Autocrine production of extracellular catalase prevents apoptosis of the human CEM T-cell line in serum-free medium.

CCRF-CEM is a human T-cell line originally isolated from a child with acute lymphoblastic leukemia. At cell densities > 2 x 10 cells per ml, CEM cells grow in serum-free medium, but at lower cell densities the cultures rapidly undergo apoptosis, or programmed cell death. The viability of lowdensity CEM cells could be preserved by supplementing the serum-free medium with "conditioned" medium from highdensity CEM cultures, but a variety of known growth factors and lymphokines were ineffective. Fractionation ofconditioned medium by sequential chromatography on DEAE-cellulose, propyl agarose, chromatofocusing, and hydrophobic-interaction HPLC resulted in the isolation of a 60-kDa protein capable of sustaining CEM growth in the absence ofserum. The active protein was identified as human catalase based on its amino acid sequence and composition and was subsequently shown to exhibit catalase activity and to be replaceable by human erythrocyte catalase or bovine liver catalase. Comparison of the level of intracellular catalase activity with the amount released into the culture medium demonstrated that the latter accounted for <3% of the total catalase activity present in the cell culture. These findings show that, despite its low amount, the catalase released by CEM cells, and perhaps by T cells in general, provides a critical rust Ilne of defense against hydrogen peroxide (11202) present in the extracellular milieu. Originally published Proceedings of the National Academy of Sciences, Vol. 90, No. 10, May 199

Attenuation modified by DIG and dust as seen in M31

The spatial distribution of dust in galaxies affects the global attenuation, and hence inferred properties, of galaxies. We trace the spatial distribution of dust in five fields (at 0.6-0.9 kpc scale) of M31 by comparing optical attenuation with the total dust mass distribution. We measure the attenuation from the Balmer decrement using Integral Field Spectroscopy and the dust mass from Herschel far-IR observations. Our results show that M31's dust attenuation closely follows a foreground screen model, contrary to what was previously found in other nearby galaxies. By smoothing the M31 data we find that spatial resolution is not the cause for this difference. Based on the emission line ratios and two simple models, we conclude that previous models of dust/gas geometry need to include a weakly or non-attenuated diffuse ionized gas (DIG) component. Due to the variation of dust and DIG scale heights with galactic radius, we conclude that different locations in galaxies will have different vertical distributions of gas and dust and therefore different measured attenuation. The difference between our result in M31 with that found in other nearby galaxies can be explained by our fields in M31 lying at larger galactic radii than the previous studies that focused on the centres of galaxies.Comment: 20 pages, 13 figures, ApJ accepted and in pres

The Structure of a Low-Metallicity Giant Molecular Cloud Complex

To understand the impact of low metallicities on giant molecular cloud (GMC) structure, we compare far infrared dust emission, CO emission, and dynamics in the star-forming complex N83 in the Wing of the Small Magellanic Cloud. Dust emission (measured by Spitzer as part of the S3MC and SAGE-SMC surveys) probes the total gas column independent of molecular line emission and traces shielding from photodissociating radiation. We calibrate a method to estimate the dust column using only the high-resolution Spitzer data and verify that dust traces the ISM in the HI-dominated region around N83. This allows us to resolve the relative structures of H2, dust, and CO within a giant molecular cloud complex, one of the first times such a measurement has been made in a low-metallicity galaxy. Our results support the hypothesis that CO is photodissociated while H2 self-shields in the outer parts of low-metallicity GMCs, so that dust/self shielding is the primary factor determining the distribution of CO emission. Four pieces of evidence support this view. First, the CO-to-H2 conversion factor averaged over the whole cloud is very high 4-11 \times 10^21 cm^-2/(K km/s), or 20-55 times the Galactic value. Second, the CO-to-H2 conversion factor varies across the complex, with its lowest (most nearly Galactic) values near the CO peaks. Third, bright CO emission is largely confined to regions of relatively high line-of-sight extinction, A_V >~ 2 mag, in agreement with PDR models and Galactic observations. Fourth, a simple model in which CO emerges from a smaller sphere nested inside a larger cloud can roughly relate the H2 masses measured from CO kinematics and dust.Comment: 17 pages, 10 figures (including appendix), accepted for publication in the Astrophysical Journa

Women’s visibility in academic seminars: Women ask fewer questions than men

The attrition of women in academic careers is a major concern, particularly in Science, Technology, Engineering, and Mathematics subjects. One factor that can contribute to the attrition is the lack of visible role models for women in academia. At early career stages, the behaviour of the local community may play a formative role in identifying ingroup role models, shaping women’s impressions of whether or not they can be successful in academia. One common and formative setting to observe role models is the local departmental academic seminar, talk, or presentation. We thus quantified women’s visibility through the question-asking behaviour of academics at seminars using observations and an online survey. From the survey responses of over 600 academics in 20 countries, we found that women reported asking fewer questions after seminars compared to men. This impression was supported by observational data from almost 250 seminars in 10 countries: women audience members asked absolutely and proportionally fewer questions than male audience members. When asked why they did not ask questions when they wanted to, women, more than men, endorsed internal factors (e.g., not working up the nerve). However, our observations suggest that structural factors might also play a role; when a man was the first to ask a question, or there were fewer questions, women asked proportionally fewer questions. Attempts to counteract the latter effect by manipulating the time for questions (in an effort to provoke more questions) in two departments were unsuccessful. We propose alternative recommendations for creating an environment that makes everyone feel more comfortable to ask questions, thus promoting equal visibility for women and members of other less visible groups

Women's visibility in academic seminars: Women ask fewer questions than men

The attrition of women in academic careers is a major concern, particularly in Science, Technology, Engineering, and Mathematics subjects. One factor that can contribute to the attrition is the lack of visible role models for women in academia. At early career stages, the behaviour of the local community may play a formative role in identifying ingroup role models, shaping women's impressions of whether or not they can be successful in academia. One common and formative setting to observe role models is the local departmental academic seminar, talk, or presentation. We thus quantified women's visibility through the question-asking behaviour of academics at seminars using observations and an online survey. From the survey responses of over 600 academics in 20 countries, we found that women reported asking fewer questions after seminars compared to men. This impression was supported by observational data from almost 250 seminars in 10 countries: women audience members asked absolutely and proportionally fewer questions than male audience members. When asked why they did not ask questions when they wanted to, women, more than men, endorsed internal factors (e.g., not working up the nerve). However, our observations suggest that structural factors might also play a role; when a man was the first to ask a question, or there were fewer questions, women asked proportionally fewer questions. Attempts to counteract the latter effect by manipulating the time for questions (in an effort to provoke more questions) in two departments were unsuccessful. We propose alternative recommendations for creating an environment that makes everyone feel more comfortable to ask questions, thus promoting equal visibility for women and members of other less visible groups