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Rolf Dermietzel

Publications and source records attributed to Rolf Dermietzel.

At least 19 recordsLinked to original sources
PubMed2007

Analysis of connexin expression during mouse Schwann cell development identifies connexin29 as a novel marker for the transition of neural crest to precursor cells.

Connexins are transmembrane proteins forming gap junction channels for direct intercellular and, for example in myelinating glia cells, intracellular communication. In mature myelin-forming Schwann cells, expression of multiple connexins, i.e. connexin (Cx) 43, Cx29, Cx32, and Cx46 (after nerve injury) has been detected. However, little is known about connexin protein expression during Schwann cell development. Here we use histochemical methods on wildtype and Cx29lacZ transgenic mice to investigate the developmental expression of connexins in the Schwann cell lineage. Our data demonstrate that in the mouse Cx43, Cx29, and Cx32 protein expression is activated in a developmental sequence that is clearly correlated with major developmental steps in the lineage. Only Cx43 was expressed from neural crest cells onwards. Cx29 protein expression was absent from neural crest cells but appeared as neural crest cells generated precursors (embryonic day 12) both in vivo and in vitro. This identifies Cx29 as a novel marker for cells of the defined Schwann cell lineage. The only exception to this were dorsal roots, where the expression of Cx29 was delayed four days relative to ventral roots and spinal nerves. Expression of Cx32 commenced postnatally, coinciding with the onset of myelination. Thus, the coordinated expression of connexin proteins in cells of the embryonic and postnatal Schwann cell lineage might point to a potential role in peripheral nerve development and maturation.

Animals↗
PubMed2006

Protein kinase A-mediated phosphorylation of connexin36 in mouse retina results in decreased gap junctional communication between AII amacrine cells.

Gap junctions in AII amacrine cells of mammalian retina participate in the coordination of the rod and cone signaling pathway involved in visual adaptation. Upon stimulation by light, released dopamine binds to D(1) receptors on AII amacrine cells leading to increased intracellular cAMP (cyclic adenosine monophosphate) levels. AII amacrine cells express the gap junctional protein connexin36 (Cx36). Phosphorylation of Cx36 has been hypothesized to regulate gap junctional activity of AII amacrine cells. However, until now in vivo phosphorylation of Cx36 has not been reported. Indeed, it had been concluded that Cx36 in bovine retina is not phosphorylated, but in vitro phosphorylation for Cx35, the bass ortholog of Cx36, had been shown. To clarify this experimental discrepancy, we examined protein kinase A (PKA)-induced phosphorylation of Cx36 in mouse retina as a possible mechanism to modulate the extent of gap junctional coupling. The cytoplasmic domains of Cx36 and the total Cx36 protein were phosphorylated in vitro by PKA. Mass spectroscopy revealed that all four possible PKA consensus motifs were phosphorylated; however, domains point mutated at the sites in question showed a prevalent usage of Ser-110 and Ser-293. Additionally, we demonstrated that Cx36 was phosphorylated in cultured mouse retina. Furthermore, activation of PKA increased the level of phosphorylation of Cx36. cAMP-stimulated, PKA-mediated phosphorylation of Cx36 protein was accompanied by a decrease of tracer coupling between AII amacrine cells. Our results link increased phosphorylation of Cx36 to down-regulation of permeability through gap junction channels mediating light adaptation in the retina.

Amacrine Cells↗
PubMed2006

Structure and function of gap junctions in the developing brain.

Gap-junction-dependent neuronal communication is widespread in the developing brain, and the prevalence of gap-junctional coupling is well correlated with specific developmental events. We summarize here our current knowledge of the contribution of gap junctions to brain development and propose that they carry out this role by taking advantage of the full complement of their functional properties. Thus, hemichannel activation may represent a key step in the initiation of Ca(2+) waves that coordinate cell cycle events during early prenatal neurogenesis, whereas both hemichannels and/or gap junctions may control the division and migration of cohorts of precursor cells during late prenatal neurogenesis. Finally, the recent discovery that pannexins, a novel group of proteins prominently expressed in the brain, are able to form both hemichannels and gap-junction channels suggests that we need to seek more than just connexins with respect to these junctions.

Animals↗
PubMed2006

Electrical synapses--gap junctions in the brain.

In the nervous system, interneuronal communication can occur via indirect or direct transmission. The mode of indirect communication involves chemical synapses, in which transmitters are released into the extracellular space to subsequently bind to the postsynaptic cell membrane. Direct communication is mediated by electrical synapses, and will be the focus of this review. The most prevalent group of electrical synapses are neuronal gap junctions (both terms are used interchangeably in this article), which directly connect the intracellular space of two cells by gap junction channels. The structural components of gap junction channels in the nervous system are connexin proteins, and, as recently identified, pannexin proteins. Connexin gap junction channels enable the intercellular, bidirectional transport of ions, metabolites, second messengers and other molecules smaller than 1 kD. More than 20 connexin genes have been found in the mouse and human genome. With the cloning of connexin36 (Cx36), a connexin protein with predominantly neuronal expression, the biochemical correlate of electrotonic transmission between neurons was identified. We outline the distribution of Cx36 as well as two other neuronal connexins (Cx57 and Cx45) in the nervous system, describing their spatial and temporal expression patterns. One focus in this review was the retina, as it shows many and diverse electrical synapses whose connexin components have been identified in fish and mammals. In view of the function of neuronal gap junctions, the network of inhibitory interneurons will be reviewed in detail, focussing on the hippocampus. Although in vivo data on pannexin proteins are still restricted to information on mRNA expression, electrophysiological data and the expression pattern in the nervous system have been included.

Animals↗
PubMed2006

Pannexin expression in the cerebellum.

Pannexin1 and pannexin2 are members of the pannexin gene family which are widely expressed in the central nervous system. Here we present an overview of pannexin expression and distribution in the mouse cerebellum. Pannexin1 and pannexin2 are expressed in the Purkinje cells and in some cells of the granule cell layer. Pannexin2 is also expressed in the stellate cells of the molecular layer. A differential expression of pannexin1 and pannexin2 mRNA is observed during cerebellar development. These findings constitute the first indication of the involvement of pannexin molecules in the developing cerebellum. Although the functional relevance of these molecules remains currently unknown, the abundance of pannexins in the Purkinje cells suggests that they may contribute to the generation of cerebellar rhythms.

Animals↗
PubMed2006

Spastic paresis after perinatal brain damage in rats is reduced by human cord blood mononuclear cells.

Brain damage around birth may cause lifelong neurodevelopmental deficits. We examined the therapeutic potential of human umbilical cord blood-derived mononuclear cells containing multipotent stem cells to facilitate motor recovery after cerebral hypoxic-ischemic damage in neonatal rats. Left carotid artery ligation followed by 8% O(2) inhalation for 80 min was performed on postnatal d 7, succeeded by intraperitoneal transplantation of human umbilical cord blood-derived mononuclear cells on postnatal d 8 in a sham-controlled design. Histologic and immunohistochemical analysis on postnatal d 21 revealed that neonates developed severe cerebral damage after the hypoxic-ischemic insult. These animals also suffered from contralateral spastic paresis, as evidenced by their locomotor behavior. After transplantation of human umbilical cord blood-derived mononuclear cells, spastic paresis was largely alleviated, resulting in a normal walking behavior. This "therapeutic" effect was accompanied by the fact that mononuclear cells had entered the brain and were incorporated around the lesion without obvious signs of transdifferentiation. This study demonstrates that intraperitoneal transplantation of human umbilical cord blood-derived mononuclear cells in a rat model of perinatal brain damage leads to both incorporation of these cells in the lesioned brain area and to an alleviation of the neurologic effects of cerebral palsy as assessed by footprint and walking pattern analysis.

Animals↗
PubMed2005

Effects of cytokines on microglial phenotypes and astroglial coupling in an inflammatory coculture model.

Cytokines play an important role in the onset, regulation, and propagation of immune and inflammatory responses within the central nervous system (CNS). The main source of cytokines in the CNS are microglial cells. Under inflammatory conditions, microglial cells are capable of producing pro- and antiinflammatory cytokines, which convey essential impact on the glial and neuronal environment. One paramount functional feature of astrocytes is their ability to form a functionally coupled syncytium. The structural link, which is responsible for the syncytial behavior of astrocytes, is provided by gap junctions. The present study was performed to evaluate the influence of inflammation related cytokines on an astroglial/microglial inflammatory model. Primary astrocytic cultures of newborn rats were cocultured with either 5% (M5) or 30% (M30) microglial cells and were incubated with the following proinflammatory cytokines: tumor necrosis factor-alpha (TNF-alpha), interleukin-1beta (IL-1beta), interleukin-6 (IL-6), interferon-gamma (IFN-gamma), and the antiinflammatory cytokines transforming growth factor-beta1 (TGF-beta1) and IFN-beta. Under these conditions, i.e., incubation with the inflammatory cytokines and the high fraction of microglia (M30), microglial cells revealed a significant increase of activated round phagocytotic cells accompanied by a reduction of astroglial connexin 43 (Cx43) expression, a reduced functional coupling together with depolarization of the membrane resting potential (MRP). When the antiinflammatory mediator TGF-beta1 was added to proinflammatory altered M30 cocultures, a reversion of microglial activation and reconstitution of functional coupling together with recovery of the astroglial MRP was achieved. Finally IFN-beta, added to M5 cocultures was able to prevent the effects of the proinflammatory cytokines TNF-alpha, IL-1beta, and IFN-gamma.

Animals↗
PubMed2005

Expression of neural connexins and pannexin1 in the hippocampus and inferior olive: a quantitative approach.

Electrical synapses (or neuronal gap junctions) are thought to be essential for the generation of synchronous oscillatory activities in various areas of the brain. In this study, we quantified the steady state mRNA expression levels of two neuronal gap junction proteins, connexin36 (Cx36) and connexin45 (Cx45), as well as of pannexin1, a member of a novel class of communicative junction forming proteins, and of connexin47 (Cx47) which is expressed in oligodendrocytes. The expression levels of these genes were compared in two regions known for oscillatory activity and which are equipped with electrically coupled neurons. Assessment of the levels of mRNA expression in the hippocampus and the nuclear complex of the inferior olive (IO) was achieved by means of laser microdissection (LMM) in combination with real time RT-PCR. Our results demonstrate the differential expression of Cx36, Cx45, pannexin1 and Cx47 in the hippocampus, with pannexin1 showing the highest level of expression followed by Cx36, Cx47, and Cx45. In the IO, pannexin1 showed a comparable expression level as in the hippocampus, but connexin expression levels were increased. Upon direct comparison, the combination of LMM and real time RT-PCR data generated specific, robust and reproducible results consistent with recent data reported about connexin expression in the nervous system. We conclude that the analytical strategy shown here provides a technological solution to overcome the less sensitive and notoriously less specific analysis of connexin expression by in situ hybridization.

Animals↗
PubMed2005

Site-specific and developmental expression of pannexin1 in the mouse nervous system.

Until recently, members of the connexin gene family were believed to comprise the sole molecular component forming gap junction channels in vertebrates. The recent discovery of the pannexin gene family has challenged this view, as these genes may encode for a putative second class of gap junction proteins in vertebrates. The expression of pannexin genes overlaps with those cellular networks known to exhibit a high degree of gap junctional coupling. We investigated the spatio-temporal mRNA distribution of one member of this gene family, pannexin1 (Panx1), in the brain and retina of mice using quantitative real-time polymerase chain reaction and a combination of in situ hybridization and immunohistochemistry for cellular resolution. Our results demonstrate a widespread expression of Panx1 in the brain, retina and other non-neuronal tissues. In the cortex, cerebellum and eye, Panx1 is expressed at early embryonic time points and peaks around embryonic day 18 followed by a decline towards adulthood. Most notably, Panx1 is detectable in neurons of many brain nuclei, which are known to be coupled by gap junctions as well as in previously unrecognized areas. Abundant expression was found in the adult hippocampal and neocortical pyramidal cells and interneurons, neurons of the reticular thalamus, the inferior olive, magnocellular hypothalamic neurons, midbrain and brain stem motoneurons, Purkinje cells and the retina.

Animals↗
PubMed2005

Loss of connexin36 increases retinal cell vulnerability to secondary cell loss.

Accruing evidence indicates that gap junctions are involved in neuronal survival after brain injury. The present study was aimed at clarifying the contribution of the neuronal gap-junction protein connexin36 (Cx36) to secondary cell loss after injury in the mouse retina. A focal retinal lesion was induced by infrared laser photocoagulation. Remarkably, this model allowed spatial and temporal definition of the lesion with high reproducibility. Moreover, Cx36 is abundantly expressed in the retina and plays an essential role in the visual transmission process. Taking advantage of these features, cell death was assessed using TUNEL assay and light and electron microscopy, and the extent of Cx36 expression was studied by immunohistochemistry, Western blot, in situ hybridization and real-time RT-PCR. Secondary cell loss was most prominent between 24 and 48 h after lesioning. This peak was accompanied by an increase in Cx36 expression. When cultured explanted retinas were subjected to gap-junction blockers a significant increase in the extent of secondary cell loss after laser photocoagulation became evident. Using the same experimental paradigm we compared the incidence of cell death in wild-type and Cx36(-/-) mice. A significant increase in total number of TUNEL-positive cells occurred in the Cx36(-/-) mice compared to controls. From these data we conclude that Cx36 contributes to the survival and resistance against damage of retinal cells and thus constitutes a protective factor after traumatic injury of the retina.

Analgesics, Non-Narcotic↗
PubMed2004

Genes controlling multiple functional pathways are transcriptionally regulated in connexin43 null mouse heart.

We have used mouse 27k cDNA arrays to compare gene expression patterns in four sets of three hearts each of neonatal wild types and four sets of three hearts each of littermates lacking the major cardiac gap junction protein, connexin43 (Cx43). Each individual set of hearts was hybridized against aliquots of an RNA standard prepared from selected mouse tissues, allowing calculation of variability and coordination of gene expression among the samples from both genotypes. Overall variance of gene expression was found to be markedly higher in wild-type hearts than in those from Cx43 null littermates. Expression levels of 586 of 5,613 adequately quantifiable distinct genes with known protein products were statistically altered in the Cx43 null hearts, 38 upregulated and 548 downregulated compared with wild types. Downregulation was confirmed for seven tested genes by quantitative RT-PCR. Functions of proteins encoded by the altered genes encompassed all functional categories, with largest percent changes in genes involved in intracellular transport and transcription factors. Among the downregulated genes in the Cx43 null hearts were those related to neuronal and glial function, suggesting that cardiac innervation might be compromised as a consequence of Cx43 deletion. This was supported by immunodetection of sympathetic innervation, using antibodies to the synaptic vesicle protein synaptophysin and to the adrenergic nerve terminal marker tyrosine hydroxylase. These findings reinforce the proposal that the cardiac abnormality in Cx43 null animals may be contributed by altered innervation and indicate that Cx43 deletion has consequences in addition to reduced intercellular communication.

Animals↗
PubMed2004

Fine-structural analysis and connexin expression in the retina of a transgenic model of Huntington's disease.

Recent studies indicate that the visual system appears more frequently affected in polyglutamine diseases than expected previously. Here, we investigated retinal degenerations in adult transgenic R6/2 mice, a model for Huntington's disease (HD). Light microscopical analysis revealed retinal dystrophy all over the retina, with central areas showing major effects. Electron microscopical analysis showed strong degenerations of outer and inner photoreceptor segments, shrinkage of photoreceptor cell somata, and signs of degeneration in photoreceptor terminals in the outer plexiform layer. Terminal deoxynucleotidyl transferase-mediated dUTP nick end labeling showed hints of apoptosis. Mutant huntingtin and ubiquitin were expressed in all classes of retinal neurons, the pigment epithelium, and to a minor extent in neuropil structures. For investigating possible links to functional impairments in the rod-cone pathway, expression levels of three connexins (Cx) were compared in R6/2 and wildtype mice retinae. In R6/2 mice, expression of Cx36, the major neuronal connexin in the retina, was slightly reduced in the outer plexiform layer, indicating affected photoreceptor terminals as detected at the electron microscopical level. In contrast, Cx45, a putative neuronal connexin in the retina, was remarkably reduced in the inner plexiform layer of R6/2 mice. This result corresponded to fainter signals of Cx45 mRNA as documented by in situ hybridization and to a lower level of mCx45 cDNA as obtained by polymerase chain reaction after reverse transcription, suggesting functional deficits in spatial processing of Cx45-mediated gap junction coupling due to transgene-induced retinal degenerations. Thus, it is important to clarify the meaning of visual involvement in HD.

Animals↗
PubMed2004

Expression pattern of lacZ reporter gene representing connexin36 in transgenic mice.

Targeted deletion of the connexin36 (Cx36) gene in the mouse genome leads to visual transmission defects, weakened synchrony of rhythmic inhibitory potentials in the neocortex, and disruption of gamma-frequency network oscillations. We have generated transgenic mice in which a reporter protein consisting of the exon1 coded N-terminal part of Cx36 fused to beta-galactosidase (N36-beta-gal) is expressed instead of Cx36. Here, we have used these mice for a detailed analysis of the reporter gene expression. By beta-gal staining of adult retina, we found expression of the lacZ reporter gene in the ganglion cell layer, in two rows of the inner nuclear layer, and in the photoreceptor layer. In the brain, beta-gal staining was present in gamma-aminobutyric acid (GABA)ergic neurons of the cerebellar nuclei, in non-GABAergic neurons of the inferior olive, in mitral cells of the olfactory bulb, and in parvalbumin-positive cells of the cerebral cortex. Outside the central nervous system, N36-beta-gal signals were detected in insulin producing beta-cells of the pancreas and in the medulla of the adrenal gland of adult Cx36(+/del[LacZ]) mice. This expression pattern suggests that Cx36 fulfills functional roles not only in several types of neurons in the retina and central nervous system but also in excitable cells of the pancreas and adrenal gland.

Animals↗
PubMed2004

Connexin32-containing gap junctions in Schwann cells at the internodal zone of partial myelin compaction and in Schmidt-Lanterman incisures.

In vertebrate peripheral nerves, the insulating myelin sheath is formed by Schwann cells, which generate flattened membrane processes that spiral around axons and form compact myelin by extrusion of cytoplasm and adhesion of apposed intracellular and extracellular membrane surfaces. Cytoplasm remains within the innermost and outermost tongues, in the paranodal loops bordering nodes of Ranvier and in Schmidt-Lanterman incisures. By immunocytochemistry, connexin32 (Cx32) protein has been demonstrated at paranodal loops and Schmidt-Lanterman incisures, and it is widely assumed that gap junctions are present in these locations, thereby providing a direct radial route for transport of ions and metabolites between cytoplasmic myelin layers. This study used freeze-fracture replica immunogold labeling to detect Cx32 in ultrastructurally defined gap junctions in Schmidt-Lanterman incisures, as well as in a novel location, between the outer two layers of internodal myelin, approximately every micrometer along the entire length of myelin, at the zone between compact myelin and noncompact myelin. Thus, these gap junctions link the partially compacted second layer of myelin to the noncompact outer tongue. Although these gap junctions are unusually small (average, 11 connexon channels), their relative abundance and regular distribution along the zone that is structurally intermediate between compact and noncompact myelin demonstrates the existence of multiple sites for unidirectional or bidirectional transport of water, ions, and small molecules between these two distinct cytoplasmic compartments, possibly to regulate or facilitate myelin compaction or to maintain the transition zone between noncompact and compact myelin.

Animals↗
PubMed2003

Molecular cloning and functional expression of zfCx52.6: a novel connexin with hemichannel-forming properties expressed in horizontal cells of the zebrafish retina.

Gap junction-mediated electrical coupling contributes to synchronous oscillatory activities of neurons, and considerable progress has been made in defining the molecular composition of gap junction channels. In particular, cloning and functional expression of gap junction proteins (connexins (Cx)) from zebrafish retina have shown that this part of the brain possesses a high degree of connexin diversity that may account for differential functional properties of electrical synapses. Here, we report the cloning and functional characterization of a new connexin, designated zebrafish Cx52.6 (zfCx52.6). This connexin shows little similarity to known connexins from fish and higher vertebrates. By combining in situ hybridization with Laser Capture Microdissection and RT-PCR, we found that this novel fish connexin is expressed in horizontal cells in the inner nuclear layer of the retina. Functional expression of zfCx52.6 in neuroblastoma cells and Xenopus oocytes led to functional gap junctional channels and, in single oocytes, induced large non-junctional membrane currents indicative of the formation of hemichannels, which were inhibited in reversible fashion by raising extracellular Ca(2+) concentrations.

Amino Acid Sequence↗
PubMed2003

Deformation of network connectivity in the inferior olive of connexin 36-deficient mice is compensated by morphological and electrophysiological changes at the single neuron level.

Compensatory mechanisms after genetic manipulations have been documented extensively for the nervous system. In many cases, these mechanisms involve genetic regulation at the transcription or expression level of existing isoforms. We report a novel mechanism by which single neurons compensate for changes in network connectivity by retuning their intrinsic electrical properties. We demonstrate this mechanism in the inferior olive, in which widespread electrical coupling is mediated by abundant gap junctions formed by connexin 36 (Cx36). It has been shown in various mammals that this electrical coupling supports the generation of subthreshold oscillations, but recent work revealed that rhythmic activity is sustained in knock-outs of Cx36. Thus, these results raise the question of whether the olivary oscillations in Cx36 knock-outs simply reflect the status of wild-type neurons without gap junctions or the outcome of compensatory mechanisms. Here, we demonstrate that the absence of Cx36 results in thicker dendrites with gap-junction-like structures with an abnormally wide interneuronal gap that prevents electrotonic coupling. The mutant olivary neurons show unusual voltage-dependent oscillations and an increased excitability that is attributable to a combined decrease in leak conductance and an increase in voltage-dependent calcium conductance. Using dynamic-clamp techniques, we demonstrated that these changes are sufficient to transform a wild-type neuron into a knock-out-like neuron. We conclude that the absence of Cx36 in the inferior olive is not compensated by the formation of other gap-junction channels but instead by changes in the cytological and electroresponsive properties of its neurons, such that the capability to produce rhythmic activity is maintained.

Adaptation, Physiological↗
PubMed2003

Microglia activation influences dye coupling and Cx43 expression of the astrocytic network.

Under inflammatory conditions, activated microglia are capable of producing proinflammatory cytokines that are reported to influence cell-to-cell communication. The present study was performed to evaluate the influence of microglial activation on the coupling efficiency of the astroglial network. Primary astrocyte cultures of newborn rats were cocultured with either 5% (M5) or 30% (M30) microglia. Microglial activation (rounded phagocytotic phenotype) was investigated using the monoclonal anti-ED1 antibody, and immunofluorescence with a polyclonal anti-Cx43 antibody was used to study astroglial Cx43 expression and distribution. Functional coupling of astrocytes was evaluated by monitoring the transfer of microinjected Lucifer yellow into neighboring cells. The data obtained can be summarized as follows: astroglia/M30 cocultures contained significantly fewer resting microglia and significantly more activated microglia than the M5 cocultures; significantly reduced astroglial Cx43 staining was found in M30 cocultures concurrently with a reduced number of dye coupled astrocytes; and the positive correlation of percent activated microglia with reduced astroglial Cx43 expression was highly significant, indicating that the degree of intercellular communication in the astroglial network may be modulated by the activation of microglia under in vitro conditions.

Animals↗