Letters in 2008

Continental rifts initiate and develop through repeated episodes of faulting and magmatism, yet strain partitioning between faulting and magmatism during discrete rifting episodes remains poorly documented. It is shown that most of the strain during the July–August 2007 seismic crisis in the Natron rift, Tanzania, was released aseismically. This event provides evidence for strain accommodation by magma intrusion, in addition to slip along normal faults, during the initial stages of continental rifting, and before significant crustal thinning.

A new method to convert secondary alcohols in their single mirror image form into tertiary alcohols has been developed. Starting from a single enantiomer of the secondary alcohol, either mirror image form of the tertiary alcohol can be made with very high levels of stereocontrol. A broad range of tertiary alcohols can now be easily made by this method with very high levels of selectivity.

There is support for the idea that there are liquid oceans on several moons of the outer planets, with Jupiter's moon Europa having received the most attention. But it is unclear how these oceans remain liquid. This paper describes strong tidal dissipation (and heating) in the liquid oceans of such moons, and shows that a previously unconsidered tidal force due to obliquity has the right form and frequency to resonantly excite large-amplitude Rossby waves.

To realize scalable quantum information networks, it will be important to develop techniques for storage and retrieval of light at the single photon level. Quantum interfaces between light and matter have been demonstrated, but mainly with atomic gases that involve sophisticated schemes to trap the atoms. This paper demonstrates a potentially more practical approach; coherent and reversible mapping of a light field with less than one photon per pulse onto an ensemble of ∼10⁷ atoms naturally trapped in a solid state medium. The state of the light is mapped onto collective atomic excitations on an optical transition and stored for a pre-programmed time up of to one microsecond before being retrieved again.

Brain development requires the coordinated differentiation and wiring of numerous neuronal cell types based on a relatively limited set of genes. This study dissects the interplay of positive and negative gene transcription regulators, which orchestrate the coordinated synthesis of specific photosensitive pigments and axon guidance molecules in a subset of Drosophila photoreceptor neurons.

This paper studies a phenomenon called contact inhibition of locomotion, whereby fibroblast cells grown in cell culture retract their protrusions and change their direction on contact. It is shown that this occurs in vivo, and the molecular basis is revealed. Neural crest cells, highly migratory cells of embryonic origin, exhibit contact inhibition of locomotion both in vivo and in vitro, which accounts for their directional migration. However, when a neural crest cell meets another cell type, it fails to display contact inhibition of locomotion, allowing it to invade the tissue.

This paper describes an in vivo assay of haematopoietic stem cell (HSC) niche formation. A population of progenitor cells is sorted from fetal bones, and when transplanted under the adult mouse kidney capsule, the cells recruit host-derived blood vessels, produce donor-derived ectopic bones, and generate a marrow cavity populated by host-derived long-term reconstituting haematopoeitic stem cells.

Mutations in BRAF and NRAS that lead to constitutive activation of MAP kinase signalling have been found at high frequencies in many melanomas. However, they have not been found in the uveal melanomas and blue nevi subtypes of melanoma. This paper shows that these subtypes instead show frequent activating mutations in the G protein α-subunit GNAQ, also leading to the activation of the MAP kinase pathway.

This study shows that blockade of PD-1 in SIV-infected macaques transiently increases the frequency, activation and functionality markers of virus-specific CD8 T cells without adverse side effects.

Eutrophication of coastal waters can cause sulphide blooms, which are toxic to marine life. It is shown that these blooms can be rapidly detoxified by sulphide-oxidizing bacteria. This finding suggests that sulphide blooms may occur more frequently than previously appreciated and that the responsible bacterial groups are important to protect coastal ecosystems.

The exosome is a multisubunit exonuclease complex that degrades many types of RNAs, in many different contexts, in a 3′ to 5′ manner. The catalytic component of the exosome is the Dis3 subunit. Dis3 contains a PIN domain, which is sometimes associated with nuclease activity. This work shows that the Dis3 PIN domain also possesses endonuclease activity (that is, it can cleave RNA internally, rather than from an end). Mutations in either this domain or in the exonuclease domain exhibit a growth phenotype, suggesting that both activities are physiologically important.

DNA strand exchange results in a physical linkage between two homologous DNAs. The RecA/RAD51 family of ATPases mediates strand exchange by forming a long filament on the DNA. This paper uses a single-molecule approach to elucidate how the filament is disassembled once the strands are exchanged, and how this process relates to the energy released by nucleotide hydrolysis.

The common dust mite allergen Der p 2 is shown to replace MD-2 as the lipopolysaccharide-binding component and facilitates signalling through TLR4. It is suggested that Der p 2 tends to be targeted by adaptive immune responses because of its auto-adjuvant properties.

Adhesion to host cells is essential for virulence of many bacterial pathogens, including pathogenic Escherichia coli. An adhesion mechanism that relies on the secreted protein EtpA is now presented. EtpA attaches to both the bacterial flagella tip and the host cell, providing an adherence mechanism that is important for E. coli pathogenesis and may be present in many other pathogens that possess EtpA homologues.

Chlamydia trachomatis is an intracellular pathogen that relies on host lipids for growth. It is shown that bacterial infection induces Golgi apparatus fragmentation through cleavage and activation of golgin-84, thereby providing a mechanism for lipid acquisition.

Networks of co-operative interactions occur in both ecological and socio-economic situations, with plant pollination by animals and interactions between manufacturing and contracting companies being respective examples. This work proposes a parsimonious model for co-operative networks that predicts the specific properties of real ecological and socio-economic networks, demonstrating that similar principles of co-operation might underlie both situations.

Recently haematopoietic stem cell niches have been shown to comprise osteoblastic and vascular microenvironments. This study describes a newly developed ex vivo real-time imaging technology and immunoassaying to trace the homing of highly purified GFP-expressing haematopoietic stem cells in response to irradiation.

To survive in an harsh environment, Caenorhabditis elegans larvae enter a state called dauer, during which the worms do not eat, remain active, but become stress-resistant and extremely long-lived. A typical dauer has reduced insulin-like signalling, full nutrient stores and changes in its metabolism. It is shown that without AMPK (LKB1) signalling dauers rapidly consume their stored energy and expire prematurely, due to vital organ failure.

High resolution combined confocal and two-photon video imaging of individual haematopoietic cells is performed in the bone marrow of living animals, examining their relationship to blood vessels, osteoblasts and endosteal surface as they home and engraft. It is found that osteoblasts were enmeshed in microvessals and different populations of haematopoeitic cells were localized in different areas according to their stage of differentiation. In settings of engraftment as well as expansion, marrow stem/progenitor cells were in closer proximity to bone and osteoblasts.

In March 2005 the Sunda megathrust earthquake, with a moment magnitude of 8.6, occurred. Concern was then focused further south on the Mentawai area, where large earthquakes had occurred in 1797 (magnitude 8.8) and 1833 (magnitude 9.0). On 12 September 2007, a magnitude 8.4 earthquake occurred, followed by a magnitude 7.9 earthquake 12 hours later. This paper shows that these earthquakes ruptured only a fraction of the area ruptured in 1833 and conclude that the stress state on the portion of the Sunda megathrust that ruptured in 1797 and 1833 was probably not adequate for the development of a single major large rupture in 2007, meaning that the potential for a large megathrust event in the Mentawai area thus remains high.