In situ Os isotopes in abyssal peridotites bridge the isotopic gap between MORBs and their source mantle

Abyssal peridotites are assumed to represent the mantle residue of mid-ocean-ridge basalts (MORBs). However, the osmium isotopic compositions of abyssal peridotites and MORB do not appear to be in equilibrium, raising questions about the cogenetic relationship between those two reservoirs. However, the cause of this isotopic mismatch is mainly due to a drastic filtering of the data based on the possibility of osmium contamination by sea water. Here we present a detailed study of magmatic sulphides (the main carrier of osmium) in abyssal peridotites and show that the 187Os/188Os ratio of these sulphides is of primary mantle origin and can reach radiogenic values suggesting equilibrium with MORB. Thus, the effect of sea water on the osmium systematics of abyssal peridotites has been overestimated and consequently there is no true osmium isotopic gap between MORBs and abyssal peridotites.     

Some generalizations relative to lithium aluminum hydride reactions

Zusammenfassung Unter den gewöhnlichen Reaktionsbedingungen bleiben-O-{ie356-1}-O- und -S-{ie356-2}-O-Gruppen durch LiAlH₄ unverändert, während -{ie356-3}-{ie356-4}-O- und möglicherweise auch-{ie356-5}-{ie356-6}-S-Gruppen an der C-O- bzw. C-S-Bindung gespalten werden. Diese Verallgemeinerungen, die sich auf aliphatische und aromatische Verbindungen, Zucker und Steroide, anwenden lassen, werden zur Bestätigung kürzlich aufgestellter Steroid- und Alkaloidformeln herangezogen. Es wird ein Reaktionsmechanismus vorgeschlagen.

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Contribution No. 8 from the Yerkes Research Laboratory, E. I. du Pont de Nemours & Co., Inc., Buffalo 7, New York.     

Long-term fluctuations of an isolated populaton of the Pacific chorus frog ( Psuedacris Regilla ) in northwestern Nevada

In 80% of the years between 1975 and 1989 chorus frogs were able to produce offspring that completed metamorphosis and became members of the next generation. During 3 of these 15 years (1975, 1983, and 1986), floods annihilated chorus frogs in the breeding pond. Between 1905 and 1989 this geographically isolated population of Pseudacris regilla , the Pacific chorus frog, located at the western edge of the Great Basin in northwestern Nevada, became reestablished after 10 natural physical disturbances including spring flash floods, numerous kill-offs by sudden drastic rises in water temperature, and stream dry-ups. Ninety percent of the frogs in this population were shades of green with black dorsal speckles and eyestripes. Predators were the belted kingfisher ( Megaceryle alcyon ), western terrestrial garter snake ( Thamnophis elegans ), and domestic house cat ( Felix domestica ).     

Small-scale convection beneath oceans and continents

Small-scale convection supplies heat flow of ～17 mW m-2 to the base of stable continents where xenolith studies resolve the geotherm.However,effects of small-scale convection are difficult to resolve in ocean basins.On first pass,most seafloor appears to subside to an asymptote compatible with ～40 mW m-2 convective heat flow.These common regions are tracked by hotspots so uplift associated with ponded mantle material is an attractive alternative.Unaffected seafloor in the North and South Atlantic continues to subside with the square root of age as expected from pure conduction.The theory of stagnant-lid convection provides good scaling relationships for heat flow.For linear viscosity,heat flow is proportional to the underlying "half-space" viscosity to the 1/3 power and the temperature to change viscosity by a factor of e to the 4/3 power.The formalism is easily modified to represent convection beneath a lid of highly viscous and buoyant cratonal lithosphere and to represent transient convection beneath thickening oceanic lithosphere.Asthenospheric mantle with linear,strongly temperature-dependent,and weakly depth-dependent viscosity is compatible with both oceanic and continental data.More complicated rheology may allow vigorous small-scale convection under most but not all old ocean basins.Still viable hypotheses require poorly understood global features,including lateral variations of asthenospheric temperature.Seismological studies have the potential to resolve the lithosphere-asthenosphere boundary,including local variations of its depth associated with small-scale convection.     

Ancestral polyploidy in seed plants and angiosperms

Whole-genome duplication (WGD), or polyploidy, followed by gene loss and diploidization has long been recognized as an important evolutionary force in animals, fungi and other organisms, especially plants. The success of angiosperms has been attributed, in part, to innovations associated with gene or whole-genome duplications, but evidence for proposed ancient genome duplications pre-dating the divergence of monocots and eudicots remains equivocal in analyses of conserved gene order. Here we use comprehensive phylogenomic analyses of sequenced plant genomes and more than 12.6 million new expressed-sequence-tag sequences from phylogenetically pivotal lineages to elucidate two groups of ancient gene duplications-one in the common ancestor of extant seed plants and the other in the common ancestor of extant angiosperms. Gene duplication events were intensely concentrated around 319 and 192 million years ago, implicating two WGDs in ancestral lineages shortly before the diversification of extant seed plants and extant angiosperms, respectively. Significantly, these ancestral WGDs resulted in the diversification of regulatory genes important to seed and flower development, suggesting that they were involved in major innovations that ultimately contributed to the rise and eventual dominance of seed plants and angiosperms.     

A murine lung cancer co-clinical trial identifies genetic modifiers of therapeutic response

Targeted therapies have demonstrated efficacy against specific subsets of molecularly defined cancers. Although most patients with lung cancer are stratified according to a single oncogenic driver, cancers harbouring identical activating genetic mutations show large variations in their responses to the same targeted therapy. The biology underlying this heterogeneity is not well understood, and the impact of co-existing genetic mutations, especially the loss of tumour suppressors, has not been fully explored. Here we use genetically engineered mouse models to conduct a 'co-clinical' trial that mirrors an ongoing human clinical trial in patients with KRAS-mutant lung cancers. This trial aims to determine if the MEK inhibitor selumetinib (AZD6244) increases the efficacy of docetaxel, a standard of care chemotherapy. Our studies demonstrate that concomitant loss of either p53 (also known as Tp53) or Lkb1 (also known as Stk11), two clinically relevant tumour suppressors, markedly impaired the response of Kras-mutant cancers to docetaxel monotherapy. We observed that the addition of selumetinib provided substantial benefit for mice with lung cancer caused by Kras and Kras and p53 mutations, but mice with Kras and Lkb1 mutations had primary resistance to this combination therapy. Pharmacodynamic studies, including positron-emission tomography (PET) and computed tomography (CT), identified biological markers in mice and patients that provide a rationale for the differential efficacy of these therapies in the different genotypes. These co-clinical results identify predictive genetic biomarkers that should be validated by interrogating samples from patients enrolled on the concurrent clinical trial. These studies also highlight the rationale for synchronous co-clinical trials, not only to anticipate the results of ongoing human clinical trials, but also to generate clinically relevant hypotheses that can inform the analysis and design of human studies.