University of Bremen

About: University of Bremen is a education organization based out in Bremen, Germany. It is known for research contribution in the topics: Population & Glacial period. The organization has 14563 authors who have published 37279 publications receiving 970381 citations. The organization is also known as: Universität Bremen.

Induction and repair inhibition of oxidative DNA damage by nickel(II) and cadmium(II) in mammalian cells

Abstract: Compounds of nickel(II) and cadmium(II) are carcinogenic to humans and to experimental animals. One frequently discussed mechanism involved in tumor formation is an increase in reactive oxygen species by both metals with the subsequent generation of oxidative DNA damage. In the present study we used human HeLa cells to investigate the potential of nickel(II) and cadmium(II) to induce DNA lesions typical for oxygen free radicals in intact cells and the effect on their repair. As indicators of oxidative DNA damage, we determined the frequencies of DNA strand breaks and of lesions recognized by the bacterial formamidopyrimidine-DNA glycosylase (Fpg protein), including 7,8-dihydro-8-oxoguanine (8-hydroxyguanine), a pre-mutagenic DNA base modification. Nickel(II) caused a slight increase in DNA strand breaks at 250 microM and higher, while the frequency of Fpg-sensitive sites was enhanced only at the cytotoxic concentration of 750 microM. The repair of oxidative DNA lesions induced by visible light was reduced at 50 microM and at 100 microM nickel(II) for Fpg-sensitive sites and DNA strand breaks, respectively; the removal of both types of lesions was blocked nearly completely at 250 microM nickel(II). In the case of cadmium(II), DNA strand breaks occurred at 10 microM and no Fpg-sensitive sites were detected. However, the repair of Fpg-sensitive DNA lesions induced by visible light was reduced at 0.5 microM cadmium(II) and higher, while the closure of DNA strand breaks was not affected. Since oxidative DNA damage is continuously induced during aerobic metabolism, an impaired repair of these lesions might well explain the carcinogenic action of nickel(II) and cadmium(II).

Decreased TCF7L2 protein levels in type 2 diabetes mellitus correlate with downregulation of GIP- and GLP-1 receptors and impaired beta-cell function

Abstract: Recent human genetics studies have revealed that common variants of the TCF7L2 (T-cell factor 7-like 2, formerly known as TCF4) gene are strongly associated with type 2 diabetes mellitus (T2DM). We have shown that TCF7L2 expression in the beta-cells is correlated with function and survival of the insulin-producing pancreatic beta-cell. In order to understand how variations in TCF7L2 influence diabetes progression, we investigated its mechanism of action in the beta-cell. We show robust differences in TCF7L2 expression between healthy controls and models of T2DM. While mRNA levels were approximately 2-fold increased in isolated islets from the diabetic db/db mouse, the Vancouver Diabetic Fatty (VDF) Zucker rat and the high fat/high sucrose diet-treated mouse compared with the non-diabetic controls, protein levels were decreased. A similar decrease was observed in pancreatic sections from patients with T2DM. In parallel, expression of the receptors for glucagon-like peptide 1 (GLP-1R) and glucose-dependent insulinotropic polypeptide (GIP-R) was decreased in islets from humans with T2DM as well as in isolated human islets treated with siRNA to TCF7L2 (siTCF7L2). Also, insulin secretion stimulated by glucose, GLP-1 and GIP, but not KCl or cyclic adenosine monophosphate (cAMP) was impaired in siTCF7L2-treated isolated human islets. Loss of TCF7L2 resulted in decreased GLP-1 and GIP-stimulated AKT phosphorylation, and AKT-mediated Foxo-1 phosphorylation and nuclear exclusion. Our findings suggest that beta-cell function and survival are regulated through an interplay between TCF7L2 and GLP-1R/GIP-R expression and signaling in T2DM.

Seasonal variability of particle flux in the Weddell Sea and its relation to ice cover

Abstract: In the Weddell Sea, primary production varies seasonally as a result of the solar cycle and the large-scale oscillation of the ice edge across much of its area. The annual ice transgression is the largest of any region on Earth1 and has a profound influence on the production and transportation of particulate matter. In order to clarify the flux, origin and mode of vertical transport of oceanic particles in the pelagic Weddell Sea, we deployed a multi-year sediment trap. The annual particle flux measured was the smallest yet observed in the world ocean, and showed extreme variability. Phytoplankton production is at least partly seeded by diatoms released from the melting of sea ice which had formed in the coastal area of the Antarctic continent. Phytoplankton production under the winter pack ice appears to be minimal.

Complete genome of the mutualistic, N2-fixing grass endophyte Azoarcus sp. strain BH72

Abstract: Azoarcus sp. strain BH72, a mutualistic endophyte of rice and other grasses, is of agrobiotechnological interest because it supplies biologically fixed nitrogen to its host and colonizes plants in remarkably high numbers without eliciting disease symptoms. The complete genome sequence is 4,376,040-bp long and contains 3,992 predicted protein-coding sequences. Genome comparison with the Azoarcus-related soil bacterium strain EbN1 revealed a surprisingly low degree of synteny. Coding sequences involved in the synthesis of surface components potentially important for plant-microbe interactions were more closely related to those of plant-associated bacteria. Strain BH72 appears to be 'disarmed' compared to plant pathogens, having only a few enzymes that degrade plant cell walls; it lacks type III and IV secretion systems, related toxins and an N-acyl homoserine lactones-based communication system. The genome contains remarkably few mobile elements, indicating a low rate of recent gene transfer that is presumably due to adaptation to a stable, low-stress microenvironment.