Isolation of Cell Nuclei Using Inert Macromolecules to Mimic the Crowded Cytoplasm

Cell nuclei are commonly isolated and studied in media which include millimolar concentrations of cations, which conserve the nuclear volume by screening the negative charges on chromatin and maintaining its compaction. However, two factors question if these ionic conditions correctly reproduce the environment of nuclei in vivo: the small-scale motion and conformation of chromatin in vivo are not reproduced in isolated nuclei, and experiments and theory suggest that small ions in the cytoplasm are not free in the soluble phase but are predominantly bound to macromolecules. We studied the possible role in maintaining the structure and functions of nuclei in vivo of a further but frequently overlooked property of the cytoplasm, the crowding or osmotic effects caused by diffusible macromolecules whose concentration, measured in several studies, is in the range of 130 mg/ml. Nuclei which conserved their volume in the cell and their ultrastructure seen by electron microscopy were released from K562 cells in media containing the inert polymer 70 kDa Ficoll (50% w/v) or 70 kDa dextran (35% w/v) to replace the diffusible cytoplasmic molecules which were dispersed on cell lysis with digitonin, with 100 µM K-Hepes buffer as the only source of ions. Immunofluorescence labelling and experiments using cells expressing GFP-fusion proteins showed that internal compartments (nucleoli, PML and coiled bodies, foci of RNA polymerase II) were conserved in these nuclei, and nascent RNA transcripts could be elongated. Our observations are consistent with the hypothesis that crowding by diffusible cytoplasmic macromolecules is a crucial but overlooked factor which supports the nucleus in vivo by equilibrating the opposing osmotic pressure cause by the high concentration of macromolecules in the nucleus, and suggest that crowded media provide more physiological conditions to study nuclear structure and functions. They may also help to resolve the long-standing paradox that the small-scale motion and irregular conformation of chromatin seen in vivo are not reproduced in nuclei isolated in conventional ionic media

Stratigraphy, geochemistry and palaeomagnetism of late quaternary bedrock and paleosols, Karisoke Area, Virunga Mountains, Northwestern Rwanda

Ein rezenter Boden und zwei begrabene Paläoböden, Einheiten II-III-IV (oberer) und IV (unterer)-V, liefern wichtige Informationen über Paläoklima und Abflußverhältnisse in den Virunga-Bergen von trockeneren zu feuchteren paläoklimatischen Phasen des Spätglazials bis zu mittleren postglazialen Zeiten. Zusammenfassend betrachtet, weist die stratigraphische Abfolge zunächst auf eine Verwitterungsperiode des Festgesteins hin, der eine Phase folgt, in der tuffige Schichten abgelagert wurden. Die Zeit war von einer Verwitterung unter trockeneren und vielleicht kälteren Bedingungen begleitet. Später, während des letzten Glazials, kam es bei verstärkter Aktivität der Flüsse zur Sedimentation von Schwemmlandablagerungen, die von einer dünnen Tuff-Schicht überdeckt wurden. Diese Sedimente sind intensiver verwittert als die liegenden Schichten. Der rezente Boden zeigt eine vergleichsweise geringe Verwitterung mobiler Elemente, was darauf hindeutet, daß die Klimaverhältnisse im späten Mittel-Holozän und Spät-Holozän etwas trockener und vielleicht kühler waren als im Früh-Holozän. Die Geochemie der drei Böden zeigt eine bedeutende Abnahme von Na, Ca und K im mittleren Paläoböden im Vergleich zum älteren Paläoböden und zu den rezenten Böden. Eisen als ein wichtiger Indikator für das Paläoklima deutet daraufhin, daß die mittleren Einheiten II und III des oberen Paläobodens unter feuchteren Klimabedingungen als heute entstanden sind. Die Radiokarbon-Datierungen des mittleren Paläobodens zeigen, daß dieser Boden einer sub-aerischen Verwitterung vom Kalambo-Interstadial (» 25000 Jahre vor heute) bis zum Mittel-Holozän ausgesetzt war. Die gesamte Verwitterung im mittleren Abschnitt ist zu weit fortgeschritten und während des Holozäns entstanden. Die relativ hohe Konzentration von Th in den anstehenden Festgesteinen, Tuffen, Schwemmlandsedimenten und Hangrutschmassen zeigt, daß Th die Quelle der Radioaktivität ist, von der andere Autoren aus den Virunga-Bergen berichten.researc

Optical Properties of High-Frequency Radio Sources from the Australia Telescope 20 GHz (AT20G) Survey

Our current understanding of radio-loud AGN comes predominantly from studies at frequencies of 5 GHz and below. With the recent completion of the Australia Telescope 20 GHz (AT20G) survey, we can now gain insight into the high-frequency radio properties of AGN. This paper presents supplementary information on the AT20G sources in the form of optical counterparts and redshifts. Optical counterparts were identified using the SuperCOSMOS database and redshifts were found from either the 6dF Galaxy survey or the literature. We also report 144 new redshifts. For AT20G sources outside the Galactic plane, 78.5% have optical identifications and 30.9% have redshift information. The optical identification rate also increases with increasing flux density. Targets which had optical spectra available were examined to obtain a spectral classification. There appear to be two distinct AT20G populations; the high luminosity quasars that are generally associated with point-source optical counterparts and exhibit strong emission lines in the optical spectrum, and the lower luminosity radio galaxies that are generally associated with passive galaxies in both the optical images and spectroscopic properties. It is suggested that these different populations can be associated with different accretion modes (cold-mode or hot-mode). We find that the cold-mode sources have a steeper spectral index and produce more luminous radio lobes, but generally reside in smaller host galaxies than their hot-mode counterparts. This can be attributed to the fact that they are accreting material more efficiently. Lastly, we compare the AT20G survey with the S-cubed semi-empirical (S3-SEX) models and conclude that the S3-SEX models need refining to correctly model the compact cores of AGN. The AT20G survey provides the ideal sample to do this.Comment: Accepted for publication in MNRA

TOPEX Radar Altimeter Engineering Assessment Report Final Update-Side B Turn-On to End-of-Mission on October 9, 2005

This is the thirteenth and final report in a series of TOPEX Radar Altimeter Engineering Assessment Reports. The initial TOPEX Radar Altimeter Engineering Assessment Report, in February 1994, presented performance results for the NASA Radar Altimeter on the TOPEX/POSEIDON spacecraft, from its launch in August 1992 to February 1994. Since the time of that initial report and prior to this report, there have been eleven interim supplemental Engineering Assessment Reports, issued in March 1995, May 1996, March 1997, June 1998, August 1999, September 2000, June 2001, March 2002, May 2003, April 2004 and September 2005. The sixth supplement in September 2000 was the first assessment report that addressed Side B performance, and presented the altimeter performance from Side B turn-on until the end of calendar year 1999. This report extends the performance assessment of Side B to the final collection of data on October 9, 2005, and includes the performance assessment of Jason-1, the TOPEX follow-on mission, launched on December 7, 2001. This report provides some comparisons of Side A and Side B performance

An Examination of the Relationship Between Perfectionism and Neurological Functioning

Clinical perfectionism is the rigid pursuit of high standards, interfering with functioning. Little research has explored neural patterns in clinical perfectionism. The present study explores neural correlates of clinical perfectionism, before and after receiving ten 50-minute, weekly sessions of acceptance and commitment therapy (ACT), as compared to low-perfectionist controls, in specific cortical structures: the dorsolateral prefrontal cortex (DLPFC), medial prefrontal cortex (MPFC), right inferior parietal lobule (IPL). Participants in the perfectionist condition (n = 43) were from a randomized controlled trial evaluating ACT for clinical perfectionism and low-perfectionist controls were undergraduate students (n = 12). Participants completed three tasks (editing a passage, mirror image tracing, circle tracing) using functional near-infrared spectroscopy (fNIRS) to measure neural activation. Results indicate that only the mirror image tracing task was associated with reduced HbT in the DLPFC and MPFC of the perfectionists whereas activation in the other tasks were relatively similar. There were no differences were observed in the right DLPFC, MPFC, and right IPL between the posttreatment perfectionist and non-perfectionist control groups. Our findings suggest an unclear relationship between neural activation and perfectionism

The properties of extragalactic radio sources selected at 20 GHz

We present some first results on the variability, polarization and general properties of radio sources selected in a blind survey at 20 GHz, the highest frequency at which a sensitive radio survey has been carried out over a large area of sky. Sources with flux densities above 100 mJy in the AT20G Pilot Survey at declination -60 to -70 were observed at up to three epochs during 2002-4, including near-simultaneous measurements at 5, 8 and 18 GHz in 2003. Of the 173 sources detected, 65% are candidate QSOs, BL Lac objects or blazars, 20% galaxies and 15% faint (b > 22 mag) optical objects or blank fields. On a 1-2 year timescale, the general level of variability at 20 GHz appears to be low. For the 108 sources with good-quality measurements in both 2003 and 2004, the median variability index at 20 GHz was 6.9% and only five sources varied by more than 30% in flux density. Most sources in our sample show low levels of linear polarization (typically 1-5%), with a median fractional polarization of 2.3% at 20 GHz. There is a trend for fainter sources to show higher fractional polarization. At least 40% of sources selected at 20GHz have strong spectral curvature over the frequency range 1-20 GHz. We use a radio `two-colour diagram' to characterize the radio spectra of our sample, and confirm that the radio-source population at 20 GHz (which is also the foreground point-source population for CMB anisotropy experiments like WMAP and Planck) cannot be reliably predicted by extrapolating the results of surveys at lower frequencies. As a result, direct selection at 20 GHz appears to be a more efficient way of identifying 90 GHz phase calibrators for ALMA than the currently-proposed technique of extrapolation from all-sky surveys at 1-5 GHz.Comment: 14-page paper plus 5-page data table. Replaced with published versio