Editors' Choice

Science  11 Jun 2021:
Vol. 372, Issue 6547, pp. 1163
  1. Plant Science

    The hard way to produce red

    1. Pamela J. Hines

    Petunia exserta is a very rare wild species able to biosynthesize red pigment to attract bird pollinators.

    CREDIT: ROMAN KOEPFLI

    The common garden petunia delivers flowers in a variety of colors and color patterns, which are pollinated by bees, hawkmoths, or hummingbirds (which are particularly fond of the color red). Throughout evolution, petunia lineages have gained, lost, and shifted color. For example, Petunia exserta has evolved a red hue new to the genus. Barardi et al. investigated how P. exserta acquired color from a colorless ancestor. The authors found that disabling mutations in a transcription factor freed up substrate for anthocyanin biosynthesis, and another transcriptional activator promoted anthocyanin biosynthesis after it shifted expression domains. The red color depends on delphinidins, which tend to be blue or purple, but when dihydroxylated in P. exserta, these pigments contribute to the red hue. In addition, lack of acylation on the anthocyanidin backbone also helps to shift the pigment toward red.

    Plant Cell 10.1093/plcell/koab114 (2021).

  2. Cell Biology

    Waste management on the go

    1. Di Jiang

    When some cells migrate, cellular fibers are pulled out from the trailing edge of cells, and 0.5- to 2-µm-diameter vesicle-like enlargements called migrasomes appear. As cells continue to inch forward, the fibers stretch to their breaking point, fragmenting and leaving the enigmatic migrasomes behind. Jiao et al. found that migrasomes resemble a dumpster containing damaged mitochondria and neutrophils. Within the cell, damaged mitochondria tend not to engage with inward-moving motor proteins. Instead, they accumulate at the periphery of the cell and collect in the trailing fibers, ending up in the migrasomes. This may be a mitochondrial quality-control mechanism used by migrating cells that have high energy demands and thus more stressed and damaged mitochondria.

    Cell 184, 2896 (2021).

  3. Neuroscience

    Entrapment prevents healing

    1. Stella M. Hurtley

    Fluorescent microscopy image of retinal tissue showing optic nerve fibers (red) connecting to retinal ganglion neurons (orange)

    IMAGE: SCIMAT/SCIENCE SOURCE

    Adult nerves usually fail to regenerate after injury. This is also true for the retinal ganglion cells (RGCs) that communicate visual information from the retina to the brain. Working with adult mice and cultured RGCs, Hilla et al. discovered a role for the chemokine receptor CXCR4 and its ligand, CXCL12, in reducing the ability of RGCs to successfully reconnect to the optic nerve. RGCs transport CXCL12 along their axons, which if cut, release the cytokine at the damage site. This in turn attracts other growing RGC axons to the injury site, functionally trapping them in the lesion and preventing them from re-establishing contact beyond the lesion site. Reducing the expression levels of either the receptor or the cytokine reduces the diversion of growing axons and promotes long-distance regeneration. Thus, targeting this pathway could potentially help with functional recovery after nerve injury.

    Proc. Natl. Acad. Sci. U.S.A. 118, e2016409118 (2021).

  4. Neuroscience

    Neuronal activity asleep

    1. Peter Stern

    Beyond down-regulating cortical activity, sleep also promotes long-term memory formation and the strengthening of synaptic connections. It is possible that both core sleep stages, slow-wave sleep (SWS) and rapid eye movement (REM) sleep, contribute to these processes. Niethard et al. used in vivo two-photon calcium imaging in mice to assess the activity of large populations of cortical layer 2/3 cells during SWS and REM sleep. Most pyramidal neurons substantially decreased their activity during SWS and REM sleep episodes. The decrease during SWS sleep, but not during REM sleep, was accompanied by increased inhibitory interneuron activity. However, a subpopulation of pyramidal cells exhibited upregulated activity during SWS. These neurons are possibly involved in memory formation, and also underwent profound down-regulation during subsequent REM sleep.

    J. Neurosci., 41, 4212 (2021).

  5. Quantum Simulation

    Extending interactions

    1. Jelena Stajic

    Optical lattices populated with atoms that hop from site to site can be used to explore non-equilibrium many-body phenomena. Typically, the atoms in such systems interact only if they occupy the same lattice site, limiting the range of physics that can be addressed. Guardado-Sanchez et al. engineered longer-range interactions between lithium atoms in a two-dimensional optical lattice by shining ultraviolet laser light along one of the axes. This resulted in an effective interaction between nearest-neighbor atoms and simultaneously suppressed hopping along the direction perpendicular to the laser beam. The researchers then initialized the system in a charge-density wave state and monitored its dynamics, finding that increasing interactions caused the system to retain the memory of its initial state longer.

    Phys. Rev. X 11, 021036 (2021).

  6. Organic Chemistry

    A stable diazoalkene

    1. Jake Yeston

    Modern organic chemistry has produced such a large array of intricately complex products that it is easy to forget the simple motifs that have eluded bulk synthesis. One such case is the diazoalkene, an unsaturated variant of the more common diazoalkanes. Consisting of three adjacent double bonds (C=C=N=N), this fragment is of particular interest as a precursor to reactive vinylidenes. Antoni et al. report the preparation of an N-heterocycle–substituted diazoalkene by oxidation of an olefinic precursor with nitrous oxide. The compound is stable in solid and solution states under inert atmosphere and reacts cleanly with isocyanides.

    Nat. Chem. 13, 587 (2021).

  7. Protein Biogenesis

    Targeting heme insertion

    1. Michael A. Funk

    Many proteins require dedicated machinery to help them fold or insert cofactors. Sutherland et al. reconstituted one such system, cytochrome c (cyt c) synthase, from both human mitochondria and a pathogenic bacterium in vitro and investigated their substrate specificities. Under these conditions, the human enzyme was far more permissive, accepting a wide range of cyt c peptide variants, as long as a thiol-containing amino acid was present in a particular motif. Unlike full-length cyt c, small peptides cannot be released from the enzyme. Designing safe and effective inhibitors of this system will require taking advantage of the differences in selectivity between species.

    eLife 10, e64891 (2021).

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