Essential requirements for robust signaling in Hfq dependent small RNA networks

Bacteria possess networks of small RNAs (sRNAs) that are important for modulating gene expression. At the center of many of these sRNA networks is the Hfq protein. Hfq's role is to quickly match cognate sRNAs and target mRNAs from among a large number of possible combinations and anneal them to form duplexes. Here we show using a kinetic model that Hfq can efficiently and robustly achieve this difficult task by minimizing the sequestration of sRNAs and target mRNAs in Hfq complexes. This sequestration can be reduced by two non-mutually exclusive kinetic mechanisms. The first mechanism involves heterotropic cooperativity (where sRNA and target mRNA binding to Hfq is influenced by other RNAs bound to Hfq); this cooperativity can selectively decrease singly-bound Hfq complexes and ternary complexes with non-cognate sRNA-target mRNA pairs while increasing cognate ternary complexes. The second mechanism relies on frequent RNA dissociation enabling the rapid cycling of sRNAs and target mRNAs among different Hfq complexes; this increases the probability the cognate ternary complex forms before the sRNAs and target mRNAs degrade. We further demonstrate that the performance of sRNAs in isolation is not predictive of their performance within a network. These findings highlight the importance of experimentally characterizing duplex formation in physiologically relevant contexts with multiple RNAs competing for Hfq. The model will provide a valuable framework for guiding and interpreting these experiments.     

Cigarette smoking among school-going adolescents in Lithuania: Results from the 2005 Global Youth Tobacco Survey

Background

The majority of people who suffer morbidity due to smoking may have initiated smoking during adolescent period. The aim of this study is to determine the prevalence and associated factors for cigarette smoking among school-going adolescents in Lithuania.

Findings

Data from the Global Youth Tobacco Survey (GYTS) 2005 were used to conduct this study. Data were analyzed using SUDAAN software 9.03. Comparisons for categorical variables were done using the Pearson's Chi-square test. The cut of point for statistical significance was set at 5% level. Logistic regression analyses were conducted to determine factors associated with the outcome. Unadjusted odds ratios (OR) and adjusted odds ratios (AOR) together with their 95% confidence intervals (CI) are reported. Of the 1822 respondents, 35.8% males and 27.1% females reported being current cigarette smokers (p < 0.001). Having friends who smoke cigarettes was associated with smoking after controlling for age, gender, parental smoking status, and perception of risks of smoking (AOR = 3.76; 95% CI [2.33, 6.90] for some friends using tobacco; and AOR = 17.18; 95% CI [10.46, 28.21] for most or all friends using tobacco). Male gender and having one or both parents who smoke cigarettes were associated with smoking (AOR = 1.31; 95% CI [1.03, 1.66]) and AOR = 1.76; 95% CI [1.37, 2.27]) respectively).

Conclusions

There is a high prevalence of cigarette smoking among Lithuanian adolescents. Male adolescents and adolescents who have friends or parents who smoke should be the main target for tobacco control in Lithuania.     

Novel fluorinated acridone derivatives. Part 1: synthesis and evaluation as potential anticancer agents

We report on the synthesis of a novel series of fluorinated acridones from 5-trifluoromethyl-1,3-cyclohexanedione. The cytotoxic activities of the compounds were studied in several cancer cells. Compounds 9a, 9c, 9e, 9f, and 9h exhibited significant anticancer activities in selected cell lines. Compound 9c is the most active showing GI₅₀ that ranged in values from 0.13 to 26 μM, covering a wide range of cancer cell lines.     

A genome-wide homologous recombination screen identifies the RNA-binding protein RBMX as a component of the DNA-damage response

Repair of DNA double-strand breaks is critical to genomic stability and the prevention of developmental disorders and cancer. A central pathway for this repair is homologous recombination (HR). Most knowledge of HR is derived from work in prokaryotic and eukaryotic model organisms. We carried out a genome-wide siRNA-based screen in human cells. Among positive regulators of HR we identified networks of DNA-damage-response and pre-mRNA-processing proteins, and among negative regulators we identified a phosphatase network. Three candidate proteins localized to DNA lesions, including RBMX, a heterogeneous nuclear ribonucleoprotein that has a role in alternative splicing. RBMX accumulated at DNA lesions through multiple domains in a poly(ADP-ribose) polymerase 1-dependent manner and promoted HR by facilitating proper BRCA2 expression. Our screen also revealed that off-target depletion of RAD51 is a common source of RNAi false positives, raising a cautionary note for siRNA screens and RNAi-based studies of HR.     

Diagnostic accuracy of case-finding questions to identify perinatal depression

Background:

Guidelines for perinatal mental health care recommend the use of two case-finding questions about depressed feelings and loss of interest in activities, despite the absence of validation studies in this context. We examined the diagnostic accuracy of these questions and of a third question about the need for help asked of women receiving perinatal care.

Methods:

We evaluated self-reported responses to two case-finding questions against an interviewer-assessed diagnostic standard (DSM-IV criteria for major depressive disorder) among 152 women receiving antenatal care at 26–28 weeks’ gestation and postnatal care at 5–13 weeks after delivery. Among women who answered “yes” to either question, we assessed the usefulness of asking a third question about the need for help. We calculated sensitivity, specificity and likelihood ratios for the two case-finding questions and for the added question about the need for help.

Results:

Antenatally, the two case-finding questions had a sensitivity of 100% (95% confidence interval [CI] 77%–100%), a specificity of 68% (95% CI 58%–76%), a positive likelihood ratio of 3.03 (95% CI 2.28–4.02) and a negative likelihood ratio of 0.041 (95% CI 0.003–0.63) in identifying perinatal depression. Postnatal results were similar. Among the women who screened positive antenatally, the additional question about the need for help had a sensitivity of 58% (95% CI 38%–76%), a specificity of 91% (95% CI 78%–97%), a positive likelihood ratio of 6.86 (95% CI 2.16–21.7) and a negative likelihood ratio of 0.45 (95% CI 0.25–0.80), with lower sensitivity and higher specificity postnatally.

Interpretation:

Negative responses to both of the case-finding questions showed acceptable accuracy for ruling out perinatal depression. For positive responses, the use of a third question about the need for help improved specificity and the ability to rule in depression.The occurrence of depressive symptoms during the perinatal period is well-recognized. The estimated prevalence is 7.4%–20% antenatally^1,2 and up to 19.2% in the first three postnatal months.³ Antenatal depression is associated with malnutrition, substance and alcohol abuse, poor self-reported health, poor use of antenatal care services and adverse neonatal outcomes.⁴ Postnatal depression has a substantial impact on the mother and her partner, the family, mother–baby interaction and on the longer-term emotional and cognitive development of the baby.⁵Screening strategies to identify perinatal depression have been advocated, and specific questionnaires for use in the perinatal period, such as the Edinburgh Postnatal Depression Scale,⁶ were developed. However, in their current recommendations, the UK National Screening Committee⁷ and the US Committee on Obstetric Practice⁸ state that there is insufficient evidence to support the implementation of universal perinatal screening programs. The initial decision in 2001 by the National Screening Committee to not support universal perinatal screening⁹ attracted particular controversy in the United Kingdom; some service providers subsequently withdrew resources for treatment of postnatal depression, and subsequent pressure by perinatal community practitioners led to modification of the screening guidance in order to clarify the role of screening questionnaires in the assessment of perinatal depression.¹⁰In 2007, the National Institute for Health and Clinical Excellence issued clinical guidelines for perinatal mental health care in the UK, which included guidance on the use of questionnaires to identify antenatal and postnatal depression.¹¹ In this guidance, a case-finding approach to identify perinatal depression was strongly recommended; it involved the use of two case-finding questions (sometimes referred to as the Whooley questions), and an additional question about the need for help asked of women who answered “yes” to either of the initial questions (Box 1).

Box 1:

Case-finding questions recommended for the identification of perinatal depression¹⁰

• “During the past month, have you often been bothered by feeling down, depressed or hopeless?”
• “During the past month, have you often been bothered by having little interest or pleasure in doing things?”
• A third question should be considered if the woman answers “yes” to either of the initial screening questions: “Is this something you feel you need or want help with?”

Useful case-finding questions should be both sensitive and specific so they accurately identify those with and without the condition. The two case-finding questions have been validated in primary care samples^12,13 and examined in other clinical populations^14–16 and are endorsed in recommendations by US and Canadian bodies for screening depression in adults.^17,18 However, at the time the guidance from the National Institute for Health and Clinical Excellence was issued, there were no validation studies conducted in perinatal populations. A recent systematic review¹⁹ identified one study conducted in the United States that validated the two questions against established diagnostic criteria in 506 women attending well-child visits postnatally;²⁰ sensitivity and specificity of the questions were 100% and 44% respectively at four weeks. The review failed to identify studies that validated the two questions and the additional question about the need for help against a gold-standard measure.We conducted a validation study to assess the diagnostic accuracy of this brief case-finding approach against gold-standard psychiatric diagnostic criteria for depression in a population of women receiving perinatal care.