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Targeting brain stem centers of cardiovascular control using adenoviral vectors: impact of promoters on transgene expression.

Adenoviral vectors (AVV) are widely used as tools for exploring gene function in studies of the central autonomic control, but the cellular specificity of the promoters commonly used in these vectors has not been studied. We evaluated AVV with four "wide-spectrum" promoters, human cytomegalovirus promoter (HCMV), synapsin-1 promoter (Syn1), tubulin-alpha1 promoter (Talpha1), and neuron-specific enolase (NSE) for their ability to express enhanced green fluorescent protein (EGFP) within the dorsal vagal complex and the adjacent brain stem. They were compared with the PRSx8 promoter, specifically designed to target catecholaminergic neurons. AdHCMVEGFP, AdSyn1EGFP-WHE (woodchuck hepatitis enhancer element), AdTalpha1EGFP, and AdNSEEGFP were unable to drive expression of EGFP in dopamine beta-hydroxylase-immunoreactive neurons of the A2 cell group, although the adjacent dorsal vagal motonucleus and especially hypoglossal motoneurons did express high levels of EGFP. AdPRSx8EGFP efficiently drove EGFP expression in the A2 cell group but also in choline acetyltransferase-positive vagal motoneurons. However, catecholaminergic neurons could be selectively and efficiently transduced via a retrograde route by injecting the vector into their target areas. Thus AVV with "wide-spectrum" promoters have strikingly different activity in the diverse cellular populations within brain stem cardiovascular control centers. The PRSx8 promoter is a valuable tool for the study of the role of catecholaminergic neurons.

Adenoviridae↗

Potential regulatory relationship between the nested gene DDC8 and its host gene tissue inhibitor of metalloproteinase-2.

Nested genes are fairly common within the mammalian nervous system, yet few studies have examined whether the guest and host genes might be coordinately regulated. Tissue inhibitors of metalloproteinase (TIMPs) inhibit extracellular matrix proteolysis mediated by metzincin proteases. TIMP-2 is the only TIMP not nested within a synapsin gene. It does, however, serve as a host for differential display clone 8 (DDC8), a testis-specific gene whose expression is upregulated during spermatogenesis. Here, we demonstrate that DDC8 is not testis specific. Furthermore, DDC8 expression in nonneural and neural tissues mimics that of TIMP-2, including its upregulation in response to traumatic brain injury, suggesting a potential regulatory relationship. The most striking observation is that the TIMP-2 knockout mouse brain contains TIMP-2 mRNA encoding exons 2-5, which are downstream of DDC8, but not exon 1, which contains the signal sequence and cysteine residue required for MMP inhibition, indicating a functional knockout. That TIMP-2 transcripts in wild-type brain contain DDC8 sequence suggests alternative splicing between the two genes.

Amino Acid Sequence↗

Neurons and their dendrites in frontotemporal dementia.

Regional and areal patterns of cell vulnerability (manifested as cell death and neuron loss) and cell sensitivity (as revealed by the presence of intracytoplasmic inclusions) are described in patients with frontotemporal dementia (FTD) and FTD+ motor neuron disease (MND). This is followed by studies geared to learning about possible mechanisms involved in selective neuron loss and studies focused on recognizing the identity of vulnerable populations of local-circuit neurons and the impact of FTD on individual cells as well as on postsynaptic and presynaptic terminals in the frontal cortex. Neuron loss is not associated with increased vulnerability to nuclear DNA fragmentation, and nor is it accompanied by modifications in the expression of the proteins Bcl-2 and Bax, and transcription factors c-Fos and c-Jun, thus suggesting that these proteins are probably not involved in cell death in these disorders. In the frontal and temporal cortices, glutamatergic pyramidal cells and calbindin-D28k-immunoreactive GABAergic local-circuit neurons are lost in the upper cortical layers. Parvalbumin-immunoreactive cells are preserved. In addition, reduction of putative postsynaptic sites (as inferred from the decreased numbers of dendritic branches in both pyramidal and nonpyramidal neurons, and of dendritic spines in pyramidal cells) in remaining neurons of the upper layers, as well as reduction of presynaptic terminals (as suggested by the decreased expression of synaptic vesicle-associated proteins, synaptophysin, synaptotagmin, rab 3a and synapsin 1, and presynaptic plasma membrane proteins SNAP-25 and syntaxin 1) in the upper layers of the frontal cortex, but not of the posterior parietal cortex, demonstrate the combined devastating effects of FTD on cortico-cortical connections.

Biomarkers↗

Environment- and age-dependent plasticity of synaptic complexes in the mushroom bodies of honeybee queens.

Diversity in behavior plays a crucial role for the division of labor in insect societies. Social insects such as honeybees provide excellent model systems to investigate neuronal principles underlying behavioral plasticity. The two female castes, queens and workers, differ substantially in anatomy, physiology, aging and behavior. The different phenotypes are induced by environmental factors rather than genetic differences. Here we investigated environment- and age-dependent effects on the synaptic organization within higher order neuropils of the honeybee brain. Synaptic complexes (microglomeruli) in sensory-input regions of the mushroom bodies, prominent higher sensory integration centers, were analyzed quantitatively using fluorescent markers and confocal microscopy. Pre- and postsynaptic compartments of individual microglomeruli were labeled by anti-synapsin immunolabeling and f-actin detection with phalloidin in dendritic spines of mushroom-body intrinsic neurons. The results demonstrate that in queens the numbers of microglomeruli in the olfactory and visual input regions of the mushroom-body calyx are significantly lower than in workers. In queens raised in incubators, microglomeruli were affected by differences in pupal rearing temperature within the range of naturally occurring temperatures (32-36 degrees C). The highest numbers of microglomeruli developed at a lower temperature compared to workers (33.5 vs. 34.5 degrees C). We found a striking adult plasticity of microglomeruli numbers throughout the extended life-span of queens. Whereas microglomeruli in the olfactory lip increased with age ( approximately 55%), microglomeruli in the visual collar significantly decreased ( approximately 35%). We propose that developmental and adult plasticity of the synaptic circuitry in the mushroom-body calyx might underlie caste- and age-specific adaptations in behavior.

Animals↗

Regulation of sodium channel gene expression by transcriptional silencing.

Fast electrical signaling in the nervous system is mediated by action potentials. The type II Na channel often is responsible for the generation of action potentials in the mammalian central nervous system. The 5' flanking sequence of the type II gene has been cloned and characterized. The presence of a 28-bp DNA element in the regulatory region is required for restricting the expression of type II reporter genes to neuronal cells (PC12). The transcription factor (REST) that binds to this silencer element in the type II gene and mediates its neuron-specific expression has been identified. In cell lines and mouse embryos, REST ist detected only in cell types that fail to express this sodium channel gene. Furthermore, cotransfection assays of PC12 cells with type II reporter genes and a recombinant REST cDNA results in silencing of the type II promoter. We propose that expression of this sodium channel reflects a 'default' pathway in neurons which is blocked by the presence of REST in nonneuronal cells and perhaps in some cells in the adult peripheral nervous system. A rapidly increasing number of genes containing an RE1-like sequence has been reported (SCG10, synapsin, Ng-CAM and DBH) suggesting that a similar silencing mechanism underlies neuron-specific expression of these genes.

Animals↗

Subcellular distribution of corticotropin-releasing-factor-like immunoreactivity in rat central nervous system.

Corticotropin-releasing-factor-like immunoreactivity (CRF-LI) was measured in a number of subcellular fractions from rat brain using a highly sensitive and specific radioimmunoassay. CRF-LI was highly enriched in the crude synaptosomal/mitochondrial fraction (P2) relative to the homogenate, P1, S1, and S2 fractions. Separation of the P2 fraction into synaptosomal, myelin, and mitochondria-enriched subfractions on a rapid one-step sucrose gradient revealed that CRF-LI was present at higher concentration in the synaptosomal fraction than in the mitochondrial and myelin fractions. The distribution of CRF-LI paralleled that of synapsin, a synaptic vesicle marker phosphoprotein, but not that of pyruvate dehydrogenase, a mitochondrial phosphoprotein. These results are consistent with a nerve terminal localization of CRF and a potential role for this peptide as a central nervous system neurotransmitter.

Animals↗

Sympathetic innervation of the cardiovascular system in the giraffe.

The extreme blood pressure gradients in the giraffe, produced by gravity and behaviour, present a special challenge to blood flow and vascular capacity regulation, e.g. via sympathetic nerves. We report the distribution of nerves in vascular tissue from giraffe extremities and neck based on immunofluorescence against specific antisera to dopamine-beta-hydroxylase, neuropeptide Y, neurofilament, and synapsin I. Sympathetic innervation of gravitation-dependent arteries in the limbs was restricted to the adventitia-media border, while in carotid arteries fibers penetrated deep into the media. Surprisingly, limb veins appeared to be devoid of sympathetic innervation, while jugular veins had a sparse innervation. The morphological response, medial hypertrophy, that parallels the hydrostatic pressure gradients in the circulation combines with the thick skin and tight underlying fascia, the 'g-suit', and an exquisitely distributed sympathetic innervation pattern to provide an effective array of mechanisms for cardiovascular regulation in the adult giraffe.

Animals↗

Cellular localization of calmodulin-dependent protein kinases I and II to A-cells and D-cells of the endocrine pancreas.

Ca2+/calmodulin-dependent protein kinases I and II, initially identified in brain on the basis of their ability to phosphorylate synapsin I, have been implicated in the regulation of Ca2+-dependent synaptic neurosecretion. Specific recombinant and synthetic peptide antibodies were used to examine the distribution of CaM kinases I and II in the rat pancreas and other tissues. The CaM kinase I antibodies detected a doublet of cytosolic proteins of approximately 38 and approximately 42 kD by immunoblot. CaM kinase I was observed in glucagon-containing A-cells at the periphery of the islet of Langerhans but had little or no overlap with pancreatic polypeptide or somatostatin cells. In contrast, CaM kinase II was localized to somatostatin-containing D-cells. CaM kinase I co-localized with glucagon secretory granules. CaM kinase II was not associated with the somatostatin granule but rather was enriched in areas of the cells that contained relatively little somatostatin. Because glucagon secretion is Ca2+-dependent, it is attractive to speculate that CaM kinase I may play a regulatory role in glucagon secretion. Glucagon and somatostatin cells both utilize intracellular Ca2+ for signaling. Therefore, specific CaM kinases may act as effectors of Ca2+ in these different cell types.

Animals↗

Immunoelectronmicroscopy of neural antigens on ultrathin frozen sections.

We have utilized immunocryoultramicrotomy to detect synapsin, somatostatin, parvalbumin, and tubulin at the ultrastructural level. Immunocryoultramicrotomy combines informative identification of morphology with accurate immunolabeling. Moreover, since no detergents or organic solvents are used to enable antibody penetration, and since no enzyme marker diffusion occurs, localization of the antigens should be more accurate. Accordingly, it was possible to localize precisely all four antigens within a well-preserved structure. Application of this method has important advantages for high-resolution localization of molecules relevant to neuronal function.

Animals↗

Solubility of cytoskeletal proteins in immunohistochemistry and the influence of fixation.

For accurate and quantitative immunohistochemical localization of antigens it is crucial to know the solubility of tissue proteins and their degree of loss during processing. In this study we focused on the solubility of several cytoskeletal proteins in cat brain tissue at various ages and their loss during immunohistochemical procedures. We further examined whether fixation affected either solubility or immunocytochemical detectability of several cytoskeletal proteins. An assay was designed to measure the solubility of cytoskeletal proteins in cryostat sections. Quantity and quality of proteins lost or remaining in tissue were measured and analyzed by electrophoresis and immunoblots. Most microtubule proteins were found to be soluble in unfixed and alcohol fixed tissues. Furthermore, the microtubule proteins remaining in the tissue had a changed cellular distribution. In contrast, brain spectrin and all three neurofilament subunits were insoluble and remained in the tissue, allowing their immunocytochemical localization in alcohol-fixed tissue. Synapsin I, a protein associated with the spectrin cytoskeleton, was soluble, and aldehyde fixation is advised for its immunohistochemical localization. With aldehyde fixation, the immunoreactivity of some antibodies against neurofilament proteins was reduced in axons unveiling novel immunogenic sites in nuclei that may represent artifacts of fixation. In conclusion, protein solubility and the effects of fixation are influential factors in cytoskeletal immunohistochemistry, and should be considered before assessments for a quantitative distribution are made.

Animals↗

Double immunofluorescent staining using two unconjugated primary antisera raised in the same species.

Monoclonal antibodies (MAbs) capable of recognizing developmental stage-specific neuronal epitopes are becoming increasingly available. Because most of these MAbs are raised in a single species (mouse), simultaneous immunofluorescent detection of multiple epitopes has been difficult. We have taken advantage of the high sensitivity of tyramide signal amplification to develop a protocol that permits simultaneous detection of two antibodies raised in the same species. One primary antibody was applied at a concentration below the detection limit of fluorescently labeled secondary antibodies, yet sufficient for detection with the tyramide system. This first primary antibody was then effectively neglected during application of a second primary antibody that was detected by conventional fluorescently labeled secondary antibodies. Specifically, dual labeling for nestin and MAP2 was used to distinguish neuronal stem cells and precursor cells from immature postmitotic neurons, and synapsin I and GAP43 immunostaining was used to distinguish neurons with established synaptic connections from developing neurons. We have used this technique for staining both tissue sections and cultured cells from the embryonic mouse brain. This technique should be widely applicable and offers a simple procedure for simultaneously detecting two antigens when antibodies from only a single species are available.

Animals↗

Synaptic proteins as multi-sensor devices of neurotransmission.

Neuronal communication is tightly regulated in time and space. Following neuronal activation, an electrical signal triggers neurotransmitter (NT) release at the active zone. The process starts by the signal reaching the synapse followed by a fusion of the synaptic vesicle (SV) and diffusion of the released NT in the synaptic cleft. The NT then binds to the appropriate receptor and induces a membrane potential change at the target cell membrane. The entire process is controlled by a fairly small set of synaptic proteins, collectively called SYCONs. The biochemical features of SYCONs underlie the properties of NT release. SYCONs are characterized by their ability to detect and respond to changes in environmental signals. For example, consider synaptotagmin I (Syt1), a prototype of a protein family with over 20 gene and variants in mammals. Syt1 is a specific example of a multi-sensor device with a large repertoire of discrete states. Several of these states are stimulated by a local concentration of signaling molecules such as Ca2+. The ability of this protein to sense signaling molecules and to adopt multiple biochemical states is shared by other SYCONs such as the synapsins (Syns). Specific biochemical states of Syns determine the accessibility of SV for NT release. Each of these states is defined by a specific alternative spliced variant with a unique profile of phosphorylation modified sites. The plasticity of the synapse is a direct reflection of SYCON's multiple biochemical states. State transitions occurs in a wide range of time scales, and therefore these molecules need to cope with events that last milliseconds (i.e., exocytosis in fast responding synapses) and with events that can carry on for many minutes (i.e., organization of SV pools). We suggest that SYCONs are optimized throughout evolution as multi-sensor devices. A full repertoire of the switches leading to alternation of protein states and a detailed characterization of protein-protein network within the synapse is critical for the development of a dynamic model of synaptic transmission.

Animals↗

Morphological plasticity in the neural circuitry responsible for seasonal breeding in the ewe.

An increase in the response of GnRH neurons to estrogen negative feedback is responsible for seasonal anestrus in the ewe, but the underlying neural mechanisms remain largely unknown. Neural plasticity may play an important role because the density of synaptic input to GnRH neurons changes with seasons. Moreover, the transition from breeding to anestrous season requires thyroid hormones, which are also required for neuronal development. In the first experiment, we examined whether the decrease in synapses on GnRH neurons is critical for the transition to anestrus by comparing synaptic input in thyroidectomized and thyroid-intact controls, using electron microscopic analysis. Thyroidectomized ewes remained in the breeding season, but the number of synaptic contacts on their GnRH cells was not different from those in thyroid-intact ewes that were anestrus. The next experiment tested whether there was a seasonal change in morphology of the A15 dopaminergic neurons that mediate estrogen negative feedback during anestrus by analyzing synapsin-positive close contacts onto A15 neurons with confocal microscopy. There was a 2-fold increase in these close contacts onto dendrites of A15 neurons in anestrus and a corresponding increase in the length of A15 dendrites at this time of year. The increase in dendritic length was blocked by thyroidectomy, but this procedure did not significantly affect synaptic input to A15 neurons. These results provide initial evidence that the seasonal change in synapses on GnRH neurons is not sufficient for the transition into anestrus but that plasticity of the A15 dopaminergic neurons mediating estrogen negative feedback may contribute to this seasonal alteration.

Anestrus↗

Protein kinase C catalyzed phosphorylation of sterol carrier protein 2.

The transport of cholesterol to the inner mitochondrial membrane, a key step in steroidogenesis, is subject to hormonal modulation that, at least in part, could be mediated by protein phosphorylation. This step is stimulated by sterol carrier protein 2 (SCP2) and Ca2+. To explore whether SCP2 itself is a potential control point for regulation by Ca2+-dependent phosphorylation we investigated whether highly purified SCP2 could serve as a substrate for major type Ca2+ and non-Ca2+-dependent protein kinases. Phosphorylation by calmodulin protein kinase II (CaM-PK II), myosin light chain kinase (MLCK), cAMP-dependent kinase (PKA) and protein kinase C (PKC) was monitored under optimal conditions for each enzyme. PKA, CaM-PK II and MLCK catalyzed the radiolabeling of histone 2A, synapsin I and myosin light chain (MLC), known substrates for these kinases, respectively, yet no phosphate transfer to SCP2 was observed. In contrast, PKC from two different sources (rat and calf brain) effectively catalyzed the phosphorylation of the highly purified SCP2. The phosphorylation of SCP2 depended on the addition of Ca2+ and phospholipids and was completely blocked by Polymyxin B, a PKC inhibitor. PKC catalyzed phosphorylation of SCP2 displayed a similar dependence on the concentration of ATP. Lineweaver Burk plots of the data indicate Km values for ATP of approximately 6 microM for the phosphorylation of SCP2. Our results, which have revealed for the first time that SCP2 is a substrate for PKC, are consistent with the possibilities that the control of steroidogenesis by tropic hormones and by PKC activation are mediated, at least in part, by the phosphorylation/dephosphorylation of SCP2.

Adenosine Triphosphate↗

Synaptic loss in Alzheimer's disease and other dementias.

The extent and location of neuronal losses necessary or sufficient to produce dementia in patients with Alzheimer's Disease (AD) is unknown. To approach this question, we studied synaptic terminals in postmortem brain tissue utilizing immunohistochemical techniques. We used antibodies against two proteins found in synaptic terminals--synapsin I and synaptophysin--as synaptic markers in the hippocampal complexes of eight patients with autopsy-proven AD and eight nondemented control subjects. Quantitative microscopy measured the regional density of synaptic staining. All AD patients showed a striking decrease in synaptic staining in the outer half of the molecular layer of the dentate gyrus compared with control brains, where the density of synaptic terminals was uniform throughout. In an additional patient with progressive degenerative dementia but without plaques or tangles on neuropathologic examination, similar depletion of synaptic staining was seen in the dentate gyrus. Quantitative densitometric analyses confirmed the focal decrease in synaptic staining in the outer half of the molecular layer in demented patients. We also found a slight increase in synaptic staining in the inner half of this layer.

Adolescent↗

Inhibition of regulated catecholamine secretion from PC12 cells by the Ca2+/calmodulin kinase II inhibitor KN-62.

When stimulated by the cholinergic agonist carbachol, PC12 cells rapidly secrete a large fraction of the intracellular catecholamines by exocytotic release from the large dense-core secretory vesicles in a Ca(2+)-dependent manner. To investigate whether Ca2+/calmodulin kinase II plays a role in the regulated secretion of catecholamines, we examined the effect of the specific Ca2+/calmodulin kinase II inhibitor KN-62 on the carbachol-induced release of norepinephrine from PC12 cells. Approximately 50% of the regulated release of norepinephrine, stimulated either by carbachol or direct depolarization, was inhibited by pretreatment with KN-62, while the remaining 50% was resistant to KN-62 and therefore independent of Ca2+/calmodulin kinase II. In contrast, H7, an inhibitor of protein kinase C, had no effect on any of the stimulated release. FURA 2 imaging experiments demonstrated that KN-62 does not act by blocking the stimulation-induced increase in intracellular [Ca2+]. The most likely model consistent with these data is that all the dense-core vesicles fuse with the plasma membrane in a Ca(2+)-dependent process, but that approximately 50% of the vesicles require an additional step that is dependent on the action of Ca2+/calmodulin kinase II. This step occurs between the influx of Ca2+ and the fusion of vesicle membranes with the plasma membrane, and may be analogous to the Ca2+/calmodulin kinase II phosphorylation of synapsin which mobilizes small, clear synaptic vesicles for exocytosis at the synapse.

1-(5-Isoquinolinesulfonyl)-2-Methylpiperazine↗

BDNF-GFP containing secretory granules are localized in the vicinity of synaptic junctions of cultured cortical neurons.

The protein family of mammalian neurotrophins, comprising nerve-growth factor (NGF), brain-derived neurotrophic factor (BDNF), neurotrophin-3 and -4/5 (NT-3, NT-4/5), supports the survival and the phenotype of neurons from the central as well as the peripheral nervous system (CNS, PNS). In addition, exogenous application of neurotrophins has recently been found to modulate synaptic transmission in the rodent CNS. However, to provide evidence for a role of neurotophins as endogenous fast acting modulators of synaptic transmission, the synaptic localization and secretion of neurotrophins needs to be shown. We have now constructed a fusion protein consisting of N-terminal BDNF (the most abundant neurotrophin in the rodent hippocampus and neocortex) and C-terminal green fluorescent protein (GFP) to elucidate the cellular localization of BDNF in cortical neurons. Transient expression of BDNF-GFP in COS-7 cells revealed that the cellular localization in the trans-Golgi network (TGN), the processing of precursor proteins and the secretion of mature BDNF-GFP is indistinguishable from the properties of untagged BDNF. Upon transient transfection of primary rat cortical neurons, BDNF-GFP was found in secretory granules of the regulated pathway of secretion, as indicated by colocalization with the secretory granule marker secretogranin II. BDNF-GFP vesicles were found in the neurites of transfected neurons with a pattern reminiscent of the localization of endogenous BDNF in untransfected cortical neurons. BDNF-GFP vesicles were found predominantly in the somatodendritic compartment of the neurons, whereas additional axonal localization was found less frequently. Immunocytochemical staining of synaptic terminals with synapsin I antibodies revealed that the density of BDNF-GFP vesicles is elevated in the vicinity of synaptic junctions, indicating that BDNF is localized appropriately to function as an acute modulator of synaptic transmission. These data suggest that BDNF-GFP will be a useful tool to investigate synaptic release of BDNF during physiological synaptic stimulation, and will thereby allow us to elucidate the participation of neurotrophin release in activity dependent synaptic plasticity.

Animals↗

A 210 kDa protein is located in a membrane-microtubule linker at the distal end of mature and nascent basal bodies.

A monoclonal antibody raised against purified flagellar basal apparatuses from the green flagellate Spermatozopsis similis reacted with a protein of 210 kDa (p210) in western blots. The protein was partially cloned by immunoscreening of a cDNA library. The sequence encoded a novel protein rich in alanine (25%) and proline (20%), which contained regions similar to proteins of comparable amino acid composition such as extracellular matrix components or the membrane-cytoskeletal linker synapsin. Using a polyclonal antibody (anti-p210) raised against the C-terminal part of p210, it was shown that the protein was highly enriched in the basal apparatuses. Immunogold electron microscopy of isolated cytoskeletons or whole cells revealed that p210 was located in the flagellar transition region. The protein was part of the Y-shaped fibrous linkers between the doublet microtubules and the flagellar membrane, as indicated by statistical analysis of post-labeled sections using anti-centrin and anti-tubulin as controls. In premitotic cells p210 was located in a fibrous layer at the distal end of nascent basal bodies, which was perforated by the outgrowing axoneme. During deflagellation the protein remained at the basal body but we observed changes in its distribution, indicating that p210 partially moved to the tip of the basal body. p210 can be used as a marker to determine basal body position, orientation (parallel or antiparallel) and number in S. similis by indirect immunofluorescence. We suppose that p210 is involved in linking basal bodies to the plasma membrane, which is an important step during ciliogenesis.

Algal Proteins↗