∼440-450 nm wavelengths, the internal quantum efficiency is estimated to be ∼13%, the highest value reported in the visible spectrum. The turnover number under visible light well exceeds 73 in 12 h. Detailed analysis further confirms the stable photocatalytic activity of the nanowire heterostructures. This work establishes the use of metal-nitrides as viable photocatalyst for solar-powered artificial photosynthesis for the production of hydrogen and other solar fuels.

Organic small hairpin RNAs (OshR): a do-it-yourself platform for transgene-based gene silencing

The RNA interference (RNAi) pathway in animal cells can be harnessed to silence gene expression with artificial small interfering RNAs (siRNAs) or transgenes that express small hairpin RNAs (shRNAs). The transgene-expressing shRNA approach has been adapted into large-scale resources for genome-wide loss-of-function screens, whereas focused studies on a narrow set of genes can be achieved by using individual shRNA constructs from these resources. Although current shRNA repositories generally work, they might fail in certain situations and therefore necessitate other alternatives. We detail here a new highly-accessible and rational design of custom shRNAs that utilizes a refined backbone configuration termed the 'organic' shRNA (OshR) platform. The OshR platform is 'organic' because it conforms more naturally to the endogenous vertebrate miRNAs by maintaining specific bulges and incorporating strategic mismatches to insure the desired guide strand is produced while reducing the accumulation of passenger strands that might contribute to off-target effects. We also demonstrate that the reliability of the OshR platform for gene silencing is increased when sequences target the 3' UnTranslated Region (3'UTR) of a gene. We further compare the OshR platform with the current and emerging shRNA designs, and propose that the OshR platform is a novel approach that can allow investigators to generate custom and effective shRNAs for individual gene functional studies.

Sema4D localizes to synapses and regulates GABAergic synapse development as a membrane-bound molecule in the mammalian hippocampus

While numerous recent advances have contributed to our understanding of excitatory synapse formation, the processes that mediate inhibitory synapse formation remain poorly defined. Previously, we discovered that RNAi-mediated knockdown of a Class 4 Semaphorin, Sema4D, led to a decrease in the density of inhibitory synapses without an apparent effect on excitatory synapse formation. Our current work has led us to new insights about the molecular mechanisms by which Sema4D regulates GABAergic synapse development. Specifically, we report that the extracellular domain of Sema4D is proteolytically cleaved from the surface of neurons. However, despite this cleavage event, Sema4D signals through its extracellular domain as a membrane-bound, synaptically localized protein required in the postsynaptic membrane for proper GABAergic synapse formation. Thus, as Sema4D is one of only a few molecules identified thus far that preferentially regulates GABAergic synapse formation, these findings have important implications for our mechanistic understanding of this process.

A loss-of-function analysis reveals that endogenous Rem2 promotes functional glutamatergic synapse formation and restricts dendritic complexity

Rem2 is a member of the RGK family of small Ras-like GTPases whose expression and function is regulated by neuronal activity in the brain. A number of questions still remain as to the endogenous functions of Rem2 in neurons. RNAi-mediated Rem2 knockdown leads to an increase in dendritic complexity and a decrease in functional excitatory synapses, though a recent report challenged the specificity of Rem2-targeted RNAi reagents. In addition, overexpression in a number of cell types has shown that Rem2 can inhibit voltage-gated calcium channel (VGCC) function, while studies employing RNAi-mediated knockdown of Rem2 have failed to observe a corresponding enhancement of VGCC function. To further investigate these discrepancies and determine the endogenous function of Rem2, we took a comprehensive, loss-of-function approach utilizing two independent, validated Rem2-targeted shRNAs to analyze Rem2 function. We sought to investigate the consequence of endogenous Rem2 knockdown by focusing on the three reported functions of Rem2 in neurons: regulation of synapse formation, dendritic morphology, and voltage-gated calcium channels. We conclude that endogenous Rem2 is a positive regulator of functional, excitatory synapse development and a negative regulator of dendritic complexity. In addition, while we are unable to reach a definitive conclusion as to whether the regulation of VGCCs is an endogenous function of Rem2, our study reports important data regarding RNAi reagents for use in future investigation of this issue.

The GTPase Rem2 regulates synapse development and dendritic morphology

Rem2 is a member of the Rad/Rem/Rem2/Gem/Kir subfamily of small Ras-like GTPases that was identified as an important mediator of synapse development. We performed a comprehensive, loss- of-function analysis of Rem2 function in cultured hippocampal neurons using RNAi to substantially decrease Rem2 protein levels. We found that knockdown of Rem2 decreases the density and maturity of dendritic spines, the primary site of excitatory synapses onto pyramidal neurons in the hippocampus. Knockdown of Rem2 also alters the gross morphology of dendritic arborizations, increasing the number of dendritic branches without altering total neurite length. Thus, Rem2 functions to inhibit dendritic branching and promote the development of dendritic spines and excitatory synapses. Interestingly, binding to the calcium-binding protein calmodulin is required for the Rem2 regulation of dendritic branching. However, this interaction is completely dispensable for synapse development. Overall, our results suggest that Rem2 regulates dendritic branching and synapse development via distinct and overlapping signal transduction pathways.

Emerging themes in GABAergic synapse development

Glutamatergic synapse development has been rigorously investigated for the past two decades at both the molecular and cell biological level yet a comparable intensity of investigation into the cellular and molecular mechanisms of GABAergic synapse development has been lacking until relatively recently. This review will provide a detailed overview of the current understanding of GABAergic synapse development with a particular emphasis on assembly of synaptic components, molecular mechanisms of synaptic development, and a subset of human disorders which manifest when GABAergic synapse development is disrupted. An unexpected and emerging theme from these studies is that glutamatergic and GABAergic synapse development share a number of overlapping molecular and cell biological mechanisms that will be emphasized in this review.

Wafer-level photocatalytic water splitting on GaN nanowire arrays grown by molecular beam epitaxy

We report on the achievement of wafer-level photocatalytic overall water splitting on GaN nanowires grown by molecular beam epitaxy with the incorporation of Rh/Cr(2)O(3) core-shell nanostructures acting as cocatalysts, through which H(2) evolution is promoted by the noble metal core (Rh) while the water forming back reaction over Rh is effectively prevented by the Cr(2)O(3) shell O(2) diffusion barrier. The decomposition of pure water into H(2) and O(2) by GaN nanowires is confirmed to be a highly stable photocatalytic process, with the turnover number per unit time well exceeding the value of any previously reported GaN powder samples.

Influence of Ni Catalyst Layer and TiN Diffusion Barrier on Carbon Nanotube Growth Rate

Dense, vertically aligned multiwall carbon nanotubes were synthesized on TiN electrode layers for infrared sensing applications. Microwave plasma-enhanced chemical vapor deposition and Ni catalyst were used for the nanotubes synthesis. The resultant nanotubes were characterized by SEM, AFM, and TEM. Since the length of the nanotubes influences sensor characteristics, we study in details the effects of changing Ni and TiN thickness on the physical properties of the nanotubes. In this paper, we report the observation of a threshold Ni thickness of about 4 nm, when the average CNT growth rate switches from an increasing to a decreasing function of increasing Ni thickness, for a process temperature of 700 degrees C. This behavior is likely related to a transition in the growth mode from a predominantly "base growth" to that of a "tip growth." For Ni layer greater than 9 nm the growth rate, as well as the CNT diameter, variations become insignificant. We have also observed that a TiN barrier layer appears to favor the growth of thinner CNTs compared to a SiO(2) layer.

An RNAi-based approach identifies molecules required for glutamatergic and GABAergic synapse development

We report the results of a genetic screen to identify molecules important for synapse formation and/or maintenance. siRNAs were used to decrease the expression of candidate genes in neurons, and synapse development was assessed. We surveyed 22 cadherin family members and demonstrated distinct roles for cadherin-11 and cadherin-13 in synapse development. Our screen also revealed roles for the class 4 Semaphorins Sema4B and Sema4D in the development of glutamatergic and/or GABAergic synapses. We found that Sema4D affects the formation of GABAergic, but not glutamatergic, synapses. Our screen also identified the activity-regulated small GTPase Rem2 as a regulator of synapse development. A known calcium channel modulator, Rem2 may function as part of a homeostatic mechanism that controls synapse number. These experiments establish the feasibility of RNAi screens to characterize the mechanisms that control mammalian neuronal development and to identify components of the genetic program that regulate synapse formation and/or maintenance.

Activity-dependent regulation of MEF2 transcription factors suppresses excitatory synapse number

In the mammalian nervous system, neuronal activity regulates the strength and number of synapses formed. The genetic program that coordinates this process is poorly understood. We show that myocyte enhancer factor 2 (MEF2) transcription factors suppressed excitatory synapse number in a neuronal activity- and calcineurin-dependent manner as hippocampal neurons formed synapses. In response to increased neuronal activity, calcium influx into neurons induced the activation of the calcium/calmodulin-regulated phosphatase calcineurin, which dephosphorylated and activated MEF2. When activated, MEF2 promoted the transcription of a set of genes, including arc and synGAP, that restrict synapse number. These findings define an activity-dependent transcriptional program that may control synapse number during development.

Calcium deficiency cannot induce obesity in rats

If intake of a required nutrient--here calcium--affects body weight, the effect must be mediated by a change in the body weight set-point. Thus, the controversial 'anti-obesity' influence of high calcium intake should decrease the body weight set-point. Diets differing in calcium content were assigned to three groups of rats. The effects of the diets on body weight, BMI, fat content, plasma calcium, body weight set-point, food intake, and preference for various calcium solutions were measured after 6 weeks of calcium deprivation or supplementation, and again after a further 6 weeks of recovery on a regular diet. After 6 weeks, the low-calcium diet had induced calcium deficiency but had failed to raise the body weight set-point. Nor had it produced obesity or fat accumulation. After 6 weeks of recovery, body weight and fat content were no higher in calcium-deprived rats than in the control or supplemented rats. In this experiment, low-calcium intake failed to cause obesity and did not raise the body weight set-point. The results indicate that calcium intake probably does not affect body weight.

The Rac1-GEF Tiam1 couples the NMDA receptor to the activity-dependent development of dendritic arbors and spines

NMDA-type glutamate receptors play a critical role in the activity-dependent development and structural remodeling of dendritic arbors and spines. However, the molecular mechanisms that link NMDA receptor activation to changes in dendritic morphology remain unclear. We report that the Rac1-GEF Tiam1 is present in dendrites and spines and is required for their development. Tiam1 interacts with the NMDA receptor and is phosphorylated in a calcium-dependent manner in response to NMDA receptor stimulation. Blockade of Tiam1 function with RNAi and dominant interfering mutants of Tiam1 suggests that Tiam1 mediates effects of the NMDA receptor on dendritic development by inducing Rac1-dependent actin remodeling and protein synthesis. Taken together, these findings define a molecular mechanism by which NMDA receptor signaling controls the growth and morphology of dendritic arbors and spines.

Development of a PCR assay for identification of staphylococci at genus and species levels

We have developed a PCR-based assay which allows the detection of staphylococci at the genus level by targeting the tuf gene, which encodes the elongation factor Tu. Degenerate PCR primers derived from consensus regions of several tuf genes were used to amplify a target region of 884 bp from 11 representative staphylococcal species. Subsequently, the entire nucleotide sequence of these amplicons was determined. The analysis of a multiple alignment of these sequences revealed regions conserved among staphylococci but distinct from those of other gram-positive bacteria genetically related to staphylococci. PCR primers complementary to these regions could amplify specifically and efficiently a DNA fragment of 370 bp for all of 27 different staphylococcal species tested. There was no amplification with genomic DNA prepared from 53 nonstaphylococcal species tested to verify the specificity of the assay (20 gram positive and 33 gram negative). Furthermore, this assay amplified efficiently all 27 American Type Culture Collection (ATCC) staphylococcal reference strains as well as 307 clinical isolates of staphylococci from the Québec City region. Analysis of the multiple sequence alignment for the 884-bp fragment for the 11 staphylococcal species as well as comparison of the sequences for the 370-bp amplicon from five unrelated ATCC and clinical strains for each of the species S. aureus, S. epidermidis, S. haemolyticus, S. hominis, and S. saprophyticus demonstrated sufficient interspecies polymorphism to generate genus- and species-specific capture probes. This sequence information allowed the development of Staphylococcus-specific and species-specific (targeting S. aureus, S. epidermidis, S. haemolyticus, S. hominis, or S. saprophyticus) capture probes hybridizing to the 370-bp amplicon. In conclusion, this PCR assay is suitable for detection of staphylococci at both genus and species levels.

Homeostatic control of presynaptic release is triggered by postsynaptic membrane depolarization

Homeostatic mechanisms regulate synaptic function to maintain nerve and muscle excitation within reasonable physiological limits. The mechanisms that initiate homeostasic changes to synaptic function are not known. We specifically impaired cellular depolarization by expressing the Kir2.1 potassium channel in Drosophila muscle. In Kir2.1-expressing muscle there is a persistent outward potassium current ( approximately 10 nA), decreased muscle input resistance (50-fold), and a hyperpolarized resting potential. Despite impaired muscle excitability, synaptic depolarization of muscle achieves wild-type levels. A quantal analysis demonstrates that increased presynaptic release (quantal content), without a change in quantal size (mEPSC amplitude), compensates for altered muscle excitation. Because morphological synaptic growth is normal, we conclude that a homeostatic increase in presynaptic release compensates for impaired muscle excitability. These data demonstrate that a monitor of muscle membrane depolarization is sufficient to initiate synaptic homeostatic compensation.

A PDK1 homolog is necessary and sufficient to transduce AGE-1 PI3 kinase signals that regulate diapause in Caenorhabditis elegans

An insulin receptor-like signaling pathway regulates Caenorhabditis elegans metabolism, development, and longevity. Inactivation of the insulin receptor homolog DAF-2, the AGE-1 PI3K, or the AKT-1 and AKT-2 kinases causes a developmental arrest at the dauer stage. A null mutation in the daf-16 Fork head transcription factor alleviates the requirement for signaling through this pathway. We show here that a loss-of-function mutation in pdk-1, the C. elegans homolog of the mammalian Akt/PKB kinase PDK1, results in constitutive arrest at the dauer stage and increased life span; these phenotypes are suppressed by a loss of function mutation in daf-16. An activating mutation in pdk-1 or overexpression of wild-type pdk-1 relieves the requirement for AGE-1 PI3K signaling. Therefore, pdk-1 activity is both necessary and sufficient to propagate AGE-1 PI3K signals in the DAF-2 insulin receptor-like signaling pathway. The activating mutation in pdk-1 requires akt-1 and akt-2 gene activity in order to suppress the dauer arrest phenotype of age-1. This indicates that the major function of C. elegans PDK1 is to transduce signals from AGE-1 to AKT-1 and AKT-2. The activating pdk-1 mutation is located in a conserved region of the kinase domain; the equivalent amino acid substitution in human PDK1 activates its kinase activity toward mammalian Akt/PKB.

Northern exposure: further analysis of the results of the Canadian aboriginal methylmercury program

An initial overall analysis of the Canadian First Nations and Inuit data on methylmercury (MeHg) levels in 38,571 Canadian Aboriginal people has been completed. Patterns of exposure and their relationship to socio-cultural issues and traditional lifestyles are now being further analyzed, especially in the light of the continuing concern regarding the significance of exposure among northern and arctic populations. A mean of 29.8 micrograms/l mercury in blood or blood equivalent, with a range of 1-225.7 micrograms/l, was found among Inuit in the Northwest Territories (NWT). Significant differences in South-North exposure and West-East exposure in NWT are discussed, as are the relationships between exposure of northern residents and development activities further south, and problems of risk management in the context of traditional arctic lifestyles. It is suggested that many of the differences are due to the greater consumption of traditional food in the North. However, with the levels found and current state of knowledge, this should not be seen as a reason to change lifestyles--a change which carries its own negative consequences.

Caenorhabditis elegans Akt/PKB transduces insulin receptor-like signals from AGE-1 PI3 kinase to the DAF-16 transcription factor

A neurosecretory pathway regulates a reversible developmental arrest and metabolic shift at the Caenorhabditis elegans dauer larval stage. Defects in an insulin-like signaling pathway cause arrest at the dauer stage. We show here that two C. elegans Akt/PKB homologs, akt-1 and akt-2, transduce insulin receptor-like signals that inhibit dauer arrest and that AKT-1 and AKT-2 signaling are indispensable for insulin receptor-like signaling in C. elegans. A loss-of-function mutation in the Fork head transcription factor DAF-16 relieves the requirement for Akt/PKB signaling, which indicates that AKT-1 and AKT-2 function primarily to antagonize DAF-16. This is the first evidence that the major target of Akt/PKB signaling is a transcription factor. An activating mutation in akt-1, revealed by a genetic screen, as well as increased dosage of wild-type akt-1 relieves the requirement for signaling from AGE-1 PI3K, which acts downstream of the DAF-2 insulin/IGF-1 receptor homolog. This demonstrates that Akt/PKB activity is not necessarily dependent on AGE-1 PI3K activity. akt-1 and akt-2 are expressed in overlapping patterns in the nervous system and in tissues that are remodeled during dauer formation.

The Fork head transcription factor DAF-16 transduces insulin-like metabolic and longevity signals in C. elegans

In mammals, insulin signalling regulates glucose transport together with the expression and activity of various metabolic enzymes. In the nematode Caenorhabditis elegans, a related pathway regulates metabolism, development and longevity. Wild-type animals enter the developmentally arrested dauer stage in response to high levels of a secreted pheromone, accumulating large amounts of fat in their intestines and hypodermis. Mutants in DAF-2 (a homologue of the mammalian insulin receptor) and AGE-1 (a homologue of the catalytic subunit of mammalian phosphatidylinositol 3-OH kinase) arrest development at the dauer stage. Moreover, animals bearing weak or temperature-sensitive mutations in daf-2 and age-1 can develop reproductively, but nevertheless show increased energy storage and longevity. Here we show that null mutations in daf-16 suppress the effects of mutations in daf-2 or age-1; lack of daf-16 bypasses the need for this insulin receptor-like signalling pathway. The principal role of DAF-2/AGE-1 signalling is thus to antagonize DAF-16. daf-16 is widely expressed and encodes three members of the Fork head family of transcription factors. The DAF-2 pathway acts synergistically with the pathway activated by a nematode TGF-beta-type signal, DAF-7, suggesting that DAF-16 cooperates with nematode SMAD proteins in regulating the transcription of key metabolic and developmental control genes. The probable human orthologues of DAF-16, FKHR and AFX, may also act downstream of insulin signalling and cooperate with TGF-beta effectors in mediating metabolic regulation. These genes may be dysregulated in diabetes.

Isokinetic rehabilitation after arthroscopic meniscectomy

The aim of this study was to assess the effects in humans of early (2 weeks) and delayed (6 weeks) isokinetic strength training in the recovery of muscle strength following an arthroscopic partial meniscectomy. The peak torque developed in the quadriceps and hamstrings and the torque developed at a knee angle of 1.05 rad were evaluated in 16 subjects, pre-operatively (pre-op), and 2, 6, and 10 weeks post-operatively (post-op), on an isokinetic device at four different velocities (1.05, 2.09, 3.14, and 4.19 rad.s-1). The fatigue characteristics of the muscles were evaluated by having the subject perform 15 maximal contractions at 3.14 rad.s-1. Training was done on the same device (three times a week for 1-2 months), beginning either 2 or 6 weeks post-op. A repeated measures analysis of variance demonstrated a time effect but no differences between groups and no interactions. Torques developed by the knee flexors and extensors were significantly smaller 2 weeks post-op than pre-op, at all velocities tested. Torques developed in the quadriceps recovered to their pre-op values by 6 weeks, and further gained significantly in strength from 6 to 10 weeks. Quadriceps torques remained weaker than the contralateral side at 10 weeks. Hamstrings torques were either higher or similar to pre-op values by 6 weeks, and demonstrated increases from 6 to 10 weeks post-op at 1.05 and 4.19 rad.s-1 only. Total work and average power developed by the quadriceps and hamstrings during the fatigue protocol changed with time in a similar manner to torque.(ABSTRACT TRUNCATED AT 250 WORDS)