PAR proteins direct asymmetry of the cell cycle regulators Polo-like kinase and Cdc25

Cell cycle lengths vary widely among different cells within an animal, yet mechanisms of cell cycle length regulation are poorly understood. In the Caenorhabditis elegans embryo, the first cell division produces two cells with different cell cycle lengths, which are dependent on the conserved partitioning-defective (PAR) polarity proteins. We show that two key cell cycle regulators, the Polo-like kinase PLK-1 and the cyclin-dependent kinase phosphatase CDC-25.1, are asymmetrically distributed in early embryos. PLK-1 shows anterior cytoplasmic enrichment and CDC-25.1 shows PLK-1-dependent enrichment in the anterior nucleus. Both proteins are required for normal mitotic progression. Furthermore, these asymmetries are controlled by PAR proteins and the muscle excess (MEX) proteins MEX-5/MEX-6, and the latter is linked to protein degradation. Our results support a model whereby the PAR and MEX-5/MEX-6 proteins asymmetrically control PLK-1 levels, which asymmetrically regulates CDC-25.1 to promote differences in cell cycle lengths. We suggest that control of Plk1 and Cdc25 may be relevant to regulation of cell cycle length in other developmental contexts.     

Cheatgrass is favored by warming but not CO2 enrichment in a semi‐arid grassland

Elevated CO₂ and warming may alter terrestrial ecosystems by promoting invasive plants with strong community and ecosystem impacts. Invasive plant responses to elevated CO₂ and warming are difficult to predict, however, because of the many mechanisms involved, including modification of phenology, physiology, and cycling of nitrogen and water. Understanding the relative and interactive importance of these processes requires multifactor experiments under realistic field conditions. Here, we test how free‐air CO₂ enrichment (to 600 ppmv) and infrared warming (+1.5 °C day/3 °C night) influence a functionally and phenologically distinct invasive plant in semi‐arid mixed‐grass prairie. Bromus tectorum (cheatgrass), a fast‐growing Eurasian winter annual grass, increases fire frequency and reduces biological diversity across millions of hectares in western North America. Across 2 years, we found that warming more than tripled B. tectorum biomass and seed production, due to a combination of increased recruitment and increased growth. These results were observed with and without competition from native species, under wet and dry conditions (corresponding with tenfold differences in B. tectorum biomass), and despite the fact that warming reduced soil water. In contrast, elevated CO₂ had little effect on B. tectorum invasion or soil water, while reducing soil and plant nitrogen (N). We conclude that (1) warming may expand B. tectorum's phenological niche, allowing it to more successfully colonize the extensive, invasion‐resistant northern mixed‐grass prairie, and (2) in ecosystems where elevated CO₂ decreases N availability, CO₂ may have limited effects on B. tectorum and other nitrophilic invasive species.     

Fossil liberation: a model to explain high biodiversity in the Triassic Cassian Formation

With 1429 animal species, the Triassic Cassian Formation in the Dolomites, Southern Alps (Italy), yields the highest species richness reported from any spatially constrained pre-Quaternary formation known to science. The high preserved diversity is partly attributable to a high primary diversity governed by the tropical setting, increasing alpha diversity, and the breadth of habitats spurring beta diversity. More important is the excellent preservation of fossils and the ease with which they can be extracted from the poorly lithified sediments. We propose the term ‘liberation Lagerstätten’ to capture this preservational window. In contrast to conservation Lagerstätten, liberation Lagerstätten like the Cassian Formation originate from normal marine conditions but low-grade diagenesis. Molluscs contribute substantially to species richness, comprising 67% of all invertebrate species in the Cassian Formation. The gastropod dominance (39% of all species) is nearly as great as in Recent tropical settings, contradicting the concept of a substantial Cenozoic rise.     

An obligate intermediate along the slow folding pathway of a group II intron ribozyme

Most RNA molecules collapse rapidly and reach the native state through a pathway that contains numerous traps and unproductive intermediates. The D135 group II intron ribozyme is unusual in that it can fold slowly and directly to the native state, despite its large size and structural complexity. Here we use hydroxyl radical footprinting and native gel analysis to monitor the timescale of tertiary structure collapse and to detect the presence of obligate intermediates along the folding pathway of D135. We find that structural collapse and native folding of Domain 1 precede assembly of the entire ribozyme, indicating that D1 contains an on-pathway intermediate to folding of the D135 ribozyme. Subsequent docking of Domains 3 and 5, for which D1 provides a preorganized scaffold, appears to be very fast and independent of one another. In contrast to other RNAs, the D135 ribozyme undergoes slow tertiary collapse to a compacted state, with a rate constant that is also limited by the formation D1. These findings provide a new paradigm for RNA folding and they underscore the diversity of RNA biophysical behaviors.     

Ectonucleoside Triphosphate Diphosphohydrolase-3 Antibody Targets Adult Human Pancreatic β Cells for In Vitro and In Vivo Analysis

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Metagenomes of the picoalga Bathycoccus from the Chile coastal upwelling

Among small photosynthetic eukaryotes that play a key role in oceanic food webs, picoplanktonic Mamiellophyceae such as Bathycoccus, Micromonas, and Ostreococcus are particularly important in coastal regions. By using a combination of cell sorting by flow cytometry, whole genome amplification (WGA), and 454 pyrosequencing, we obtained metagenomic data for two natural picophytoplankton populations from the coastal upwelling waters off central Chile. About 60% of the reads of each sample could be mapped to the genome of Bathycoccus strain from the Mediterranean Sea (RCC1105), representing a total of 9 Mbp (sample T142) and 13 Mbp (sample T149) of non-redundant Bathycoccus genome sequences. WGA did not amplify all regions uniformly, resulting in unequal coverage along a given chromosome and between chromosomes. The identity at the DNA level between the metagenomes and the cultured genome was very high (96.3% identical bases for the three larger chromosomes over a 360 kbp alignment). At least two to three different genotypes seemed to be present in each natural sample based on read mapping to Bathycoccus RCC1105 genome.     

Bioactivity and molecular modelling of diphenylsulfides and diphenylselenides

Bis(2-bromo-4,5-dimethoxyphenyl)sulfide (5) and bis(2-bromo-4,5-dimethoxyphenyl) selenide (7) have been shown to block cells in the G2/M phase of the cell cycle, whereas the debromo (4, 6) equivalents do not. The dibromoselenide (7) is cytotoxic to tumour cells in vitro and has been shown to increase the mitotic index of treated cells. These biological effects are consistent with disruption of the mitotic apparatus. This agent does not inhibit microtubule assembly in vitro, but does bind to tubulin. Molecular modelling of these structures indicates that their spatial and electronic structures may make an important contribution to the biological activity.