Variation in the bark call of the red squirrel ( Tamiasciurus hudsonicus )

Calls of the red squirrel ( Tamiasciurus hudsonicus; n = 122) were recorded in wild populations from 15 localities in Arizona, New Mexico, Colorado, Utah, Wyoming, Montana, Idaho, and Washington. Computer-generated audiospectrograms of 20- or 30-second samples from a calling bout of each individual were analyzed. Eighteen bark types (distinct forms of the bark call) were identified plus a 19th category that included rarely used, longer bark calls. The frequency of use of each bark type within the sample was recorded for each squirrel. Differences in frequency of use of the various bark types were found among subspecies, within subspecies, and within populations; additionally, the southern subspecies utilized a reduced number of bark types. The large number of different bark types and the variation in bark type usage within populations suggest the potential for communication of such information as individual identification, behavioral states, or gender identification.     

The auroral footprint of Enceladus on Saturn

Although there are substantial differences between the magnetospheres of Jupiter and Saturn, it has been suggested that cryovolcanic activity at Enceladus could lead to electrodynamic coupling between Enceladus and Saturn like that which links Jupiter with Io, Europa and Ganymede. Powerful field-aligned electron beams associated with the Io-Jupiter coupling, for example, create an auroral footprint in Jupiter's ionosphere. Auroral ultraviolet emission associated with Enceladus-Saturn coupling is anticipated to be just a few tenths of a kilorayleigh (ref. 12), about an order of magnitude dimmer than Io's footprint and below the observable threshold, consistent with its non-detection. Here we report the detection of magnetic-field-aligned ion and electron beams (offset several moon radii downstream from Enceladus) with sufficient power to stimulate detectable aurora, and the subsequent discovery of Enceladus-associated aurora in a few per cent of the scans of the moon's footprint. The footprint varies in emission magnitude more than can plausibly be explained by changes in magnetospheric parameters--and as such is probably indicative of variable plume activity.     

A conditional knockout resource for the genome-wide study of mouse gene function

Gene targeting in embryonic stem cells has become the principal technology for manipulation of the mouse genome, offering unrivalled accuracy in allele design and access to conditional mutagenesis. To bring these advantages to the wider research community, large-scale mouse knockout programmes are producing a permanent resource of targeted mutations in all protein-coding genes. Here we report the establishment of a high-throughput gene-targeting pipeline for the generation of reporter-tagged, conditional alleles. Computational allele design, 96-well modular vector construction and high-efficiency gene-targeting strategies have been combined to mutate genes on an unprecedented scale. So far, more than 12,000 vectors and 9,000 conditional targeted alleles have been produced in highly germline-competent C57BL/6N embryonic stem cells. High-throughput genome engineering highlighted by this study is broadly applicable to rat and human stem cells and provides a foundation for future genome-wide efforts aimed at deciphering the function of all genes encoded by the mammalian genome.     

Crystal structure of 15-mer DNA duplex containing unpaired bases

Errors during DNA replication or repair can lead to the presence of unpaired or inserted bases in the double helix, as well as to mismatched base pairs. So far only structures of the latter type have been characterized by X-ray crystallography. We report here a 3-A crystal structure of DNA 15-mer d(CGCGAAATTTACGCG), which forms a duplex with two unpaired adenine residues looped outside the B-type helix. This arrangement is in disagreement with the nuclear magnetic resonance spectroscopy results for the same 15-mer in solution, indicating polymorphic nature of the structure adopted by this sequence.