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Spontaneous Activation (spontaneous + activation)
Selected AbstractsDominance of the lurcher mutation in heteromeric kainate and AMPA receptor channelsEUROPEAN JOURNAL OF NEUROSCIENCE, Issue 5 2001Martin K. Schwarz Abstract Homomeric glutamate receptor (GluR) channels become spontaneously active when the last alanine residue within the invariant SYTANLAAF-motif in the third membrane segment is substituted by threonine. The same mutation in the orphan GluR,2 channel is responsible for neurodegeneration in ,Lurcher' (Lc) mice. Since most native GluRs are composed of different subunits, we investigated the effect of an Lc-mutated subunit in heteromeric kainate and AMPA receptors expressed in HEK293 cells. Kainate receptor KA2 subunits, either wild type or carrying the Lc mutation (KA2Lc), are retained inside the cell but are surface-expressed when assembled with GluR6 sununits. Importantly, KA2Lc dominates the gating of KA2Lc/GluR6WT channels, as revealed by spontaneous activation and by slowed desensitization and deactivation kinetics of ligand-activated whole-cell currents. Moreover, the AMPA receptor subunit GluR-BLc(Q) which forms spontaneously active homomeric channels with rectifying current-voltage relationships, dominates the gating of heteromeric GluR-BLc(Q)/GluR-A(R) channels. The spontaneous currents of these heteromeric AMPAR channels show linear current,voltage relationships, and the ligand-activated whole-cell currents display slower deactivation and desensitization kinetics than the respective wild-type channels. For heteromeric Lc-mutated kainate and AMPA receptors, the effects on kinetics were reduced relative to the homomeric Lc-mutated forms. Thus, an Lc-mutated subunit can potentially influence heteromeric channel function in vivo, and the severity of the phenotype will critically depend on the levels of homomeric GluRLc and heteromeric GluRLc/GluRWT channels. [source] Declining expression of a single epithelial cell-autonomous gene accelerates age-related thymic involutionAGING CELL, Issue 3 2010Liguang Sun Summary Age-related thymic involution may be triggered by gene expression changes in lymphohematopoietic and/or nonhematopoietic thymic epithelial cells (TECs). The role of epithelial cell-autonomous gene FoxN1 may be involved in the process, but it is still a puzzle because of the shortage of evidence from gradual loss-of-function and exogenous gain-of-function studies. Using our recently generated loxP -floxed- FoxN1(fx) mouse carrying the ubiquitous CreERT (uCreERT) transgene with a low dose of spontaneous activation, which causes gradual FoxN1 deletion with age, we found that the uCreERT -fx/fx mice showed an accelerated age-related thymic involution owing to progressive loss of FoxN1+ TECs. The thymic aging phenotypes were clearly observable as early as at 3,6 months of age, resembling the naturally aged (18,22-month-old) murine thymus. By intrathymically supplying aged wild-type mice with exogenous FoxN1-cDNA, thymic involution and defective peripheral CD4+ T-cell function could be partially rescued. The results support the notion that decline of a single epithelial cell-autonomous gene FoxN1 levels with age causes primary deterioration in TECs followed by impairment of the total postnatal thymic microenvironment, and potentially triggers age-related thymic involution in mice. [source] Effects of delayed excision of oviducts/ovaries on mouse oocytes and embryosMOLECULAR REPRODUCTION & DEVELOPMENT, Issue 4 2007De-Qiang Miao Abstract To achieve the best and reproducible results of experiments, effects of delayed excision of oviducts/ovaries on mouse ovarian/ovulated oocytes and embryos have been studied. Oviducts/ovaries were excised at different times after death of mice and effects of the postmortem interval on ovarian/ovulated oocytes and embryos were analyzed. When oviduct excision was delayed 10 min, many ovulated oocytes lysed or underwent in vitro spontaneous activation, and this postmortem effect aggravated with the extension of postmortem interval and oocyte aging. Oocytes from different mouse strains responded differently to delayed oviduct removal. Delayed oviduct excision did not cause lysis of zygotes or embryos but compromised their developmental potential. When ovaries were excised at 30 min after death, percentages of atretic follicles increased while blastocyst cell number declined significantly after oocyte maturation in vitro. Preservation of oviducts in vitro, in intact or opened abdomen at different temperatures and histological analysis of oviducts from different treatments suggested that toxic substance(s) were secreted from the dying oviducts which induced oocyte lysis and spontaneous activation and both this effect itself and the sensitivity of oocytes to this effect was temperature dependent. It is concluded that a short delay of oviduct/ovary removal had marked detrimental effects on oocytes and embryos. This must be taken into account in experiments using oocytes or embryos from slaughtered animals. The data may also be important for estimation of the time of death in forensic medicine and for rescue of oocytes from deceased valuable or endangered mammals. Mol. Reprod. Dev. 74: 468,477, 2007. © 2006 Wiley-Liss, Inc. [source] Hypoxanthine (HX) inhibition of in vitro meiotic resumption in goat oocytesMOLECULAR REPRODUCTION & DEVELOPMENT, Issue 3 2003Suofeng Ma Abstract To improve in vitro maturation and to understand the mechanism for meiotic resumption of oocytes, meiotic progression, and its control by hypoxanthine (HX) were studied in goat oocytes. Ovaries were obtained from a local abattoir, and cumulus,oocyte complexes (COCs) and follicular fluid were collected from follicles of different surface diameters (SDs). The meiotic competence and progression of oocytes were observed, and the concentration of HX in the follicular fluid and culture media was measured by high-performance liquid chromatography (HPLC). Full meiotic competence of goat oocytes was acquired in follicles of ,1.5 mm in SD with 90% of the oocytes developing to metaphase II (MII) stage after 24 hr in culture. The HX concentration in follicular fluid decreased with follicle development, from the highest level of 1.16 mM in ,0.5 mm follicles to the lowest level of 0.45 mM in ,5 mm follicles. HX inhibited meiotic resumption of goat oocytes in a concentration-related manner but this inhibitory effect declined gradually. When we renewed the medium at 4 hr of HX-199 (TCM-199 supplemented with 4 mM HX) culture, the percentage of oocytes with intact germinal vesicle (GV) did not increase but decreased significantly instead. HPLC measurement of HX in the HX-199 culture drops indicated that the HX concentration declined from 0 hr to 4 hr of culture and after medium renewal at 4 hr of culture. By adding dibutyryl cAMP (db-cAMP) at medium renewal, we found that db-cAMP held up the decline of GV percentages. Together, these results were consistent with the possibility that the decline of HX inhibitory effect was not due to HX depletion but rather due to the negative feedback of the metabolites on its further uptake by oocytes. Goat oocytes were capable of normal nuclear maturation and activation after temporal arrest by HX, but prolonged exposure to HX induced spontaneous activation. Mol. Reprod. Dev. 66: 306,313, 2003. © 2003 Wiley-Liss, Inc. [source] Measuring Associative Strength: Category-Item Associations and Their Activation from MemoryPOLITICAL PSYCHOLOGY, Issue 1 2000Russell H. Fazio Three measures of the strength of association between a category and members of the category were investigated: (a) a naming measure, in which the participants (93 undergraduates) were asked to list the members of a category and the listing order was assumed to reflect associative strength; (b) a latency measure, which assessed the latency to correctly identify specific items as members or nonmembers of a given category; and (c) a facilitation measure, in which the spontaneous activation of an item upon presentation of a category label as a prime was assessed by considering the extent to which the prime facilitated recognition of an initially degraded (visually obscured) item. The three measures correlated substantially, thus validating the naming and latency measures as reasonable approximations of the likelihood that a given item will receive activation in memory when the category is presented. Many of the constructs of interest to survey researchers can be viewed similarly as associations in memory, and the naming and latency measures can be fruitfully used in surveys; research attesting to the utility of namingand latency data is reviewed. [source] Mechanism of cell death and disease resistance induction by transgenic expression of bacterio-opsinTHE PLANT JOURNAL, Issue 5 2002Dominique Pontier Summary One of the earliest signal transduction events that trigger the hypersensitive response (HR) of plants against pathogen attack is thought to be an alteration of proton flux across the plasma membrane (PM). However, no direct genetic evidence for the involvement of PM-localised proton channels or pumps in the induction of this response has been reported. We previously showed that expression of the bacterial proton pump bacterio-opsin (bO) in transgenic plants resulted in the spontaneous activation of the HR. Here we show that the bO protein is likely localised to the PM in transgenic tobacco plants. Furthermore, mutational analysis shows that induction of the HR by bO expression is dependent upon the capability of bO to translocate protons. Although bO functions as a light-driven proton pump in Halobacteria when assembled with retinal, we also show by mutational analysis that this chromophore binding is unnecessary for its in planta activity. Taken together, our results suggest that expression of bO in plants leads to the insertion of a passive proton channel into the PM. The activity of this channel in the PM results in spontaneous activation of cell death and HR-associated phenotypes including enhanced resistance to a broad spectrum of plant pathogens. Our work provides direct molecular evidence to support a working model in which alterations in ionic homeostasis at the level of the PM may work as one of the critical steps in the signalling pathway for the activation of the HR. [source] Calcineurin deficiency decreases inflammatory lesions in transforming growth factor ,1-deficient miceCLINICAL & EXPERIMENTAL IMMUNOLOGY, Issue 3 2009R. Bommireddy Summary Transforming growth factor (TGF) ,1) is an immunoregulatory cytokine involved in self-tolerance and lymphocyte homeostasis. Tgfb1 knock-out (KO) mice develop severe multi-focal autoimmune inflammatory lesions due to [Ca2+]i deregulation in T cells, and die within 3 weeks after birth. Because the calcineurin inhibitor FK506 inhibits the hyperresponsiveness of Tgfb1,/, thymocytes, and because calcineurin A, (CNA,)-deficient mice do not reject allogenic tumours, we have generated Tgfb1,/,Cnab,/, mice to address whether CNA, deficiency prevents T cell activation and inflammation in Tgfb1,/, mice. Here we show that in Tgfb1,/,Cnab,/, mice inflammation is reduced significantly relative to that in Tgfb1,/, mice. However, both CD4+ and CD8+ T cells in double knock-out (DKO) mice are activated, as revealed by up-regulation of CD11a lymphocyte function-associated antigen-1 (LFA-1), CD44 and CD69 and down-regulation of CD62L. These data suggest that deficiency of CNA, decreases inflammatory lesions but does not prevent activation of autoreactive T cells. Also Tgfb1,/, T cells can undergo activation in the absence of CNA,, probably by using the other isoform of calcineurin (CNA,) in a compensatory manner. CNA,-deficient T cells undergo spontaneous activation in vivo and are activated upon anti-T cell receptor stimulation in vitro. Understanding the role of calcineurin in T cell regulation should open up new therapeutic opportunities for inflammation and cancer. [source] | ||||||||||