Volume 506 Issue 7488, 20 February 2014

Science has a part to play in ensuring protection for defendants with intellectual disabilities.

Many bemoan the shortage of helium for the lab, but for geologists, its true value is in the ground.

Research and development into diseases affecting the world’s poorest people will not benefit from the agency’s policy, warns Mary Moran.

The week in science: Inquiry launched into stem-cell reprogramming study; Europe moves closer to approving third transgenic crop; and politicians vow to get tougher on poaching.

Chinese government to provide incentives for heavy polluters to go green, but analysts question whether its wider air-quality strategy goes far enough.

Gravitational lensing solves puzzle from the Big Bang’s echo.

Ambitious initiative targets Pacific currents, regional climate and deep-sea ecology.

Vote for immigration quotas leads to suspension of talks over Horizon 2020 programme.

Some Google Lunar X Prize contenders book launches for 2015 — but many say that is a stretch.

Country’s system of political patronage in science exposed.

Before it shattered near the Sun, Comet ISON became a scientific celebrity. Now researchers are trying to piece together its lessons.

The US Supreme Court years ago ruled against applying the death penalty to people unable to understand the legal process. Now it must grapple with the science of how intellectual disability is measured.

Plans for a 300-kilometre waterway joining the Pacific and Atlantic oceans need independent environmental assessment, urge Axel Meyer and Jorge A. Huete-Pérez.

For medical use, human stool should be considered a tissue, not a drug, argue Mark B. Smith, Colleen Kelly and Eric J. Alm.

Two accounts take contrasting lessons from nuclear accidents, finds Mark Peplow.

Anthony King enjoys a collection of instructive failures.

Observations of the supernova remnant Cassiopeia A offer an unprecedented look back at the centre of this explosion, and support the hypothesis that spatial asymmetry is key to explaining the event. See Letter p.339

A protein produced by endothelial cells that line blood vessels has been found to regulate the timing of cell proliferation following liver injury, further demonstrating the role of vascular signals in tissue regeneration.

The early development of acute leukaemias is assumed for the most part to be clinically silent and transient. But it now seems that ancestral precancerous cells are identifiable and persistent. See Article p.328

Experiments conducted at the US National Ignition Facility have cleared a hurdle on the road to nuclear fusion in the laboratory, encouraging fusion scientists around the world. See Letter p.343

Ribosomes, the cell's protein-synthesis machines, are assembled from their components in a defined order. It emerges that the first assembly step must overcome dynamic structural rearrangements. See Article p.334

In advanced age, the stem cells responsible for muscle regeneration switch from reversible quiescence to irreversible senescence. Targeting a driver of senescence revives muscle stem cells and restores regeneration. See Article p.316

How atmospheric oxygen concentrations evolved from only small amounts for the early Earth to about 21 per cent today remains uncertain; here our latest understanding of the evolution of Earth’s oxygen levels is discussed.

This study shows that ageing satellite cells undergo an irreversible transition from a quiescent to a pre-senescent state that results in the loss of muscle regeneration in sarcopenia; furthermore, increased expression of p16^INK4a is identified as a common feature of senescent satellite cells.

Through the use of a novel three-dimensional imaging technique, used in conjunction with a multicolour reporter that allows lineage tracing and cell tracking of entire mammary ducts in vivo, bipotent stem cells are shown to have a central role in both puberty and long-term maintenance; in addition, long-lived luminal progenitor cells with a prominent role in ductal expansion are identified.

The authors identify pre-leukaemic haematopoietic stem cells (HSCs) in patients with acute myeloid leukaemia; these pre-leukaemic HSCs have the capacity of normal multi-lineage haematopoietic differentiation with a competitive growth advantage over wild-type HSCs, and owing to their persistence may serve as a reservoir for therapeutic resistance and relapse.

Three-colour fluorescence resonance energy transfer and molecular dynamics simulations are used to study the events occurring early in assembly of the 30S ribosome; within a non-native intermediate S4 ribosomal protein–16S RNA structure, S4 is capable of altering the RNA helix dynamics to facilitate conformation changes that enable subsequent protein binding.

The observation of non-uniformly distributed titanium emission in the interior of Cassiopeia A, a core-collapse supernova, is an indicator of asymmetries in the stellar explosion and provides strong evidence for the development of low-mode convective instabilities in such supernovae.

Fusion fuel gains greater than unity — which are crucial to the generation of fusion energy — are achieved on the US National Ignition Facility using the ‘high-foot’ implosion method, which reduces instability in the implosion of the fuel.

Nanoribbons of graphene grown on electronics-grade silicon carbide conduct electrons much better than expected; at room temperature, the charge carriers travel through the nanoribbons without scattering for a surprisingly long distance, more than ten micrometres.

The study of gas emission rates, chemistry and isotopic analyses show that the rate of helium-4 emission from the crust at Yellowstone is orders of magnitude greater than any conceivable rate of generation within the crust; this implies that helium has accumulated for hundreds of millions of years in deeper Archaean cratonic rocks, only to be liberated over the past two million years by crustal metamorphism induced by the Yellowstone hotspot.

Increased trait differences among sympatric lineages of ovenbirds are explained by their greater evolutionary age compared with allopatric lineages.

Laboratory infection experiments and field data show that emerging infectious diseases of honeybees are widespread infectious agents within the pollinator assemblage; the prevalence of deformed wing virus (DWV) and the parasite Nosema ceranae in honeybees and bumblebees is linked, and sympatric bumblebees and honeybees are infected by the same DWV strains, indicating ongoing disease transmission.

Unlike the tidal (in and out) breathing of mammals, bird lungs have unidirectional airflow patterns; here the savannah monitor lizard is shown to have unidirectional airflow too, with profound implications for the evolution of unidirectional airflow in reptiles, predating the origin of birds.

Whole-exome sequencing and analysis of 115 cervical carcinoma–normal paired samples, in addition to transcriptome and whole-genome sequencing for a subset of these tumours, reveal novel genes mutated at significant levels within this cohort and provide evidence that HPV integration is a common mechanism for target gene overexpression; results also compare mutational landscapes between squamous cell carcinomas and adenocarcinomas.

A genome-wide association study meta-analysis of more than 100,000 subjects of European and Asian ancestries reveals 42 new risk loci for rheumatoid arthritis, with follow-up studies identifying 98 biological candidate genes that are either already being targeted by drugs or could be in the future.

Chimaeric human–murine adeno-associated virus (AAV) capsids are described that transduce human primary hepatocytes more efficiently than currently used AAV vectors; the novel vectors may be good clinical candidates.

In the predominantly diploid yeast Saccharomyces cerevisiae, regulatory control of mating is separate from meiosis; here the related hemiascomycete yeast Candida lusitaniae is shown to have coordinated regulatory control of mating and meiosis, favouring the formation of haploids.

The Tet family of dioxygenase enzymes convert 5-methylcytosine to 5-hydroxymethylcytosine, 5-formylcytosine and 5-carboxylcytosine, which has an effect on gene expression; here the structure of NgTet1, a Tet-like protein with the same activity as mammalian Tet1, is determined, showing that NgTet1 uses a base-flipping mechanism to access 5-methylcytosine.

Navigating discussions with potential employers requires preparation and maintaining grace under pressure.

Protégés receive scant counsel on work–life conflicts.

Rise in enrolments for professional science masters programmes slows down.

Junior researchers need stronger career guidance.

Grounds for despair.