Quantifying non-star formation associated 8um dust emission in NGC 628

Combining Ha and IRAC images of the nearby spiral galaxy NGC 628, we find that between 30-43% of its 8um dust emission is not related to recent star formation. Contributions from dust heated by young stars are separated by identifying HII regions in the Ha map and using these areas as a mask to determine the 8um dust emission that must be due to heating by older stars. Corrections are made for sub-detection-threshold HII regions, photons escaping from HII regions and for young stars not directly associated to HII regions (i.e. 10-100 Myr old stars). A simple model confirms this amount of 8um emission can be expected given dust and PAH absorption cross-sections, a realistic star-formation history, and the observed optical extinction values. A Fourier power spectrum analysis indicates that the 8um dust emission is more diffuse than the Ha emission (and similar to observed HI), supporting our analysis that much of the 8um-emitting dust is heated by older stars. The 8um dust-to-Ha emission ratio declines with galactocentric radius both within and outside of HII regions, probably due to a radial increase in disk transparency. In the course of this work, we have also found that intrinsic diffuse Ha fractions may be lower than previously thought in galaxies, if the differential extinction between HII regions and diffuse regions is taken into account.Comment: 14 pages, 11 figures, accepted in Ap

Experiences of Female and Male Medical Students With Death, Dying, and Palliative Care: One Size Does Not Fit All

Background: Medical students learn about death, dying, and palliative care (DDPC) through formal curricular offerings and informal clinical experiences; however, the lessons learned in the clinic may be at odds with the formal curriculum. Reflective writing is a means for students to “bracket” their DDPC experiences and reconcile conflicts between the formal and informal curriculum. Objectives: The aim of this study is to compare the level of reflection demonstrated in medical students’ narratives on DDPC with other experiences and to examine the domains of professionalism that students perceive to be prevalent in their DDPC experiences. Methods: Third-year medical students submitted professionalism narratives during their internal medicine clerkship. We identified a subset of narratives related to DDPC (n = 388) and randomly selected control narratives (n = 153). We assessed the level of reflection demonstrated in the narratives using a validated rubric and analyzed the professionalism domains that students identified as relevant to their experience. Results: There was no difference in reflective level between DDPC and control narratives. Within the DDPC group, female students demonstrated higher reflection (2.24 ± 0.71) than male students (2.01 ± 0.77; P < .001). Caring, compassion and communication, and honor and integrity were prominent among DDPC narratives. More females identified caring, compassion, and communication as relevant to their DDPC experiences, whereas more males identified altruism. Conclusion: Males and females have different perceptions of DDPC experiences, and female students appear to be more deeply impacted. These findings can help clinical faculty engage students more effectively with this challenging topic

Soluble expression, purification and characterization of the full length IS2 Transposase

<p>Abstract</p> <p>Background</p> <p>The two-step transposition pathway of insertion sequences of the IS<it>3 </it>family, and several other families, involves first the formation of a branched figure-of-eight (F-8) structure by an asymmetric single strand cleavage at one optional donor end and joining to the flanking host DNA near the target end. Its conversion to a double stranded minicircle precedes the second insertional step, where both ends function as donors. In IS<it>2</it>, the left end which lacks donor function in Step I acquires it in Step II. The assembly of two intrinsically different protein-DNA complexes in these F-8 generating elements has been intuitively proposed, but a barrier to testing this hypothesis has been the difficulty of isolating a full length, soluble and active transposase that creates fully formed synaptic complexes <it>in vitro </it>with protein bound to both binding and catalytic domains of the ends. We address here a solution to expressing, purifying and structurally analyzing such a protein.</p> <p>Results</p> <p>A soluble and active IS<it>2 </it>transposase derivative with GFP fused to its C-terminus functions as efficiently as the native protein in <it>in vivo </it>transposition assays. <it>In vitro </it>electrophoretic mobility shift assay data show that the partially purified protein prepared under native conditions binds very efficiently to cognate DNA, utilizing both N- and C-terminal residues. As a precursor to biophysical analyses of these complexes, a fluorescence-based random mutagenesis protocol was developed that enabled a structure-function analysis of the protein with good resolution at the secondary structure level. The results extend previous structure-function work on IS<it>3 </it>family transposases, identifying the binding domain as a three helix H + HTH bundle and explaining the function of an atypical leucine zipper-like motif in IS<it>2</it>. In addition gain- and loss-of-function mutations in the catalytic active site define its role in regional and global binding and identify functional signatures that are common to the three dimensional catalytic core motif of the retroviral integrase superfamily.</p> <p>Conclusions</p> <p>Intractably insoluble transposases, such as the IS<it>2 </it>transposase, prepared by solubilization protocols are often refractory to whole protein structure-function studies. The results described here have validated the use of GFP-tagging and fluorescence-based random mutagenesis in overcoming this limitation at the secondary structure level.</p

Dithiol-based compounds maintain expression of antioxidant protein peroxiredoxin 1 that counteracts toxicity of mutant huntingtin

Mitochondrial dysfunction and elevated reactive oxygen species are strongly implicated in both aging and various neurodegenerative disorders, including Huntington disease (HD). Because reactive oxygen species can promote the selective oxidation of protein cysteine sulfhydryl groups to disulfide bonds we examined the spectrum of disulfide-bonded proteins that were specifically altered in a HD context. Protein extracts from PC12 cells overexpressing the amino-terminal fragment of the Huntingtin (Htt) protein with either a nonpathogenic or pathogenic polyglutamine repeat (Htt-103Q) were resolved by redox two-dimensional PAGE followed by mass spectrometry analysis. Several antioxidant proteins were identified that exhibited changes in disulfide bonding unique to Htt-103Q expressing cells. In particular, the antioxidant protein peroxiredoxin 1 (Prx1) exhibited both decreased expression and hyperoxidation in response to mutant Htt expressed in either PC12 cells or immortalized striatal cells exposed to 3-nitropropionic acid. Ectopic expression of Prx1 in PC12 cells attenuated mutant Httinduced toxicity. In contrast, short hairpin RNA-mediated knockdown of Prx1 potentiated mHtt toxicity. Furthermore, treatment with the dithiol-based compounds dimercaptopropanol and dimercaptosuccinic acid suppressed toxicity in bothHD cell models, whereas monothiol compounds were relatively ineffective. Dimercaptopropanol treatment also prevented mutant Htt-induced loss of Prx1 expression in both cell models. Our studies reveal for the first time that pathogenic Htt can affect the expression and redox state of antioxidant proteins; an event countered by specific dithiol-based compounds. These findings should provide a catalyst to explore the use of dithiolbased drugs for the treatment of neurodegenerative diseases. © 2012 by The American Society for Biochemistry and Molecular Biology, Inc