Asymmetric glycerophospholipids impart distinctive biophysical properties to lipid bilayers

Phospholipids are a diverse group of biomolecules consisting of a hydrophilic headgroup and two hydrophobic acyl tails. The nature of the head and length and saturation of the acyl tails are important for defining the biophysical properties of lipid bilayers. It has recently been shown that the membranes of certain yeast species contain high levels of unusual asymmetric phospholipids consisting of one long and one medium-chain acyl moiety, a configuration not common in mammalian cells or other well-studied model yeast species. This raises the possibility that structurally asymmetric glycerophospholipids impart distinctive biophysical properties to the yeast membranes. Previously, it has been shown that lipids with asymmetric length tails form a mixed interdigitated gel phase and exhibit unusual endotherm behavior upon heating and cooling. Here, however, we address physiologically relevant temperature conditions and, using atomistic molecular dynamics simulations and environmentally sensitive fluorescent membrane probes, characterize key biophysical parameters (such as lipid packing, diffusion coefficient, membrane thickness, and area per lipid) in membranes composed of both length-asymmetric glycerophospholipids and ergosterol. Interestingly, we show that saturated but asymmetric glycerophospholipids maintain membrane lipid order across a wide range of temperatures. We also show that these asymmetric lipids can substiture of unsaturated symmetric lipids in the phase behaviour of ternary lipid bilayers. This may allow cells to maintain membrane fluidity, even in environments that lack oxygen, which is required for the synthesis of unsaturated lipids and sterols.     

The demography of Yellow Wagtails Motacilla flava on abandoned fields in northern European Russia

Capsule Apparent survival rates of Yellow Wagtails breeding in abandoned fields in Russia are determined by previous breeding success.

Aims To examine apparent survival and its link to previous breeding success in Yellow Wagtails breeding in abandoned fields in the Vologda region, northern European Russia.

Methods We ringed and measured apparent survival of Yellow Wagtails at two abandoned agricultural sites over eight years (2005–2012). We modelled the impact of age, nest stage, and time of season on daily nest survival rates.

Results Predation was the main cause of nest failure. Nest daily survival rate was highest at the beginning of the breeding season. Overall nest survival probability was 0.40?±?0.02. Adult apparent survival after successful breeding was 0.42?±?0.06 and after unsuccessful breeding this was 0.13?±?0.06.

Conclusion Reproductive success can be regarded as the crucial demographic parameter of the local Yellow Wagtail population in northern European Russia. Apparent survival after successful breeding is significantly higher than after unsuccessful breeding, because unsuccessful breeders probably move to new breeding sites the following year. High adult survival may be particularly important to Yellow Wagtail population dynamics in the study region, because second breeding attempts are apparently unusual.     

Patterns of Biofilm Succession on a Sheltered Rocky Shore in Hong Kong

Successional patterns are dependent on the nature of the substratum, water flow, concentrations of organics as well as the availability of bacteria, algal spores and invertebrate larvae in the coastal environment. Bacteria play an especially important role in biofilm formation as they are generally the earliest colonizers. In the present study, both winter and summer biofilm succession patterns were examined on glass coverslips inverted on experimental racks attached at two tidal levels on a sheltered shore in Hong Kong. In the succession, bacteria were followed by diatoms and cyanobacteria. Encrusting algae appeared in the late stages of the experiment (day 80 in summer and day 60 in winter). Colonization by bacteria was much slower in summer and their density remained low throughout the experimental period. The first appearance of diatoms and cyanobacteria, however, was more rapid in the summer. Bacteria and diatoms on the low-shore surfaces also had a faster succession rate than on the high-shore surfaces, suggesting that desiccation/aerial temperature are the causal factors for such differences.     

Growing seasons of Nordic mountain birch in northernmost Europe as indicated by long-term field studies and analyses of satellite images

The phenophases first greening (bud burst) and yellowing of Nordic mountain birch (Betula pubescens ssp.tortuosa, also called B. p. ssp. czerepanovii) were observed at three sites on the Kola Peninsula in northernmost Europe during the period 1964–2003, and at two sites in the trans-boundary Pasvik-Enare region during 1994–2003. The field observations were compared with satellite images based on the GIMMS-NDVI dataset covering 1982–2002 at the start and end of the growing season. A trend for a delay of first greening was observed at only one of the sites (Kandalaksha) over the 40 year period. This fits well with the delayed onset of the growing season for that site based on satellite images. No significant changes in time of greening at the other sites were found with either field observations or satellite analyses throughout the study period. These results differ from the earlier spring generally observed in other parts of Europe in recent decades. In the coldest regions of Europe, e.g. in northern high mountains and the northernmost continental areas, increased precipitation associated with the generally positive North Atlantic Oscillation in the last few decades has often fallen as snow. Increased snow may delay the time of onset of the growing season, although increased temperature generally causes earlier spring phenophases. Autumn yellowing of birch leaves tends towards an earlier date at all sites. Due to both later birch greening and earlier yellowing at the Kandalaksha site, the growing season there has also become significantly shorter during the years observed. The sites showing the most advanced yellowing in the field throughout the study period fit well with areas showing an earlier end of the growing season from satellite images covering 1982–2002. The earlier yellowing is highly correlated with a trend at the sites in autumn for earlier decreasing air temperature over the study period, indicating that this environmental factor is important also for autumn phenophases.     

Steroidogenesis in adrenal glands of young and adult female mice with hyperexpression of the Aguoti gene

Dominant mutation Agouti yellow (AY) leads to ectopic overexpression of the Agouti gene and yellow coat color in mice. Furthermore, the mutation Ay increased adrenal response to emotional stress. The study assessed whether pleiotropic effect of the mutation Ay on adrenals function was dependent on sex and age. 3- and 15-week old female C57B1/6J mice of two agouti-genotypes: Ay/a (ectopic Agouti-gene overexpression) and a/a (absence of Agouti-protein), were investigated. Cyclic AMP level (adenylate cyclase activity) and corticosterone production in adrenal isolated cells stimulated by ACTH and dibutyrul cAMP (db-cAMP) were measured. ACTH increased cAMP accumulation to the same extent in Ay/a- and a/a-mouse adrenal cells of both ages. The dibutyrul cAMP-induced corticosterone production was higher in Ay/a than in a/a-mouse adrenal cells of both ages. The ACTH-induced corticosterone production in 3-week- old Ay/a-m/CQ was lower and in 15-week old Ay/a-mice was higher than in a/a-mice of the respective ages. The ACTH- and db-cAMP-induced steroidogenesis was not changed in Ay/a-mice and decreased in a/a-mice with age. Thus, in females as well as in males, the mutation Agouti yellow did not affect adenylate cyclase activity, increased db-cAMP-induced corticosterone production and disturbed development of adrenal cortex.     

Stress-hyperresponsive period in postnatal development of hypothalamic-hypophyseal-adrenal system in mice

OBJECTIVE OF THE STUDY: to compare response to stress, activity of adenylatcyclase and enzymes of steroidogenesis in adrenal cells in 3-week and adult (15-week) mice. In 3-week mice, basal and stressor level of blood corticosterone was increased. Their response to stress was faster developing as compared with adult mice. In vitro, 3-week mice had enhanced adrenal sensitivity to ACTH, corticosterone release in response to ACTH, exogenous cAMP and progesterone; and the cAMP level in the cells stimulated with ACTH and forscoline. Thus, in 3-week mice, a stress-hyperresponsive period occurs due to increased release of corticosterone and adrenal sensitivity to ACTH. The reason of this involves enhanced activity of adenylatcyclase and intracellular enzymes of steroidogenesis.     

Antagonist-mediated down-regulation of toll-like receptors increases the prevalence of human papillomavirus infection in systemic lupus erythematosus

IntroductionPrevalence of an abnormal Papanicolaou smear was significantly increased in lupus patients in cross-sectional studies, associated with a higher prevalence of high-risk human papillomavirus (HPV) infection. The nucleic acid-specific Toll-like receptors (TLRs) locate at the endolysosomal compartments and trigger the induction of cytokines for the innate immune response. This study evaluated whether abnormal host innate immune response in lupus patients may enhance HPV persistence.MethodsProtein levels of TLRs 3, 7, 8 and 9 in cervical epithelial cells of lupus patients and controls with or without HPV infection were assessed using flow cytometry. Characteristics associated with the differential expression of TLRs in systemic lupus erythematosus (SLE) were elucidated. The effect and interferon-stimulated genes (ISGs) (ISG15 and Mx-1) gene expressions were then measured in oncogenic HeLa (HPV18), CaSki (HPV) and C33A (HPV negative) cell lines using flow cytometry and quantitative real-time PCR. Ex vivo productions of cytokines and interferon-gamma (IFN-γ) upon TLR ligands stimulations were subsequently measured using cytometric bead array and ELISA.ResultsFor subjects with HPV infection, levels of TLR3 and TLR7 were significantly lower in lupus patients compared with controls. Significantly decreased TLRs 7, 8 and 9 levels were observed in HPV-negative SLE compared to healthy controls. For SLE with and without HPV infection, TLR7 and 9 levels were significantly lower in infected SLE than those in HPV-negative patients. Independent explanatory variables associated with down-regulation of TLR7 level included HPV infection and a higher cumulative dose of prednisolone; while a higher cumulative dose of hydroxychloroquine and HPV infection were associated with down-regulation of TLR9 level. In cervical cell lines, TLRs 3, 7, 8, 9 protein levels and antiviral ISG15 and Mx-1 gene expressions were inhibited in two oncogenic HPV types. Functional data showed that the induction of pro-inflammatory cytokines by TLR ligands (R837, ssRNA and ODN2395) was greatly impaired in CaSki and HeLa than C33A cells.ConclusionsIn conclusion, prednisolone and TLR antagonist (hydroxychloroquine) may down-regulate protein levels of TLR7 and TLR9 in lupus patients, thereby decreasing the innate immune response against HPV infection. Upon infection, HPV further down-regulate TLR7 and 9 levels for viral persistence. Furthermore, reduction of nucleic acid-sensing TLRs 7, 8 and 9 in carcinogenic HPVs ensures that the expression of inducible pro-inflammatory cytokines is minimized to prevent the expression of antiviral ISGs (ISG15 and Mx-1) on a biologically relevant antiviral response.     

Evolution of DNA polymerases: an inactivated polymerase-exonuclease module in Pol ε and a chimeric origin of eukaryotic polymerases from two classes of archaeal ancestors

Background  

Evolution of DNA polymerases, the key enzymes of DNA replication and repair, is central to any reconstruction of the history of cellular life. However, the details of the evolutionary relationships between DNA polymerases of archaea and eukaryotes remain unresolved.