Altered patterns of multiple recombinant events are associated with nondisjunction of chromosome 21

We have previously examined characteristics of maternal chromosomes 21 that exhibited a single recombination on 21q and proposed that certain recombination configurations are risk factors for either meiosis I (MI) or meiosis II (MII) nondisjunction. The primary goal of this analysis was to examine characteristics of maternal chromosomes 21 that exhibited multiple recombinant events on 21q to determine whether additional risk factors or mechanisms are suggested. In order to identify the origin (maternal or paternal) and stage (MI or MII) of the meiotic errors, as well as placement of recombination, we genotyped over 1,500 SNPs on 21q. Our analyses included 785 maternal MI errors, 87 of which exhibited two recombinations on 21q, and 283 maternal MII errors, 81 of which exhibited two recombinations on 21q. Among MI cases, the average location of the distal recombination was proximal to that of normally segregating chromosomes 21 (35.28 vs. 38.86 Mb), a different pattern than that seen for single events and one that suggests an association with genomic features. For MII errors, the most proximal recombination was closer to the centromere than that on normally segregating chromosomes 21 and this proximity was associated with increasing maternal age. This pattern is same as that seen among MII errors that exhibit only one recombination. These findings are important as they help us better understand mechanisms that may underlie both age-related and nonage-related meiotic chromosome mal-segregation.     

Expression of three mitochondrial solute carriers, citrin, aralar1 and ornithine transporter, in relation to urea cycle in mice

The present report describes the expression profiles of different tissues and developmental changes of mouse aspartate/glutamate carrier (AGC) genes, Slc25a13 and Slc25a12, and an ornithine transporter gene, Ornt1, in relation to urea cycle enzyme genes, carbamoylphosphate synthetase I (CPS) and argininosuccinate synthetase (ASS). Slc25a13 encodes citrin, recently found to be deficient in adult-onset type II citrullinemia and to function as AGC together with its isoform and product of Slc25a12, aralar1. Citrin was broadly distributed, but mainly in the liver, kidney and heart. Aralar1 was expressed in diaphragm, skeletal muscle, heart, brain and kidney, but not in the liver. These distribution profiles are different from the restricted of Ornt1, ASS and CPS. Citrin, ASS, CPS and Ornt1 showed similar patterns of developmental changes in the liver and small intestine, where they play a role in urea and arginine synthesis. Dietary, hormonal and physical manipulations caused varied changes of CPS, ASS and Ornt1 in the liver, but the change of citrin was not so marked as that of the others. Analysis using RT-PCR and restriction enzyme digestion revealed that the ornithine transporter most expressed is Ornt1, although Ornt2 is detectable at a minute level. All these results suggest that citrin as AGC plays a role in urea synthesis as well as many fundamental metabolic pathways in the liver, and shares metabolic functions with aralar1 in other tissues, and that Ornt1 is an important component in urea synthesis in the liver and in arginine synthesis in the small intestine during the neonatal period.     

Comparison of enterotoxigenic Escherichia coli isolated from surface water and diarrhoeal stool samples in Bangladesh

Enterotoxigenic Escherichia coli (ETEC) is a common cause of bacterial infection leading to acute watery diarrhea in infants and young children. Although the prevalence of ETEC is high in Bangladesh and infections can be spread through food and contaminated water, limited information is available about ETEC in the surface water. We carried out studies to isolate ETEC from surface water samples from ponds, rivers, and a lake from a site close to field areas known to have a high incidence of diarrhea in Dhaka, Bangladesh, and Matlab, Bangladesh. ETEC strains isolated from the water sources were compared with ETEC strains isolated from patients with diarrhea at two hospitals in these areas. ETEC were isolated from 30% (45 of 150) of the samples from the surface water sources and 19% (518 of 2700) of the clinical specimens. One hundred ETEC strains isolated from patients with similar phenotypes as the environmental strains were compared for phenotypic and genotypic properties. The most common O serogroups on ETEC were O6, O25, O78, O115, and O126 in both types of strains. Pulsed-field gel electrophoresis analyses of the ETEC strains showed that multiple clones of ETEC were present within each colonization factor type and that some clones detected in the environment were also isolated from the stools of patients. The strains showed multiple and similar antibiotic resistance patterns. This study shows that ETEC is prevalent in surface water sources in Bangladesh suggesting a possible reason for the endemicity of this pathogen in Bangladesh.     

Mast cells, macrophages, and crown-like structures distinguish subcutaneous from visceral fat in mice

Obesity is accompanied by adipocyte death and accumulation of macrophages and mast cells in expanding adipose tissues. Considering the differences in biological behavior of fat found in different anatomical locations, we explored the distribution of mast cells, solitary macrophages, and crown-like structures (CLS), the surrogates for dead adipocytes, in subcutaneous and abdominal visceral fat of lean and diet-induced obese C57BL/6 mice. In fat depots of lean mice, mast cells were far less prevalent than solitary macrophages. Subcutaneous fat contained more mast cells, but fewer solitary macrophages and CLS, than visceral fat. Whereas no significant change in mast cell density of subcutaneous fat was observed, obesity was accompanied by a substantial increase in mast cells in visceral fat. CLS became prevalent in visceral fat of obese mice, and the distribution paralleled mast cells. Adipose tissue mast cells contained and released preformed TNF-α, the cytokine implicated in the pathogenesis of obesity-linked insulin resistance. In summary, subcutaneous fat differed from visceral fat by immune cell composition and a lower prevalence of CLS both in lean and obese mice. The increase in mast cells in visceral fat of obese mice suggests their role in the pathogenesis of obesity and insulin resistance.     

Staurosporine induced poly (ADP-ribose) polymerase independent cell death in Dictyostelium discoideum

In the present study D. discoideum has been used as a model organism to understand the role of poly (ADP-ribose) polymerase (PARP) in caspase independent paraptotic cell death pathways. D. discoideum lacks caspases and Bcl-2 family proteins; nevertheless it has 9 potential genes for PARP. PARP has been known to get activated in various cell death associated diseases. In this study kinetics of cell death induced by staurosporine (STS), a bacterial alkaloid, was established to unravel the role of PARP. It was found that STS induced cell death in D. discoideum did not involve PARP activation, however it involved cathepsin D. Results indicated that an alternative mechanism may be existing in D. discoideum that lacks Bcl-2 family proteins for STS induced cell death that evades Bax involvement.     

Genetic heterogeneity of primary open-angle glaucoma in Pakistan

BackgroundGlaucoma is a neurodegenerative ophthalmic disorder and is considered among the leading causes of irreversible blindness. Primary open-angle glaucoma (POAG) is the most common type of glaucoma that affects after 30 years of life, progressing slowly, and manifests as decreased visual acuity leading to blindness if not treated. POAG is genetically heterogeneous, inherited most commonly in autosomal dominant mode. Several genes have been reported for POAG with myocilin (Myoc) being most common. The present study has been conducted to screen 25 POAG families with 2 or more affected members for their association with Myoc and CYP1B1 (the most common gene in primary congenital glaucoma).MethodsAfter approval from Institutional Ethical Review Committee (ERC), 25 POAG families were enrolled from the southern province (Sindh) of Pakistan. Written informed consent was obtained from all participating individuals and diagnosis was confirmed by consultant ophthalmologists using various instruments and means. Venous blood was obtained from affected individuals and their normal family members for DNA extraction and subsequent analysis.ResultsAll samples were initially screened for the Myoc gene followed by CYP1B1. Screening for Myoc revealed one previously reported variant c.144G>T in POAG-06 whereas screening for CYP1B1 in all 25 families showed a novel variant c.649G>A in POAG-02. The pathogenicity of the novel variant was confirmed using various bioinformatics tools.ConclusionThis is the first report of any POAG family found associated with a novel variant in CYP1B1 from the southern province of Pakistan whereas one family found associated with a reported variant in Myoc. The remaining 23 POAG families did not found to be associated with either Myoc or CYP1B1 indicating genetic heterogeneity of the population in this part of the world.