Chlorophyll fluorescence quenching in the alga Euglena gracilis

When far red light preincubated cells of Euglena gracilis are transferred to dark or light, chlorophyll fluorescence (F₀ and F_m) decreases. Non-photochemical quenching in the dark is suggested to be induced partly by chlororespiration and partly by changes in the distribution of excitation energy between the photosystems. Depending on the light intensities it was possible to resolve the non-photochemical quenching into at least three different components. The slowest relaxation phase of non-photochemical quenching occurred only after exposure to high light and was assigned to photoinhibition. The other two components were an energy-dependent quenching (qE), and the one which we attribute to a spill over mechanism. We suggest that both photosystems use a common antenna system consisting of LHC I and LHC II proteins. In contrast to higher plants, qE in Euglena gracilis is independent of the xanthophyll cycle and an aggregation of LHC II. This revised version was published online in June 2006 with corrections to the Cover Date.     

A secreted BMP antagonist, Cer1, fine tunes the spatial organization of the ureteric bud tree during mouse kidney development

The epithelial ureteric bud is critical for mammalian kidney development as it generates the ureter and the collecting duct system that induces nephrogenesis in dicrete locations in the kidney mesenchyme during its emergence. We show that a secreted Bmp antagonist Cerberus homologue (Cer1) fine tunes the organization of the ureteric tree during organogenesis in the mouse embryo. Both enhanced ureteric expression of Cer1 and Cer1 knock out enlarge kidney size, and these changes are associated with an altered three-dimensional structure of the ureteric tree as revealed by optical projection tomography. Enhanced Cer1 expression changes the ureteric bud branching programme so that more trifid and lateral branches rather than bifid ones develop, as seen in time-lapse organ culture. These changes may be the reasons for the modified spatial arrangement of the ureteric tree in the kidneys of Cer1+ embryos. Cer1 gain of function is associated with moderately elevated expression of Gdnf and Wnt11, which is also induced in the case of Cer1 deficiency, where Bmp4 expression is reduced, indicating the dependence of Bmp expression on Cer1. Cer1 binds at least Bmp2/4 and antagonizes Bmp signalling in cell culture. In line with this, supplementation of Bmp4 restored the ureteric bud tip number, which was reduced by Cer1+ to bring it closer to the normal, consistent with models suggesting that Bmp signalling inhibits ureteric bud development. Genetic reduction of Wnt11 inhibited the Cer1-stimulated kidney development, but Cer1 did not influence Wnt11 signalling in cell culture, although it did inhibit the Wnt3a-induced canonical Top Flash reporter to some extent. We conclude that Cer1 fine tunes the spatial organization of the ureteric tree by coordinating the activities of the growth-promoting ureteric bud signals Gndf and Wnt11 via Bmp-mediated antagonism and to some degree via the canonical Wnt signalling involved in branching.     

Binding of oxindole-Schiff base copper(II) complexes to DNA and its modulation by the ligand

Previous studies on copper(II) complexes with oxindole-Schiff base ligands have shown their potential antitumor activity towards different cells, inducing apoptosis through a preferential attack to DNA and/or mitochondria. Herein, we better characterize the interactions between some of these copper(II) complexes and DNA. Investigations on its binding ability to DNA were carried out by fluorescence measurements in competitive experiments with ethidium bromide, using plasmidial or calf-thymus DNA. These results indicated an efficient binding process similar to that observed with copper(II)-phenanthroline species, [Cu(o-phen)₂]²⁺, with binding constants in the range 3 to 9 × 10² M^− 1. DNA cleavage experiments in the presence and absence of distamycin, a recognized binder of DNA, indicated that this binding probably occurs at major or minor groove, leading to double-strand DNA cleavage, and being modulated by the imine ligand. Corroborating these data, discrete changes in EPR spectra of the studied complexes were observed in the presence of DNA, while more remarkable changes were observed in the presence of nucleotides (AMP, GMP, CMP or UMP). Additional evidence for preferential coordination of the copper centers to the bases guanine or cytosine was obtained from titrations of these complexes with each nucleotide, monitored by absorption spectral changes. Therefore, the obtained data point out to their action as groove binders to DNA bases, rather than as intercalators or covalent cross-linkers. Further investigations by SDS PAGE using ³²P-ATP or ³²P-oligonucleotides attested that no hydrolysis of phosphate linkage in DNA or RNA occurs, in the presence of such complexes, confirming their main oxidative mechanism of action.     

Report from the second cytomegalovirus and immunosenescence workshop

The Second International Workshop on CMV & Immunosenescence was held in Cambridge, UK, 2-4th December, 2010. The presentations covered four separate sessions: cytomegalovirus and T cell phenotypes; T cell memory frequency, inflation and immunosenescence; cytomegalovirus in aging, mortality and disease states; and the immunobiology of cytomegalovirus-specific T cells and effects of the virus on vaccination. This commentary summarizes the major findings of these presentations and references subsequently published work from the presenter laboratory where appropriate and draws together major themes that were subsequently discussed along with new areas of interest that were highlighted by this discussion.     

Interleukin-6 enhances insulin secretion by increasing glucagon-like peptide-1 secretion from L cells and alpha cells

Exercise, obesity and type 2 diabetes are associated with elevated plasma concentrations of interleukin-6 (IL-6). Glucagon-like peptide-1 (GLP-1) is a hormone that induces insulin secretion. Here we show that administration of IL-6 or elevated IL-6 concentrations in response to exercise stimulate GLP-1 secretion from intestinal L cells and pancreatic alpha cells, improving insulin secretion and glycemia. IL-6 increased GLP-1 production from alpha cells through increased proglucagon (which is encoded by GCG) and prohormone convertase 1/3 expression. In models of type 2 diabetes, the beneficial effects of IL-6 were maintained, and IL-6 neutralization resulted in further elevation of glycemia and reduced pancreatic GLP-1. Hence, IL-6 mediates crosstalk between insulin-sensitive tissues, intestinal L cells and pancreatic islets to adapt to changes in insulin demand. This previously unidentified endocrine loop implicates IL-6 in the regulation of insulin secretion and suggests that drugs modulating this loop may be useful in type 2 diabetes.     

Prevalence of hepatitis B and C virus infection among leprosy patients in a leprosy-endemic region of central Brazil

Leprosy and hepatitis B virus (HBV) are highly endemic in some regions of the state of Mato Grosso, in central Brazil. The association of leprosy with HBV and hepatitis C virus (HCV) was assessed using a seroprevalence study and 191 leprosy outpatients were included. Demographic data and the clinical classification of leprosy were recorded. Evidence of previous HBV infection was present in 53 patients (27.7%, 95% confidence interval: 21.9-34.5) and two (1%) were HBsAg positive. Five (2.6%) had antibodies to HCV. The prevalence of previous exposure to HBV was higher than expected for an adult population in central Brazil. In contrast, the prevalence of anti-HCV antibodies was not much higher regarding the age range of participants. HBV markers were associated with a higher number of sex partners and the use of injections without proper sterilisation of the syringes. The number of HBV carriers was small, suggesting that there was no increased likelihood of chronification among these patients.