ROS1 5-methylcytosine DNA glycosylase is a slow-turnover catalyst that initiates DNA demethylation in a distributive fashion

Arabidopsis ROS1 belongs to a family of plant 5-methycytosine DNA glycosylases that initiate DNA demethylation through base excision. ROS1 displays the remarkable capacity to excise 5-meC, and to a lesser extent T, while retaining the ability to discriminate effectively against C and U. We found that replacement of the C5-methyl group by halogen substituents greatly decreased excision of the target base. Furthermore, 5-meC was excised more efficiently from mismatches, whereas excision of T only occurred when mispaired with G. These results suggest that ROS1 specificity arises by a combination of selective recognition at the active site and thermodynamic stability of the target base. We also found that ROS1 is a low-turnover catalyst because it binds tightly to the abasic site left after 5-meC removal. This binding leads to a highly distributive behaviour of the enzyme on DNA substrates containing multiple 5-meC residues, and may help to avoid generation of double-strand breaks during processing of bimethylated CG dinucleotides. We conclude that the biochemical properties of ROS1 are consistent with its proposed role in protecting the plant genome from excess methylation.     

Genotype Distribution of Vitamin D Receptor Polymorphisms among Indonesian Patients with Chronic Hepatitis B

Background:Chronic hepatitis B is a necro-inflammatory of the liver parenchyma caused by hepatitis B virus (HBV) infection leading to liver cirrhosis and hepatocellular carcinoma (HCC). Genetic variants including single nucleotide polymorphisms (SNPs) within genes regulating immune response may contribute to the progression of chronic hepatitis B (CHB) infection. This study aimed to examine the genotype distribution of vitamin D receptor (VDR) polymorphism among patients with CHB infection and to study its association with the development of cirrhosis and hepatoma.Methods:This cross-sectional study analysed 75 CHB patients, consisting of 36 CHB patients without cirrhosis, 25 CHB patients with cirrhosis, and 14 CHB patients with hepatoma. VDR polymorphism was examined using the Amplification Refractory Mutation System Polymerase Chain Reaction (ARMS-PCR) method.Results:Alanine aminotransferase (ALT) and alpha fetoprotein (AFP) levels did not show any significant differences between study groups, but albumin levels in CHB patients with cirrhosis and hepatoma were significantly lower than CHB patients without cirrhosis (p< 0.05). In contrast, the bilirubin levels in CHB patients with cirrhosis was higher than in CHB patients’ cirrhosis. The most common genotypes of VDR polymorphisms were Ff (57.3%), TT (72%), aa (48%) and bb (74.7%) for Fok1, Taq1, Apa1 and Bsm1 respectively. There was no significant different in the genotype distribution of VDR polymorphism between CHB patients without cirrhosis and CHB with cirrhosis or hepatoma. Conclusion:This study suggest that VDR gene polymorphism may not contribute to the progression of CHB infection.Key Words: Cirrhosis, Hepatitis B, Hepatoma, Polymorphism, Vitamin D Receptor     

Age-associated adipose tissue inflammation promotes monocyte chemotaxis and enhances atherosclerosis

Although aging enhances atherosclerosis, we do not know if this occurs via alterations in circulating immune cells, lipid metabolism, vasculature, or adipose tissue. Here, we examined whether aging exerts a direct pro-atherogenic effect on adipose tissue in mice. After demonstrating that aging augmented the inflammatory profile of visceral but not subcutaneous adipose tissue, we transplanted visceral fat from young or aged mice onto the right carotid artery of Ldlr^−/− recipients. Aged fat transplants not only increased atherosclerotic plaque size with increased macrophage numbers in the adjacent carotid artery, but also in distal vascular territories, indicating that aging of the adipose tissue enhances atherosclerosis via secreted factors. By depleting macrophages from the visceral fat, we identified that adipose tissue macrophages are major contributors of the secreted factors. To identify these inflammatory factors, we found that aged fat transplants secreted increased levels of the inflammatory mediators TNFα, CXCL2, and CCL2, which synergized to promote monocyte chemotaxis. Importantly, the combined blockade of these inflammatory mediators impeded the ability of aged fat transplants to enhance atherosclerosis. In conclusion, our study reveals that aging enhances atherosclerosis via increased inflammation of visceral fat. Our study suggests that future therapies targeting the visceral fat may reduce atherosclerosis disease burden in the expanding older population.     

Demethylation initiated by ROS1 glycosylase involves random sliding along DNA

Active DNA demethylation processes play a critical role in shaping methylation patterns, yet our understanding of the mechanisms involved is still fragmented and incomplete. REPRESSOR OF SILENCING 1 (ROS1) is a prototype member of a family of plant 5-methylcytosine DNA glycosylases that initiate active DNA demethylation through a base excision repair pathway. As ROS1 binds DNA non-specifically, we have critically tested the hypothesis that facilitated diffusion along DNA may contribute to target location by the enzyme. We have found that dissociation of ROS1 from DNA is severely restricted when access to both ends is obstructed by tetraloops obstacles. Unblocking any end facilitates protein dissociation, suggesting that random surface sliding is the main route to a specific target site. We also found that removal of the basic N-terminal domain of ROS1 significantly impairs the sliding capacity of the protein. Finally, we show that sliding increases the catalytic efficiency of ROS1 on 5-meC:G pairs, but not on T:G mispairs, thus suggesting that the enzyme achieves recognition and excision of its two substrate bases by different means. A model is proposed to explain how ROS1 finds its potential targets on DNA.     

Chromosome C-banding techniques in Dictyocaulus filaria (Rudolphi, 1809) Railliet and Henry, 1907

C-banding has been performed on Dictyocaulus filaria using both original and modified techniques. The karyotype is reported based on C band observations. The existence of large heterochromatic blocks appears to be the cause of the low chiasmata frequency.