Division-site selection, cell separation, and formation of anucleate minicells inSchizosaccharomyces pombe mutants resistant to cell-wall lytic enzymes

Summary In most eukaryotic organisms that have cell walls, cell separation or cytokinesis is a degradative enzymatic process. In the fission yeastSchizosaccharomyces pombe, it is a post-M-phase event that includes the degradation of part of the cell wall and the primary septum. We describe the isolation of mutants partially defective in cytokinesis by enrichment of clones resistant to cell-wall lytic enzymes. The mutations confer mycelial morphology (chains of non-separated cells) and define four genes.Sep2-SA2 was subjected to detailed genetic and cytological analysis. Its cells frequently form complex septa composed of multiple layers, which appear as twin septa separated by anucleate minicells if the cell length is extended. This suggests that a polar signal-like mechanism may also operate inS. pombe during division-site selection andsep2 ⁺ takes part in it.Sep2 ⁺ seems to be involved in several cell cycle functions because its mutation can transiently block cell-cycle progression after nuclear division and provoke a transition from haploidy to diploidy in the double mutantsep2-SA2 cexl-SA2. Cexl-SA2 is another novel mutation which causes cell-length extension.Abbreviations DAPI 4,6-diamidino-2-phenylindole - YEA yeast extract agar - YEL yeast extract liquid - SMA synthetic minimal agar - MEA malt extract agar     

Ryanodine-sensitive,thapsigargin-insensitive calcium uptake in rat ventricle homogenates

Thapsigargin is a natural product that specifically inhibits all known SERCA calcium pumps with high affinity. We investigated the effects of thapsigargin on cardiac sarcoplasmic reticulum (SR) by measuring the oxalate-supported calcium uptake rate in the unfractionated homogenate and in the isolated SR fraction. The uptake rate in both the isolated SR and unfractionated homogenate are stimulated about two-fold by preincubation with high concentrations of ryanodine, which closes the SR efflux channel. Thapsigargin stoichiometrically and completely inhibited the calcium uptake rate in the isolated SR, both in the presence and absence of SR channel blockade. In contrast, thapsigargin nearly completely inhibited the homogenate calcium uptake only in the absence of SR channel blockade; in the presence of blockade, about 20% of the uptake activity was insensitive to thapsigargin. This result unmasks a thapsigargin-insensitive, ryanodine-sensitive component of calcium uptake in the heart. This activity is in an oxalate-permeable pool and is inhibited by cyclopiazonic acid, another inhibitor of the SERCA calcium pumps. There was no TG-insensitive activity in the rat EDL muscle homogenate. The absence of thapsigargin-insensitive uptake activity in the isolated SR can be attributed to its inactivation during the isolation of the SR. The oxalate permeability and ryanodine sensitivity suggest that the TG-insensitive calcium uptake activity is closely related to the classical SR. The different thapsigargin sensitivities suggests the existence of two kinds of intracellular calcium pumps in the heart.     

Synthesis of the vasoactive intestinal peptide (VIP) : III. The sequence 7–13

The protected heptapeptide derivative t-butyloxycarbonyl- -threonyl-β-benzyl- -aspartyl- -asparaginyl-O-benzyl- -tyrosyl- -threonyl-nitro- -arginyl- - leucine methyl ester was prepared by stepwise chain lengthening. The protecting groups on the side chains of arginine, tyrosine, and aspartic acid residues were removed by hydrogenolysis and the partially deprotected heptapeptide ester converted to the hydrazide, an intermediate in the synthesis of the (porcine) vasoactive intestinal peptide (VIP).After the removal of the tert-butyloxycarbonyl group, the heptapeptide ester was exposed to the action of trypsin which split off its C-terminal residue, -leucine methyl ester. The hexapeptide was then exposed to chymotrypsin, which cleaved it into an acidic, and a basic fragment. The former was, under the conditions used, indistinguishable on paper chromatography and paper electrophoresis from the tetrapeptide threonyl-aspartyl-asparaginyl-tyrosine which had previously been isolated from natural VIP, of which it comprises the sequence 7–10. Similarly, the basic fragment was indistinguishable from threonyl-arginine, the sequence 11–12 of VIP. This intestinal peptide increases visceral blood flow and reduces blood pressure in the dog, and also causes relaxation of different smooth muscle preparations, e.g., the trachea of guinea pigs. The principal aim of the present synthesis is to provide independent evidence for the sequence of (porcine) VIP.     

Observation of the protonated semiquinone intermediate in isolated reaction centers from Rhodobacter sphaeroides: implications for the mechanism of electron and proton transfer in proteins.

A proton-activated electron transfer (PAET) mechanism, involving a protonated semiquinone intermediate state, had been proposed for the electron-transfer reaction k(2)AB [Q(A)(-)(*)Q(B)(-)(*) + H(+) <--> Q(A)(-)(*)(Q(B)H)(*) --> Q(A)(Q(B)H)(-)] in reaction centers (RCs) from Rhodobacter sphaeroides [Graige, M. S., Paddock, M. L., Bruce, M. L., Feher, G., and Okamura, M. Y. (1996) J. Am. Chem. Soc. 118, 9005-9016]. Confirmation of this mechanism by observing the protonated semiquinone (Q(B)H)(*) had not been possible, presumably because of its low pK(a). By replacing the native Q(10) in the Q(B) site with rhodoquinone (RQ), which has a higher pK(a), we were able to observe the (Q(B)H)(*) state. The pH dependence of the semiquinone optical spectrum gave a pK(a) = 7.3 +/- 0.2. At pH < pK(a), the observed rate for the reaction was constant and attributed to the intrinsic electron-transfer rate from Q(A)(-)(*) to the protonated semiquinone (i.e., k(2)AB = k(ET)(RQ) = 2 x 10(4) s(-)(1)). The rate decreased at pH > pK(a) as predicted by the PAET mechanism in which fast reversible proton transfer precedes rate-limiting electron transfer. Consequently, near pH 7, the proton-transfer rate k(H) > 10(4) s(-)(1). Applying the two step mechanism to RCs containing native Q(10) and taking into account the change in redox potential, we find reasonable values for the fraction of (Q(B)H)(*) congruent with 0.1% (consistent with a pK(a)(Q(10)) of approximately 4.5) and k(ET)(Q(10)) congruent with 10(6) s(-)(1). These results confirm the PAET mechanism in RCs with RQ and give strong support that this mechanism is active in RCs with Q(10) as well.     

Adaptive Changes in Postsynaptic Dopamine Receptors Despite Unaltered Dopamine Dynamics in Mice Lacking Monoamine Oxidase B

Monoamine oxidase (MAO) B is considered a key enzyme in dopamine metabolism. The present studies, conducted in MAO B knockout mice, show that lack of MAO B does not alter extracellular levels of dopamine in striatum. Similarly, the synthesis, storage, uptake, and release of dopamine are also unaltered. However, autoradiography revealed a significant up-regulation of the D2-like dopamine receptors in the striatum of MAO B knockout mice. Mutant mice also exhibit a functional supersensitivity of D1-dopamine receptors in the nucleus accumbens. Thus, the agonist SKF 38,393-induced c-Fos immunoreactivity was significantly increased in knockout mice as compared with wild-type controls. In view of the apparently normal basal dopamine dynamics observed in MAO B knockout mice, we hypothesize that a dopamine-independent mechanism underlies adaptations in dopamine receptor function that occur as a consequence of MAO B depletion. Finally, these findings suggest that chronic administration of MAO inhibitors, as occurs in the treatment of Parkinson's disease and depression, may be associated with an increased responsiveness of CNS neurons to dopamine receptor ligands.     

Detection of the Bcl I polymorphism of the glucocorticoid receptor gene by single-tube allele-specific polymerase chain reaction

The Bcl I polymorphism of the glucocorticoid receptor gene, recently identified as an intronic C to G change 646 nucleotides downstream of exon 2, has been associated with increased sensitivity to glucocorticoids and its potential relevance in metabolic disturbances and in various disorders has been extensively investigated. In the present study, we designed a single-tube allele-specific polymerase chain reaction for genotyping this polymorphism in peripheral blood DNA samples. When the Bcl I polymorphism was detected with this novel method in a cohort of 247 healthy subjects, the observed genotype distribution matched the Hardy–Weinberg equilibrium (100 subjects homozygous for the wild-type, 124 heterozygous and 23 homozygous for the mutant allele). In 50 randomly selected subjects the Bcl I polymorphism was also determined using a traditional restriction fragment length polymorphism technique and DNA sequencing, and the results showed 100% coincidence with those obtained by our novel method. The method proved to be more rapid and less labour-intensive compared to currently used techniques, and it avoided the use of extensive instrumentals. We assume that this novel method may have a broad utility in clinical and molecular epidemiological studies aimed to elucidate the impact of the Bcl I polymorphism of the glucocorticoid receptor gene either on metabolic disturbances, or various disorders, including cancer treatment and hormone substitution therapies.     

Presence of Anti-Microbial Antibodies in Liver Cirrhosis – A Tell-Tale Sign of Compromised Immunity?

Background

Bacterial translocation plays important role in the complications of liver cirrhosis. Antibody formation against various microbial antigens is common in Crohn''s disease and considered to be caused by sustained exposure to gut microflora constituents. We hypothesized that anti-microbial antibodies are present in patients with liver cirrhosis and may be associated with the development of bacterial infections.

Methodology/Principal Findings

Sera of 676 patients with various chronic liver diseases (autoimmune diseases:266, viral hepatitis C:124, and liver cirrhosis of different etiology:286) and 100 controls were assayed for antibodies to Saccharomyces cerevisiae(ASCA) and to antigens derived from two intestinal bacterial isolates (one gram positive, one gram negative, neither is Escherichia coli). In patients with liver cirrhosis, we also prospectively recorded the development of severe episodes of bacterial infection. ASCA and anti-OMP Plus™ antibodies were present in 38.5% and 62.6% of patients with cirrhosis and in 16% and 20% of controls, respectively (p<0.001). Occurrence of these antibodies was more frequent in cases of advanced cirrhosis (according to Child-Pugh and MELD score; p<0.001) or in the presence of ascites (p<0.001). During the median follow-up of 425 days, 81 patients (28.3%) presented with severe bacterial infections. Anti-microbial antibody titers (p = 0.003), as well as multiple seroreactivity (p = 0.036), was associated with infectious events. In logistic regression analysis, the presence of ascites (OR:1.62, 95%CI:1.16–2.25), co-morbidities (OR:2.22, 95%CI:1.27–3.86), and ASCA positivity (OR:1.59, 95%CI:1.07–2.36) were independent risk factors for severe infections. A shorter time period until the first infection was associated with the presence of ASCA (p = 0.03) and multiple seropositivity (p = 0.037) by Kaplan-Meier analysis, and with Child-Pugh stage (p = 0.018, OR:1.85) and co-morbidities (p<0.001, OR:2.02) by Cox-regression analysis.

Conclusions/Significance

The present study suggests that systemic reactivity to microbial components reflects compromised mucosal immunity in patients with liver cirrhosis, further supporting the possible role of bacterial translocation in the formation of anti-microbial antibodies.