Bacterial pathogens encode suppressors of RNA-mediated silencing

Bacterial suppressors of silencing that inhibit multiple steps of plant microRNA biogenesis and function have recently been identified

RNA silencing in plants: Flash report!

Earlier this year plant scientists met in Santa Fe, New Mexico at the Keystone Symposium "RNA Silencing Mechanisms in Plants". Sessions included small RNA biogenesis and signalling, development and stress responses, small RNA-directed DNA methylation, and interaction with pathogens. This report highlights some of the prominent and recurring themes at the meeting and emerging arenas of future research.RIGHTS : This article is licensed under the BioMed Central licence at http://www.biomedcentral.com/about/license which is similar to the 'Creative Commons Attribution Licence'. In brief you may : copy, distribute, and display the work; make derivative works; or make commercial use of the work - under the following conditions: the original author must be given credit; for any reuse or distribution, it must be made clear to others what the license terms of this work are

PolIVb influences RNA-directed DNA methylation independently of its role in siRNA biogenesis.

Comparative StudyJournal ArticleResearch Support, Non-U.S. Gov'tThis article contains supporting information online at www.pnas.org/cgi/content/full/0709632105/DC1. Freely available online through the PNAS open access option. © 2008 by The National Academy of Sciences of the USADNA-dependent RNA polymerase (Pol)IV in Arabidopsis exists in two isoforms (PolIVa and PolIVb), with NRPD1a and NRPD1b as their respective largest subunits. Both isoforms are implicated in production and activity of siRNAs and in RNA-directed DNA methylation (RdDM). Deep sequence analysis of siRNAs in WT Arabidopsis flowers and in nrpd1a and nrpd1b mutants identified >4,200 loci producing siRNAs in a PolIV-dependent manner, with PolIVb reinforcing siRNA production by PolIVa. Transposable element identity and pericentromeric localization are both features that predispose a locus for siRNA production via PolIV proteins and determine the extent to which siRNA production relies on PolIVb. Detailed analysis of DNA methylation at PolIV-dependent loci revealed unexpected deviations from the previously noted association of PolIVb-dependent siRNA production and RdDM. Notably, PolIVb functions independently in DNA methylation and siRNA generation. Additionally, we have uncovered siRNA-directed loss of DNA methylation, a process requiring both PolIV isoforms. From these findings, we infer that the role of PolIVb in siRNA production is secondary to a role in chromatin modification and is influenced by chromatin context

Positive changes among patients with advanced colorectal cancer and their family caregivers: a qualitative analysis

OBJECTIVE: This study assessed positive changes in patients with advanced colorectal cancer and their family caregivers following diagnosis. We compared self-reported positive changes within patient-caregiver dyads as well as self-reports and patient reports of positive changes in caregivers. DESIGN: Individual, semi-structured qualitative interviews were conducted with 23 patients with advanced colorectal cancer and 23 caregivers. A theoretical thematic analysis of interview transcripts was framed by posttraumatic growth theory. RESULTS: Patients and caregivers described five positive changes: closer relationships with others, greater appreciation of life, clarifying life priorities, increased faith, and more empathy for others. Additionally, only caregivers reported better health habits following the cancer diagnosis, and a minority of patients and caregivers reported no positive changes. In about half of cases, patients reported at least one positive change that was identical to that of their caregiver. However, in most cases, patient and caregiver reports of the caregiver's positive change were discrepant. CONCLUSION: Findings suggest that positive changes are a shared experience for many patient-caregiver dyads and obtaining both patient and caregiver reports of caregiver positive changes provides a more comprehensive understanding of their experience. Interventions may capitalise on positive changes to promote meaningful living in the context of advanced cancer

Family Caregiving Challenges in Advanced Colorectal Cancer: Patient and Caregiver Perspectives

Purpose Family caregivers of advanced colorectal cancer patients may be at increased risk for psychological distress. Yet their key challenges in coping with the patient’s illness are not well understood. Soliciting both patient and caregiver perspectives on these challenges would broaden our understanding of the caregiving experience. Thus, the purpose of this research was to identify caregivers’ key challenges in coping with their family member’s advanced colorectal cancer from the perspective of patients and caregivers. Methods Individual, semi-structured qualitative interviews were conducted with 23 advanced colorectal cancer patients and 23 primary family caregivers. Interview data were analyzed via thematic analysis. Results In nearly all cases, patient and caregiver reports of the caregiver’s key challenge were discrepant. Across patient and caregiver reports, caregivers’ key challenges included processing emotions surrounding the patient’s initial diagnosis or recurrence and addressing the patient’s practical and emotional needs. Other challenges included coping with continual uncertainty regarding the patient’s potential functional decline and prognosis and observing the patient suffer from various physical symptoms. Conclusions Findings suggest that eliciting the perspectives of both patients and caregivers regarding caregivers’ challenges provides a more comprehensive understanding of their experience. Results also point to the need to assist caregivers with the emotional and practical aspects of caregiving

Avoidant Coping and Self-efficacy Mediate Relationships between Perceived Social Constraints and Symptoms among Long-term Breast Cancer Survivors

Objective Many breast cancer survivors feel constrained in discussing their cancer experience with others. Limited evidence suggests that social constraints (e.g., avoidance and criticism) from loved ones may negatively impact breast cancer survivors' global health, but research has yet to examine relationships between social constraints and common physical symptoms. Informed by social cognitive processing theory, this study examined whether perceived social constraints from partners and healthcare providers (HCPs) were associated with fatigue, sleep disturbance, and attentional functioning among long-term breast cancer survivors (N = 1052). In addition, avoidant coping and self-efficacy for symptom management were examined as potential mediators of these relationships. Methods Long-term breast cancer survivors (mean years since diagnosis = 6) completed questionnaires assessing social constraints from partners and HCPs, avoidant coping, self-efficacy for symptom management, and symptoms (i.e., fatigue, sleep disturbance, and attentional functioning). Structural equation modeling was used to evaluate the hypothesized relationships among variables in two models: one focused on social constraints from partners and one focused on social constraints from HCPs. Results Both models demonstrated good fit. Consistent with theory and prior research, greater social constraints from both partners and HCPs were associated with greater symptom burden (i.e., greater fatigue and sleep disturbance, poorer attentional functioning). In addition, all relationships were mediated by avoidant coping and self-efficacy for symptom management. Conclusions Findings are consistent with social cognitive processing theory and suggest that symptom management interventions may be enhanced by addressing the impact of social constraints from survivors' partners and HCPs on their coping and self-efficacy

An atypical epigenetic mechanism affects uniparental expression of Pol IV-dependent siRNAs.

BACKGROUND: Small RNAs generated by RNA polymerase IV (Pol IV) are the most abundant class of small RNAs in flowering plants. In Arabidopsis thaliana Pol IV-dependent short interfering (p4-si)RNAs are imprinted and accumulate specifically from maternal chromosomes in the developing seeds. Imprinted expression of protein-coding genes is controlled by differential DNA or histone methylation placed in gametes. To identify epigenetic factors required for maternal-specific expression of p4-siRNAs we analyzed the effect of a series of candidate mutations, including those required for genomic imprinting of protein-coding genes, on uniparental expression of a representative p4-siRNA locus. RESULTS: Paternal alleles of imprinted genes are marked by DNA or histone methylation placed by DNA METHYLTRANSFERASE 1 or the Polycomb Repressive Complex 2. Here we demonstrate that repression of paternal p4-siRNA expression at locus 08002 is not controlled by either of these mechanisms. Similarly, loss of several chromatin modification enzymes, including a histone acetyltransferase, a histone methyltransferase, and two nucleosome remodeling proteins, does not affect maternal expression of locus 08002. Maternal alleles of imprinted genes are hypomethylated by DEMETER DNA glycosylase, yet expression of p4-siRNAs occurs irrespective of demethylation by DEMETER or related glycosylases. CONCLUSIONS: Differential DNA methylation and other chromatin modifications associated with epigenetic silencing are not required for maternal-specific expression of p4-siRNAs at locus 08002. These data indicate that there is an as yet unknown epigenetic mechanism causing maternal-specific p4-siRNA expression that is distinct from the well-characterized mechanisms associated with DNA methylation or the Polycomb Repressive Complex 2

Analysis of small RNA in fission yeast; centromeric siRNAs are potentially generated through a structured RNA

The formation of heterochromatin at the centromeres in fission yeast depends on transcription of the outer repeats. These transcripts are processed into siRNAs that target homologous loci for heterochromatin formation. Here, high throughput sequencing of small RNA provides a comprehensive analysis of centromere-derived small RNAs. We found that the centromeric small RNAs are Dcr1 dependent, carry 5′-monophosphates and are associated with Ago1. The majority of centromeric small RNAs originate from two remarkably well-conserved sequences that are present in all centromeres. The high degree of similarity suggests that this non-coding sequence in itself may be of importance. Consistent with this, secondary structure-probing experiments indicate that this centromeric RNA is partially double-stranded and is processed by Dicer in vitro. We further demonstrate the existence of small centromeric RNA in rdp1Δ cells. Our data suggest a pathway for siRNA generation that is distinct from the well-documented model involving RITS/RDRC. We propose that primary transcripts fold into hairpin-like structures that may be processed by Dcr1 into siRNAs, and that these siRNAs may initiate heterochromatin formation independent of RDRC activity