Telomere Recognition and Assembly Mechanism of Mammalian Shelterin

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Mouthpart morphology and feeding behavior of the invasive kudzu bug,Megacopta cribraria (Hemiptera: Plataspidae)

The invasive kudzu bug, Megacopta cribraria, was first reported in North America in 2009 and has subsequently spread through most of the southeastern United States, causing yield loss in soybean. Since detection in the USA, research has focused mainly on managing this newly established pest, but many important characteristics of the pest's mouthpart morphology and feeding behavior are unknown. Qualitative and quantitative comparisons of nymph and adult mouthparts and sensilla were made through scanning electron microscopy and light microscopy, and feeding behavior was examined using electropenetrography (EPG) and paraffin histology. Morphologies observed were similar to what has previously been reported for other piercing–sucking hemipterans. The relationship between rostrum length and body size (pronotum width and dorsal length) exhibited negative allometry. Rostrum length exhibited an isometric relationship with interocular width. Adult females (n=9) probed soybean stems 1.3±0.8 times in 9 h, with an average probe time of 2.3±1.3 h. EPG waveforms were characterized and correlated with behavior. Salivary sheaths were shown to terminate in the vascular tissue; four of five sheaths terminated in the phloem. This is the first time that the feeding behavior of a member of the Plataspidae has been recorded using EPG. Results add to our current limited knowledge of plataspid mouthpart morphology and provide a baseline for further research on the feeding behaviors of M. cribraria and other soybean‐feeding hemipterans.     

Failure to Replicate a Genetic Association May Provide Important Clues About Genetic Architecture

Replication has become the gold standard for assessing statistical results from genome-wide association studies. Unfortunately this replication requirement may cause real genetic effects to be missed. A real result can fail to replicate for numerous reasons including inadequate sample size or variability in phenotype definitions across independent samples. In genome-wide association studies the allele frequencies of polymorphisms may differ due to sampling error or population differences. We hypothesize that some statistically significant independent genetic effects may fail to replicate in an independent dataset when allele frequencies differ and the functional polymorphism interacts with one or more other functional polymorphisms. To test this hypothesis, we designed a simulation study in which case-control status was determined by two interacting polymorphisms with heritabilities ranging from 0.025 to 0.4 with replication sample sizes ranging from 400 to 1600 individuals. We show that the power to replicate the statistically significant independent main effect of one polymorphism can drop dramatically with a change of allele frequency of less than 0.1 at a second interacting polymorphism. We also show that differences in allele frequency can result in a reversal of allelic effects where a protective allele becomes a risk factor in replication studies. These results suggest that failure to replicate an independent genetic effect may provide important clues about the complexity of the underlying genetic architecture. We recommend that polymorphisms that fail to replicate be checked for interactions with other polymorphisms, particularly when samples are collected from groups with distinct ethnic backgrounds or different geographic regions.     

Functional interactions of meiotic recombination factors Rdh54 and Dmc1

Genetic studies in budding and fission yeasts have provided evidence that Rdh54, a Swi2/Snf2-like factor, synergizes with the Dmc1 recombinase to mediate inter-homologue recombination during meiosis. Rdh54 associates with Dmc1 in the yeast two-hybrid assay, but whether the Rdh54–Dmc1 interaction is direct and the manner in which these two recombination factors may functionally co-operate to accomplish their biological task have not yet been defined. Here, using purified Schizosaccharomyces pombe proteins, we demonstrate complex formation between Rdh54 and Dmc1 and enhancement of the recombinase activity of Dmc1 by Rdh54. Consistent with published cytological and chromatin immunoprecipitation data that implicate Rdh54 in preventing the non-specific association of Dmc1 with chromatin, we show here that Rdh54 mediates the efficient removal of Dmc1 from dsDNA. These functional attributes of Rdh54 are reliant on its ATPase function. The results presented herein provide valuable information concerning the Rdh54–Dmc1 protein pair that is germane for understanding their role in meiotic recombination. The biochemical systems established in this study should be useful for the continuing dissection of the action mechanism of Rdh54 and Dmc1.     

Staphylococcus epidermidis polysaccharide intercellular adhesin induces IL-8 expression in human astrocytes via a mechanism involving TLR2

Staphylococcus epidermidis is an opportunistic biofilm-forming pathogen associated with neurosurgical device-related meningitis. Expression of the polysaccharide intercellular adhesin (PIA) on its surface promotes S. epidermidis biofilm formation. Here we investigated the pro-inflammatory properties of PIA against primary and transformed human astrocytes. PIA induced IL-8 expression in a dose- and/or time-dependent manner from U373 MG cells and primary normal human astrocytes. This effect was inhibited by depletion of N -acetyl-β- d -glucosamine polymer from the PIA preparation with Lycopersicon esculentum lectin or sodium meta -periodate. Expression of dominant-negative versions of the TLR2 and TLR4 adaptor proteins MyD88 and Mal in U373 MG cells inhibited PIA-induced IL-8 production. Blocking IL-1 had no effect. PIA failed to induce IL-8 production from HEK293 cells stably expressing TLR4. However, in U373 MG cells which express TLR2, neutralization of TLR2 impaired PIA-induced IL-8 production. In addition to IL-8, PIA also induced expression of other cytokines from U373 MG cells including IL-6 and MCP-1. These data implicate PIA as an important immunogenic component of the S. epidermidis biofilm that can regulate pro-inflammatory cytokine production from human astrocytes, in part, via TLR2.     

Functional significance of the Rad51-Srs2 complex in Rad51 presynaptic filament disruption

The SRS2 (Suppressor of RAD Six screen mutant 2) gene encodes an ATP-dependent DNA helicase that regulates homologous recombination in Saccharomyces cerevisiae. Mutations in SRS2 result in a hyper-recombination phenotype, sensitivity to DNA damaging agents and synthetic lethality with mutations that affect DNA metabolism. Several of these phenotypes can be suppressed by inactivating genes of the RAD52 epistasis group that promote homologous recombination, implicating inappropriate recombination as the underlying cause of the mutant phenotype. Consistent with the genetic data, purified Srs2 strongly inhibits Rad51-mediated recombination reactions by disrupting the Rad51-ssDNA presynaptic filament. Srs2 interacts with Rad51 in the yeast two-hybrid assay and also in vitro. To investigate the functional relevance of the Srs2-Rad51 complex, we have generated srs2 truncation mutants that retain full ATPase and helicase activities, but differ in their ability to interact with Rad51. Importantly, the srs2 mutant proteins attenuated for Rad51 interaction are much less capable of Rad51 presynaptic filament disruption. An internal deletion in Srs2 likewise diminishes Rad51 interaction and anti-recombinase activity. We also present evidence that deleting the Srs2 C-terminus engenders a hyper-recombination phenotype. These results highlight the importance of Rad51 interaction in the anti-recombinase function of Srs2, and provide evidence that this Srs2 function can be uncoupled from its helicase activity.     

Light Exposure at Night Disrupts Host/Cancer Circadian Regulatory Dynamics: Impact on the Warburg Effect,Lipid Signaling and Tumor Growth Prevention

The central circadian clock within the suprachiasmatic nucleus (SCN) plays an important role in temporally organizing and coordinating many of the processes governing cancer cell proliferation and tumor growth in synchrony with the daily light/dark cycle which may contribute to endogenous cancer prevention. Bioenergetic substrates and molecular intermediates required for building tumor biomass each day are derived from both aerobic glycolysis (Warburg effect) and lipid metabolism. Using tissue-isolated human breast cancer xenografts grown in nude rats, we determined that circulating systemic factors in the host and the Warburg effect, linoleic acid uptake/metabolism and growth signaling activities in the tumor are dynamically regulated, coordinated and integrated within circadian time structure over a 24-hour light/dark cycle by SCN-driven nocturnal pineal production of the anticancer hormone melatonin. Dim light at night (LAN)-induced melatonin suppression disrupts this circadian-regulated host/cancer balance among several important cancer preventative signaling mechanisms, leading to hyperglycemia and hyperinsulinemia in the host and runaway aerobic glycolysis, lipid signaling and proliferative activity in the tumor.