Research articles

Mitochondrial reactive oxygen species are shown to be required for activation of the NLRP3 inflammasome by various stimuli.

Three distinct models for the recently discovered super-Earth (masses 2–10 times that of Earth) planet GJ 1214b that are consistent with its mass and radius have been suggested. Breaking the degeneracy between these models requires obtaining constraints on the planet's atmospheric composition. Here, a ground based measurement of the transmission spectrum of GJ 1214b between 780 and 1,000 nm is reported. The lack of features in this spectrum rules out cloud free atmospheres composed primarily of hydrogen. If the planet's atmosphere is hydrogen-dominated, then it must contain clouds or hazes that are optically thick at pressures <200 mbar. Alternatively, the data are also consistent with the presence of a dense water vapour atmosphere.

Haematopoietic stem cells (HSCs) are very sensitive to energetic and oxidative stress, and modulation of the balance between their quiescence and proliferation is needed to respond to metabolic stress while preserving HSCs' long-term regenerative capacity. Here the tumour suppressor Lkb1 is shown to promote stem-cell maintenance and tissue regeneration by regulating energy metabolism and by preventing aneuploidy.

A crystal structure of bacterial RNA polymerase (RNAP) bound to the transcription inhibitor Gfh1 reveals the mechanism of inhibition by Gfh1 and an alternative ratcheted state of RNAP.

Innate differences between male and female behaviours must be inscribed in their respective genomes, but how these encode distinct neuronal circuits remains largely unclear. Focusing on sex specific responses to the cVA pheromone in fruitflies, a chain of four successive neurons carrying olfactory signals down to motor centres has been identified, with all male to female anatomical differences lying downstream of a conserved sensory cell. The techniques developed should help others in the task of neuronal circuit mapping, which remains daunting even for the relatively simple fly brain.

Haematopoietic stem cells (HSCs) are very sensitive to energetic and oxidative stress, and modulation of the balance between their quiescence and proliferation is needed to respond to metabolic stress while preserving HSCs' long term regenerative capacity. Here the tumour suppressor Lkb1 is shown to have a crucial role in maintaining energy homeostasis in haematopoietic cells — an effect largely independent of AMPK and mTOR signalling.

During translation, tRNAs enter the ribosome and then move sequentially through three sites, known as A, P and E, as they transfer their attached amino acids onto the growing peptide chain. How the ribosome facilitates tRNA translocation between the sites remains largely unknown. Now a study uses multiparticle cryoelectron microscopy of a ribosome bound to the translation elongation factor, EF-G, to get information about tRNA movement. It identifies two new substates and sees that translocation is linked to unratcheting of the 30S ribosomal subunit.

The E1 and E2 glycoproteins of alphaviruses form heterodimers and assemble into spikes on the virus surface, which mediate receptor binding and endocytosis. When the virion encounters acidic pH in the endosome E1 and E2 dissociate and E1 triggers fusion with the endosomal membrane. Two papers now provide the first crystal structures for glycoprotein complexes incorporating E2 at acidic and neutral pH, respectively. Together they provide insight into how fusion activation is controlled in alphaviruses.

Multipotent stem cells expressing Lgr5 are known to generate all cell types of the intestinal epithelium (enterocytes, goblet cells, Paneth cells and enteroendocrine cells). A new study shows that Paneth cells have an essential role for intestinal crypt and stem cell maintenance by supplying essential niche signals to the Lgr5-expressing cells.

It is shown that amyloid-β oligomers interact with the receptor tyrosine kinase EphB2 and trigger its degradation. EphB2 regulates NMDA-type glutamate receptors and its depletion in normal mice reduces NMDA receptor currents and impairs long-term potentiation, both of which are important for memory formation. Increasing EphB2 levels in a mouse model of Alzheimer's disease improves memory.

Here it is shown that reactivation of endogenous telomerase activity in mice extends telomeres, reduces DNA damage signalling, allows resumption of proliferation in quiescent cultures, and eliminates degenerative phenotypes across multiple organs including testes, spleens and intestines. Accumulating evidence implicating telomere damage as a driver of age-associated organ decline and disease and the reversal of damage observed here support the development of regenerative strategies designed to restore telomere integrity.

The acceleration of the expansion of the Universe is attributed to a 'dark energy' component that opposes gravity. These authors report an analysis of the symmetry properties of distant pairs of galaxies from archival data. This allows them to determine that the Universe is flat, and by alternately fixing its spatial geometry and the dark energy equation-of-state parameter, w_X, they establish at the 68.3 per cent confidence level that −0.85 > w_X > −1.12 and 0.60 < Ω_X < 0.80, where Ω_X is the abundance of dark energy.

p53 is an important tumour suppressor gene. Two papers now show in a Kras-driven lung cancer model that p53-mediated tumour suppression is only engaged late during tumour progression, when the Kras oncogenic signal reaches a threshold sufficient to activate the ARF–p53 pathway. Therefore, p53 re-expression in p53-deficient lung tumours does not restrict early stages of tumorigenesis, but induces tumour regression of more aggressive tumours.

The development of table-top femtosecond electron diffraction sources in recent years has opened up a new way to observe atomic motions in crystalline materials undergoing structural changes. Here, the technique is used to study the charge density wave material 1T-TaS₂, where a modulation of the electron density is accompanied by a periodic lattice distortion. In this femtosecond electron diffraction experiment, where atomic motions are observed in response to a 140 femtosecond optical pulse, the periodic lattice distortion is found to collapse on an exceptionally fast timescale (about 250 femtoseconds), indicative of an electronically driven process involving a highly cooperative process.

Protein machineries that move along the DNA, such as DNA polymerases and helicases, will necessarily encounter other bound proteins interacting with specific sites. Using 'curtains' of labelled DNA, this study measured whether such bound proteins interfere with the activity of the bacterial DNA translocase RecBCD. The translocase is able to push the proteins over nonspecific sites for thousands of base pairs before they are displaced.

Masses of pulsating classical Cepheid supergiants derived from stellar pulsation theory are smaller than the masses derived from stellar evolution theory. An independent determination for a classical Cepheid in a binary system is needed to determine which is correct. These authors report the discovery of a classical Cepheid in the Large Magellanic Cloud. They determine the mass to a precision of one per cent and show that it agrees with its pulsation mass.

p53 is an important tumour suppressor gene. Two papers now show in a Kras-driven lung cancer model that p53-mediated tumour suppression is only engaged late during tumour progression, when the Kras oncogenic signal reaches a threshold sufficient to activate the ARF–p53 pathway. Therefore, p53 re-expression in p53-deficient lung tumours does not restrict early stages of tumorigenesis, but induces tumour regression of more aggressive tumours.

Bose–Einstein condensation has been observed in several physical systems, but is not predicted to occur for blackbody radiation such as photons. However, it becomes theoretically possible in the presence of thermalization processes that conserve photon number. These authors experimentally realise such conditions, observing Bose–Einstein condensation of photons in a dye-filled optical microcavity. The effect is of interest for fundamental studies and may lead to new coherent ultraviolet sources.