Volume 509 Number 7501

Editorials

Still much to learn about mice p.399

A project that aims to mutate every gene in the mouse genome to improve our knowledge of mouse biology should help to avoid irreproducible results and costly failures in drug development.

doi: 10.1038/509399a

Not on the label p.399

A US push to flag foods as genetically engineered is hard to swallow.

doi: 10.1038/509399b

Out with a bang p.400

The discovery of a Wolf-Rayet supernova rebuts the idea that the biggest stars go quietly.

doi: 10.1038/509400a

News

Submersible loss hits research p.408

But scientists remain positive about the future of deep-sea exploration despite disintegration of unique US Nereus craft.

doi: 10.1038/509408a

Jelly genome mystery p.411

Publication of the draft genetic sequence of a comb jelly reveals a nervous system like no other.

doi: 10.1038/509411a

News Features

The power of three p.414

Techniques that transfer DNA from diseased human eggs to healthy ones — creating offspring with three biological parents — are on the verge of clinical use.

doi: 10.1038/509414a

Carving up the Amazon p.418

A rash of road construction is causing widespread change in the world's largest tropical forest — with potentially global consequences.

doi: 10.1038/509418a

News & Views

Keeping one's sex p.430

Progeny of the protist Paramecium tetraurelia always retain the parental mating type. This inheritance is revealed to result from an RNA-guided DNA-deletion pathway that protects the genome from foreign DNA sequences. See Article p.447

doi: 10.1038/nature13333

Windy stars that go with a bang p.431

The probable signature of an ageing massive star's stellar wind has been detected shortly after the star underwent a supernova explosion. The finding suggests that such windy stars can have bright, observable deaths. See Letter p.471

doi: 10.1038/509431a

Double function at the blood–brain barrier p.432

Two aspects of the blood–brain barrier — the transport of lipids to the brain and the transport of molecules across cells lining blood vessels — have been shown to be regulated by the same protein, Mfsd2a. See Letters p.503 & p.507

doi: 10.1038/nature13339

Selectivity from flexibility p.434

Porous materials called metal–organic frameworks hold promise for many applications, including molecular separations. One such material has been discovered that shape-shifts to amplify its selectivity for a target molecule.

doi: 10.1038/509434a

Darwinian tumour suppression p.435

Competition for access to a survival factor has been found to explain why incoming cells from the bone marrow replace resident cells in the thymus. Reducing this competition can cause tumours to form. See Article p.465

doi: 10.1038/nature13337

Fertile fields for seismicity p.436

An analysis of crustal uplift around California's San Joaquin Valley, caused by groundwater extraction, reveals that such removal leads to both seasonal and long-term unclamping of the nearby San Andreas Fault system. See Letter p.483

doi: 10.1038/nature13338

Review

The role of senescent cells in ageing p.439

Cellular senescence has recently been shown to have roles in complex biological processes other than protection against cancer, and to represent a series of progressive and diverse cellular states after initial growth arrest; better understanding of mechanisms underlying its progression and of acute and chronic senescent cells may lead to new therapeutic strategies for age-related pathologies.

doi: 10.1038/nature13193

Articles

Genome-defence small RNAs exapted for epigenetic mating-type inheritance p.447

The molecular basis for mating-type determination in the ciliate Paramecium has been elucidated, revealing a novel function for a class of small RNAs — these scnRNAs are typically involved in reprogramming the Paramecium genome during sexual reproduction by recognizing and excising transposable elements, but they are now found to be co-opted to switch off expression of the newly identified mating-type gene mtA by excising its promoter, and to mediate epigenetic inheritance of mating types across sexual generations.

doi: 10.1038/nature13318

Amygdala interneuron subtypes control fear learning through disinhibition p.453

Plasticity within neuronal microcircuits is believed to be the substrate of learning, and this study identifies two distinct disinhibitory mechanisms involving interactions between PV+ and SOM+ interneurons that dynamically regulate principal neuron activity in the amygdala and thereby control auditory fear learning.

doi: 10.1038/nature13258

Cell competition is a tumour suppressor mechanism in the thymus p.465

T cells develop from thymic precursor cells that are constantly replaced with newly arriving bone marrow progenitor cells, and the ‘old’ and ‘new’ cells are shown here to compete; in the absence of cell competition, when the influx of new bone marrow progenitor cells is blocked, the old cells acquire the ability to self-renew and eventually become transformed, leading to the development of a form of leukaemia.

doi: 10.1038/nature13317

Letters

A Wolf–Rayet-like progenitor of SN 2013cu from spectral observations of a stellar wind p.471

The explosive fate of massive Wolf–Rayet stars (WRSs) is a key open question in stellar physics. An appealing option is that hydrogen-deficient WRSs are the progenitors of some hydrogen-poor supernova explosions of types IIb, Ib and Ic (ref. 2). A blue object, having luminosity and colours consistent with those of some WRSs, has recently been identified in pre-explosion images at the location of a supernova of type Ib (ref. 3), but has not yet been conclusively determined to have been the progenitor. Similar work has so far only resulted in non-detections. Comparison of early photometric observations of type Ic supernovae with theoretical models suggests that the progenitor stars had radii of less than 1012 centimetres, as expected for some WRSs. The signature of WRSs, their emission line spectra, cannot be probed by such studies. Here we report the detection of strong emission lines in a spectrum of type IIb supernova 2013cu (iPTF13ast) obtained approximately 15.5 hours after explosion (by ‘flash spectroscopy’, which captures the effects of the supernova explosion shock breakout flash on material surrounding the progenitor star). We identify Wolf–Rayet-like wind signatures, suggesting a progenitor of the WN(h) subclass (those WRSs with winds dominated by helium and nitrogen, with traces of hydrogen). The extent of this dense wind may indicate increased mass loss from the progenitor shortly before its explosion, consistent with recent theoretical predictions.

doi: 10.1038/nature13304

Mfsd2a is a transporter for the essential omega-3 fatty acid docosahexaenoic acid p.503

Mfsd2a is the major transporter of the omega-3 fatty acid docosahexaenoic acid (DHA) into brain, with Mfsd2a-knockout mice showing reduced DHA in brain, neuronal cell loss in hippocampus and cerebellum, behavioural disorders and reduced brain size; DHA is transported in a sodium-dependent manner, in the form of lysophosphatidylcholines (LPCs) carrying long-chain fatty acids.

doi: 10.1038/nature13241

Mfsd2a is critical for the formation and function of the blood–brain barrier p.507

Mfsd2a is a key regulator of blood–brain barrier (BBB) formation and function in mice: Mfsd2a is selectively expressed in BBB-containing blood vessels in the CNS; Mfsd2a−/− mice have a leaky BBB and increased vesicular transcytosis in CNS endothelial cells; and Mfsd2a endothelial expression is regulated by pericytes to facilitate BBB integrity.

doi: 10.1038/nature13324

Structure of the AcrAB–TolC multidrug efflux pump p.512

Many bacteria are able to survive in the presence of antibiotics in part because they possess pumps that can remove a broad range of small molecules; here, the structure of one such pump, AcrAB–TolC, is determined using X-ray crystallography and cryo-electron microscopy.

doi: 10.1038/nature13205