Letters in 2008

A late-autumn shoulder is consistently observed in the seasonal cycles of atmospheric methane at high latitude sites, but the sources responsible remain uncertain. This study reports methane flux measurements from a high Arctic setting during the onset of soil freezing. The integral of the emissions during this freeze-in period amount to approximately the same amount of methane emitted during the entire summer season. It is found that the observed early winter emission burst improves the agreement between the simulated seasonal cycle and atmospheric data from latitudes north of 60°N. The results suggest that permafrost associated freeze-in bursts of methane emissions from tundra regions could be an important component of the seasonal distribution of methane emissions from high latitudes.

When seen in ultraviolet light, Venus has contrast features that arise from the non-uniform distribution of unknown absorbers within the sulphuric acid clouds. This paper reports multi-wavelength imaging that reveals that the dark low latitudes are dominated by convective mixing that brings the ultraviolet absorbers up from depth. The bright and uniform mid-latitude clouds reside in the 'cold collar', which suppresses vertical mixing. In low and middle latitudes, the visible cloud top is located at a constant altitude of 72 ± 1 km in both the ultraviolet dark and bright regions, indicating that the brightness variations result from compositional differences caused by the colder environment.

This study reports an optical spectrum of Tycho Brahe's supernova near maximum brightness, obtained from a scattered-light echo more than four centuries after the direct light of the explosion swept past Earth. It is found that SN 1572 belongs to the majority class of normal type Ia supernovae.

It has been a goal in applied physics to construct devices in which superconductivity can be switched on and off with an electric field. Recently, it was shown that the conducting interface between LaAlO₃ and SrTiO₃ (both in bulk form are insulators) can produce a two-dimensional superconducting condensate. This paper now uses the electric field effect, which tunes the charge carrier density, to explore the phase diagram of the system.

Early hypotheses suggested that the digits of tetrapods (land vertebrates) were homologues of fin radials, but this idea fell out of favour on the basis of developmental studies and also on the fin of Panderichthys, a fish closely related to land vertebrates, which appeared to lack distal digit-like fin radials. A new CT study of a classic specimen of Panderichthys shows that the old interpretation was in error. Panderichthys did indeed have digit-like radials: nothing stands in the way of the era of fish fingers.

Brain–machine interfaces are a promising approach for treating spinal cord injury-caused paralysis by rerouting control signals from the brain directly to the muscles. This paper demonstrates that monkeys can directly control stimulation of muscles using the activity of neurons in motor cortex, restoring goal-directed movement to a transiently paralysed arm. In addition, monkeys learned to use these artificial connections so that single neurons previously not associated with the movement could be used to control functional stimulation.

Tamoxifen is commonly used for breast cancer therapy. This paper shows that the transcriptional repression of the ERBB2 oncogene by tamoxifen in breast cancer cells is affected by an antagonistic interaction between the transcriptional regulators PAX2 and AIB-1. This affects the ability of tamoxifen to inhibit cancer cell proliferation. The relative levels of PAX2 and AIP1 in breast cancer patients treated with tamoxifen correlates with relapse-free survival.

A role for Sox18 transcription factor has been suggested by lymphatic dysfunction in the human syndrome hypotrichosis-lymphedema-telangiectasia (HLT), which is caused by mutations in Sox18. This paper shows that Sox18 directly activates Prox1 transcription. Sox18-null embryos show a complete absence of Prox1-positive lymphatic endothelial cells emanating from the cardinal vein.

Shiga toxigenic Escherichia coli causes severe gastrointestinal disease, which is in part mediated by subtilase cytotoxin. The B subunit of this toxin is now shown to have high affinity to glycans containing N-glycolylneuraminic acid, a saccharide that is not synthesized by humans. Instead it is ingested by dietary intake of red meat and dairy products and subsequently incorporated into intestinal and kidney tissue.

Endolysosomal proteolytric cleavage is shown to be required for TLR9 activation by CpG

Suppressing the homologous recombination of repetitive DNA sequences is important for maintaining genome stability, and packaging of repeat DNA into silent chromatin was generally thought to protect it from recombination. Yeast ribosomal DNA (rDNA) repetitive sequences are shown to associate with the nuclear periphery via inner nuclear membrane proteins, and this tethering is required for rDNA stability. Sir2-dependent silencing is not sufficient to inhibit rDNA recombination.

Species-specific recognition between the egg extracellular matrix (zona pellucida) and sperm is the first step of mammalian fertilization. This paper reports the 2.3 Å resolution structure of the 'zona pellucida filament' of the egg, which act as sperm receptors. The structure supports the presence of ZP–N repeats within the amino-terminal region of ZP2 and other vertebrate zona pellucida/vitelline proteins, and has implications for egg coat architecture and the post-fertilization block to polyspermy and speciation.

This paper documents the evolutionary interaction between the innate immunity gene protein kinase R (PKR), its substrate elF2α, and its poxvirus mimic K3L. It is concluded that the rapid evolution of the PKR gene may be due to viral mimicry.

In teleosts, proper balance and hearing depend on mechanical sensors in the inner ear. These sensors include actin-based microvilli and microtubule-based cilia that extend from the surface of sensory hair cells and attach to biomineralized 'ear stones', orotoliths. This paper show that in zebra fish, fluid flow generated by cilia influences the number, growth and localization of otoliths, as well as their mineralization during development.

The human microbiota has been implicated in many health-related issues. In this study, the microbiota composition of monozygotic and dizygotic twins and their mothers is examined. Although a core microbiome could not be defined on a phylogenetic level, the data suggests that core functions are conserved.

MicroRNAs are expressed in a type of heart cell known as cardiomyocytes and their aberrant regulation was correlated with heart disease. This study looks at how miRNAs in other heart cells may contribute to disease. It is found that in cardiac fibroblasts, miR-21 is upregulated in diseased heart. This activates a signalling pathway that exacerbates cardiac disease. By using an RNA molecule directed against miR-21, it was possible to reverse these effects, demonstrating that therapeutic treatment to downregulate a microRNA can be effective in vivo.

220-million-year-old fossils from southwestern China represent the most primitive turtle known, and shed light on intermediate steps in the acquisition of the unique and highly specialized turtle body-plan.

The ideal in organic synthesis is to prepare complex molecules using the smallest possible number of steps. Also important is atom economy, limiting waste by ensuring that most of atoms present in the reactants end up in the product. This paper demonstrates both of these principles to great effect in the synthesis of bryostatin 16, a biologically active, naturally occurring compound. The synthesis uses nearly half the number of steps of previously reported routes to bryostatins.

The Meridional Overturning Circulation (MOC) mixes heat and salinity among ocean basins and between deep and shallow waters. Global climate effects, including moderation of the climate of western Europe, are extensive. Changes in the strength of the MOC could thus have dramatic impacts for local to regional climate change, but evidence for systematic changes is, to date, equivocal. Analysis of the residuals between a coarse resolution ocean model and a model with a localized fine-resolution grid shows that the input of warm and salty water transferred around the southern tip of Africa (termed the Agulhas leakage) contributes strongly to the strength of the MOC.

An examination of inclusion assemblages in Hadean zircons from Jack Hills (Western Australia) is presented, which constrain the magmatic formation conditions to about 700 °C and 7 kbars. This result implies a near-surface heat flow about 3–5 times lower than estimates of global Hadean heat flow. As the only site of magmatism on modern Earth that is characterized by heat flow of about one-quarter of the global average is above subduction zones, it is suggested that the magmas from which the Jack Hills Hadean zircons crystallized were formed largely in an underthrust environment, perhaps similar to modern convergent margins.