Apoptosis initiated by Bcl-2-regulated caspase activation independently of the cytochrome c/Apaf-1/caspase-9 apoptosome

Apoptosis is an evolutionarily conserved cell suicide process executed by cysteine proteases (caspases) and regulated by the opposing factions of the Bcl-2 protein family. Mammalian caspase-9 and its activator Apaf-1 were thought to be essential, because mice lacking either of them display neuronal hyperplasia and their lymphocytes and fibroblasts seem resistant to certain apoptotic stimuli. Because Apaf-1 requires cytochrome c to activate caspase-9, and Bcl-2 prevents mitochondrial cytochrome c release, Bcl-2 is widely believed to inhibit apoptosis by safeguarding mitochondrial membrane integrity. Our results suggest a different, broader role, because Bcl-2 overexpression increased lymphocyte numbers in mice and inhibited many apoptotic stimuli, but the absence of Apaf-1 or caspase-9 did not. Caspase activity was still discernible in cells lacking Apaf-1 or caspase-9, and a potent caspase antagonist both inhibited apoptosis and retarded cytochrome c release. We conclude that Bcl-2 regulates a caspase activation programme independently of the cytochrome c/Apaf-1/caspase-9 'apoptosome', which seems to amplify rather than initiate the caspase cascade.     

Determining the composition of the Earth

A long-standing question in the planetary sciences asks what the Earth is made of. For historical reasons, volatile-depleted primitive materials similar to current chondritic meteorites were long considered to provide the 'building blocks' of the terrestrial planets. But material from the Earth, Mars, comets and various meteorites have Mg/Si and Al/Si ratios, oxygen-isotope ratios, osmium-isotope ratios and D/H, Ar/H2O and Kr/Xe ratios such that no primitive material similar to the Earth's mantle is currently represented in our meteorite collections. The 'building blocks' of the Earth must instead be composed of unsampled 'Earth chondrite' or 'Earth achondrite'.     

Cultivation of the ubiquitous SAR11 marine bacterioplankton clade

The alpha-proteobacterial lineage that contains SAR11 and related ribosomal RNA gene clones was among the first groups of organisms to be identified when cultivation-independent approaches based on rRNA gene cloning and sequencing were applied to survey microbial diversity in natural ecosystems. This group accounts for 26% of all ribosomal RNA genes that have been identified in sea water and has been found in nearly every pelagic marine bacterioplankton community studied by these methods. The SAR11 clade represents a pervasive problem in microbiology: despite its ubiquity, it has defied cultivation efforts. Genetic evidence suggests that diverse uncultivated microbial taxa dominate most natural ecosystems, which has prompted widespread efforts to elucidate the geochemical activities of these organisms without the benefit of cultures for study. Here we report the isolation of representatives of the SAR11 clade. Eighteen cultures were initially obtained by means of high-throughput procedures for isolating cell cultures through the dilution of natural microbial communities into very low nutrient media. Eleven of these cultures have been successfully passaged and cryopreserved for future study. The volume of these cells, about 0.01 micro m(3), places them among the smallest free-living cells in culture.     

Regulation of ethylene gas biosynthesis by the Arabidopsis ETO1 protein

Ethylene gas is used as a hormone by plants, in which it acts as a critical growth regulator. Its synthesis is also rapidly evoked in response to a variety of biotic and abiotic stresses. The Arabidopsis ethylene-overproducer mutants eto2 and eto3 have previously been identified as having mutations in two genes, ACS5 and ACS9, respectively; these encode isozymes of 1-aminocyclopropane-1-carboxylic acid synthase (ACS), which catalyse the rate-limiting step in ethylene biosynthesis. Here we report that another ethylene-overproducer mutation, eto1, is in a gene that negatively regulates ACS activity and ethylene production. The ETO1 protein directly interacts with and inhibits the enzyme activity of full-length ACS5 but not of a truncated form of the enzyme, resulting in a marked accumulation of ACS5 protein and ethylene. Overexpression of ETO1 inhibited induction of ethylene production by the plant growth regulator cytokinin, and promoted ACS5 degradation by a proteasome-dependent pathway. ETO1 also interacts with CUL3, a constituent of ubiquitin ligase complexes in which we propose that ETO1 serves as a substrate-specific adaptor protein. ETO1 thus has a dual mechanism, inhibiting ACS enzyme activity and targeting it for protein degradation. This permits rapid modulation of the concentration of ethylene.     

Effectiveness of the global protected area network in representing species diversity

The Fifth World Parks Congress in Durban, South Africa, announced in September 2003 that the global network of protected areas now covers 11.5% of the planet's land surface. This surpasses the 10% target proposed a decade earlier, at the Caracas Congress, for 9 out of 14 major terrestrial biomes. Such uniform targets based on percentage of area have become deeply embedded into national and international conservation planning. Although politically expedient, the scientific basis and conservation value of these targets have been questioned. In practice, however, little is known of how to set appropriate targets, or of the extent to which the current global protected area network fulfils its goal of protecting biodiversity. Here, we combine five global data sets on the distribution of species and protected areas to provide the first global gap analysis assessing the effectiveness of protected areas in representing species diversity. We show that the global network is far from complete, and demonstrate the inadequacy of uniform--that is, 'one size fits all'--conservation targets.     

Mutant small heat-shock protein 27 causes axonal Charcot-Marie-Tooth disease and distal hereditary motor neuropathy

Charcot-Marie-Tooth disease (CMT) is the most common inherited neuromuscular disease and is characterized by considerable clinical and genetic heterogeneity. We previously reported a Russian family with autosomal dominant axonal CMT and assigned the locus underlying the disease (CMT2F; OMIM 606595) to chromosome 7q11-q21 (ref. 2). Here we report a missense mutation in the gene encoding 27-kDa small heat-shock protein B1 (HSPB1, also called HSP27) that segregates in the family with CMT2F. Screening for mutations in HSPB1 in 301 individuals with CMT and 115 individuals with distal hereditary motor neuropathies (distal HMNs) confirmed the previously observed mutation and identified four additional missense mutations. We observed the additional HSPB1 mutations in four families with distal HMN and in one individual with CMT neuropathy. Four mutations are located in the Hsp20-alpha-crystallin domain, and one mutation is in the C-terminal part of the HSP27 protein. Neuronal cells transfected with mutated HSPB1 were less viable than cells expressing the wild-type protein. Cotransfection of neurofilament light chain (NEFL) and mutant HSPB1 resulted in altered neurofilament assembly in cells devoid of cytoplasmic intermediate filaments.     

How Prometheus creates structure in Saturn's F ring

Images of Saturn's narrow and contorted F ring returned by the Cassini spacecraft have revealed phenomena not previously detected in any planetary ring system. The perturbing effect of the inner shepherding satellite, Prometheus, seems to introduce channels through the F ring and a 'streamer'--a line of particles that link the ring to the satellite. The detailed mechanism for the formation of these features has been lacking an explanation. Here we show that these phenomena can be understood in terms of a simple gravitational interaction as Prometheus approaches and recedes from the F ring every 14.7 hours. Our numerical models show that as Prometheus recedes from its closest approach to the F ring, it draws out ring material; one orbital period later, this affected region has undergone keplerian shear and is visible as a channel, in excellent agreement with structures seen in the Cassini images. Prometheus' periodic disruption of the F ring will become more pronounced as the two orbits approach their minimum separation in 2009. The model predicts that the appearance of streamers and the associated channels will vary in a regular fashion on a timescale of one orbital period.     

Vertebrate Smoothened functions at the primary cilium

The unanticipated involvement of several intraflagellar transport proteins in the mammalian Hedgehog (Hh) pathway has hinted at a functional connection between cilia and Hh signal transduction. Here we show that mammalian Smoothened (Smo), a seven-transmembrane protein essential for Hh signalling, is expressed on the primary cilium. This ciliary expression is regulated by Hh pathway activity; Sonic hedgehog or activating mutations in Smo promote ciliary localization, whereas the Smo antagonist cyclopamine inhibits ciliary localization. The translocation of Smo to primary cilia depends upon a conserved hydrophobic and basic residue sequence homologous to a domain previously shown to be required for the ciliary localization of seven-transmembrane proteins in Caenorhabditis elegans. Mutation of this domain not only prevents ciliary localization but also eliminates Smo activity both in cultured cells and in zebrafish embryos. Thus, Hh-dependent translocation to cilia is essential for Smo activity, suggesting that Smo acts at the primary cilium.