Effects of arsenic exposure on the frequency of HPRT-mutant lymphocytes in a population of copper roasters in Antofagasta, Chile: a pilot study

A pilot biomarker study was conducted to investigate the feasibility of using the hypoxanthine guanine phosphoribosyltransferase (HPRT) gene in peripheral blood lymphocytes as a biomarker for detecting genetic effects of arsenic exposure. Blood and urine samples were obtained from workers highly exposed to arsenic in a copper roasting plant in Antofagasta, Chile. Individuals were classified according to their job titles into three potential exposure groups: high, medium, and low. To confirm exposure, arsenic concentration was determined in urine samples. The HPRT mutant frequencies were measured in lymphocytes from 15 individuals ranging in age from 24 to 66 years. The mean mutant frequencies for the three exposure groups were: low (9×10⁻⁶), medium (11×10⁻⁶), and high (24×10⁻⁶). An increased mutant frequency was observed in the highly exposed group, but the response was so slight that it is not likely that this assay will be capable of providing dose–response information across a range of lower, more typical environmental arsenic levels.     

The changing face of genus Homo

Since its introduction in the 18th century, the genus Homo has undergone a number of reinterpretations, all of which have served to make it a more inclusive taxon. In this paper, we trace this trend towards greater inclusiveness, and explain how it has affected the way Homo is defined. We then demonstrate that the current criteria for identifying species of Homo are difficult, if not impossible, to operate using paleoanthropological evidence. We discuss alternative, verifiable, criteria, and show that when these new criteria are applied to Homo, two species, Homo habilis and Homo rudolfensis, fail to meet them. We contend that the lowest boundary of Homo should be redrawn so that the earliest species in the genus is Homo ergaster, or early African Homo erectus. The appearance of this species at around 1.9 Myr appears to mark a distinct shift in hominin adaptive strategy involving morphological and behavioral innovations.     

Starch as a sugar reservoir for nematode-induced syncytia

The plant parasitic nematode Heterodera schachtii invades the roots of Arabidopsis thaliana to induce nematode feeding structures in the central cylinder. During nematode development, the parasites feed exclusively from these structures. Thus, high sugar import and specific sugar processing of the affected plant cells is crucial for nematode development. In the present work, we found starch accumulation in nematode feeding structures and therefore studied the expression genes involved in the starch metabolic pathway. The importance of starch synthesis was further shown using the Atss1 mutant line. As it is rather surprising to find starch accumulation in cells characterised by a high nutrient loss, we speculate that starch serves as long- and short-term carbohydrate storage to compensate the staggering feeding behaviour of the parasites.Key words: Heterodera schachtii, Arabidopsis, nematode, starch metabolism, syncytiaThe obligate plant parasitic nematode Heterodera schachtii is entirely dependent on a system of nutrient supply provided by the plant. Host plants—among those the model plant Arabidopsis thaliana—have to endure invasion of second stage juveniles and the establishment of nematode feeding structures in the plant''s vascular cylinder. For induction of the specific feeding structures, the juveniles pierce one single plant cell with their stylet and inject secretions, thus triggering the formation of a syncytium by local cell walls dissolutions.¹ Further, the central vacuole of the syncytial cells disintegrates, nuclei enlarge and many organelles proliferate.¹ About 24 hours after feeding site induction, the nematode juveniles start feeding in repetitive cycles.² Syncytia have previously been described as strong sinks in the plant''s transport system.³ Thus, in the recent years several studies were carried out to discover solute supply to syncytial cells.^4–7 To our present knowledge, syncytia are symplasmically isolated in the first days of nematode development. During that period, the nematodes depend on transport protein activity in the syncytia plasmamembranes. At later stages plasmodesmata appear to open to the phloem elements, facilitating symplasmic transport.Incoming solutes may either be taken up by the feeding nematode or are synthesised and catalysed by the syncytium''s metabolism. Due to the microscopically observable high density of the cytosol¹ and the increased osmotic pressure,⁸ syncytia appear to accumulate high solute concentrations. In fact, significantly increased sucrose levels have been found in syncytia in comparison to non-infected control roots.⁷ In case of high sugar levels, plant cells generally synthesize starch in order to reduce emerging osmotic stress.⁹ The aim of the work of Hofmann et al.,¹⁰ was to elucidate if starch is utilised as carbohydrate storage in nematode-induced syncytia and to study expression of genes involved in starch metabolism with an emphasis on nematode development.Starch levels of nematode induced syncytia and roots of non-infected plants grown on sand/soil culture were measured by high performance liquid chromatography (HPLC). The results showed a high accumulation of starch in syncytia that was steadily decreasing during nematode development. The accumulation of starch could further be localised within syncytial cells by electron microscopy. Based on these results, we studied the gene expression of the starch metabolic pathway by Affymetrix gene chip analysis. About half of the 56 involved genes were significantly upregulated in syncytia compared to the control and only two genes were significantly downregulated. Thus, the high induction of the gene expression is consistent with the high starch accumulation. Finally, we applied an Arabidopsis mutant line lacking starch synthase I expression that has been described previously.¹¹ Starch synthase I was the second highest upregulated gene in syncytia. It catalyses the linkage of ADP-glucose to the non-reducing end of an a-glucan, forming the linear glucose chains of amylopectin. In a nematode infection assay we were able to prove the significant importance of the gene for nematode development.With the presented results, we can unambiguously prove the accumulation of starch and the induction of the gene expression of the starch metabolic pathway in nematode-induced syncytia. The primary question however is: why do syncytia accumulate soluble sugars and starch although their metabolism is highly induced and nematodes withdraw solutes during continuously repeating feeding cycles?One explanation may be found where least expected—in nematode feeding. It is the feeding activity that induced solute import mechanisms into syncytia resulting in a newly formed sink tissue. However, during moulting events to the third, the fourth juvenile stage and to the adult stage nematodes interrupt feeding for about 20 hours.² During this period sugar supply mechanisms will most probably not be altered thus leading to increasing levels of sugars in the syncytium. Starch may serve as short-term carbohydrate buffering sugar excess. Further, starch may serve as long-term carbohydrate storage during nematode development. In the early stages of juvenile development nematodes withdraw considerably small quantities (about 0,8-times the syncytium volume a day).¹² At later stages, nutrient demand increases so that adult fertilised females require 4-times the syncytium volume per day in order to accomplish egg production.¹² Thus, excessive sugar supply in the first days may be accumulated as starch that gets degraded at later stages when more energy is required from the parasites. Consequently, starch reserve serves as both short-term and long-term carbohydrate storage in nematode-induced syncytia in order to buffer changing feeding pattern of the parasites.? Open in a separate windowFigure 1Arabidopsis wild-type Columbia-0 plants were grown in sand/soil culture. Nematode-induced syncytia and non-infected control roots were harvested at 10, 15 and 20 days after inoculation (dai) and starch content was measured as glucose (Glc) equivalents. Values are means ± SE, n = 3. Different letters indicate significant variations (p < 0.05). © ASPBOpen in a separate windowFigure 2Transmission electron microscope picture of a cross-section of a syncytium associated with female fourth stage juvenile (H. schachtii) induced in roots of Arabidopsis. Bar = 2 µm. S, syncytium; Se, sieve tube; arrow, plastid; asterisk, starch granule. © ASPB     

Immunoglobulin G galactosylation and sialylation are associated with pregnancy-induced improvement of rheumatoid arthritis and the postpartum flare: results from a large prospective cohort study

Introduction  

Improvement of rheumatoid arthritis (RA) during pregnancy has been causatively associated with increased galactosylation of immunoglobulin G (IgG) N-glycans. Since previous studies were small, did not include the postpartum flare and did not study sialylation, these issues were addressed in the present study.     

Tiam1 takes PARt in cell polarity

Cell polarity is an essential requirement for the proper tissue development of complex organisms. This is underscored by in vivo studies showing that loss of cell polarity contributes to the formation and progression of tumours. Evolutionary conserved multiprotein complexes, such as the Par3-Par6-aPKC or, in short, the Par polarity complex, regulate the establishment of cell polarity. The small Rho GTPases CDC42 and Rac control the activation of the Par polarity complex. Evidence now implicates the Rac activator Tiam1 as a crucial component of the Par complex in regulating neuronal (axonal) and epithelial (apical-basal) polarity. Our current knowledge places Tiam1 at the centre of a pivotal biological process, the establishment and maintenance of cell polarity, and suggests that deregulation of the Tiam1-Par complex contributes to tumourigenicity.     

From evidence to practice: development of web-based Dutch lipid reference values

IntroductionIn the Netherlands, the total number of yearly measured lipid profiles exceeds 500,000. While lipid values are strongly affected by age and sex, until recently, no up-to-date age- and sex-specific lipid reference values were available. We describe the translation of big-cohort lipid data into accessible reference values, which can be easily incorporated in daily clinical practice.MethodsLipid values (total cholesterol, LDL cholesterol, HDL cholesterol and triglycerides) from all healthy adults and children in the LifeLines cohort were used to generate age- and sex-specific percentiles. A combination of RStudio, Cascading Style Sheets and HyperText Markup Language was used to interactively display the percentiles in a responsive web layout.ResultsAfter exclusion of subjects reporting cardiovascular disease or lipid-lowering therapy at baseline, 141,611 subjects were included. On the website, input fields were created for age, sex and all main plasma lipids. Upon input of these values, corresponding percentiles are calculated, and output is displayed in a table and an interactive graph for each lipid. The website has been made available in both Dutch and English and can be accessed at www.lipidtools.com.ConclusionWe constructed the first searchable, national lipid reference value tool with graphical display in the Netherlands to use in screening for dyslipidaemias and to reduce the underuse of lipid-lowering therapy in Dutch primary prevention. This study illustrates that data collected in big-cohort studies can be made easily accessible with modern digital techniques and preludes the digital health revolution yet to come.     

The cation-π interaction between Lys53 and the flavin of fructosamine oxidase (FAOX-II) is critical for activity

Fructosamine oxidases (FAOXs) are flavin-containing enzymes that catalyze the oxidative deglycation of low molecular weight fructosamines or Amadori products. The fructosamine substrate is oxidized by the flavin in the reductive half-reaction, and the reduced flavin is then oxidized by molecular oxygen in the oxidative half-reaction. The crystal structure of FAOX-II from Aspergillus fumigatus reveals a unique interaction between Lys53 and the isoalloxazine. The ammonium nitrogen of the lysine is in contact with and nearly centered over the aromatic ring of the flavin on the si-face. Here, we investigate the importance of this unique interaction on the reactions catalyzed by FAOX by studying both half-reactions of the wild-type and Lys53 mutant enzymes. The positive charge of Lys53 is critical for flavin reduction but plays very little role in the reaction with molecular oxygen. The conservative mutation of Lys53 to arginine had minor effects on catalysis. However, removing the charge by replacing Lys53 with methionine caused more than a million-fold decrease in flavin reduction, while only slowing the oxygen reaction by ～30-fold.