Evidence for recycled Archaean oceanic mantle lithosphere in the Azores plume

The compositional differences between mid-ocean-ridge and ocean-island basalts place important constraints on the form of mantle convection. Also, it is thought that the scale and nature of heterogeneities within plumes and the degree to which heterogeneous material endures within the mantle might be reflected in spatial variations of basalt composition observed at the Earth's surface. Here we report osmium isotope data on lavas from a transect across the Azores archipelago which vary in a symmetrical pattern across what is thought to be a mantle plume. Many of the lavas from the centre of the plume have lower 187Os/188Os ratios than most ocean-island basalts and some extend to subchondritic 187Os/188Os ratios-lower than any yet reported from ocean-island basalts. These low ratios require derivation from a depleted, harzburgitic mantle, consistent with the low-iron signature of the Azores plume. Rhenium-depletion model ages extend to 2.5 Gyr, and we infer that the osmium isotope signature is unlikely to be derived from Iberian subcontinental lithospheric mantle. Instead, we interpret the osmium isotope signature as having a deep origin and infer that it may be recycled, Archaean oceanic mantle lithosphere that has delaminated from its overlying oceanic crust. If correct, our data provide evidence for deep mantle subduction and storage of oceanic mantle lithosphere during the Archaean era.     

Deficiency of glutaredoxin 5 reveals Fe-S clusters are required for vertebrate haem synthesis

Iron is required to produce haem and iron-sulphur (Fe-S) clusters, processes thought to occur independently. Here we show that the hypochromic anaemia in shiraz (sir) zebrafish mutants is caused by deficiency of glutaredoxin 5 (grx5), a gene required in yeast for Fe-S cluster assembly. We found that grx5 was expressed in erythroid cells of zebrafish and mice. Zebrafish grx5 rescued the assembly of grx5 yeast Fe-S, showing that the biochemical function of grx5 is evolutionarily conserved. In contrast to yeast, vertebrates use iron regulatory protein 1 (IRP1) to sense intracellular iron and regulate mRNA stability or the translation of iron metabolism genes. We found that loss of Fe-S cluster assembly in sir animals activated IRP1 and blocked haem biosynthesis catalysed by aminolaevulinate synthase 2 (ALAS2). Overexpression of ALAS2 RNA without the 5' iron response element that binds IRP1 rescued sir embryos, whereas overexpression of ALAS2 including the iron response element did not. Further, antisense knockdown of IRP1 restored sir embryo haemoglobin synthesis. These findings uncover a connection between haem biosynthesis and Fe-S clusters, indicating that haemoglobin production in the differentiating red cell is regulated through Fe-S cluster assembly.     

波浪作用下油脂冰内溢油行为物理模拟实验技术

为在实验室条件下研究波浪-油脂冰、波浪-油脂冰-溢油的相互作用,建立了与化学实验室相应水平量级的物理模拟实验技术.设计制作了微型波浪实验水槽,用化学实验室的振荡台作为动力源;水槽经过保温处理,能够在低温实验室使用;物理模拟水槽及测试设备等所使用的玻璃和塑料材料对溢油没有吸附.利用图像分析技术给出波浪要素.实验技术可控制油脂冰在波浪作用下总量保持不变.通过对系列实验结果分析,得到油脂冰制备温度条件以及波长、波高同振荡台传动臂调节孔位置、频率和水槽水深的关系,实现了对实验油脂冰厚度和波浪要素的控制.整套实验技术可以开展波浪、油脂冰与溢油相互作用的物理模拟.     

The Integrability of Ovals: Newton's Lemma 28 and Its Counterexamples

Principia (Book 1, Sect. 6), Newton's Lemma 28 on the algebraic nonintegrability of ovals has had an unusually mixed reception. Beginning in 1691 with Jakob Bernoulli (who accepted the lemma) and Huygens and Leibniz (who rejected it and offered counterexamples), Lemma 28 has a history of eliciting seemingly contradictory reactions. In more recent times, D.T. Whiteside in 1974 gave an “unchallengeable counterexample,” while the mathematician V.I. Arnol'd in 1987 sided with Bernoulli and called Newton's argument an “astonishingly modern topological proof.” This disagreement mostly stems, we argue, from Newton's vague statement of the lemma. Indeed, we identify several different interpretations of Lemma 28, any one of which Newton may have been intending to assert, and we then test a number of proposed counterexamples to see which, if any, are true counterexamples to one or more of these versions of the lemma. Following this, we study Newton's argument for the lemma to see whether and where it fails to be convincing. In the end, our study of Newton's Lemma 28 provides an answer to the question, Who is right: Huygens, Leibniz, Whiteside and the others who reject the lemma, or Bernoulli, Arnol'd, and the others who accept it? (Received November 6, 2000)     

FMRFamide reverses protein phosphorylation produced by 5-HT and cAMP in Aplysia sensory neurons

Neurotransmitter can modulate neuronal activity through a variety of second messengers that act on ion channels and other substrate proteins. The most commonly described effector mechanism for second messengers in neurons depends on protein phosphorylation mediated by one of three sets of kinases: the cyclic AMP-dependent protein kinases, the Ca2+-calmodulin-dependent protein kinases, and the Ca2+-phospholipid-dependent protein kinases. In addition, some neurotransmitters and second messengers can also inhibit protein phosphorylation by lowering cAMP levels (either by inhibiting adenylyl cyclase or activating phosphodiesterases). This raises the question: can neurotransmitters also modulate neuronal activity by decreasing protein phosphorylation that is independent of cAMP? Various biochemical experiments show that a decrease in protein phosphorylation can arise through activation of a phosphatase or inhibition of kinases. In none of these cases, however, is the physiological role for the decrease in protein phosphorylation known. Here we report that in Aplysia sensory neurons, the presynaptic inhibitory transmitter FMRFamide decreases the resting levels of protein phosphorylation without altering the level of cAMP. Furthermore, FMRFamide overrides the cAMP-mediated enhancement of transmitter release produced by 5-hydroxytryptamine (5-HT), and concomitantly reverses the cAMP-dependent increase in protein phosphorylation produced by 5-HT. These findings indicate that a receptor-mediated decrease in protein phosphorylation may play an important part in the modulation of neurotransmitter release.     

LKB1 modulates lung cancer differentiation and metastasis

Germline mutation in serine/threonine kinase 11 (STK11, also called LKB1) results in Peutz-Jeghers syndrome, characterized by intestinal hamartomas and increased incidence of epithelial cancers. Although uncommon in most sporadic cancers, inactivating somatic mutations of LKB1 have been reported in primary human lung adenocarcinomas and derivative cell lines. Here we used a somatically activatable mutant Kras-driven model of mouse lung cancer to compare the role of Lkb1 to other tumour suppressors in lung cancer. Although Kras mutation cooperated with loss of p53 or Ink4a/Arf (also known as Cdkn2a) in this system, the strongest cooperation was seen with homozygous inactivation of Lkb1. Lkb1-deficient tumours demonstrated shorter latency, an expanded histological spectrum (adeno-, squamous and large-cell carcinoma) and more frequent metastasis compared to tumours lacking p53 or Ink4a/Arf. Pulmonary tumorigenesis was also accelerated by hemizygous inactivation of Lkb1. Consistent with these findings, inactivation of LKB1 was found in 34% and 19% of 144 analysed human lung adenocarcinomas and squamous cell carcinomas, respectively. Expression profiling in human lung cancer cell lines and mouse lung tumours identified a variety of metastasis-promoting genes, such as NEDD9, VEGFC and CD24, as targets of LKB1 repression in lung cancer. These studies establish LKB1 as a critical barrier to pulmonary tumorigenesis, controlling initiation, differentiation and metastasis.     

No evidence for thick deposits of ice at the lunar south pole

Shackleton crater at the Moon's south pole has been suggested as a possible site of concentrated deposits of water ice, on the basis of modelling of bi-static radar polarization properties and interpretations of earlier Earth-based radar images. This suggestion, and parallel assumptions about other topographic cold traps, is a significant element in planning for future lunar landings. Hydrogen enhancements have been identified in the polar regions, but these data do not identify the host species or its local distribution. The earlier Earth-based radar data lack the resolution and coverage for detailed studies of the relationship between radar scattering properties, cold traps in permanently shadowed areas, and local terrain features such as the walls and ejecta of small craters. Here we present new 20-m resolution, 13-cm-wavelength radar images that show no evidence for concentrated deposits of water ice in Shackleton crater or elsewhere at the south pole. The polarization properties normally associated with reflections from icy surfaces in the Solar System were found at all the observed latitudes and are strongly correlated with the rock-strewn walls and ejecta of young craters, including the inner wall of Shackleton. There is no correlation between the polarization properties and the degree of solar illumination. If the hydrogen enhancement observed by the Lunar Prospector orbiter indicates the presence of water ice, then our data are consistent with the ice being present only as disseminated grains in the lunar regolith.     

Potential for controlling the spread of Centaurea maculosa with grass competition

Spotted knapweed ( Centaurea maculosa Lam.) is a major rangeland and roadside weed of the northern Rocky Mountains. It is often found in plant communities dominated by Pseudoroegneria spicatum or Festuca idahoensis , but it rarely invades roadsides dominated by Bromus tnermis Leyss. Aboveground biomass of the 3 grass species grown in mixture with Centaurea was compared to growth in monoculture at a range of nitrogen input levels. The results suggest that Bromus is capable of suppressing the growth of Centaurea with the degree of suppression increasing with increasing nitrogen levels. The 2 native grasses had no impact on Centaurea under the controlled environment conditions of this study.