Separase sensor reveals dual roles for separase coordinating cohesin cleavage and cdk1 inhibition

Complete dissociation of sister chromatid cohesion and subsequent induction of poleward movement of disjoined sisters are two essential events underlying chromosome segregation; however, how cells coordinate these two processes is not well understood. Here, we developed a fluorescence-based sensor for the protease separase that mediates cohesin cleavage. We found that separase undergoes an abrupt activation shortly before anaphase onset in the vicinity of chromosomes. This activation profile of separase depends on the abilities of two of its binding proteins, securin and cyclin B1, to inhibit its protease activity and target it to chromosomes. Subsequent to its proteolytic activation, separase then binds to and inhibits a subset of cyclin B1-cdk1, which antagonizes cdk1-mediated phosphorylation on chromosomes and facilitates poleward movement of sisters in anaphase. Therefore, by consecutively acting as a protease and a cdk1 inhibitor, separase coordinates two key processes to achieve simultaneous and abrupt separation of sister chromatids.     

Alterations in peripheral blood memory B cells in patients with active rheumatoid arthritis are dependent on the action of tumour necrosis factor

Introduction  

Disturbances in peripheral blood memory B cell subpopulations have been observed in various autoimmune diseases, but have not been fully delineated in rheumatoid arthritis (RA). Additionally, the possible role of tumour necrosis factor (TNF) in regulating changes in specific peripheral blood memory B cell subsets in RA is still unclear.     

Chylomicron remnants are increased in the postprandial state in CD36 deficiency

The clustering of risk factors including dyslipidemia, hyperglycemia, and hypertension is highly atherogenic along with the excess of remnants from triglyceride (TG)-rich lipoproteins. CD36 is involved in the uptake of long-chain fatty acids (LCFAs) in muscles and small intestines. Patients with CD36 deficiency (CD36-D) have postprandial hypertriglyceridemia, insulin resistance, and hypertension. To investigate the underlying mechanism of postprandial hypertriglyceridemia in CD36-D, we analyzed lipoprotein profiles of CD36-D patients and CD36-knockout (CD36-KO) mice after oral fat loading (OFL). In CD36-D patients, plasma triglycerides, apolipoprotein B-48 (apoB-48), free fatty acids (FFAs), and free glycerol levels were much higher after OFL than those of controls, along with increases in chylomicron (CM) remnants and small dense low-density lipoprotein (sdLDL) particles. In CD36-KO mice, lipoproteins smaller than CM in size in plasma and intestinal lymph were markedly increased after OFL and mRNA levels of genes involved in FFA biosynthesis, such as fatty acid binding protein (FABP)-1 and FAS, were significantly increased. These results suggest that CD36-D might increase atherosclerotic risk by enhancing plasma level of CM remnants due to the increased synthesis of lipoproteins smaller than CM in size in the intestine.     

Generation and characterization of cells that can be conditionally depleted of mitochondrial SOD2

Manganese-dependent superoxide dismutase (SOD2) serves as the primary defense against mitochondrial superoxide, and decreased SOD2 activity results in a range of pathologies. To investigate the events occurring soon after depletion of SOD2, we generated SOD2 gene knockout chicken DT40 cells complemented with a human SOD2 (hSOD2) cDNA, whose expression can be switched off by doxycycline (Dox). When SOD2 was depleted by the addition of Dox, the cells grew slightly slower and formed fewer colonies than cells expressing hSOD2. In addition, these cells showed a high sensitivity to paraquat, which produces superoxide, and died through apoptosis. In contrast to results obtained with mouse and DrosophilaSod2 mutants, we found no indication of an increase in DNA lesions due to depletion of SOD2.     

Virus-like particles associated with mass mortalities of the pen shell Atrina pectinata in Japan

Mass mortalities of the pen shell Atrina pectinata occurred in the fishing grounds of Ariake Bay, in southwestern Japan, during late spring and summer in 2003 and 2004. Histological examination revealed extensive necrosis in the epithelial cells of the kidney and gill, and impairment of the endothelial cells of the mantle arteria. Although cestode larvae belonging to the genus Tylocephalum were found in the mantle, adductor muscle, kidney, and digestive gland, their prevalence and the intensity of infection were low. Examinations of moribund pen shells for Haplosporidium spp. infection using PCR analysis and for Perkinsus spp. infection using Ray's fluid thioglycollate medium were negative. Unenveloped virus-like particles were detected by transmission electron microscopy in the cytoplasm of affected kidney and gill cells of moribund pen shells. They were icosahedral spherical and 50 to 55 nm in diameter. These virus-like particles found in moribund pen shells are different from those described in other marine mollusks, and may be the causative agent of the mass mortalities of pen shells.     

Comparison of MR images and histochemical localization of intra-arterially administered microglia surrounding beta-amyloid deposits in the rat brain

The therapeutic use of microglial cells has recently received some attention for the treatment of Alzheimer disease (AD), but few non-invasive techniques exist for monitoring the cells after administration. Here we present a magnetic resonance imaging (MRI) technique for tracking microglia injected intra-arterially in vivo. We micro-injected Abeta42 into the left hippocampus and saline into the right hippocampus of rats. We then administered microglia, which were labeled with enhanced green fluorescent protein (EGFP) gene and Resovist, into the carotid artery. After monitoring exogenously administered microglia using MRI, we compared the MR images and the histochemical localization of administered microglia. MRI revealed clear signal changes attributable to Resovist-containing microglia in Abeta-injected areas. Histochemistry demonstrated that EGFP-positive microglia accumulated around Abeta deposits and internalized the peptide. This study demonstrates the usefulness of MRI for non-invasive monitoring of exogenous microglia, and suggests a promising future for microglia/macrophages as therapeutic tools for AD.