Deficits in memory and motor performance in synaptotagmin IV mutant mice

Conserved expression of the zebrafish syt4 gene in GABAergic neurons in the cerebellum of adult fishes revealed by mammalian SYT4 immunoreactive-like signals

Synaptotagmin 4 (syt4) belongs to the synaptotagmin protein family, which has 17 and 28 family members in human and zebrafish, respectively. In zebrafish and rodents, syt4 is known to express abundantly in the entire central nervous system in the early developmental stages. In adult rodents, the gene expression shifts to be predominant in the cerebellum, mostly in Purkinje cells, a type of GABAergic neurons. However, there is no report of the expression pattern of syt4 in the adult zebrafish brain. Therefore, we hypothesize that the expression of syt4 is conserved in adult zebrafish and is specific to the GABAergic neurons, likely Purkinje cells, in the cerebellum. To examine the hypothesis, we first show that only one copy of syt4 gene remains in the zebrafish genome, and it is orthologous to the gene in other vertebrates. We further observe mammalian SYT4 antibody immunoreactive-like (mSYT4-ir) signals in several structures in the hindbrain including the medial divisions of the valvula cerebelli and the corpus cerebelli. In addition, our observations indicate the presence of mSYT4-ir signals in GABAergic neurons, most notably in the Purkinje cell layer of the molecular layer in the aforementioned structures. Conversely, mSYT4-ir signals are not observed in glutamatergic or cholinergic neurons. Therefore, we deduce that the syt4 gene in zebrafish exhibits a homologous expression pattern to those of previously studied vertebrate species, which is revealed by the positive immunoreactive-like signals of mammalian SYT4 antibodies.

The translational genetics of ADHD and related phenotypes in model organisms

Attention-deficit/hyperactivity disorder (ADHD) is a highly prevalent neurodevelopmental disorder resulting from the interaction between genetic and environmental risk factors. It is well known that ADHD co-occurs frequently with other psychiatric disorders due, in part, to shared genetics factors. Although many studies have contributed to delineate the genetic landscape of psychiatric disorders, their specific molecular underpinnings are still not fully understood. The use of animal models can help us to understand the role of specific genes and environmental stimuli-induced epigenetic modifications in the pathogenesis of ADHD and its comorbidities. The aim of this review is to provide an overview on the functional work performed in rodents, zebrafish and fruit fly and highlight the generated insights into the biology of ADHD, with a special focus on genetics and epigenetics. We also describe the behavioral tests that are available to study ADHD-relevant phenotypes and comorbid traits in these models. Furthermore, we have searched for new models to study ADHD and its comorbidities, which can be useful to test potential pharmacological treatments.

Implication of synaptotagmins 4 and 7 in activity-dependent somatodendritic dopamine release in the ventral midbrain

Dopamine (DA) neurons can release DA not just from axon terminals, but also from their somatodendritic (STD) compartment through a mechanism that is still incompletely understood. Using voltammetry in mouse mesencephalic brain slices, we find that STD DA release has low capacity and shows a calcium sensitivity that is comparable to that of axonal release. We find that the molecular mechanism of STD DA release differs from axonal release with regard to the implication of synaptotagmin (Syt) calcium sensors. While individual constitutive knockout of Syt4 or Syt7 is not sufficient to reduce STD DA release, the removal of both isoforms reduces this release by approximately 50%, leaving axonal release unimpaired. Our work unveils clear differences in the mechanisms of STD and axonal DA release.

Distribution of Copy Number Variation in SYT11 Gene and Its Association with Growth Conformation Traits in Chinese Cattle

Simple Summary

It is known that many different breeds of cattle are widely distributed in China. However, due to a lengthy selection of draught direction, there are obvious shortcomings in Chinese cattle, such as less meat production, slow weight gain, poor meat quality, and a lack of specialized beef cattle breeds. Animal breeding heavily benefits from molecular technologies, among which molecular genetic markers were widely used to improve the economic traits of beef cattle. Because the copy number variation (CNV) involves a longer DNA sequence or even the entire functional gene, it may have a greater impact on the phenotype. Recent studies have indicated that CNVs are widespread in the Chinese cattle genome. By investigating the effects of CNVs on gene expression and cattle traits, we aim to find those genomic variations which could significantly affect cattle traits, and which could provide a basis for genetic selection and molecular breeding of local Chinese cattle.

Abstract

Currently, studies of the SYT11 gene mainly focus on neurological diseases such as schizophrenia and Parkinson’s disease. However, some studies have shown that the C2B domain of SYT11 can interact with RISC components and affect the gene regulation of miRNA, which is important for cell differentiation, proliferation, and apoptosis, and therefore has an impact on muscle growth and development in animals. The whole-genome resequencing data detected a CNV in the SYT11 gene, and this may affect cattle growth traits. In this study, CNV distribution of 672 individuals from four cattle breeds, Yunling, Pinan, Xianan, and Qinchuan, were detected by qPCR. The relationship between CNV, gene expression and growth traits was further investigated. The results showed that the proportion of multiple copy types was the largest in all cattle breeds, but there were some differences among different breeds. The normal type had higher gene expression than the abnormal copy type. The CNVs of the SYT11 gene were significantly correlated with body length, cannon circumference, chest depth, rump length, and forehead size of Yunling cattle, and was significantly correlated with the bodyweight of Xianan cattle, respectively. These data improve our understanding of the effects of CNV on cattle growth traits. Our results suggest that the CNV of SYT11 gene is a protentional molecular marker, which may be used to improve growth traits in Chinese cattle.

Glucose Overload Inhibits Glutamatergic Synaptic Transmission: A Novel Role for CREB-Mediated Regulation of Synaptotagmins 2 and 4

Glucose metabolism derangement is critically involved in the age-related memory loss but the underlying molecular mechanisms are still poorly understood. In a mouse model of type 1 diabetes we found memory impairment associated with inhibition of the transcription factor CREB and alteration of pre- and post-synaptic protein expression in the hippocampus. Accordingly, glucose excess negatively affected activity-dependent CREB phosphorylation and CREB-mediated mRNA expression of synaptic proteins in hippocampal primary neurons. Specifically, glucose excess inhibited the activity-dependent recruitment of CREB on the regulatory sequences of synaptotagmin (SYT) 2 and 4 promoters and the expression of SYT4 protein. As a result, high glucose affected both the frequency of miniature excitatory postsynaptic currents and NMDA receptor-mediated currents in autaptic hippocampal neuronal cultures. Collectively, our findings highlight novel mechanisms underlying hyperglycaemia-related memory loss, including CREB-dependent downregulation of synaptotagmin expression.

The diversity of synaptotagmin isoforms

The synaptotagmin family of molecules is known for regulating calcium-dependent membrane fusion events. Mice and humans express 17 synaptotagmin isoforms, where most studies have focused on isoforms 1, 2, and 7, which are involved in synaptic vesicle exocytosis. Recent work has highlighted how brain function relies on additional isoforms, with roles in postsynaptic receptor endocytosis, vesicle trafficking, membrane repair, synaptic plasticity, and protection against neurodegeneration, for example, in addition to the traditional concept of synaptotagmin-mediated neurotransmitter release - in neurons as well as glia, and at different timepoints. In fact, it is not uncommon for the same isoform to feature several splice isoforms, form homo- and heterodimers, and function in different subcellular locations and cell types. This review aims to highlight the diversity of synaptotagmins, offers a concise summary of key findings on all isoforms, and discusses different ways of grouping these.

Exocytosis in mouse vestibular Type II hair cells shows a high-order Ca2+ dependence that is independent of synaptotagmin-4

Mature hair cells transduce information over a wide range of stimulus intensities and frequencies for prolonged periods of time. The efficiency of such a demanding task is reflected in the characteristics of exocytosis at their specialized presynaptic ribbons. Ribbons are electron-dense structures able to tether a large number of releasable vesicles allowing them to maintain high rates of vesicle release. Calcium entry through rapidly activating, non-inactivating CaV 1.3 (L-type) Ca2+ channels in response to cell depolarization causes a local increase in Ca2+ at the ribbon synapses, which is detected by the exocytotic Ca2+ sensors. The Ca2+ dependence of vesicle exocytosis at mammalian vestibular hair cell (VHC) ribbon synapses is believed to be linear, similar to that observed in mature cochlear inner hair cells (IHCs). The linear relation has been shown to correlate with the presence of the Ca2+ sensor synaptotagmin-4 (Syt-4). Therefore, we studied the exocytotic Ca2+ dependence, and the release kinetics of different vesicle pool populations, in Type II VHCs of control and Syt-4 knockout mice using patch-clamp capacitance measurements, under physiological recording conditions. We found that exocytosis in mature control and knockout Type II VHCs displayed a high-order dependence on Ca2+ entry, rather than the linear relation previously observed. Consistent with this finding, the Ca2+ dependence and release kinetics of the ready releasable pool (RRP) of vesicles were not affected by an absence of Syt-4. However, we did find that Syt-4 could play a role in regulating the release of the secondary releasable pool (SRP) in these cells. Our findings show that the coupling between Ca2+ influx and neurotransmitter release at mature Type II VHC ribbon synapses is faithfully described by a nonlinear relation that is likely to be more appropriate for the accurate encoding of low-frequency vestibular information, consistent with that observed at low-frequency mammalian auditory receptors.

Genetic Access to Gustatory Disgust-Associated Neurons in the Interstitial Nucleus of the Posterior Limb of the Anterior Commissure in Male Mice

Orofacial and somatic disgust reactions are observed in rats following intraoral infusion of not only bitter quinine (innate disgust) but also sweet saccharin previously paired with illness (learned disgust). It remains unclear, however, whether these innate and learned disgust reactions share a common neural basis and which brain regions, if any, host it. In addition, there is no established method to genetically access neurons whose firing is associated with disgust (disgust-associated neurons). Here, we examined the expression of cFos and Arc, two markers of neuronal activity, in the interstitial nucleus of the posterior limb of the anterior commissure (IPAC) of male mice that showed innate disgust and mice that showed learned disgust. Furthermore, we used a targeted recombination in active populations (TRAP) method to genetically label the disgust-associated neurons in the IPAC with YFP. We found a significant increase of both cFos-positive neurons and Arc-positive neurons in the IPAC of mice that showed innate disgust and mice that showed learned disgust. In addition, TRAP following quinine infusion (Quinine-TRAP) resulted in significantly more YFP-positive neurons in the IPAC, compared to TRAP following water infusion. A significant number of the YFP-positive neurons following Quinine-TRAP were co-labeled with Arc following the second quinine infusion, confirming that Quinine-TRAP preferentially labeled quinine-activated neurons in the IPAC. Our results suggest that the IPAC activity is associated with both innate and learned disgust and that disgust-associated neurons in the IPAC are genetically accessible by TRAP.

Capture of Dense Core Vesicles at Synapses by JNK-Dependent Phosphorylation of Synaptotagmin-4

Delivery of neurotrophins and neuropeptides via long-range trafficking of dense core vesicles (DCVs) from the cell soma to nerve terminals is essential for synapse modulation and circuit function. But the mechanism by which transiting DCVs are captured at specific sites is unknown. Here, we discovered that Synaptotagmin-4 (Syt4) regulates the capture and spatial distribution of DCVs in hippocampal neurons. We found that DCVs are highly mobile and undergo long-range translocation but switch directions only at the distal ends of axons, revealing a circular trafficking pattern. Phosphorylation of serine 135 of Syt4 by JNK steers DCV trafficking by destabilizing Syt4-Kif1A interaction, leading to a transition from microtubule-dependent DCV trafficking to capture at en passant presynaptic boutons by actin. Furthermore, neuronal activity increased DCV capture via JNK-dependent phosphorylation of the S135 site of Syt4. Our data reveal a mechanism that ensures rapid, site-specific delivery of DCVs to synapses.

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Syt4-bearing dense core vesicles in axons traffic continually in a circular pattern

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Phosphorylation of S135 of Syt4 by JNK destabilizes Syt4-Kif1A binding

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Destabilized Syt4-Kif1A binding promotes capture of vesicles at synapses by actin

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Neuronal activity increases vesicle capture via S135-dependent JNK phosphorylation

The Synaptotagmins: Calcium Sensors for Vesicular Trafficking

The synaptotagmin family of vesicle proteins is believed to mediate calcium-dependent regulation of membrane trafficking. Detailed biochemical and in vivo studies of the most characterized isoform, synaptotagmin 1 (syt 1), have provided compelling evidence that it functions as a calcium sensor for fast neurotransmitter release at synapses. However, the function of the remaining isoforms is unclear, and multiple roles have been hypothesized for several of these. Recent evidence in Drosophila has given insight into the function of some of the remaining synaptotagmin family members. Of the five evolutionarily conserved isoforms in Drosophila, only two, syt 1 and syt 4, localize to most, if not all, synapses. The former is localized to presynaptic terminals, whereas the latter is predominantly postsynaptic. This suggests an intriguing possibility that syt 4 may mediate a postsynaptic vesicle trafficking pathway, providing a molecular basis for an evolutionarily conserved bidirectional vesicular trafficking communication system at synapses.

Upregulation and axonal transport of synaptotagmin-IV in the direct-pathway medium spiny neurons in hemi-parkinsonian rats induced by dopamine D1 receptor stimulation

Synaptotagmin-IV (Syt-IV) may function as a regulator of Ca(2+) -dependent synaptic transmission. In the hemi-parkinsonian rats with unilateral lesions of dopaminergic nigrostriatal neurons Syt-IV and substance-P (SP) mRNAs could be upregulated within the dopaminergically hypersensitive striatum of the lesioned brain hemisphere via the stimulation of striatal dopamine D1 (D1-R), but not D2 receptors. The hypersensitive D1-R-mediated transmission may be the culprit for the undesired expression of levodopa-induced dyskinesia, implying the involvement of Syt-IV and SP in the process. First, striatal cellular phenotypes expressing Syt-IV were determined. It was found to be expressed in all striatal neurons and a small population of astrocytes. Then it was examined, if the D1-R-mediated upregulation of Syt-IV mRNA may result in the upregulation of the translated protein. It was found that, after acute stimulation with a selective D1 agonist, (±)-6-chloro-7,8-dihydroxy-3-allyl-1-phenyl-2,3,4,5-tetrahydro-1H-3-benzazepine hydrobromide (SKF-82958), Syt-IV was elevated within the SP-expressing striatal neurons of the lesioned side. This was followed by the upregulation of Syt-IV, but not of its mRNA, within the ipsilateral target nuclei of the direct-pathway medium spiny neurons, indicating axonal transport of de novo synthesized protein to their SP-positive synaptic terminals. However, despite the striatal upregulation of SP and Syt-IV following a similar time-course, their subcellular co-localization within the axonal terminals was not found. It was therefore suggested that Syt-IV may regulate the hypersensitive striatal synaptic transmission, although via a SP-independent mechanism.

Alteration in synaptic junction proteins following traumatic brain injury

Extensive research and scientific efforts have been focused on the elucidation of the pathobiology of cellular and axonal damage following traumatic brain injury (TBI). Conversely, few studies have specifically addressed the issue of synaptic dysfunction. Synaptic junction proteins may be involved in post-TBI alterations, leading to synaptic loss or disrupted plasticity. A Synapse Protein Database on synapse ontology identified 109 domains implicated in synaptic activities and over 5000 proteins, but few of these demonstrated to play a role in the synaptic dysfunction after TBI. These proteins are involved in neuroplasticity and neuromodulation and, most importantly, may be used as novel neuronal markers of TBI for specific intervention.

The association of brain structure with gait velocity in older adults: a quantitative volumetric analysis of brain MRI

INTRODUCTION

While cortical processes play an important role in controlling locomotion, the underlying structural brain changes associated with slowing of gait in aging are not yet fully established. Our study aimed to examine the relationship between cortical gray matter volume (GM), white matter volume (WM), ventricular volume (VV), hippocampal and hippocampal subfield volumes, and gait velocity in older adults free of dementia.

METHODS

Gait and cognitive performance was tested in 112 community-residing adults, age 70 years and over, participating in the Einstein Aging Study. Gait velocity (cm/s) was obtained using an instrumented walkway. Volumetric MRI measures were estimated using a FreeSurfer software. We examined the cross-sectional relationship of GM, WM, VV, and hippocampal total and subfield volumes and gait velocity using linear regression models. In complementary models, the effect of memory performance on the relationship between gait velocity and regional volumes was evaluated.

RESULTS

Slower gait velocity was associated with smaller cortical GM and total hippocampal volumes. There was no association between gait velocity and WM or VV. Among hippocampal subfields, only smaller presubiculum volume was significantly associated with decrease in gait velocity. Addition of the memory performance to the models attenuated the association between gait velocity and all volumetric measures.

CONCLUSIONS

Our findings indicate that total GM and hippocampal volumes as well as specific hippocampal subfield volumes are inversely associated with locomotor function. These associations are probably affected by cognitive status of study population.

Perinatal high-fat diet increases hippocampal vulnerability to the adverse effects of subsequent high-fat feeding

Epidemiological observations report an increase in fat consumption associated with low intake of n-3 relative to n-6 polyunsaturated fatty acids (PUFAs) in women of childbearing age. However, the impact of these maternal feeding habits on cognitive function in the offspring is unknown. This study aims to investigate the impact of early exposure to a high-fat diet (HFD) with an unbalanced n-6/n-3 PUFAs ratio on hippocampal function in adult rats. Furthermore, we explored the effects of perinatal HFD combined with exposure to HFD after weaning. Dams were fed a control diet (C, 12% of energy from lipids, n-6/n-3 PUFAs ratio: 5) or HFD (HF, 39% of energy from lipids, n-6/n-3 PUFAs ratio: 39) throughout gestation and lactation. At weaning, offspring were placed either on control (C-C, HF-C) or high-fat (HF-HF) diets. In adulthood, hippocampus-dependent memory was assessed using the water-maze task and potential hippocampal alterations were determined by studying PUFA levels, gene expression, neurogenesis and astrocyte morphology. Perinatal HFD induced long-lasting metabolic alterations and some changes in gene expression in the hippocampus, but had no effect on memory. In contrast, spatial memory was impaired in animals exposed to HFD during the perinatal period and maintained on this diet. HF-HF rats also exhibited low n-3 and high n-6 PUFA levels, decreased neurogenesis and downregulated expression of several plasticity-related genes in the hippocampus. To determine the contribution of the perinatal diet to the memory deficits reported in HF-HF animals, an additional experiment was conducted in which rats were only exposed to HFD starting at weaning (C-HF). Interestingly, memory performance in this group was similar to controls. Overall, our results suggest that perinatal exposure to HFD with an unbalanced n-6/n-3 ratio sensitizes the offspring to the adverse effects of subsequent high-fat intake on hippocampal function.

Resveratrol improved the spatial learning and memory in subclinical hypothyroidism rat induced by hemi-thyroid electrocauterization

The major purpose of this study was to investigate the effect of resveratrol (RES) on the spatial learning and memory ability in subclinical hypothyroidism (SCH) rat model and the potential mechanism. A SCH rat model was induced by hemi-thyroid electrocauterization and the activity of hypothalamus-pituitary-thyroid (HPT) axis was detected. The spatial learning and memory ability was tested using Morris water maze (MWM) and Y-maze. The protein expressions of synaptotagmin-1 (syt-1) and brain-derived neurotrophic factor (BDNF) in the hippocampus were measured via western blot. The results showed that SCH rat model was successfully duplicated. The SCH rats showed impaired learning and memory in the behavioral tests. However, these changes were reversed by the treatment of RES (15mg/kg) and levothyroxine (LT4). Moreover, RES treated rats exhibited reduced plasma TSH level and hypothalamic thyrotropin releasing hormone (TRH) mRNA expression, which suggested that the imbalance of HPT axis in the SCH rats could be reversed by RES treatment. Furthermore, RES treatment up-regulated the protein levels of syt-1 and BDNF in hippocampus. These findings indicated an amelioration effect of RES on the spatial learning and memory in the SCH rats, the mechanism of which might be involved with its ability of modifying the hyperactive HPT axis and up-regulating the hippocampal hypo-expression of syt-1 and BDNF.

Cholinergic efferent synaptic transmission regulates the maturation of auditory hair cell ribbon synapses

Spontaneous electrical activity generated by developing sensory cells and neurons is crucial for the maturation of neural circuits. The full maturation of mammalian auditory inner hair cells (IHCs) depends on patterns of spontaneous action potentials during a ‘critical period’ of development. The intrinsic spiking activity of IHCs can be modulated by inhibitory input from cholinergic efferent fibres descending from the brainstem, which transiently innervate immature IHCs. However, it remains unknown whether this transient efferent input to developing IHCs is required for their functional maturation. We used a mouse model that lacks the α9-nicotinic acetylcholine receptor subunit (α9nAChR) in IHCs and another lacking synaptotagmin-2 in the efferent terminals to remove or reduce efferent input to IHCs, respectively. We found that the efferent system is required for the developmental linearization of the Ca²⁺-sensitivity of vesicle fusion at IHC ribbon synapses, without affecting their general cell development. This provides the first direct evidence that the efferent system, by modulating IHC electrical activity, is required for the maturation of the IHC synaptic machinery. The central control of sensory cell development is unique among sensory systems.

Up-regulation of Synaptotagmin IV within amyloid plaque-associated dystrophic neurons in Tg2576 mouse model of Alzheimer's disease

AIM

To investigate the involvement of the vesicular membrane trafficking regulator Synaptotagmin IV (Syt IV) in Alzheimer's disease pathogenesis and to define the cell types containing increased levels of Syt IV in the β-amyloid plaque vicinity.

METHODS

Syt IV protein levels in wild type (WT) and Tg2576 mice cortex were determined by Western blot analysis and immunohistochemistry. Co-localization studies using double immunofluorescence staining for Syt IV and markers for astrocytes (glial fibrillary acidic protein), microglia (major histocompatibility complex class II), neurons (neuronal specific nuclear protein), and neurites (neurofilaments) were performed in WT and Tg2576 mouse cerebral cortex.

RESULTS

Western blot analysis showed higher Syt IV levels in Tg2576 mice cortex than in WT cortex. Syt IV was found only in neurons. In plaque vicinity, Syt IV was up-regulated in dystrophic neurons. The Syt IV signal was not up-regulated in the neurons of Tg2576 mice cortex without plaques (resembling the pre-symptomatic conditions).

CONCLUSIONS

Syt IV up-regulation within dystrophic neurons probably reflects disrupted vesicular transport or/and impaired protein degradation occurring in Alzheimer's disease and is probably a consequence but not the cause of neuronal degeneration. Hence, Syt IV up-regulation and/or its accumulation in dystrophic neurons may have adverse effects on the survival of the affected neuron.

Synaptotagmin-12 phosphorylation by cAMP-dependent protein kinase is essential for hippocampal mossy fiber LTP

Synaptotagmin-12 (Syt12) is an abundant synaptic vesicle protein that--different from other synaptic vesicle-associated synaptotagmins--does not bind Ca(2+). Syt12 is phosphorylated by cAMP-dependent protein kinase-A at serine-97 in an activity-dependent manner, suggesting a function for Syt12 in cAMP-dependent synaptic plasticity. To test this hypothesis, we here generated (1) Syt12 knock-out mice and (2) Syt12 knockin mice carrying a single amino-acid substitution [the serine-97-to-alanine- (S97A)-substitution]. Both Syt12 knock-out mice and Syt12 S97A-knockin mice were viable and fertile, and exhibited no measurable change in basal synaptic strength or short-term plasticity as analyzed in cultured cortical neurons or in acute hippocampal slices. However, both Syt12 knock-out and Syt12 S97A-knockin mice displayed a major impairment in cAMP-dependent mossy-fiber long-term potentiation (LTP) in the CA3 region of the hippocampus. This impairment was observed using different experimental configurations for inducing and monitoring mossy-fiber LTP. Moreover, although the Syt12 knock-out had no effect on the short-term potentiation of synaptic transmission induced by the adenylate-cyclase activator forskolin in cultured cortical neurons and in the CA1 region of the hippocampus, both the Syt12 knock-out and the Syt12 S97A-knockin impaired the long-term increase in mossy-fiber synaptic transmission induced by forskolin. Thus, Syt12 is essential for cAMP-dependent presynaptic LTP at mossy-fiber synapses, and a single amino-acid substitution that blocks the cAMP-dependent phosphorylation of Syt12 is sufficient to impair the function of Syt12 in mossy-fiber LTP, suggesting that cAMP-dependent phosphorylation of Syt12 on serine-97 contributes to the induction of mossy-fiber LTP.

Developmental expression and subcellular distribution of synaptotagmin 11 in rat hippocampus

Synaptotagmins are required for Ca(2+)-dependent membrane-trafficking in either neuronal synaptic vesicles or cellular membranes. Previous reports suggested that the synaptotagmin 11 (syt11) gene is involved in the development of schizophrenia based on the genomic analysis of patients. Parkin protein binds to the C2 domains of Syt11 which leads to the polyubiquitination of Syt11. However, where and how Syt11 performs its role in the brain is largely unknown. Here, we report that Syt11 is expressed mainly in the brain. In addition, exogenously expressed Syt11 in HEK293 cells can form higher molecular weight complex via its transmembrane domain. Also, Syt11 is targeted to both dendrite and axon compartments. Immunocytochemistry showed that Syt11 is juxtaposed to postsynaptic markers in both excitatory and inhibitory synapses. Both neuroligin 1 and 2, which are postsynaptic cell adhesion molecules and differentially induce excitatory and inhibitory presynapses, respectively, recruit Syt11 in neuron coculture. Immunogold electron microscopy analysis revealed that Syt11 exists mainly in presynaptic neurotransmitter vesicles and plasma membrane, and rarely in postsynaptic sites. These results suggest that Syt11 may contribute to the regulation of neurotransmitter release in the excitatory and inhibitory presynapses, and postsynapse-targeted membrane trafficking in dendrites.

Altered expression of synaptotagmin 13 mRNA in adult mouse brain after contextual fear conditioning

Contextual fear memory processing requires coordinated changes in neuronal activity and molecular networks within brain. A large number of fear memory-related genes, however, still remain to be identified. Synaptotagmin 13 (Syt13), an atypical member of synaptotagmin family, is highly expressed in brain, but its functional roles within brain have not yet been clarified. Here, we report that the expression of Syt13 mRNA in adult mouse brain was altered following contextual fear conditioning. C57BL/6 mice were exposed to a novel context and stimulated by strong electrical footshock according to a contextual fear conditioning protocol. After 24 h, the mice were re-exposed to the context without electrical footshock for the retrieval of contextual fear memory. To investigate the relationship between Syt13 and contextual fear memory, we carried out in situ hybridization and analyzed gene expression patterns for Syt13 at four groups representing temporal changes in brain activity during contextual fear memory formation. Contextual fear conditioning test induced significant changes in mRNA levels for Syt13 within various brain regions, including lateral amygdala, somatosensory cortex, piriform cortex, habenula, thalamus, and hypothalamus, during both acquisition and retrieval sessions. Our data suggest that Syt13 may be involved in the process of contextual fear memory.

Distinct subsets of Syt-IV/BDNF vesicles are sorted to axons versus dendrites and recruited to synapses by activity

BDNF plays a critical role in the regulation of synaptic strength and is essential for long-term potentiation, a phenomenon that underlies learning and memory. However, whether BDNF acts in a diffuse manner or is targeted to specific neuronal subcompartments or synaptic sites to affect circuit function remains unknown. Here, using photoactivation of BDNF or syt-IV (a regulator of exocytosis present on BDNF-containing vesicles) in transfected rat hippocampal neurons, we discovered that distinct subsets of BDNF vesicles are targeted to axons versus dendrites and are not shared between these compartments. Moreover, syt-IV- and BDNF-harboring vesicles are recruited to both presynaptic and postsynaptic sites in response to increased neuronal activity. Finally, using syt-IV knockout mouse neurons, we found that syt-IV is necessary for both presynaptic and postsynaptic scaling of synaptic strength in response to changes in network activity. These findings demonstrate that BDNF-containing vesicles can be targeted to specific sites in neurons and suggest that syt-IV-regulated BDNF secretion is subject to spatial control to regulate synaptic function in a site-specific manner.

Web-based genome-wide association study identifies two novel loci and a substantial genetic component for Parkinson's disease

Although the causes of Parkinson's disease (PD) are thought to be primarily environmental, recent studies suggest that a number of genes influence susceptibility. Using targeted case recruitment and online survey instruments, we conducted the largest case-control genome-wide association study (GWAS) of PD based on a single collection of individuals to date (3,426 cases and 29,624 controls). We discovered two novel, genome-wide significant associations with PD-rs6812193 near SCARB2 (p = 7.6 × 10(-10), OR = 0.84) and rs11868035 near SREBF1/RAI1 (p = 5.6 × 10(-8), OR = 0.85)-both replicated in an independent cohort. We also replicated 20 previously discovered genetic associations (including LRRK2, GBA, SNCA, MAPT, GAK, and the HLA region), providing support for our novel study design. Relying on a recently proposed method based on genome-wide sharing estimates between distantly related individuals, we estimated the heritability of PD to be at least 0.27. Finally, using sparse regression techniques, we constructed predictive models that account for 6%-7% of the total variance in liability and that suggest the presence of true associations just beyond genome-wide significance, as confirmed through both internal and external cross-validation. These results indicate a substantial, but by no means total, contribution of genetics underlying susceptibility to both early-onset and late-onset PD, suggesting that, despite the novel associations discovered here and elsewhere, the majority of the genetic component for Parkinson's disease remains to be discovered.

Neuropeptide exocytosis involving synaptotagmin-4 and oxytocin in hypothalamic programming of body weight and energy balance

Hypothalamic neuropeptides play essential roles in regulating energy and body weight balance. Energy imbalance and obesity have been linked to hypothalamic signaling defects in regulating neuropeptide genes; however, it is unknown whether dysregulation of neuropeptide exocytosis could be critically involved. This study discovered that synaptotagmin-4, an atypical modulator of synaptic exocytosis, is expressed most abundantly in oxytocin neurons of the hypothalamus. Synaptotagmin-4 negatively regulates oxytocin exocytosis, and dietary obesity is associated with increased vesicle binding of synaptotagmin-4 and thus enhanced negative regulation of oxytocin release. Overexpressing synaptotagmin-4 in hypothalamic oxytocin neurons and centrally antagonizing oxytocin in mice are similarly obesogenic. Synaptotagmin-4 inhibition prevents against dietary obesity by normalizing oxytocin release and energy balance under chronic nutritional excess. In conclusion, the negative regulation of synaptotagmin-4 on oxytocin release represents a hypothalamic basis of neuropeptide exocytosis in controlling obesity and related diseases.

Deletion of SNAP-23 results in pre-implantation embryonic lethality in mice

SNARE-mediated membrane fusion is a pivotal event for a wide-variety of biological processes. SNAP-25, a neuron-specific SNARE protein, has been well-characterized and mouse embryos lacking Snap25 are viable. However, the phenotype of mice lacking SNAP-23, the ubiquitously expressed SNAP-25 homolog, remains unknown. To reveal the importance of SNAP-23 function in mouse development, we generated Snap23-null mice by homologous recombination. We were unable to obtain newborn SNAP-23-deficient mice, and analysis of pre-implantation embryos from Snap23^Δ/wt matings revealed that Snap23-null blastocysts were dying prior to implantation at embryonic day E3.5. Thus these data reveal a critical role for SNAP-23 during embryogenesis.

Upregulation of synaptotagmin IV inhibits transmitter release in PC12 cells with targeted synaptotagmin I knockdown

BACKGROUND

The function of synaptotagmins (syt) in Ca2+-dependent transmitter release has been attributed primarily to Ca2+-dependent isoforms such as syt I. Recently, syt IV, an inducible Ca2+-independent isoform has been implicated in transmitter release. We postulated that the effects of syt IV on transmitter release are dependent on the expression of syt I.

RESULTS

To test this, we increased syt IV expression in PC12 cells by either upregulation with forskolin treatment or overexpression with transfection. Two separately generated stable PC12 cell lines with syt I expression abolished by RNAi targeting were used and compared to control cells. We measured catecholamine release from single vesicles by amperometry and neuropeptide Y release from populations of cells by an immunoassay. In syt I targeted cells with forskolin-induced syt IV upregulation, amperometry measurements showed a reduction in the number of release events and the total amount of transmitter molecules released per cell. In cells with syt IV overexpressed, similar amperometry results were obtained, except that the rate of expansion for full fusion was slowed. Neuropeptide Y (NPY) release from syt I knockdown cells was decreased, and overexpression of syt IV did not rescue this effect.

CONCLUSIONS

These data support an inhibitory effect of syt IV on release of vesicles and their transmitter content. The effect became more pronounced when syt I expression was abolished.

Rat and Drosophila synaptotagmin 4 have opposite effects during SNARE-catalyzed membrane fusion

Synaptotagmins (Syt) are a large family of proteins that regulate membrane traffic in neurons and other cell types. One isoform that has received considerable attention is SYT4, with apparently contradictory reports concerning the function of this isoform in fruit flies and mice. SYT4 was reported to function as a negative regulator of neurotrophin secretion in mouse neurons and as a positive regulator of secretion of a yet to be identified growth factor from muscle cells in flies. Here, we have directly compared the biochemical and functional properties of rat and fly SYT4. We report that rat SYT4 inhibited SNARE-catalyzed membrane fusion in both the absence and presence of Ca²⁺. In marked contrast, fly SYT4 stimulated SNARE-mediated membrane fusion in response to Ca²⁺. Analysis of chimeric molecules, isolated C2 domains, and point mutants revealed that the C2B domain of the fly protein senses Ca²⁺ and is sufficient to stimulate fusion. Rat SYT4 was able to stimulate fusion in response to Ca²⁺ when the conserved Asp-to-Ser Ca²⁺ ligand substitution in its C2A domain was reversed. In summary, rat SYT4 serves as an inhibitory isoform, whereas fly SYT4 is a bona fide Ca²⁺ sensor capable of coupling Ca²⁺ to membrane fusion.

Synaptotagmins in neurodegeneration

Synaptotagmins (Syts) are transmembrane proteins involved in the regulation of membrane trafficking. Here, we summarize literature data that provide growing evidence that several Syts are involved in the pathophysiological mechanisms of temporal lobe epilepsy and Parkinson's disease, as well as few reports related to brain ischemia and Alzheimer's disease (AD). We also report new data from our laboratories, showing changes of the expression of several Syts in Tg2576 mouse model of AD that may be related to neuroinflammation surrounding the beta-amyloid plaques. Furthermore, we demonstrate N-methyl-D-aspartate receptor-mediated upregulation of Syt 4 mRNA in a model of excitotoxic striatal lesion induced by unilateral striatal injection of quinolinic acid, associating the upregulation of Syt 4 with mechanisms of excitotoxicity. We propose that pharmacological manipulation of Syt expression in animal models of neurodegeneration should be further explored, as it may help to clarify the role of individual Syt isoforms in the regulation of membrane trafficking in neurodegeneration.

Loss of synaptotagmin IV results in a reduction in synaptic vesicles and a distortion of the Golgi structure in cultured hippocampal neurons

Fusion of synaptic vesicles with the plasma membrane is mediated by the SNARE (soluble NSF attachment receptor) proteins and is regulated by synaptotagmin (syt). There are at least 17 syt isoforms that have the potential to act as modulators of membrane fusion events. Synaptotagmin IV (syt IV) is particularly interesting; it is an immediate early gene that is regulated by seizures and certain classes of drugs, and, in humans, syt IV maps to a region of chromosome 18 associated with schizophrenia and bipolar disease. Syt IV has recently been found to localize to dense core vesicles in hippocampal neurons, where it regulates neurotrophin release. Here we have examined the ultrastructure of cultured hippocampal neurons from wild-type and syt IV -/- mice using electron tomography. Perhaps surprisingly, we observed a potential synaptic vesicle transport defect in syt IV -/- neurons, with the accumulation of large numbers of small clear vesicles (putative axonal transport vesicles) near the trans-Golgi network. We also found an interaction between syt IV and KIF1A, a kinesin known to be involved in vesicle trafficking to the synapse. Finally, we found that syt IV -/- synapses exhibited reduced numbers of synaptic vesicles and a twofold reduction in the proportion of docked vesicles compared to wild-type. The proportion of docked vesicles in syt IV -/- boutons was further reduced, 5-fold, following depolarization.

Synaptotagmin IV determines the linear Ca2+ dependence of vesicle fusion at auditory ribbon synapses

Mammalian cochlear inner hair cells (IHCs) are specialized for the dynamic coding of continuous and finely graded sound signals. This ability is largely conferred by the linear Ca(2+) dependence of neurotransmitter release at their synapses, which is also a feature of visual and olfactory systems. The prevailing hypothesis is that linearity in IHCs occurs through a developmental change in the Ca(2+) sensitivity of synaptic vesicle fusion from the nonlinear (high order) Ca(2+) dependence of immature spiking cells. However, the nature of the Ca(2+) sensor(s) of vesicle fusion at hair cell synapses is unknown. We found that synaptotagmin IV was essential for establishing the linear exocytotic Ca(2+) dependence in adult rodent IHCs and immature outer hair cells. Moreover, the expression of the hitherto undetected synaptotagmins I and II correlated with a high-order Ca(2+) dependence in IHCs. We propose that the differential expression of synaptotagmins determines the characteristic Ca(2+) sensitivity of vesicle fusion at hair cell synapses.

MRI- and MRS-derived hippocampal correlates of quantitative locomotor function in older adults

Gait measures have been shown to predict cognitive decline and dementia in older adults. Investigation of the neurobiology associated with locomotor function is needed to elucidate this relationship with cognitive abilities. This study aimed to examine magnetic resonance imaging (MRI; hippocampal volume)- and proton magnetic resonance spectroscopy (MRS; N-acetylaspartate to creatine (NAA/Cr) ratios)-derived hippocampal correlates of quantitative gait function (swing time (seconds), stride length (cm), and stride length variability (standard deviation)) in a subset of 48 nondemented older adults (24 males; mean age=81 years) drawn from the Einstein Aging Study, a community-based sample of individuals over the age of 70 residing in Bronx, New York. Linear regression analyses controlling for age were used to examine hippocampal volume and neurochemistry as predictors of gait function. We found that stride length was associated with hippocampal volume (beta=0.36, p=0.03; overall model R(2)=0.33, p=0.01), but not hippocampal neurochemistry (beta=0.09, p=0.48). Stride length variability was more strongly associated with hippocampal NAA/Cr (beta=-0.38, p=0.01; overall model R(2)=0.14, p=0.04) than hippocampal volume (beta=-0.33, p=0.08). Gait swing time was not significantly related to any neuroimaging measure. These relationships remained significant after accounting for memory and clinical gait impairments. These findings suggest that nondemented older adults exhibit increased stride length variability that is associated with lower levels of hippocampal neuronal metabolism, but not hippocampal volume. Conversely, decreased stride length is associated with smaller hippocampal volumes, but not hippocampal neurochemistry. Distinct neurobiological hippocampal substrates may support decreased stride length and increased stride length variability in older adults.

Differential effects of treadmill running and wheel running on spatial or aversive learning and memory: roles of amygdalar brain-derived neurotrophic factor and synaptotagmin I

Chronic exercise has been reported to improve cognitive function. However, whether and how different types of exercise affect various learning and memory tasks remain uncertain. To address this issue, male BALB/c mice were trained for 4 weeks under two different exercise protocols: moderate treadmill running or voluntary wheel running. After exercise training, their spatial memory and aversive memory were evaluated by a Morris water maze and by one-trial passive avoidance (PA), respectively. Levels of neural plasticity-related proteins, i.e. brain-derived neurotrophic factor (BDNF), tropomyosin-related kinase B (TrkB) and synaptotagmin I (Syt I), in hippocampus and amygdala were determined by ELISA or immunoblotting. Finally, the functional roles of these proteins in the basolateral amygdala were verified by locally blocking them with K252a (a TrkB kinase inhibitor), or lentivirus expressing Syt I shRNA. We found that (1) although both moderate treadmill running and wheel running improved the Morris water maze performance, only the former improved PA performance; (2) likewise, both exercise protocols upregulated the BDNF-TrkB pathway and Syt I in the hippocampus, whereas only treadmill exercise upregulated their expression levels in the amygdala; (3) local injection of K252a abolished the treadmill exercise-facilitated PA performance and upregulation of amygdalar TrkB and Syt I; and (4) local administration of Syt I shRNA abolished the treadmill exercise-facilitated PA performance and upregulation of amygdalar Syt I. Therefore, our results support the notion that different forms of exercise induce neuroplasticity changes in different brain regions, and thus exert diverse effects on various forms of learning and memory.

Synaptotagmin-IV modulates synaptic function and long-term potentiation by regulating BDNF release

Synaptotagmin-IV (syt-IV) is a membrane trafficking protein that influences learning and memory, but its localization and role in synaptic function remain unclear. Here we discovered that syt-IV localizes to BDNF-containing vesicles in hippocampal neurons. Syt-IV/BDNF-harboring vesicles undergo exocytosis in both axons and dendrites, and syt-IV inhibits BDNF release at both sites. Knockout of syt-IV increases, and over-expression decreases, the rate of FM dye destaining from presynaptic terminals indirectly via changes in post-synaptic release of BDNF. Hence, post-synaptic syt-IV regulates the trans-synaptic action of BDNF to control presynaptic vesicle dynamics. Furthermore, selective loss of presynaptic syt-IV increased spontaneous quantal release, while loss of post-synaptic syt-IV increased quantal amplitude. Finally, syt-IV knockout mice exhibit enhanced LTP, which depends entirely on disinhibition of BDNF release. Thus, regulation of BDNF secretion by syt-IV emerges as a mechanism to maintain synaptic strength within a useful range during long-term potentiation.

Synaptotagmin IV: a multifunctional regulator of peptidergic nerve terminals

Many members of the synaptotagmin (Syt) protein family bind Ca(2+) and trigger exocytosis, but some Syt proteins appear to have no Ca(2+)-dependent actions and their biological functions remain obscure. Syt IV is an activity-induced brain protein with no known Ca(2+)-dependent interactions and its subcellular localization and biological functions have sparked considerable controversy. We found Syt IV on both micro- and dense-core vesicles in posterior pituitary nerve terminals in mice. In terminals from Syt IV knockout mice compared with those from wild types, low Ca(2+) entry triggered more exocytosis, high Ca(2+) entry triggered less exocytosis and endocytosis was accelerated. In Syt IV knockouts, dense-core and microvesicle fusion was enhanced in cell-attached patches and dense-core vesicle fusion pores had conductances that were half as large as those in wild types. Given the neuroendocrine functions of the posterior pituitary, changes in Syt IV levels could be involved in endocrine transitions involving alterations in the release of the neuropeptides oxytocin and vasopressin.

Behavioral characterization of P311 knockout mice

P311 is an 8-kDa protein that is expressed in many brain regions, particularly the hippocampus, cerebellum and olfactory lobes, and is under stringent regulation by developmental, mitogenic and other physiological stimuli. P311 is thought to be involved in the transformation and motility of neural cells; however, its role in normal brain physiology is undefined. To address this point, P311-deficient mice were developed through gene targeting and their behaviors were characterized. Mutants displayed no overt abnormalities, bred normally and had normal survival rates. Additionally, no deficiencies were noted in motor co-ordination, balance, hearing or olfactory discrimination. Nevertheless, P311-deficient mice showed altered behavioral responses in learning and memory. These included impaired responses in social transmission of food preference, Morris water maze and contextual fear conditioning. Additionally, mutants displayed altered emotional responses as indicated by decreased freezing in contextual and cued fear conditioning and reduced fear-potentiated startle. Together, these data establish P311 as playing an important role in learning and memory processes and emotional responses.

Synaptotagmin IV regulates dense core vesicle (DCV) release in LbetaT2 cells

Synaptotagmins (Syts) are calcium-binding proteins which are conserved from nematodes to humans. Fifteen Syts have been identified in mammalian species. Syt I is recognized as a Ca(2+) sensor for the synchronized release of synaptic vesicles in some types of neurons, but its role in the secretion of dense core vesicles (DCVs) remains unclear. The function of Syt IV is of particular interest because it is rapidly up-regulated by chronic depolarization and seizures. Using RNAi-mediated gene silencing, we have explored the role of Syt I and IV on secretion in a pituitary gonadotrope cell line. Downregulation of Syt IV clearly reduced Ca(2+)-triggered exocytosis of dense core vesicles (DCVs) in LbetaT2 cells. Syt I silencing, however, had no effect on vesicular release.

JNK phosphorylates synaptotagmin-4 and enhances Ca2+-evoked release

Ca2+ influx induced by membrane depolarization triggers the exocytosis of secretory vesicles in various cell types such as endocrine cells and neurons. Peptidyl growth factors enhance Ca2+-evoked release, an effect that may underlie important adaptive responses such as the long-term potentiation of synaptic transmission induced by growth factors. Here, we show that activation of the c-Jun N-terminal kinase (JNK) plays an essential role in nerve growth factor (NGF) enhancement of Ca2+-evoked release in PC12 neuroendocrine cells. Moreover, JNK associated with phosphorylated synaptotagmin-4 (Syt 4), a key mediator of NGF enhancement of Ca2+-evoked release in this system. NGF treatment led to phosphorylation of endogenous Syt 4 at Ser135 and translocation of Syt 4 from immature to mature secretory vesicles in a JNK-dependent manner. Furthermore, mutation of Ser135 abrogated enhancement of Ca2+-evoked release by Syt 4. These results provide a molecular basis for the effect of growth factors on Ca2+-mediated secretion.

Huntingtin-interacting protein 1 influences worm and mouse presynaptic function and protects Caenorhabditis elegans neurons against mutant polyglutamine toxicity

Huntingtin-interacting protein 1 (HIP1) was identified through its interaction with htt (huntingtin), the Huntington's disease (HD) protein. HIP1 is an endocytic protein that influences transport and function of AMPA and NMDA receptors in the brain. However, little is known about its contribution to neuronal dysfunction in HD. We report that the Caenorhabditis elegans HIP1 homolog hipr-1 modulates presynaptic activity and the abundance of synaptobrevin, a protein involved in synaptic vesicle fusion. Presynaptic function was also altered in hippocampal brain slices of HIP1-/- mice demonstrating delayed recovery from synaptic depression and a reduction in paired-pulse facilitation, a form of presynaptic plasticity. Interestingly, neuronal dysfunction in transgenic nematodes expressing mutant N-terminal huntingtin was specifically enhanced by hipr-1 loss of function. A similar effect was observed with several other mutant proteins that are expressed at the synapse and involved in endocytosis, such as unc-11/AP180, unc-26/synaptojanin, and unc-57/endophilin. Thus, HIP1 is involved in presynaptic nerve terminal activity and modulation of mutant polyglutamine-induced neuronal dysfunction. Moreover, synaptic proteins involved in endocytosis may protect neurons against amino acid homopolymer expansion.

Structure of synaptophysin: a hexameric MARVEL-domain channel protein

Synaptophysin I (SypI) is an archetypal member of the MARVEL-domain family of integral membrane proteins and one of the first synaptic vesicle proteins to be identified and cloned. Most all MARVEL-domain proteins are involved in membrane apposition and vesicle-trafficking events, but their precise role in these processes is unclear. We have purified mammalian SypI and determined its three-dimensional (3D) structure by using electron microscopy and single-particle 3D reconstruction. The hexameric structure resembles an open basket with a large pore and tenuous interactions within the cytosolic domain. The structure suggests a model for Synaptophysin's role in fusion and recycling that is regulated by known interactions with the SNARE machinery. This 3D structure of a MARVEL-domain protein provides a structural foundation for understanding the role of these important proteins in a variety of biological processes.

Reduced CXCL12/CXCR4 results in impaired learning and is downregulated in a mouse model of Alzheimer disease

Alzheimer disease (AD) is characterized by the presence of plaques and tangles in parallel with progressive cognitive decline. The underlying cause of the cognitive decline is unknown. The purpose of this study was to identify factors that could affect learning and memory using the Tg2576 mouse model of AD. Un-biased GeneChip analysis at the time-point coinciding with the onset of behavioral deficits but prior to plaque deposition revealed that Tg2576 show altered gene expression for a number of molecules including the chemokine CXCL12. We show that this chemokine's mRNA, protein and receptor are downregulated in this mouse model coinciding with cognitive deficits. Furthermore, we demonstrate that CXCL12 levels are decreased in AD patients as compared to controls. To determine if CXCL12 might be related to impaired learning and memory, we chronically treated young non-transgenic mice with an antagonist to the CXCL12 receptor to simulate the reduction seen in transgenic animals. Treated animals showed selectively impaired learning and memory suggesting a potential role for this chemokine in cognitive functioning.

Upregulation of synaptotagmin IV protein in kainate-induced seizures

Synaptotagmin IV is a product of immediate early-response gene. It is involved in the regulated neurosecretion in the brain. Its putative role, however, in vesicular transport and localization in secretor y vesicles is still a matter of debate. Here we followed the spatiotemporal pattern of synaptotagmin IV protein upregulation in the hippocampus, caudate putamen, nucleus accumbens, nucleus amygdalae, piriform and entorhinal cortices of rats with kainate-induced seizures. We found that upregulation pattern paralleled the direction of depolarization through the hippocampus and also reflecting seizure activity spreading to other brain regions. We speculate that synaptotagmin IV may have a role in the vesicular transport of the upregulated peptides and proteins involved in the plasticity and/or neurodegeneration provoked by the kainate.

Whole genome expression analyses of single- and double-knock-out mice implicate partially overlapping functions of alpha- and gamma-synuclein

alpha-Synuclein has been implicated in the pathogenesis of Parkinson's disease. The function of alpha-synuclein has not been deciphered yet; however, it might play a role in vesicle function, transport, or as a chaperone. alpha-Synuclein belongs to a family of three proteins, which includes beta- and gamma-synuclein. gamma-Synuclein shares 60% similarity with alpha-synuclein. Similar to alpha-synuclein, a physiological function for gamma-synuclein has not been defined yet, but it has been implicated in tumorgenesis and neurodegeneration. Interestingly, neither alpha- (SNCA(-/-)), gamma- (SNCG(-/-)), nor alpha/gamma- (SNCA_G(-/-)) deficient mice are present with any obvious phenotype. Using microarray analysis, we thus investigated whether deficiency of alpha- and gamma-synuclein leads to similar compensatory mechanisms at the RNA level and whether similar transcriptional signatures are altered in the brain. Sixty-five genes were differentially expressed in all mice. SNCA(-/-) mice and SNCG(-/-) mice shared 84 differentially expressed genes, SNCA(-/-) and SNCA_G(-/-) expressed 79 genes, and SNCG(-/-) and SNCA_G(-/-) expressed 148 genes. For many of the physiological pathways such as dopamine receptor signaling (down-regulated), cellular development, nervous system function, and cell death (up-regulated), we found groups of genes that were similarly altered in SNCA(-/-) and SNCG(-/-) mice. In one of the pathways altered in both models, we found Mapk1 as the core transcript. Other gene groups, however, such as TGF-beta signaling and apoptosis pathways genes were significantly up-regulated in the SNCA(-/-) mice but down-regulated in SNCG(-/-) mice. beta-synuclein expression was not significantly altered in any of the models.

Singing, but not seizure, induces synaptotagmin IV in zebra finch song circuit nuclei

Synaptotagmins are a family of proteins that function in membrane fusion events, including synaptic vesicle exocytosis. Within this family, synaptotagmin IV (Syt IV) is unique in being a depolarization-induced immediate early gene (IEG). Experimental perturbation of Syt IV modulates neurotransmitter release in mice, flies, and PC12 cells, and modulates learning in mice. Despite these features, induction of Syt IV expression by a natural behavior has not been previously reported. We used the zebra finch, a songbird species, to investigate Syt IV because song is a naturally learned behavior whose neuroanatomical basis is largely identified. We observed that, similar to rodents, Syt IV is inducible in songbirds. This induction was selective and depended on the nature of neuronal depolarization. Generalized seizures caused by the GABA(A) receptor antagonist, metrazole, induced the IEG, ZENK, in zebra finch brain. However, these same seizures failed to induce Syt IV in song control areas. In contrast, when nontreated birds sang, three song control areas showed striking Syt IV induction. Further, this induction appeared sensitive to the social context in which song was sung. Together, these data suggest that neural activity during singing can drive Syt IV expression within song circuitry whereas generalized seizure activity fails to do so even though song control areas are depolarized. Our findings indicate that, within this neural circuit for a procedurally learned sensorimotor behavior, Syt IV is selective and requires precisely patterned neural activity and/or neuromodulation associated with singing.

Brain regions and genes affecting postural control

Postural control is integrated in all facets of motor commands. The role of cortico-subcortical pathways underlying postural control, including cerebellum and its afferents (climbing, mossy, and noradrenergic fibers), basal ganglia, motor thalamus, and parieto-frontal neocortex has been identified in animal models, notably through the brain lesion technique in rats and in mice with spontaneous and induced mutations. These studies are complemented by analyses of the factors underlying postural deficiencies in patients with cerebellar atrophy. With the gene deletion technique in mice, specific genes expressed in cerebellum encoding glutamate receptors (Grid2 and Grm1) and other molecules (Prkcc, Cntn6, Klf9, Syt4, and En2) have also been shown to affect postural control. In addition, transgenic mouse models of the synucleinopathies and of Huntington's disease cause deficiencies of motor coordination resembling those of patients with basal ganglia damage.

Critical appraisal of DNA microarrays in psychiatric genomics

Transcriptome profiling using DNA microarrays are data-driven approaches with the potential to uncover unanticipated relationships between gene expression alterations and psychiatric disorders. Studies to date have yielded both convergent and divergent findings. Differences may be explained, at least in part, by the use of a variety of microarray platforms and analytical approaches. Consistent findings across studies suggest, however, that important relationships may exist between altered gene expression and genetic susceptibility to psychiatric disorders. For example, GAD67, RGS4, DTNBP1, NRG1, and GABRAB2 show expression alterations in the postmortem brain of subjects with schizophrenia, and these genes have been also implicated as putative, heritable schizophrenia susceptibility genes. Thus, we propose that for some genes, altered expression in the postmortem human brain may have a dual origin: polymorphisms in the candidate genes themselves or upstream genetic-environmental factors that converge to alter their expression level. We hypothesize that certain gene products, which function as "molecular hubs," commonly show altered expression in psychiatric disorders and confer genetic susceptibility for one or more diseases. Microarray gene expression studies are ideally suited to reveal these putative disease-associated molecular hubs and to identify promising candidates for genetic association studies.