Editors' Choice

Science  01 Feb 2008:
Vol. 319, Issue 5863, pp. 549

    The Largest of the Small

    The moist forests of the Udzungwa Mountains in south-central Tanzania have yielded an astonishing number of previously undescribed vertebrate species during the past decade. The latest of these, reported by Rovero et al., is a remarkable new elephant shrew or sengi, named Rhynchocyon udzungwensis. Related neither to elephants nor to shrews (being much smaller than the former and much larger than the latter), the elephant shrews are an order of mammals that appear to have evolved hardly at all since the Miocene. The new species is the largest sengi of all, weighing in at an average of 700 g and measuring half a meter from the elongated snout to the tip of its tail. On the basis of sighting frequency, Rovero et al. estimate a total population of 15,000 to 24,000 occupying an area of 300 km2. This giant sengi lives in mountain forests 1000 m above sea level; its habitat, along with those of other endemic species of the Udzungwa Mountains, is currently protected and relatively little disturbed by humans. The discovery of yet another new species is a further confirmation of the conservation value of these mountains. — AMS

    J. Zool. 274, 10.1111/j.1469-7998.2007.00363.x (2008).


    The Order of Ordering

    When polymers partially crystallize from the melt state, they often pack by formation of lamellae, or stacks of folded, ordered chain segments separated by regions of noncrystalline material. Prior studies suggested that crystallization might be occurring through a spinodal-assisted ordering, associated with the formation of a smectic-like liquid crystalline phase that preceded the formation of the first nuclei. Panine et al. used high-brilliance x-ray scattering to look at the earliest stages of crystallization in isotatic polypropylene. They found ordering in the wide-angle x-ray scattering (WAXS) data before the small-angle x-ray scattering (SAXS) data, thus supporting the formation of ordered nuclei at the local scale before more global, liquid crystalline-like ordering. This finding contrasted with earlier SAXS before WAXS data used to support the spinodal hypothesis, which may have been due to detector limitations. More intriguing is that the earliest SAXS peaks support a smectic-like ordering of the nuclei (rather than just the polymer chains); thus, at these intermediate times, the nuclei may arrange into an ordered structure before growing into the large well-organized lamellae as proposed in a number of recent simulation studies. — MSL

    Polymer 10.1016/j.polymer.2007.12.026 (2008).


    Waking Up to Orexin

    What do narcolepsy and anesthesia have in common? Almost a decade ago, a mouse model for human narcolepsy was developed on the basis of results demonstrating that the neuropeptide orexin promoted wakefulness and that genetic ablation of orexinergic neurons yielded mice with behavioral and physiological symptoms remarkably like those of narcoleptic humans. Anesthesia, on the other hand, can be induced by a wide variety of agents such as isoflurane or sevoflurane but has resisted efforts to identify its neural loci of action.

    In their mouse model, Kelz et al. find that the neural systems innervated by orexinergic neurons are central in the emergence from (though not the induction of) an anesthetized state. Both isoflurane and sevoflurane reduced the percentage of active orexin neurons to the levels seen during non-rapid eye movement sleep, yet an orexin receptor antagonist surprisingly did not change the rate of entry into anesthesia. Nevertheless, the same antagonist did markedly delay recovery from an anesthetized state, and a similar delay was observed in orexin-deficient mice and also is seen in some human narcoleptic patients. — GJC

    Proc. Natl. Acad. Sci. U.S.A. 105, 10.1073/pnas.0707146105 (2008).


    Assemble Before Use

    At sites of vascular injury, a large multimeric glycoprotein (von Willebrand's factor; VWF) secreted from endothelial cells binds platelets to form a hemostatic plug. Within endothelial cells, VWF multimers pack as ordered tubules into cigar-shaped secretory granules called Weibel-Palade bodies; this packaging is essential for orderly secretion of VWF filaments.

    Using only the N-terminal propeptide D1D2 and the adjacent D'D3 domains, Huang et al. have reconstituted in vitro the formation of Weibel-Palade body-like tubules, which occurs at low pH (6.2) and in the presence of Ca2+. Electron microscopic reconstruction showed that the tubules formed a right-handed helix with 4.2 units per turn, with the repeating unit containing a D'D3 dimer and two propeptides. The authors suggest that these domains form the core of the tubules, with the remaining C-terminal portion of the protein decorating the outside. In the Golgi, the relatively acidic pH and high Ca2+ would increase the interaction between D1D2 and D'D3, juxtaposing the two D3 domains and facilitating intersubunit disulfide bond formation and multimerization. The higher pH in blood would weaken these interactions and allow the helical tubules to unfurl without tangling. — VV

    Proc. Natl. Acad. Sci. U.S.A. 105, 482 (2008).