Consequences of long-term selenium-deficient diet on the prostacyclin and thromboxane release from rat aorta

It is known that peroxides, which are increased during Se deficiency because of reduced glutathione peroxidase (GSH-Px) activity, can influence the prostacyclin I₂/thromboxane A₂ (PGI₂/TXA₂) ratio. In this study we analyzed the PGI₂ and TXA₂ formation of aortas of long-term Se-deficient rats. Despite low GSH-Px activity in the Se-deficient group, the basal PGI₂ and TXA₂ formation was not different versus control animals (PGI₂: 2295 ± 1134 pg/mg vs 2940 ± 1134 pg/mg; TXA₂: 3.83 ± 1.06 pg/mg vs 5.67 ± 2.99 pg/mg). However, we checked the capacity of the aortas of Se-deficient rats to compensate for a suddenly increased peroxide concentration. After peroxide stimulation, the PGI₂ release was significantly lower in the Se-deficient group compared to the control group (PGI₂: 3507 ± 1829 pg/mg vs 7986 ± 2636 pg/mg). Again, the TXA₂ release did not show any differences. The release ratio of PGI₂/TXA₂ decreased under peroxide stress in Se-deficient animals. Although long-term Se deficiency showed a relatively well-balanced metabolism under resting conditions, sudden stress, accompanied by an excessive radical production, cannot be compensated.     

NS-417, a Novel Compound with Neurotrophic-Like Effects

NS-417 (5-(4-Chlorophenyl)-8-methyl-6-7-8-9-tetrahydro-1-H-pyrrolo[3.2-h]isoquinoline-2,3-dione-3-oxim hydrochloric acid salt) belongs to a new chemical series of compounds. NS-417 rescued differentiated PC12 cells from death induced by withdrawal of serum and nerve growth factor. Furthermore, NS-417 stimulated neurotrophic factor-induced neurite outgrowth in undifferentiated PC12 cells. In accordance with this observation, NS-417 potentiated NGF-induced signaling, such as activation of the extracellular signal-regulated kinases ERK1 and ERK2 and the Akt kinase. NS-417 also enhanced ERK activation induced by 10 minutes stimulation with NGF, bFGF or EGF in PC12 cells. In addition to the effect in PC12 cells, NS-417 increased the number of tyrosine hydroxylase (TH) positive cells in cultures established from dissociated E14 rat ventral mesencephali.     

Robust circadian rhythmicity of Per1 and Per2 mutant mice in constant light,and dynamics of Per1 and Per2 gene expression under long and short photoperiods

The Per1 and Per2 genes are components of the mammalian circadian clock. Mutations in these genes alter phase resetting in response to a nocturnal light pulse, and Per2 mutant mice are known to become arrhythmic in constant darkness. We show that under constant light conditions, Per2 mutant mice exhibit robust activity rhythms as well as body temperature rhythms with a period length that is less than 24 h. In Per1 mutants, the period length of both activity and body temperature rhythms is longer than 24 h in constant light. Per1 mutants prolong their period length (tao) when illuminance is increased, whereas Per2 mutants shorten their endogenous period. Additionally, the authors show that the circadian pattern of Per1 and Per2 gene expression in mice is modified under different photoperiods and that there is a mutual influence of these genes on their timing of expression. We propose that, in mice, the phase relationship between Per1 and Per2 gene expression might be critical for transducing day length information to the organism. Per1 could be part of a morning oscillator tracking dawn, and Per2 could be part of an evening oscillator tracking dusk.     

FtsH is involved in the early stages of repair of photosystem II in Synechocystis sp PCC 6803

When plants, algae, and cyanobacteria are exposed to excessive light, especially in combination with other environmental stress conditions such as extreme temperatures, their photosynthetic performance declines. A major cause of this photoinhibition is the light-induced irreversible photodamage to the photosystem II (PSII) complex responsible for photosynthetic oxygen evolution. A repair cycle operates to selectively replace a damaged D1 subunit within PSII with a newly synthesized copy followed by the light-driven reactivation of the complex. Net loss of PSII activity occurs (photoinhibition) when the rate of damage exceeds the rate of repair. The identities of the chaperones and proteases involved in the replacement of D1 in vivo remain uncertain. Here, we show that one of the four members of the FtsH family of proteases (cyanobase designation slr0228) found in the cyanobacterium Synechocystis sp PCC 6803 is important for the repair of PSII and is vital for preventing chronic photoinhibition. Therefore, the ftsH gene family is not functionally redundant with respect to the repair of PSII in this organism. Our data also indicate that FtsH binds directly to PSII, is involved in the early steps of D1 degradation, and is not restricted to the removal of D1 fragments. These results, together with the recent analysis of ftsH mutants of Arabidopsis, highlight the critical role played by FtsH proteases in the removal of damaged D1 from the membrane and the maintenance of PSII activity in vivo.     

Dysfunctional MreB inhibits chromosome segregation in Escherichia coli

The mechanism of prokaryotic chromosome segregation is not known. MreB, an actin homolog, is a shape-determining factor in rod-shaped prokaryotic cells. Using immunofluorescence microscopy we found that MreB of Escherichia coli formed helical filaments located beneath the cell surface. Flow cytometric and cytological analyses indicated that MreB-depleted cells segregated their chromosomes in pairs, consistent with chromosome cohesion. Overexpression of wild-type MreB inhibited cell division but did not perturb chromosome segregation. Overexpression of mutant forms of MreB inhibited cell division, caused abnormal MreB filament morphology and induced severe localization defects of the nucleoid and of the oriC and terC chromosomal regions. The chromosomal terminus regions appeared cohered in both MreB-depleted cells and in cells overexpressing mutant forms of MreB. Our observations indicate that MreB filaments participate in directional chromosome movement and segregation.     

Polyamine transport and role of potE in response to osmotic stress in Escherichia coli

When transport of polyamines in Escherichia coli was examined, putrescine excretion was observed under two different physiological conditions: (i) strictly correlated to growth and (ii) following a hyperosmotic shock. Spermidine was not excreted. Characterization of a deletion mutant showed that PotE is not involved in these transport processes.     

Three-dimensional structure of Chlamydomonas reinhardtii and Synechococcus elongatus photosystem II complexes allows for comparison of their oxygen-evolving complex organization

Electron microscopy and single-particle analyses have been carried out on negatively stained photosystem II (PSII) complexes isolated from the green alga Chlamydomonas reinhardtii and the thermophilic cyanobacterium Synechococcus elongatus. The analyses have yielded three-dimensional structures at 30-A resolution. Biochemical analysis of the C. reinhardtii particle suggested it to be very similar to the light-harvesting complex II (LHCII).PSII supercomplex of spinach, a conclusion borne out by its three-dimensional structure. Not only was the C. reinhardtii LHCII.PSII supercomplex dimeric and of comparable size and shape to that of spinach, but the structural features for the extrinsic OEC subunits bound to the lumenal surface were also similar thus allowing identification of the PsbO, PsbP, and PsbQ OEC proteins. The particle isolated from S. elongatus was also dimeric and retained its OEC proteins, PsbO, PsbU, and PsbV (cytochrome c(550)), which were again visualized as protrusions on the lumenal surface of the complex. The overall size and shape of the cyanobacterial particle was similar to that of a PSII dimeric core complex isolated from spinach for which higher resolution structural data are known from electron crystallography. By building the higher resolution structural model into the projection maps it has been possible to relate the positioning of the OEC proteins of C. reinhardtii and S. elongatus with the underlying transmembrane helices of other major intrinsic subunits of the core complex, D1, D2, CP47, and CP43 proteins. It is concluded that the PsbO protein is located over the CP47 and D2 side of the reaction center core complex, whereas the PsbP/PsbQ and PsbV/PsbU are positioned over the lumenal surface of the N-terminal region of the D1 protein. However, the mass attributed to PsbV/PsbU seems to bridge across to the PsbO, whereas the PsbP/PsbQ proteins protrude out more from the lumenal surface. Nevertheless, within the resolution and quality of the data, the relative positions of the center of masses for OEC proteins of C. reinhardtii and S. elongatus are similar and consistent with those determined previously for the OEC proteins of spinach.     

Dopamine-induced translocation of protein kinase C isoforms visualized in renal epithelial cells

Short-term regulation of sodiummetabolism is dependent on the modulation of the activity of sodiumtransporters by first and second messengers. In understanding diseasesassociated with sodium retention, it is necessary to identify thecoupling between these messengers. We have examined whether dopamine,an important first messenger in tubular cells, activates andtranslocates various protein kinase C (PKC) isoforms. We used aproximal tubular-like cell line, LLCPK-1 cells, in which dopamine wasfound to inhibit Na⁺-K⁺-ATPase in aPKC-dependent manner. Translocation of PKC isoforms was studied withboth subcellular fractionation and confocal microscopy. Both techniquesrevealed a dopamine-induced translocation from cytosol to plasmamembrane of PKC- and -, but not of PKC-, -, and -. Theprocess of subcellular fractionation resulted in partial translocationof PKC-. This artifact was eliminated in confocal studies. Confocalimaging permitted detection of translocation within 20 s.Translocation was abolished by a phospholipase C inhibitor and by anantagonist against the dopamine 1 subtype (D₁) but not the2 subtype of receptor (D₂). In conclusion, this studyvisualizes in renal epithelial cells a very rapid activation of thePKC- and - isoforms by the D₁ receptor subtype.