Editors' Choice

Science  18 Jul 2014:
Vol. 345, Issue 6194, pp. 281
  1. Speciation

    Putting the genetic breaks on breeding

    1. Laura M. Zahn
    Mules: An example of hybrid sterility in actionPHOTO: © IMAGEBROKER/ALAMY

    Several genetic barriers prevent species from interbreeding. For instance, when two different species mate, their offspring are often infertile. Identifying the genetic causes of this hybrid sterility provides insight into how species evolve genetically. Zanders et al. examined two closely related yeast species, which share 99.5% of their DNA sequence. They found that crosses between the species could not produce fertile offspring because of meiotic drive loci, genetic elements that are preferentially transmitted to the offspring within a species. The three DNA sites, which were present in one of the species, blocked the hybrid from developing spores that contained chromosomes from the other species. This study highlights how quickly barriers to fertility can arise between two closely related species.

    eLife 10.7554/eLife.02630.001 (2014).

  2. Cell Nucleus

    Packaging DNA for a better nucleus

    1. Guy Riddihough

    Nuclear pores oversee the movement of proteins, DNA, and RNA across the nuclear membrane between the nucleus and cytoplasm—an essential duty for proper cell function and survival. Two studies now report that for these pores to form, the cell requires nucleosomes, short lengths of DNA wrapped around a protein core that package chromosomes into the nucleus. Inoue and Zhang and Zierhut et al. use either mouse zygotes or frog (Xenopus) egg extracts to show that nucleosomes bind to and recruit the nuclear pore protein ELYS (embryonic large molecule derived from yolk sac) to DNA, driving the initial steps of nuclear pore assembly. In this way, cells might ensure that a functional nucleus only forms around properly packaged chromosomes.

    Nat. Struct. Mol. Biol. 10.1038/nsmb.2839; 10.1038/nsmb.2845 (2014).

  3. Atmospheric Science

    Looking for signs of ozone recovery

    1. Julia Fahrenkamp-Uppenbrink

    How effective is the Montreal Protocol, the international treaty aimed at protecting the stratospheric ozone layer? Since the treaty was adopted in 1989, manufacturers have gradually stopped producing numerous chemicals that deplete ozone. Scientists have predicted that ozone will recover as a result. Coldewey-Egbers et al. use an extensive data set to test whether recovery can be detected yet. They conclude that in mid-latitudes, at least five more years of data are needed to unequivocally detect signs of recovery, because natural variability masks the ozone recovery. At lower latitudes, where the trend in ozone concentration is smaller, even more data will be needed.

    Geophys. Res. Lett. 10.1002/2014GL060212 (2014).

  4. Physics

    A copper oxide's electronic structure

    1. Jelena Stajic
    Superconducting copper-oxide electronic structurePHOTO: NICOLLE R. FULLER

    Physicists still do not understand why some copper-oxide compounds become superconducting at relatively high temperatures. Even more basic issues have remained controversial as well, such as the electronic structure of the normal (i.e., nonsuperconducting) state from which superconductivity emerges. Sebastian et al. chose YBa2Cu3O6.56 as a good representative of a subclass of these compounds and used high magnetic fields to suppress its superconductivity and reach its normal state. They analyzed the wiggles of the electrical resistivity to map out the shape of the so-called Fermi surface, which separates the quantum states filled with electrons from the empty ones. They found an undulating shape that suggested that the electronic structure was organized differently from what one expects based on the crystal lattice structure alone.

    Nature 10.1038/nature13326 (2014).

  5. Circadian Rhythms

    Tick tock, synchronizing biological clocks

    1. L. Bryan Ray

    Studies of coupled oscillators started in the 1600s, when the man who invented the pendulum clock set a pair of clocks side by side in a single case and noticed that they started ticking in unison. In mammalian cells, the machinery that controls the cell division cycle turns out to be similarly synchronized with the daily circadian clock, which allows cells to get on the same seasonal and day-night schedules. Feillet et al. imaged single live mammalian cells in culture and performed mathematical modeling. They showed that the daily circadian clock and the cell division cycle oscillate together at the same frequency. This may have clinical relevance: Circadian disruption is a risk factor for some cancers.

    Proc. Natl. Acad. Sci. U.S.A. 10.1073pnas.1320474111 (2014).

  6. Climate Change

    Measuring sea ice through thick and thin

    1. H. Jesse Smith

    Sea ice in the Arctic's Fram Straight is only half as thick as it was a decade ago, Renner and colleagues report. Measuring ice both at the surface and from the air with an instrument towed below a helicopter, they found that the ice in that region thinned by more than 50% between 2003 and 2012. The patterns of variability that they see most likely are caused by thinning occurring more broadly across the Arctic, rather than being just a regional effect. These observations are consistent with the contemporaneous reduction of the area covered by sea ice that has occurred in the Arctic and should help provide a better understanding of both the magnitude and the causes of the loss.

    Geophys. Res. Lett. 10.1002/2014GL060369 (2014).

  7. Gut Motility

    Macrophages help food move through

    1. Kristen L. Mueller
    Muscularis macrophages (green) on nerve fibers (red)PHOTO: MILENA BOGUNOVIC

    Food needs a complex array of cellular interactions to move through the body. Neurons, muscle cells, and interstitial cells all cooperate to ease it through the gastrointestinal (GI) tract. Now Muller et al. report intestinal muscularis macrophages, a type of immune cell that resides in the smooth muscles that surround the GI tract, participate, too. These macrophages secrete a substance called bone morphogenetic protein 2 (BMP2), which binds to enteric neurons and directs them to coordinate the muscle cell contractions that squeeze food through. The neurons, in turn, produce a growth factor required by the macrophages. Macrophage-neuron crosstalk is essential: When mice don't have enough of the growth factor, BMP2, or muscularis macrophages, they have defects in gut muscle contractions.

    Cell 10.1016/j.cell.2014.04.050 (2014).