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A Medvedev

Publications and source records attributed to A Medvedev.

At least 37 records · Page 2Linked to original sources
PubMed1998

Induction of the nuclear orphan receptor RORgamma during adipocyte differentiation of D1 and 3T3-L1 cells.

Here, we analyzed the expression of the three members of the retinoid-like orphan receptor (ROR) nuclear receptor subfamily during adipocyte differentiation. RORalpha and RORgamma mRNA were upregulated during adipocyte differentiation in preadipocyte D1 and 3T3-L1 cells, whereas RORbeta mRNA could not be detected. The induction of RORalpha and RORgamma mRNA succeeded the induction of peroxisome proliferator-activated receptor gamma (PPARgamma) and CCAAT/enhancer binding protein alpha and occurred at a similar time interval as did the increase in aP2 and lipoprotein lipase mRNA. Like the expression of PPARgamma and aP2, the induction of RORgamma mRNA was repressed by tumor necrosis factor alpha and transforming growth factor beta. The induction of adipogenesis by prostaglandin D2 and two thiazolidinediones in the multipotent stem cells C3H10T1/2 was also accompanied by an induction in RORgamma mRNA. In contrast to parental cells, clofibrate induces adipogenesis and RORalpha and RORgamma mRNA in BALB/c3T3 cells that ectopically express PPARgamma. RORgamma mediates its effect on transcription through specific response elements. Cotransfection of RORalpha or RORgamma and (RORgamma response element)4-chloramphenicol acetyltransferase into preadipocyte D1 cells induced transactivation of chloramphenicol acetyltransferase about 100-fold, suggesting that ROR plays a role in the regulation of gene expression in adipocytes. The nuclear orphan receptor Rev-ErbAalpha, which did not exhibit transactivation function, was able to inhibit transactivation by RORgamma at two different levels. Our results show that RORgamma is induced during adipocyte differentiation in D1 and 3T3-L1 cells and functions as an active transcription factor, suggesting a role for RORgamma in the regulation of gene expression during this differentiation process.

3T3 Cells↗
PubMed1997

Genomic structure and chromosomal mapping of the nuclear orphan receptor ROR gamma (RORC) gene.

The nuclear orphan receptor subfamily ROR/RZR is part of the steroid and thyroid hormone/retinoid receptor superfamily and consists of three different genes, alpha, beta, and gamma. In this study, we determined the genomic structure of mouse ROR gamma and the chromosomal localization of both mouse ROR gamma and human ROR gamma (HGMW-approved symbol RORC). The genomic structure of the mouse ROR gamma gene was derived from the analysis of P1 vector clones containing large genomic fragments encoding ROR gamma. These results revealed that the mROR gamma gene has a complex structure consisting of 11 exons separated by 10 introns spanning more than 21 kb of genomic DNA. The DNA-binding domain is contained in two exons, 3 and 4, each encoding one zinc-finger. The splice site between exon 3 and exon 4 is identical to that found in RAR and TR3 receptors. ROR gamma is expressed as two mRNAs, 2.3 and 3.0 kb in size, that are derived by the use of alternative polyadenylation signals. We show by fluorescence in situ hybridization that the mouse ROR gamma gene is located on chromosome 3, in a region that corresponds to band 3F2.1-2.2. The human ROR gamma was mapped to chromosome region 1q21. The results demonstrate that the ROR gamma genes are located in chromosomal regions that are syntenic between mouse and human.

Alternative Splicing↗
PubMed1997

Characterization of the response element and DNA binding properties of the nuclear orphan receptor germ cell nuclear factor/retinoid receptor-related testis-associated receptor.

Recently, we have reported the cloning of the germ cell-specific, nuclear orphan receptor germ cell nuclear factor (GCNF)/RTR. In this study, we characterize the RTR response elements by an electrophoretic mobility shift assay/polymerase chain reaction-based, DNA binding site selection strategy. RTR binds with the greatest affinity to response elements containing TCA(AG(G/T)TCA)2 (consensus RTR response element; conRTRE), to which it binds as a homodimer. RTR is also able to bind as a monomer to a single core motif TCAAG(G/T)TCA, albeit with a lower affinity. Mutation analysis supports the specific requirements of the 5'-flanking sequence and the core motif of the RTRE for optimal binding of RTR. An RTR-specific antiserum (RTR-Ab2) was raised that causes supershift of the RTR-conRTRE complex in EMSA. Based on the sequence of the conRTRE, we located a putative RTRE, referred to as P2-RE, in the 5' promoter-flanking region of the mouse protamine 2 gene, which is induced during the same stage of spermatogenesis as RTR. The ability of RTR-Ab2 to cause a supershift of an RTR-RTRE complex with nuclear extracts from different tissues correlated with the tissue- and development-specific expression of RTR. Transfection of RTR in CV-1 cells was unable to cause RTRE-dependent transactivation of a CAT reporter gene; however, an RTR-VP16 fusion protein could induce transactivation through several RTREs, including P2-RE.

Amino Acid Sequence↗
PubMed1997

cDNA cloning, genomic structure, and chromosome mapping of the human epithelial membrane protein CL-20 gene (EMP1), a member of the PMP22 family.

CL-20 is a novel gene encoding a protein that is structurally related to but distinct from the peripheral myelin protein PMP22. Like PMP22, CL-20 is likely to play important roles in the regulation of cell proliferation, differentiation, and cell death. In this study, we describe the cloning and sequencing of a cDNA encoding the human homologue of CL-20 and characterize the genomic structure of this gene. The hCL-20 gene (HGMW-approved symbol EMP1) encodes a protein of 157 amino acids that exhibits 76% identity to the rabbit CL-20 and to the rat EMP-1, which have been described recently, and 39% identity to human PMP22. CL-20 contains four hydrophobic domains, suggesting that it is an integral membrane protein. In particular the second hydrophobic domain encoded within the fourth exon is highly conserved among CL-20, EMP-1, and PMP22, suggesting a functional role for this region. CL-20 mRNA is abundant in squamous-differentiated bronchial epithelial cells; however, low levels of CL-20 mRNA can be detected in several human tissues by Northern analysis. Retinoic acid, which inhibits squamous differentiation, represses CL-20 expression in normal human bronchial epithelial cells. The genomic structure of the hCL-20 gene was analyzed using a P1 vector containing this gene. The hCL-20 gene contains five exons about 0.2, 0.12, 0.1, 0.14, and 2.2 kb and four introns about 15, 1.9, 0.1, and 0.7 kb. We have mapped the hCL-20 gene to chromosome 12p12 by fluorescence in situ hybridization.

Amino Acid Sequence↗
PubMed1997

Fos induction following systemic kainic acid: early expression in hippocampus and later widespread expression correlated with seizure.

We determined the distribution of Fos protein expression in a model of generalised epilepsy caused by excessive neuronal excitation. Fos immunoreactivity was mapped in forebrain in unrestrained rats, previously prepared with an indwelling venous catheter, after the intravenous administration of kainic acid (10 mg/kg). We determined cerebral activation following various periods of exposure to kainic acid by using intravenous administration of pentobarbitone to prevent further activation. Within a few minutes, kainic acid caused episodes of staring, sniffing, wet dog shakes, nodding and chewing. Fos induction occurred initially and simultaneously in hippocampus, subiculum, septum and entorhinal cortex as early as 9.5 min after kainate injection. After up to 40 min of staring, sniffing, wet dog shakes, nodding and chewing, Fos induction was not further increased above levels present within the first 9.5 min. After 56 +/- 6 min a motor convulsion occurred, initially affecting the jaw, head and tail and variably extending to the forelimbs, trunk or hindlimbs. Following the convulsive event, additional Fos was expressed in hippocampus, thalamus, caudate-putamen and other subcortical structures and in the cerebral cortex. Fos induction was sometimes asymmetric in entorhinal, visual, piriform, cingulum, parietal and frontal cortices and in amygdala and dorsal endopiriform area. Electroencephalographic recordings after a few minutes exposure to kainic acid revealed an increased amplitude of fast frequencies in hippocampus which appeared to correlate with Fos induction in this structure. The findings are generally consistent with the reported distribution and slow development of kainic acid-induced seizure activity using electrophysiological and deoxyglucose methods. However, the Fos distribution suggests that (i) hippocampal, possibly dentate, activation precedes significant activation elsewhere, (ii) extensive involvement of other cerebral structures and cerebral cortex occurs simultaneously and correlates with motor seizures and (iii) brain structures can be recruited asymmetrically.

Animals↗
PubMed1996

Cloning of a cDNA encoding the murine orphan receptor RZR/ROR gamma and characterization of its response element.

In this study, we describe the cloning of the mouse homologue of the orphan receptor, RZR/ROR gamma, a member of the nuclear receptor superfamily, from a mouse muscle cDNA library. The amino acid sequence of mouse ROR gamma (mROR gamma) is highly homologous to that of human ROR gamma, with an overall identity of 88%. Northern blot analysis using RNA from different tissues showed that mROR gamma was found to be highly expressed in skeletal muscle, liver and kidney. Analysis of the ROR gamma-response element using in vitro synthesized ROR gamma revealed that it binds as a monomer to response elements composed of a single core motif GGTCA preceded by a 6 bp AT-rich sequence. The ROR gamma-binding specificity was further defined by mutational analysis of the consensus RORE. ROR gamma was able to activate RORE-dependent transcription of the CAT reporter gene in mouse fibroblast D1 cells. ROR alpha 1 and ROR gamma inhibit the transactivation induced by GAL4(DBD)-ROR gamma in fibroblast D1 cells suggesting that these receptors compete for binding to the same coactivators.

Amino Acid Sequence↗
PubMed1996

The geometric structure, construction, and interpretation of path-following (trail-making) tests.

Diagnostic comparisons of performance on parts A and B of the Trail Making Test (TMT) assume that path structure in the two parts is equivalent but that task complexity is greater for B. The two parts are shown to differ with respect to length and angular variability. However, measures of fractal dimension show no difference in structural complexity between paths A and B. This analysis suggests a principled method for generating alternative pathways, varying in complexity, and opens the way for a systematic study of path-following. It also suggests that path-following may be interpretable within a general approach, in which perceptual, linguistic, reasoning and motor processes are seen as related through different groups of geometric transformations.

Adult↗
PubMed1996

Frontal cortex leads other brain structures in generalised spike-and-wave spindles and seizure spikes induced by picrotoxin.

Generaliszed spike-and-wave (SW) spindles (5-7 Hz) associated with myoclonic jerks precede the occurrence of regular spikes (2-3 Hz) associated with convulsive seizure induced by picrotoxin. SW spindles occur spontaneously in rodent and cat under some experimental conditions and are considered to be models of human generalised epilepsy. These spindles have been proposed as being led by a thalamic pacemaker. To examine this possibility in picrotoxin-induced SW spindles and seizure spikes, we recorded EEG using chronically implant unipolar electrodes during intravenous picrotoxin infusion in freely behaving rat. The 6 EEG signals were digitally sampled at 1000 Hz. Linear correlation, spectral, coherence and phase analyses were undertaken to determine time differences (TDs) between EEG channels and the brain structure leading seizure activity. One frontal cortex led all other structures during SW spindles. TD between SW spindles in the leading frontal cortex (Fr1) and the contralateral Fr1 was 3.6 + / - 0.5 msec. All ipsilateral structures (hippocampus, thalamus, amygdala, caudate nucleus and occipital cortex) were delayed by more than 3 msec from Fr1 (intralaminar thalamic nuclei - by 6.3 + / - 0.9 msec). TDs of SW spindles between subcortical regions were less than 1.5 msec. Similar relationships with slightly smaller TDs were found with spikes during convulsive seizure except TDs between frontal cortices did not significantly differ from zero. We suggest that seizure activity induced by picrotoxin is led by one Fr1 during SW spindles and by both frontal cortices working as one system during convulsive seizure.

Animals↗
PubMed1996

Opioid receptor activation resets the hypothalamic clock generating growth hormone secretory bursts in the rat.

Plasma growth hormone (GH) concentrations were measured serially every 20 min for 6 h in unrestrained chronically-catheterised male rats to define physiological GH pulsatile secretory patterns. Bursts of GH secretion lasted 69 +/- 5 min and occurred every 177 +/- 4 min. Intravenous administration of the opioid receptor agonist morphine (200 micrograms/kg) caused an immediate GH burst of normal duration (63 +/- 3 min) in all animals. This burst of secretion occurred whatever the phase of the background GH cycle and was followed by normal trough GH levels; a second GH burst occurred 177 +/- 6 min later, an inter-burst period not different from controls. Opioid receptor blockade with naloxone (5 mg/kg) administered i.v. every 20 min during spontaneous GH bursts significantly lengthened the interburst interval from 177 +/- 4 to 200 +/- 9 min (P = 0.015). Naloxone did not affect synchronisation of the GH rhythm induced by morphine but lengthened the duration of GH secretory bursts from 69 +/- 5 to 94 +/- 9 min (P = 0.017). The findings indicate that opioid receptor activation resets the hypothalamic mechanism generating pulsatile GH secretion and that both the period of the GH rhythm and duration of the GH burst is normally shortened by opioid mechanisms.

Animals↗
PubMed1995

Distribution of Fos-positive neurons in cortical and subcortical structures after picrotoxin-induced convulsions varies with seizure type.

The distribution of Fos protein was mapped in rat brain following a single non-focal convulsive seizure. Single seizures were induced with intravenous picrotoxin in unhandled animals housed in isolation. Different convulsive behaviours occurred unpredictably. The least severe seizures were predominantly localised to the face, head and forelimbs, without loss of posture control (restricted seizures). The most extensive seizures affected all limbs and trunk, sometimes with falling (generalised seizures). There was a correlation between seizure behaviour and distribution of Fos induction. After restricted seizures, Fos was induced at highest levels in neocortex and piriform cortex and was prominent in entorhinal cortex, caudal-ventral caudate-putamen and amygdala. Regions of thalamus were consistently and lightly labelled, but Fos induction did not occur in hippocampus. After generalised seizures, there was Fos induction in cortex but less than after restricted seizures and, in three of four animals, also in dentate gyrus, hippocampus and subiculum. There was occasional or variable labelling of thalamus, basolateral amygdala and caudate-putamen. One animal with generalised seizures showed no hippocampal Fos induction. The findings indicate that picrotoxin induces seizures with at least two different patterns of neuronal involvement. The cortex, part of the caudate-putamen, amygdala and thalamus are involved in restricted seizures while the hippocampus, cortex and thalamus are involved in generalised seizures. The results do not support the view that generalised seizures are a progression from restricted forms. Cortical Fos involvement is entirely consistent with the participation of cortex in non-focal epilepsy. In these non-focal seizures, the dentate-hippocampus may be a source of excitation to cortex in the generalised group while the cortex appears to be the predominant site of excitation in the restricted group.

Animals↗
PubMed1995

Isatin is a potent endogenous antagonist of guanylate cyclase-coupled atrial natriuretic peptide receptors.

Isatin (indole-2,3-dione) is an endogenous compound with anxiogenic properties. In the brain, highest levels (0.1 microgram/g) have been found in the rat hippocampus. In the present study, we show that isatin has little effect on a wide range of neurotransmitter and hormonal receptors but that it acts as an inhibitor of atrial natriuretic peptide (ANP) binding, with an IC50 of 4x 10(-7) M. It also inhibits ANP-activated particulate guanylate cyclase from rat kidney, heart and brain membranes in dose-dependent fashion, varying also with ANP concentration. These findings suggest that isatin is a new endogenous regulator of mammalian ANP activity, with potential implications for the control of both anxiety and natriuresis.

Animals↗
PubMed1994

Tumor necrosis factor receptor p75 mediates cell-specific activation of nuclear factor kappa B and induction of human cytomegalovirus enhancer.

The functional role of human tumor necrosis factor receptor (TNFR) p75 was studied by the use of TNFR p75-specific agonistic antibodies. Human SW480T adenocarcinoma cells, stably transfected with a reporter construct containing beta-galactosidase under the control of human cytomegalovirus immediate early enhancer, were stimulated with anti-TNFR p75 polyclonal antiserum or monoclonal antibodies followed by measurement of beta-galactosidase activity and analysis by electrophoretic mobility shift assays. It was found that cross-linking of TNFR p75 led to strong induction of the human cytomegalovirus enhancer as well as activation of nuclear factor-kappa B (NF-kappa B). Stimulation of TNFR p75 also mediated activation of NF-kappa B in human KYM-1 rhabdomyosarcoma cells but not in other cell types such as U937 and HL-60 monocytic cells or in Eahy 926 endothelial cells. NF-kappa B activation induced by TNFR p75 was delayed approximately 15 min compared with NF-kappa B activation induced by TNFR p55, indicating that the two TNFRs activate NF-kappa B through different signaling pathways. The data presented in this study identify intracellular responses mediated by TNFR p75 which have not been reported previously and suggest that TNFR p75-induced activation of NF-kappa B is strictly cell type-specific.

Base Sequence↗
PubMed1993

Lipid peroxidation affects catalytic properties of rat liver mitochondrial monoamine oxidases and their sensitivity to proteolysis.

1. Lipid peroxidation (LPO) in rat liver mitochondria decreased the activity of monoamine oxidase (MAO) with physiological substrates serotonin and 2-phenylethylamine (by 15-30%) and induced deamination of glucosamine, which was highly sensitive to selective MAO A inhibitor pirlindole. 2. The LPO-induced changes in catalytic properties of MAOs are accompanied by their increased susceptibility to trypsinolysis, however sensitivity to inhibition by imipramine, chlorpromazine and spermine are insignificantly changed. 3. It is suggested that these results reflect LPO-induced conformational changes of enzyme molecules in membrane rather than their membrane topography.

Animals↗
PubMedDate not supplied

Analysis of a new PM motor design for a rotary dynamic blood Pump.

The permanent magnet (PM) motor for a rotary dynamic blood pump requires high power density to coordinate the motor size with the limited pump space and high efficiency to reduce the size and weight of the associated batteries. The motor also serves as a passive axial magnetic thrust bearing, a reacting hydraulic force, and provides a stabilizing force for the radial journal bearing. This article presents analysis of a new PM motor for the blood pump application. High power density is achieved by using the Halbach magnetic array, and high efficiency is accomplished by optimizing the rotor magnet assembly and the stator slots/windings. While both radial and axial forces are greatly enhanced, pulsating components of the torque and force are also significantly reduced.

Biomechanical Phenomena↗
PubMedDate not supplied

Design of a DSP controller for an innovative ventricular assist system.

The design and development of the digital signal processor controller for an innovative ventricular assist system is presented. A DSP56005 is used as the central processor, with other peripheral components. System hardware and software were developed through the advanced development system, and stand alone operation of the system was also accomplished. Two different control modes--current control mode and speed control mode--were developed and investigated. Performance of efficiency and dynamic response were examined through experimental testing.

Biomedical Engineering↗