人类基因组序列图并非完美

在被问及人类基因组最新的一张碱基序列图时,冰岛科学家们认为其中有大约100个片段需要认真修改。 凯撒西部保留地大学(Case Western Reserve)的     

A short-term sink for atmospheric CO2 in subtropical mode water of the North Atlantic Ocean

Large-scale features of ocean circulation, such as deep water formation in the northern North Atlantic Ocean, are known to regulate the long-term physical uptake of CO2 from the atmosphere by moving CO2-laden surface waters into the deep ocean. But the importance of CO2 uptake into water masses that ventilate shallower ocean depths, such as subtropical mode waters of the subtropical gyres, are poorly quantified. Here we report that, between 1988 and 2001, dissolved CO2 concentrations in subtropical mode waters of the North Atlantic have increased at a rate twice that expected from these waters keeping in equilibrium with increasing atmospheric CO2. This accounts for an extra 0.4-2.8 Pg C (1 Pg = 10(15) g) over this period (that is, about 0.03-0.24 Pg C yr(-1)), equivalent to 3-10% of the current net annual ocean uptake of CO2 (ref. 3). We suggest that the lack of strong winter mixing events, to greater than 300 m in depth, in recent decades is responsible for this accumulation, which would otherwise disturb the mode water layer and liberate accumulated CO2 back to the atmosphere. However, future climate variability (which influences subtropical mode water formation) and changes in the North Atlantic Oscillation (leading to a return of deep winter mixing events) may reduce CO2 accumulation in subtropical mode waters. We therefore conclude that, although CO2 uptake by subtropical mode waters in the North Atlantic--and possibly elsewhere--does not always represent a long-term CO2 sink, the phenomenon is likely to contribute substantially to interannual variability in oceanic CO2 uptake.     

Does the river blenny Salaria fluviatilis (Asso, 1801) (Actinopterygii: Perciformes) still survive on the Mediterranean island of Cyprus?

The river blenny (Salaria fluviatilis) is rarely mentioned in the natural history literature of Cyprus. This has led to doubts about its existence there. Mistakes with mismatched fish collections have occurred in the past, so it is worth asking whether the recorded specimens are actually from Cyprus and whether the species survives there today. Archived correspondence from the original specimen collector confirms that the record of S. fluviatilis on Cyprus is genuine, yet our extensive surveys there during the last 4 years have failed to locate the fish. A review of the species’ Mediterranean island distribution shows that it exists on 10 islands that are either close to the mainland or are relatively very large in areal extent. Although the mystery of S. fluviatilis survival on Cyprus lingers, efforts must be made to survey all potential habitats and consider planning a re-introduction project if the population is confirmed as extinct.     

Additions to knowledge of Paleocene mammals from the North Horn Formation, central Utah

The distinctive but inadequately known Paleocene faunas of central Utah are significant in that they sample a time interval not well represented by sequences in other areas. New materials from the Wagon Road (late Puercan) and Dragon (early Torrejonian) local faunas, North Horn Formation, provide additional information on the composition of the assemblages and systematics of included mammal taxa. The proteutherian ? Propalaeosinopa is recorded for the first time, from the Wagon Road fauna, indicating a significant extension for the enigmatic family Pantolestidae, otherwise first known from the Torrejonian. Associated premolars of Aphronorus simpsoni , a pentacodontid proteutherian from the Dragon fauna, indicated that the species is more distinct from its Torrejonian congener, A. fraudator , than previously suspected. New materials of Desmatoclaenus hermaeus uphold the synonymy of this species with D. paracreodus and permit more adequate definition of the genus with respect to the arctocyonid Loxolophus and the phenacodontid Tetraclaenodon ; because Desmatoclaenus appears to share derived morphology with Loxolophus , we refer it to the basal condylarth family Arctocyonidae. The periptychid condylarth Haploconus , represented in the Wagon Road fauna by the geologically oldest described species of the genus, H. elachistsus , is shown to be distinctive in the configuration of lower molars and premolars; H. elachistus appears to be more primitive than species known from the Torrejonian of New Mexico. Some features of Haploconus are suggestive of the Conacodontinae, a distinctive clade of diminutive periptychids.     

Altered proteostasis in aging and heat shock response in C. elegans revealed by analysis of the global and de novo synthesized proteome

Protein misfolding and aggregation as a consequence of impaired protein homeostasis (proteostasis) not only characterizes numerous age-related diseases but also the aging process itself. Functionally related to the aging process are, among others, ribosomal proteins, suggesting an intimate link between proteostasis and aging. We determined by iTRAQ quantitative proteomic analysis in C. elegans how the proteome changes with age and in response to heat shock. Levels of ribosomal proteins and mitochondrial chaperones were decreased in aged animals, supporting the notion that proteostasis is altered during aging. Mitochondrial enzymes of the tricarboxylic acid cycle and the electron transport chain were also reduced, consistent with an age-associated energy impairment. Moreover, we observed an age-associated decline in the heat shock response. In order to determine how protein synthesis is altered in aging and in response to heat shock, we complemented our global analysis by determining the de novo proteome. For that, we established a novel method that enables both the visualization and identification of de novo synthesized proteins, by incorporating the non-canonical methionine analogue, azidohomoalanine (AHA), into the nascent polypeptides, followed by reacting the azide group of AHA by ‘click chemistry’ with an alkyne-labeled tag. Our analysis of AHA-tagged peptides demonstrated that the decreased abundance of, for example, ribosomal proteins in aged animals is not solely due to degradation but also reflects a relative decrease in their synthesis. Interestingly, although the net rate of protein synthesis is reduced in aged animals, our analyses indicate that the synthesis of certain proteins such as the vitellogenins increases with age.     

A Raf-induced allosteric transition of KSR stimulates phosphorylation of MEK

In metazoans, the Ras-Raf-MEK (mitogen-activated protein-kinase kinase)-ERK (extracellular signal-regulated kinase) signalling pathway relays extracellular stimuli to elicit changes in cellular function and gene expression. Aberrant activation of this pathway through oncogenic mutations is responsible for a large proportion of human cancer. Kinase suppressor of Ras (KSR) functions as an essential scaffolding protein to coordinate the assembly of Raf-MEK-ERK complexes. Here we integrate structural and biochemical studies to understand how KSR promotes stimulatory Raf phosphorylation of MEK (refs 6, 7). We show, from the crystal structure of the kinase domain of human KSR2 (KSR2(KD)) in complex with rabbit MEK1, that interactions between KSR2(KD) and MEK1 are mediated by their respective activation segments and C-lobe αG helices. Analogous to BRAF (refs 8, 9), KSR2 self-associates through a side-to-side interface involving Arg?718, a residue identified in a genetic screen as a suppressor of Ras signalling. ATP is bound to the KSR2(KD) catalytic site, and we demonstrate KSR2 kinase activity towards MEK1 by in vitro assays and chemical genetics. In the KSR2(KD)-MEK1 complex, the activation segments of both kinases are mutually constrained, and KSR2 adopts an inactive conformation. BRAF allosterically stimulates the kinase activity of KSR2, which is dependent on formation of a side-to-side KSR2-BRAF heterodimer. Furthermore, KSR2-BRAF heterodimerization results in an increase of BRAF-induced MEK phosphorylation via the KSR2-mediated relay of a signal from BRAF to release the activation segment of MEK for phosphorylation. We propose that KSR interacts with a regulatory Raf molecule in cis to induce a conformational switch of MEK, facilitating MEK's phosphorylation by a separate catalytic Raf molecule in trans.     

Linking mantle plumes, large igneous provinces and environmental catastrophes

Large igneous provinces (LIPs) are known for their rapid production of enormous volumes of magma (up to several million cubic kilometres in less than a million years), for marked thinning of the lithosphere, often ending with a continental break-up, and for their links to global environmental catastrophes. Despite the importance of LIPs, controversy surrounds even the basic idea that they form through melting in the heads of thermal mantle plumes. The Permo-Triassic Siberian Traps--the type example and the largest continental LIP--is located on thick cratonic lithosphere and was synchronous with the largest known mass-extinction event. However, there is no evidence of pre-magmatic uplift or of a large lithospheric stretching, as predicted above a plume head. Moreover, estimates of magmatic CO(2) degassing from the Siberian Traps are considered insufficient to trigger climatic crises, leading to the hypothesis that the release of thermogenic gases from the sediment pile caused the mass extinction. Here we present petrological evidence for a large amount (15?wt%) of dense recycled oceanic crust in the head of the plume and develop a thermomechanical model that predicts no pre-magmatic uplift and requires no lithospheric extension. The model implies extensive plume melting and heterogeneous erosion of the thick cratonic lithosphere over the course of a few hundred thousand years. The model suggests that massive degassing of CO(2) and HCl, mostly from the recycled crust in the plume head, could alone trigger a mass extinction and predicts it happening before the main volcanic phase, in agreement with stratigraphic and geochronological data for the Siberian Traps and other LIPs.     

Has the Earth's sixth mass extinction already arrived?

Palaeontologists characterize mass extinctions as times when the Earth loses more than three-quarters of its species in a geologically short interval, as has happened only five times in the past 540?million years or so. Biologists now suggest that a sixth mass extinction may be under way, given the known species losses over the past few centuries and millennia. Here we review how differences between fossil and modern data and the addition of recently available palaeontological information influence our understanding of the current extinction crisis. Our results confirm that current extinction rates are higher than would be expected from the fossil record, highlighting the need for effective conservation measures.