K2P18.1 translates T cell receptor signals into thymic regulatory T cell development

It remains largely unclear how thymocytes translate relative differences in T cell receptor (TCR) signal strength into distinct developmental programs that driv...     

Sampling multiple life stages significantly increases estimates of marine biodiversity

Biodiversity assessments are critical for setting conservation priorities, understanding ecosystem function and establishing a baseline to monitor change. Surveys of marine biodiversity that rely almost entirely on sampling adult organisms underestimate diversity because they tend to be limited to habitat types and individuals that can be easily surveyed. Many marine animals have planktonic larvae that can be sampled from the water column at shallow depths. This life stage often is overlooked in surveys but can be used to relatively rapidly document diversity, especially for the many species that are rare or live cryptically as adults. Using DNA barcode data from samples of nemertean worms collected in three biogeographical regions—Northeastern Pacific, the Caribbean Sea and Eastern Tropical Pacific—we found that most species were collected as either benthic adults or planktonic larvae but seldom in both stages. Randomization tests show that this deficit of operational taxonomic units collected as both adults and larvae is extremely unlikely if larvae and adults were drawn from the same pool of species. This effect persists even in well-studied faunas. These results suggest that sampling planktonic larvae offers access to a different subset of species and thus significantly increases estimates of biodiversity compared to sampling adults alone. Spanish abstract is available in the electronic supplementary material.     

Sexual selection for bright females prevails under light pollution

The functions of sexually selected traits are particularly sensitive to changes in the environment because the traits have evolved to in-crease mating success u...     

Hybrid Frequencies Confirm Limit to Coinfection in the RNA Bacteriophage φ6

Coinfection of the same host cell by multiple viruses may lead to increased competition for limited cellular resources, thus reducing the fitness of an individual virus. Selection should favor viruses that can limit or prevent coinfection, and it is not surprising that many viruses have evolved mechanisms to do so. Here we explore whether coinfection is limited in the RNA bacteriophage 6 that infects Pseudomonas phaseolicola. We estimated the limit to coinfection in 6 by comparing the frequency of hybrids produced by two marked phage strains to that predicted by a mathematical model based on differing limits to coinfection. Our results provide an alternative method for estimating the limit to coinfection and confirm a previous estimate between two to three phages per host cell. In addition, our data reveal that the rate of coinfection at low phage densities may exceed that expected through random Poisson sampling. We discuss whether phage 6 has evolved an optimal limit that balances the costly and beneficial fitness effects associated with multiple infections.     

SHP-2 positively regulates myogenesis by coupling to the Rho GTPase signaling pathway

Myogenesis is an intricate process that coordinately engages multiple intracellular signaling cascades. The Rho family GTPase RhoA is known to promote myogenesis, however, the mechanisms controlling its regulation in myoblasts have yet to be fully elucidated. We show here that the SH2-containing protein tyrosine phosphatase, SHP-2, functions as an early modulator of myogenesis by regulating RhoA. When MyoD was expressed in fibroblasts lacking functional SHP-2, muscle-specific gene activity was impaired and abolition of SHP-2 expression by RNA interference inhibited muscle differentiation. By using SHP-2 substrate-trapping mutants, we identified p190-B RhoGAP as a SHP-2 substrate. When dephosphorylated, p190-B RhoGAP has been shown to stimulate the activation of RhoA. During myogenesis, p190-B RhoGAP was tyrosyl dephosphorylated concomitant with the stimulation of SHP-2's phosphatase activity. Moreover, overexpression of a catalytically inactive mutant of SHP-2 inhibited p190-B RhoGAP tyrosyl dephosphorylation, RhoA activity, and myogenesis. These observations strongly suggest that SHP-2 dephosphorylates p190-B RhoGAP, leading to the activation of RhoA. Collectively, these data provide a mechanistic basis for RhoA activation in myoblasts and demonstrate that myogenesis is critically regulated by the actions of SHP-2 on the p190-B Rho GAP/RhoA pathway.     

Diazaborine treatment of yeast cells inhibits maturation of the 60S ribosomal subunit

Diazaborine treatment of yeast cells was shown previously to cause accumulation of aberrant, 3'-elongated mRNAs. Here we demonstrate that the drug inhibits maturation of rRNAs for the large ribosomal subunit. Pulse-chase analyses showed that the processing of the 27S pre-rRNA to consecutive species was blocked in the drug-treated wild-type strain. The steady-state level of the 7S pre-rRNA was clearly reduced after short-term treatment with the inhibitor. At the same time an increase of the 35S pre-rRNA was observed. Longer incubation with the inhibitor resulted in a decrease of the 27S precursor. Primer extension assays showed that an early step in 27S pre-rRNA processing is inhibited, which results in an accumulation of the 27SA2 pre-rRNA and a strong decrease of the 27SA3, 27SB1L, and 27SB1S precursors. The rRNA processing pattern observed after diazaborine treatment resembles that reported after depletion of the RNA binding protein Nop4p/Nop77p. This protein is essential for correct pre-27S rRNA processing. Using a green fluorescent protein-Nop4 fusion, we found that diazaborine treatment causes, within minutes, a rapid redistribution of the protein from the nucleolus to the periphery of the nucleus, which provides a possible explanation for the effect of diazaborine on rRNA processing.     

Substrate specificities and electron paramagnetic resonance properties of benzylsuccinate synthases in anaerobic toluene and<Emphasis Type="Italic"> m</Emphasis>-xylene metabolism

The anaerobic degradation pathways of toluene and m-xylene are initiated by addition of a fumarate cosubstrate to the methyl group of the hydrocarbon, yielding (R)-benzylsuccinate and (3-methylbenzyl)succinate, respectively, as first intermediates. These reactions are catalyzed by a novel glycyl-radical enzyme, (R)-benzylsuccinate synthase. Substrate specificities of benzylsuccinate synthases were analyzed in Azoarcus sp. strain T and Thauera aromatica strain K172. The enzyme of Azoarcus sp. strain T converts toluene, but also all xylene and cresol isomers, to the corresponding succinate adducts, whereas the enzyme of T. aromatica is active with toluene and all cresols, but not with any xylene isomer. This corresponds to the capabilities of Azoarcus sp. strain T to grow on either toluene or m-xylene, and of T. aromatica to grow on toluene as sole hydrocarbon substrate. Thus, differences in the substrate spectra of the respective benzylsuccinate synthases of the two strains contribute to utilization of different aromatic hydrocarbons, although growth on different substrates also depends on additional determinants. We also provide direct evidence by electron paramagnetic resonance (EPR) spectroscopy that glycyl radical enzymes corresponding to substrate-induced benzylsuccinate synthases are specifically detectable in anoxically prepared extracts of toluene- or m-xylene-grown cells. The presence of the EPR signals and the determined amount of the radical are consistent with the respective benzylsuccinate synthase activities. The properties of the EPR signals are highly similar to those of the prototype glycyl radical enzyme pyruvate formate lyase, but differ slightly from previously reported parameters for partially purified benzylsuccinate synthase.     

Multichannel apparatus for parallel monitoring of light scattering in Dictyostelium discoideum cell suspensions

Suspensions of Dictyostelium discoideum amoebae display free-running light scattering oscillations at the onset of development. We describe a device to monitor these oscillations in several samples in parallel. The apparatus consists of a thermostated cuvette holder where up to eight cuvettes containing cell suspension are inserted. Cells are aerated and kept in suspension via an airlift. Infrared light emitted from a five-diode array passes through the suspension and is detected by an array of five light detecting diodes. The resulting signal is digitized and recorded with a sampling rate of two measuring points/second. The parallel analysis approach allows determination of the effects of adding of agents or of variations in the external conditions in the same batch of amoebae at the same developmental time point. This represents an advantage over the conventional single cuvette approach, as oscillation characteristics themselves are developmentally regulated. Moreover, as the new experimental setup enables simultaneous analyses of up to eight samples, the behavior of wild-type and several mutant strains can be compared under identical experimental conditions.