Sequencing studies from several model systems have suggested that diverse and abundant small RNAs may be derived from tRNA, but the function of these molecules remains undefined. Here, we demonstrate that one such tRNA-derived fragment, cloned from human mature B cells and designated CU1276, in fact possesses the functional characteristics of a microRNA, including a DICER1 -dependent biogenesis, physical association with Argonaute proteins, and the ability to repress mRNA transcripts in a sequence-specific manner. Expression of CU1276 is abundant in normal germinal center B cells but absent in germinal center-derived lymphomas, suggesting a role in the pathogenesis of this disease. Furthermore, CU1276 represses endogenous RPA1 , an essential gene involved in many aspects of DNA dynamics, and consequently, expression of this tRNA-derived microRNA in a lymphoma cell line suppresses proliferation and modulates the molecular response to DNA damage. These results establish that functionally active microRNAs can be derived from tRNA, thus defining a class of genetic entities with potentially important biological roles.

The development of insecticides requires valid risk assessment procedures to avoid causing harm to beneficial insects and especially to pollinators such as the honeybee Apis mellifera. In addition to testing according to current guidelines designed to detect bee mortality, tests are needed to determine possible sublethal effects interfering with the animal's vitality and behavioral performance. Several methods have been used to detect sublethal effects of different insecticides under laboratory conditions using olfactory conditioning. Furthermore, studies have been conducted on the influence insecticides have on foraging activity and homing ability which require time-consuming visual observation. We tested an experimental design using the radiofrequency identification (RFID) method to monitor the influence of sublethal doses of insecticides on individual honeybee foragers on an automated basis. With electronic readers positioned at the hive entrance and at an artificial food source, we obtained quantifiable data on honeybee foraging behavior. This enabled us to efficiently retrieve detailed information on flight parameters. We compared several groups of bees, fed simultaneously with different dosages of a tested substance. With this experimental approach we monitored the acute effects of sublethal doses of the neonicotinoids imidacloprid (0.15–6 ng/bee) and clothianidin (0.05–2 ng/bee) under field-like circumstances. At field-relevant doses for nectar and pollen no adverse effects were observed for either substance. Both substances led to a significant reduction of foraging activity and to longer foraging flights at doses of ≥0.5 ng/bee (clothianidin) and ≥1.5 ng/bee (imidacloprid) during the first three hours after treatment. This study demonstrates that the RFID-method is an effective way to record short-term alterations in foraging activity after insecticides have been administered once, orally, to individual bees. We contribute further information on the understanding of how honeybees are affected by sublethal doses of insecticides.

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IntroductionBCL6 has emerged as a critical regulator of germinal centers (GCs), the sites where B cells undergo somatic hypermutation (SHM) and class switch recombination of their immunoglobulin genes (Ig) and are then selected on the basis of the production of antibodies with high affinity for the antigen. 1 BCL6 is also a frequently activated oncogene in the pathogenesis of human B-cell lymphomas, most of which derive from the GC B cells. The BCL6 gene encodes a 95-kDA nuclear phosphoprotein belonging to the BTB/POZ zinc-finger (ZF) family of transcription factors. 2-4 BCL6 functions as a transcriptional repressor via its C-terminal zinc-finger domain that binds to specific DNA sequences in the promoter region of target genes and 2 transcriptional repression domains 5 that interact with distinct corepressor complexes during the GC reaction. [6][7][8][9] Within the B-cell lineage, the BCL6 protein is expressed at high levels only in mature B cells within GCs. 10 GC formation and the development of normal T cell-dependent humoral immune responses require expression of BCL6 because BCL6-null mice do not form GCs and are unable to produce high-affinity antibodies. 2,4 BCL6 expression is regulated by several signals that are crucial for GC development. Activation of B-cell receptor (BCR) induces mitogen-activated protein kinase (MAPK)-mediated phosphorylation of the BCL6 protein, which targets BCL6 for rapid degradation by the ubiquitin proteasome pathway. 11 Stimulation of the CD40 receptor by CD40 ligands expressed by T cells leads to transcriptional down-regulation of BCL6 via a signaling pathway that involves nuclear factor (NF)-B-mediated transcriptional activation of interferon regulatory factor 4 (IRF4), which, in turn, directly represses BCL6 transcription. 12,13 BCL6 degradation is induced by DNA damage via a pathway that is distinct from the one induced by BCR, 14 whereas BCL6 function is also inactivated by acetylation, which triggers its dissociation from corepressor complexes. 15 These findings indicate that although BCL6 is required for GC formation, its downregulation may be critical for B cells to exit the GC and differentiate toward memory and plasma cells.A variety of structural alterations of the BCL6 gene are associated with its deregulated expression in B-cell lymphomas. Chromosomal translocations juxtaposing heterologous promoters to the BCL6 coding domain are found in approximately 40% of diffuse large B-cell lymphoma (DLBCL) and in a minority (5%-10%) of follicular lymphoma (FL). [16][17][18] The common denominator of these promoters is their constitutive activity in the B-cell lineage and in particular their persistent activity in post-GC cells such as immunoblasts and plasma cells, in contrast with the GC-specific activity of the BCL6 promoter. 19 In addition, although alterations of the 5Ј noncoding region of BCL6 by SHM is a feature of normal GC B cells, 20,21 specific mutations found only in DLBCL lead to the deregulated expression of BCL6 through disruption of the sequences mediating a...

The BCL6 proto-oncogene encodes a transcriptional repressor that is required for germinal center (GC) formation and whose deregulation by genomic lesions is implicated in the pathogenesis of GC-derived diffuse large B cell lymphoma (DLBCL) and, less frequently, follicular lymphoma (FL). The biological function of BCL6 is only partially understood because no more than a few genes have been functionally characterized as direct targets of BCL6 transrepression activity. Here we report that the anti-apoptotic proto-oncogene BCL2 is a direct target of BCL6 in GC B cells. BCL6 binds to the BCL2 promoter region by interacting with the transcriptional activator Miz1 and suppresses Miz1-induced activation of BCL2 expression. BCL6-mediated suppression of BCL2 is lost in FL and DLBCL, where the 2 proteins are pathologically coexpressed, because of BCL2 chromosomal translocations and other mechanisms, including Miz1 deregulation and somatic mutations in the BCL2 promoter region. These results identify an important function for BCL6 in facilitating apoptosis of GC B cells via suppression of BCL2, and suggest that blocking this pathway is critical for lymphomagenesis.apoptosis ͉ DLBCL ͉ germinal center T he BCL6 proto-oncogene encodes a transcriptional repressor of the POZ/BTB zinc-finger protein family (1, 2), which binds to specific DNA sequences and represses the transcription of its target genes via recruitment of corepressor complexes (1-4). In the B-cell lineage, BCL6 is expressed in germinal centers (GC) (5), the site in which B cells undergo somatic hypermutation (SHM) and class-switch recombination (CSR) of immunoglobulin (Ig) genes, and are selected on the basis of the production of antibodies with high affinity for the antigen (6). BCL6 is also an essential requirement for GC formation, because mice lacking BCL6 cannot form these structures (7-9). BCL6 expression is then turned off at the end of the GC reaction by a variety of signals, including CD40 receptor engagement (10-12), B-cell receptor (BCR) signaling (13), and genotoxic stress (14). Downregulation of BCL6 is necessary for GC B cells to mature toward plasma cells, because BCL6 is a repressor of PRDM1, a master regulator of plasma cell differentiation (15,16).In Ϸ30% of diffuse large B cell lymphoma (DLBCL) and 10% of follicular lymphoma (FL) cases, chromosomal translocations juxtapose heterologous partner chromosomes to the intact coding region of BCL6 (17-19), leading to its deregulated expression by promoter substitution (20). In addition, SHM-derived mutations in the BCL6 5Ј regulatory region (21-23) deregulate BCL6 expression by disrupting its negative autoregulatory circuit in Ϸ10% of DL-BCL (24, 25) and by preventing CD40-induced IRF4-mediated downregulation in a minority of cases (12). The role of BCL6 in lymphoma pathogenesis is underscored by the fact that mice expressing deregulated BCL6 alleles develop DLBCL (26).A critical issue in the understanding of BCL6 function in GC development and lymphomagenesis is the identification of its regulatory pr...

Abstract. Worldwide, flow regimes are being modified by various anthropogenic impacts and climate change induces an additional risk. Rising temperatures, declining snow cover and changing precipitation patterns will interact differently at different locations. Consequently, in distinct climate zones, unequal consequences can be expected in matters of water stress, flood risk, water quality, and food security. In particular, river ecosystems and their vital ecosystem services will be compromised as their species richness and composition have evolved over long time under natural flow conditions. This study aims at evaluating the exclusive impacts of climate change on river flow regimes in Europe. Various flow characteristics are taken into consideration and diverse dynamics are identified for each distinct climate zone in Europe. In order to simulate present-day natural flow regimes and future flow regimes under climate change, the global hydrology model WaterGAP3 is applied. All calculations for current and future conditions (2050s) are carried out on a 5 × 5 European grid. To address uncertainty, bias-corrected climate forcing data of three different global climate models are used to drive WaterGAP3. Finally, the hydrological alterations of different flow characteristics are quantified by the Indicators of Hydrological Alteration approach. Results of our analysis indicate that on the European scale, climate change can be expected to modify flow regimes remarkably. This is especially the case in the Mediterranean (due to drier conditions with reduced precipitation across the year) and in the boreal climate zone (due to reduced snowmelt, increased precipitation, and strong temperature rises). In the temperate climate zone, impacts increase from oceanic to continental. Regarding single flow characteristics, strongest impacts on timing were found for the boreal climate zone. This applies for both high and low flows. Flow magnitudes, in turn, will be predominantly altered in the Mediterranean but also in the Northern climates. At the end of this study, typical future flow regimes under climate change are illustrated for each climate zone.

The full set of microRNAs (miRNAs) in the human genome is not known. Because presently known miRNAs have been identified by virtue of their abundant expression in a few cell types, many tissue-specific miRNAs remain unrevealed. To understand the role of miRNAs in B-cell function and lymphomagenesis, we generated short-RNA libraries from normal human B cells at different stages of development (naïve, germinal-center, memory) and from a Burkitt lymphoma cell-line. A combination of cloning and computational analysis identified 178 miRNAs (miRNome) expressed in normal and/or transformed B-cell libraries. Most notably, the B-cell miRNome included 75 miRNAs which to our knowledge have not been previously reported and of which 66 have been validated by RNA blot and/or RT-PCR analyses. Numerous miRNAs were expressed in a stage- or transformation-specific fashion in B cells, suggesting specific functional or pathologic roles. These results provide a resource for studying the role of miRNAs in B-cell development, immune function, and lymphomagenesis.