Volume 548 Number 7668



News Features

News & Views

Diversity reaches the stars p.396

Cells called astrocytes promote and maintain neuronal function. The discovery that astrocytes vary in their gene expression, protein levels, cellular structure and function suggests that they are specialized to support distinct circuits.

doi: 10.1038/548396a

History of black holes revealed by their spin p.397

Four probable detections of gravitational waves have so far been reported, each associated with the merger of two black holes. Analysis of the signals allows formation theories of such black-hole systems to be tested. See Letter p.426

doi: 10.1038/548397a

At the heart of gene edits in human embryos p.398

The gene-editing technology CRISPR–Cas has been used in human embryos grown in vitro to correct a disease-associated mutation. The introduction of editing components at fertilization aided repair efficiency. See Article p.413

doi: 10.1038/nature23533

Magnetic molecules back in the race p.400

Single-molecule magnets have potential data-storage applications, but will need to work at a much higher temperature than has been possible. Two studies suggest that this goal could be met in the near future. See Letter p.439

doi: 10.1038/548400a

Role of mutation in fly-wing evolution p.401

Analysis of wing variation within and between fly species reveals an unexpectedly slow evolutionary rate. Variations due to mutation and interspecific differences are similar, perhaps as a result of complex genetic interactions. See Letter p.447

doi: 10.1038/nature23536

Ancient ice and the global methane cycle p.403

An analysis of 12,000-year-old Antarctic ice revises our understanding of natural methane emissions to the atmosphere, and constrains estimates of the sensitivity of natural methane sources to abrupt climate-warming events. See Letter p.443

doi: 10.1038/548403a

Probiotic prevents infections in newborns p.404

A major cause of death and disease in babies is the failure of their developing immune systems to block life-threatening infections. A clinical trial reports that the use of a probiotic can help to prevent such infections. See Article p.407

doi: 10.1038/nature23540



Large turbulent reservoirs of cold molecular gas around high-redshift starburst galaxies p.430

Starburst galaxies at the peak of cosmic star formation are among the most extreme star-forming engines in the Universe, producing stars over about 100 million years (ref. 2). The star-formation rates of these galaxies, which exceed 100 solar masses per year, require large reservoirs of cold molecular gas to be delivered to their cores, despite strong feedback from stars or active galactic nuclei. Consequently, starburst galaxies are ideal for studying the interplay between this feedback and the growth of a galaxy. The methylidyne cation, CH+, is a most useful molecule for such studies because it cannot form in cold gas without suprathermal energy input, so its presence indicates dissipation of mechanical energy or strong ultraviolet irradiation. Here we report the detection of CH+ (J = 1–0) emission and absorption lines in the spectra of six lensed starburst galaxies at redshifts near 2.5. This line has such a high critical density for excitation that it is emitted only in very dense gas, and is absorbed in low-density gas. We find that the CH+ emission lines, which are broader than 1,000 kilometres per second, originate in dense shock waves powered by hot galactic winds. The CH+ absorption lines reveal highly turbulent reservoirs of cool (about 100 kelvin), low-density gas, extending far (more than 10 kiloparsecs) outside the starburst galaxies (which have radii of less than 1 kiloparsec). We show that the galactic winds sustain turbulence in the 10-kiloparsec-scale environments of the galaxies, processing these environments into multiphase, gravitationally bound reservoirs. However, the mass outflow rates are found to be insufficient to balance the star-formation rates. Another mass input is therefore required for these reservoirs, which could be provided by ongoing mergers or cold-stream accretion. Our results suggest that galactic feedback, coupled jointly to turbulence and gravity, extends the starburst phase of a galaxy instead of quenching it.

doi: 10.1038/nature23298

Minimal geological methane emissions during the Younger Dryas–Preboreal abrupt warming event p.443

Methane (CH4) is a powerful greenhouse gas and plays a key part in global atmospheric chemistry. Natural geological emissions (fossil methane vented naturally from marine and terrestrial seeps and mud volcanoes) are thought to contribute around 52 teragrams of methane per year to the global methane source, about 10 per cent of the total, but both bottom-up methods (measuring emissions) and top-down approaches (measuring atmospheric mole fractions and isotopes) for constraining these geological emissions have been associated with large uncertainties. Here we use ice core measurements to quantify the absolute amount of radiocarbon-containing methane (14CH4) in the past atmosphere and show that geological methane emissions were no higher than 15.4 teragrams per year (95 per cent confidence), averaged over the abrupt warming event that occurred between the Younger Dryas and Preboreal intervals, approximately 11,600 years ago. Assuming that past geological methane emissions were no lower than today, our results indicate that current estimates of today’s natural geological methane emissions (about 52 teragrams per year) are too high and, by extension, that current estimates of anthropogenic fossil methane emissions are too low. Our results also improve on and confirm earlier findings that the rapid increase of about 50 per cent in mole fraction of atmospheric methane at the Younger Dryas–Preboreal event was driven by contemporaneous methane from sources such as wetlands; our findings constrain the contribution from old carbon reservoirs (marine methane hydrates, permafrost and methane trapped under ice) to 19 per cent or less (95 per cent confidence). To the extent that the characteristics of the most recent deglaciation and the Younger Dryas–Preboreal warming are comparable to those of the current anthropogenic warming, our measurements suggest that large future atmospheric releases of methane from old carbon sources are unlikely to occur.

doi: 10.1038/nature23316

Polylox barcoding reveals haematopoietic stem cell fates realized in vivo p.456

Developmental deconvolution of complex organs and tissues at the level of individual cells remains challenging. Non-invasive genetic fate mapping1 has been widely used, but the low number of distinct fluorescent marker proteins limits its resolution. Much higher numbers of cell markers have been generated using viral integration sites2, viral barcodes3, and strategies based on transposons4 and CRISPR–Cas9 genome editing5; however, temporal and tissuespecific induction of barcodes in situ has not been achieved. Here we report the development of an artificial DNA recombination locus (termed Polylox) that enables broadly applicable endogenous barcoding based on the Cre–loxP recombination system6,7. Polylox recombination in situ reaches a practical diversity of several hundred thousand barcodes, allowing tagging of single cells. We have used this experimental system, combined with fate mapping, to assess haematopoietic stem cell (HSC) fates in vivo. Classical models of haematopoietic lineage specification assume a tree with few major branches. More recently, driven in part by the development of more efficient single-cell assays and improved transplantation efficiencies, different models have been proposed, in which unilineage priming may occur in mice and humans at the level of HSCs8–10. We have introduced barcodes into HSC progenitors in embryonic mice, and found that the adult HSC compartment is a mosaic of embryoderived HSC clones, some of which are unexpectedly large. Most HSC clones gave rise to multilineage or oligolineage fates, arguing against unilineage priming, and suggesting coherent usage of the potential of cells in a clone. The spreading of barcodes, both after induction in embryos and in adult mice, revealed a basic split between common myeloid–erythroid development and common lymphocyte development, supporting the long-held but contested view of a tree-like haematopoietic structure.

doi: 10.1038/nature23653

CDK4/6 inhibition triggers anti-tumour immunity p.471

Mouse models of breast carcinoma and other solid tumours show that selective cyclin-dependent kinase 4 and 6 (CDK4/6) inhibitors not only induce tumour cell cycle arrest but also promote anti-tumour immunity.

doi: 10.1038/nature23465

Mechanism of intracellular allosteric β2AR antagonist revealed by X-ray crystal structure p.480

G-protein-coupled receptors (GPCRs) pose challenges for drug discovery efforts because of the high degree of structural homology in the orthosteric pocket, particularly for GPCRs within a single subfamily, such as the nine adrenergic receptors. Allosteric ligands may bind to less-conserved regions of these receptors and therefore are more likely to be selective. Unlike orthosteric ligands, which tonically activate or inhibit signalling, allosteric ligands modulate physiologic responses to hormones and neurotransmitters, and may therefore have fewer adverse effects. The majority of GPCR crystal structures published to date were obtained with receptors bound to orthosteric antagonists, and only a few structures bound to allosteric ligands have been reported. Compound 15 (Cmpd-15) is an allosteric modulator of the β2 adrenergic receptor (β2AR) that was recently isolated from a DNA-encoded small-molecule library. Orthosteric β-adrenergic receptor antagonists, known as beta-blockers, are amongst the most prescribed drugs in the world and Cmpd-15 is the first allosteric beta-blocker. Cmpd-15 exhibits negative cooperativity with agonists and positive cooperativity with inverse agonists. Here we present the structure of the β2AR bound to a polyethylene glycol-carboxylic acid derivative (Cmpd-15PA) of this modulator. Cmpd-15PA binds to a pocket formed primarily by the cytoplasmic ends of transmembrane segments 1, 2, 6 and 7 as well as intracellular loop 1 and helix 8. A comparison of this structure with inactive- and active-state structures of the β2AR reveals the mechanism by which Cmpd-15 modulates agonist binding affinity and signalling.

doi: 10.1038/nature23652