诺卡氏菌对油酸的羟基化作用

诺卡氏菌(Nocardia sp．N13)休止细胞对油酸(顾-9-十八碳烯酸)进行羟基化作用。用休止细胞转化时最适温度为30℃,最适pH为6．5,当菌体(干菌)与底物的最适比例为20 ：1对,对油酸的转化率为83．4％,不同的表面活性剂影响转化的效果。N13休止细胞在磷酸缓冲液中重复转化3次仍可保持50％左右的转化率。红外光谱、质谱、棱磁共振鉴定产物为10－羟基硬脂酸。     

Molecular steps of G‐overhang generation at human telomeres and its function in chromosome end protection

Telomeric G‐overhangs are required for the formation of the protective telomere structure and telomerase action. However, the mechanism controlling G‐overhang generation at human telomeres is poorly understood. Here, we show that G‐overhangs can undergo cell cycle‐regulated changes independent of telomerase activity. G‐overhangs at lagging telomeres are lengthened in S phase and then shortened in late S/G2 because of C‐strand fill‐in, whereas the sizes of G‐overhangs at leading telomeres remain stable throughout S phase and are lengthened in G2/M. The final nucleotides at measurable C‐strands are precisely defined throughout the cell cycle, indicating that C‐strand resection is strictly regulated. We demonstrate that C‐strand fill‐in is mediated by DNA polymerase α (polα) and controlled by cyclin‐dependent kinase 1 (CDK1). Inhibition of CDK1 leads to accumulation of lengthened G‐overhangs and induces telomeric DNA damage response. Furthermore, depletion of hStn1 results in elongation of G‐overhangs and an increase in telomeric DNA damage. Our results suggest that G‐overhang generation at human telomeres is regulated by multiple tightly controlled processes and C‐strand fill‐in is under the control of polα and CDK1.     

Causal link between microsatellite instability and hMRE11 dysfunction in human cancers

Maintenance of genomic integrity is essential for cell survival, and genomic instability is a commonly recognized intrinsic property of all cancers. Microsatellite instability (MSI) represents a frequently occurring and easily traceable simple form of sequence variation, signified by the contraction or expansion of specific DNA sequences containing short tandem repeats. MSI is frequently detected in tumor cells with DNA mismatch repair (MMR) deficiency. It is commonly conceived that instability at individual microsatellite loci can arise spontaneously in cells independent of MMR status, and different microsatellite loci are generally not affected uniformly by MMR deficiency. It is well recognized that MMR deficiency per se is not sufficient to initiate tumorigenesis; rather, the biological effects have to be exerted by mutations in genes controlling cell survival, DNA damage response, and apoptosis. Recently, shortening of an intronic hMRE11 poly(T)11 tract has been associated with MMR deficiency, raising the possibility that hMRE11 may be inactivated by defective MMR. However, the molecular nature underlying this association is presently unknown, and review of the current literature suggests that hMRE11 is most likely involved with the MMR pathway in a more complex fashion than simply being a MMR target gene. An alternative scenario is proposed to better reconcile the differences among various studies. The potential role of hMRE11 in telomere repeats stability is also discussed.     

Human telomeres maintain their overhang length at senescence

Normal human cells in culture enter replicative senescence after a finite number of population doublings. The exact molecular mechanisms triggering the growth arrest are poorly understood. A recent report on the disappearance of the G-rich 3' telomeric overhang in senescent cells led to the hypothesis that loss of the 3' G-rich overhang is the molecular signal that triggers senescence. Here, we describe a quantitative assay to measure the length of the G-rich 3' telomeric overhangs from cultured cells. Using both this assay and the conventional nondenaturing hybridization assay for measuring G-rich overhangs, we show that normal human fibroblasts can maintain their overhangs at senescence. Furthermore, cells do not lose their overhangs when they bypass senescence after the inactivation of p53 and Rb. We thus conclude that a global reduction in overhang length is not the molecular signal that triggers replicative senescence.     

Telomere-end processing the terminal nucleotides of human chromosomes

Mammalian telomeres end in single-stranded, G-rich 3' overhangs resulting from both the "end-replication problem" (the inability of DNA polymerase to replicate the very end of the telomeres) and postreplication processing. Telomeric G-rich overhangs are precisely defined in ciliates; the length and the terminal nucleotides are fixed. Human telomeres have very long overhangs that are heterogeneous in size (35-600 nt), indicating that their processing must differ in some respects from model organisms. We developed telomere-end ligation protocols that allowed us to identify the terminal nucleotides of both the C-rich and the G-rich telomere strands. Up to approximately 80% of the C-rich strands terminate in CCAATC-5', suggesting that after replication a nuclease with high specificity or constrained action acts on the C strand. In contrast, the G-terminal nucleotide was less precise than Tetrahymena and Euplotes but still had a bias that changed as a function of telomerase expression.     

Human telomeres have different overhang sizes at leading versus lagging strands

G-rich 3' telomeric overhangs are required both for forming the distinct telomere structures to protect chromosome ends and for extending telomeres by telomerase. However, little is known about the molecular mechanisms generating telomere overhangs in human cells. We show here that cultured normal human diploid cells have longer G overhangs at telomeres generated by lagging-strand synthesis than by leading-strand synthesis. We also demonstrate that telomerase expression results in elongated overhangs at the leading daughter telomeres. Thus, the overhangs at the leading and lagging daughter telomeres are generated differently in human cells, and telomerase may preferentially affect overhangs generated at the telomeres produced by leading-strand synthesis.     

Human Stn1 protects telomere integrity by promoting efficient lagging-strand synthesis at telomeres and mediating C-strand fill-in

Telomere maintenance is critical for genome stability. The newly-identified Ctc1/Stn1/Ten1 complex is important for telomere maintenance, though its precise role is unclear. We report here that depletion of hStn1 induces catastrophic telomere shortening, DNA damage response, and early senescence in human somatic cells. These phenotypes are likely due to the essential role of hStn1 in promoting efficient replication of lagging-strand telomeric DNA. Downregulation of hStn1 accumulates single-stranded G-rich DNA specifically at lagging-strand telomeres, increases telomere fragility, hinders telomere DNA synthesis, as well as delays and compromises telomeric C-strand synthesis. We further show that hStn1 deficiency leads to persistent and elevated association of DNA polymerase α (polα) to telomeres, suggesting that hStn1 may modulate the DNA synthesis activity of polα rather than controlling the loading of polα to telomeres. Additionally, our data suggest that hStn1 is unlikely to be part of the telomere capping complex. We propose that the hStn1 assists DNA polymerases to efficiently duplicate lagging-strand telomeres in order to achieve complete synthesis of telomeric DNA, therefore preventing rapid telomere loss.     

Correlations between Clinical Features and Mortality in Patients with Vibrio vulnificus Infection

Vibrio vulnificus is a common gram-negative bacterium, which might cause morbidity and mortality in patients following consumption of seafood or exposure to seawater in Southeast China. We retrospectively analyzed clinical data of patients with laboratory confirmed V. vulnificus infection. Twenty one patients were divided into a survival group and a non-surviving (or death) group according to their clinical outcome. Clinical data and measurements were statistically analyzed. Four patients (19.05%) died and five patients gave positive cultures from bile fluid, and 16 other patients gave positive culture from blood or blisters. Ten patients (47.62%) had an underlying liver disease and marine-related events were found in sixteen patients (76.2%). Patients with heavy drinking habits might be at increased mortality (p = 0.028). Clinical manifestations of cellulitis (47.6%), septic shock (42.9%) and multiple organ failure (28.6%) were statistically significant when comparing survivors and non-survivors (p = 0.035, p = 0.021 and p = 0.003, respectively). The laboratory results, including hemoglobin < 9.0 g/L (p = 0.012), platelets < 2.0×10⁹ /L, prothrombin time activity (PTA) <20%, decreased serum creatinine and increased urea nitrogen were statistically significant (p = 0.012, p = 0.003, p = 0.028 and p = 0.028, respectively). Patients may be at a higher risk of mortality under situations where they have a history of habitual heavy alcoholic drink consumption (p = 0.028, OR = 22.5, 95%CI 1.5–335.3), accompanied with cellulitis, shock, multiple organ failure, and laboratory examinations that are complicated by decreased platelets, hemoglobin and significantly prolonged prothrombin time (PT).     

Pneumonia in patients with cirrhosis: risk factors associated with mortality and predictive value of prognostic models

Background

Cirrhosis always goes with profound immunity compromise, and makes those patients easily be the target of pneumonia. Cirrhotic patients with pneumonia have a dramatically increased mortality. To recognize the risk factors of mortality and to optimize stratification are critical for improving survival rate.

Methods

Two hundred and three cirrhotic patients with pneumonia at a tertiary care hospital were included in this retrospective study. Demographical, clinical and laboratory parameters, severity models and prognosis were recorded. Multivariate Cox regression analysis was used to identify independent predictors of 30-day and 90-day mortality. Area under receiver operating characteristics curves (AUROC) was used to compare the predictive value of different prognostic scoring systems.

Results

Patients with nosocomial acquired or community acquired pneumonia indicated similar prognosis after 30- and 90-day follow-up. However, patients triggered acute-on-chronic liver failure (ACLF) highly increased mortality (46.4% vs 4.5% for 30-day, 69.6% vs 11.2% for 90-day). Age, inappropriate empirical antibiotic therapy (HR: 2.326 p?=?0.018 for 30-day and HR: 3.126 p?<?0.001 for 90-day), bacteremia (HR: 3.037 p?=?0.002 for 30-day and HR: 2.651 p?=?0.001 for 90-day), white blood cell count (WBC) (HR: 1.452 p?<?0.001 for 30-day and HR: 1.551 p?<?0.001 for 90-day) and total bilirubin (HR: 1.059 p?=?0.002 for 90-day) were independent factors for mortality in current study. Chronic liver failure–sequential organ failure assessment (CLIF-SOFA) displayed highest AUROC (0.89 and 0.90, 95% CI: 0.83–0.95 and 0.85–0.95 for 30-day and 90-day respectively) in current study.

Conclusions

This study found age, bacteremia, WBC, total bilirubin and inappropriate empirical antibiotic therapy were independently associated with increased mortality. Pneumonia triggered ACLF remarkably increased mortality. CLIF-SOFA was more accurate in predicting mortality than other five prognostic models (model for end-stage liver disease (MELD), MELD-Na, quick sequential organ failure assessment (qSOFA), pneumonia severity index (PSI), Child-Turcotte-Pugh (CTP) score).

     

Single step genome-wide association studies based on genotyping by sequence data reveals novel loci for the litter traits of domestic pigs

In this study, data genotyping by sequence (GBS) was used to perform single step GWAS (ssGWAS) to identify SNPs associated with the litter traits in domestic pigs and search for candidate genes in the region of significant SNPs. After quality control, 167,355 high-quality SNPs from 532 pigs were obtained. Phenotypic traits on 2112 gilt litters from 532 pigs were recorded including total number born (TNB), number born alive (NBA), and litter weight born alive (LWB). A single-step genomic BLUP approach (ssGBLUP) was used to implement the genome-wide association analysis at a 5% genome-wide significance level. A total of 8, 23 and 20 significant SNPs were associated with TNB, NBA, and LWB, respectively, and these significant SNPs accounted for 62.78%, 79.75%, and 58.79% of genetic variance. Furthermore, 1 (SSC14: 16314857), 4 (SSC1: 81986236, SSC1: 66599775, SSC1: 161999013, and SSC1: 267883107), and 5 (SSC9: 29030061, SSC2: 32368561, SSC5: 110375350, SSC13: 45619882 and SSC13: 45647829) significant SNPs for TNB, NBA, and LWB were inferred to be novel loci. At SSC1, the AIM1 and FOXO3 genes were found to be associated with NBA; these genes increase ovarian reproductive capacity and follicle number and decrease gonadotropin levels. The genes SLC36A4 and INTU are involved in cell growth, cytogenesis and development were found to be associated with LWB. These significant SNPs can be used as an indication for regions in the Sus scrofa genome for variability in litter traits, but further studies are expected to confirm causative mutations.