Do OB Runaway Stars Have Pulsar Companions?

We have conducted a VLA search for radio pulsars at the positions of 44 nearby OB runaway stars. The observations involved both searching images for point sources of continuum emission and a time series analysis. Our mean flux sensitivity to pulsars slower than 50 ms was 0.2 mJy. No new pulsars were found in the survey. The size of the survey, combined with the high sensitivity of the observations, sets a significant constraint on the probability, $f_p$, of a runaway OB star having an observable pulsar companion. We find $f_p \le 6.5$\% with 95\% confidence, if the general pulsar luminosity function is applicable to OB star pulsar companions. If a pulsar beaming fraction of \onethird\ is assumed, then we estimate that fewer than 20\% of runaway OB stars have neutron star companions, unless pulsed radio emission is frequently obscured by the OB stellar wind. Our result is consistent with the dynamical (or cluster) ejection model for the formation of OB runaways. The supernova ejection model is not ruled out, but is constrained by these observations to allow only a small binary survival fraction, which may be accommodated if neutron stars acquire significant natal kicks. According to Leonard, Hills and Dewey (1994), a 20\% survival fraction corresponds to a 3-d kick velocity of 420 km s$^{-1}$. This value is in close agreement with recent revisions of the pulsar velocity distribution.Comment: Submitted to the Astronomical Journal. 16 pages. Latex uses aaspp4.sty. 3 postscript figures. Address correspondence to Colin Philp ([email protected]). Revision was to replace .ps file with latex fil

Chromatid Segregation at Anaphase Requires the barren Product, a Novel Chromosome-Associated Protein That Interacts with Topoisomerase II

AbstractWe have isolated a Drosophila gene, barren (barr), required for sister-chromatid segregation in mitosis. barr encodes a novel protein that is present in proliferating cells and has homologs in yeast and human. Mitotic defects in barr embryos become apparent during cycle 16, resulting in a loss of PNS and CNS neurons. Centromeres move apart at the metaphase–anaphase transition and Cyclin B is degraded, but sister chromatids remain connected, resulting in chromatin bridging. This phenotype is similar to that described in TOP2 mutants in yeast. Barren protein localizes to chromatin throughout mitosis. Colocalization and biochemical experiments indicate that Barren associates with Topoisomerase II throughout mitosis and alters the activity of Topoisomerase II. We propose that this association is required for proper chromosomal segregation by facilitating the decatenation of chromatids at anaphase

The potential therapeutic effect of manipulating the extracellular matrix in idiopathic pulmonary fibrosis

Background: Idiopathic Pulmonary Fibrosis (IPF) is a physiologically devastating disease. The debilitating nature and high mortality rates make this one of the most lethal conditions, usually associated with median time to mortality of around 3 years. Increased deposition of extracellular matrix (ECM) and fibroblast accumulation are hallmarks of idiopathic pulmonary fibrosis (IPF). We hypothesise that the ECM in IPF is structurally abnormal by virtue of aberrant cross linking and promotes fibroblast accumulation. This study examined the structure and biological activity of IPF derived ECM and how this related to the expression of ECM cross linking enzymes as well as how inhibiting Transglutaminase 2 affects active fibrosis in the murine Bleomycin model. Methods: Primary fibroblasts from 3 patients with IPF and 3 controls were isolated from biopsy samples and characterised by immunocytochemistry. ECM from these cells was deposited onto tissue culture plastic, cells removed using ammonium hydroxide and confirmed by electron microscopy (SEM). IPF and control cells were then grown on their own ECM or ECM derived from other cells. ECM was labelled with 3H-proline and digested with recombinant proteases and tritium liberation counted by scintillation as a measure of collagen proteolysis. A pilot study was carried out where C57BL/5J mice received a single intratracheal instillation of Bleomycin (2mg/kg) and administered cystamine dihydrochloride by intraperitoneal injection (IP), once a day for ten consecutive days at 40mg/kg or 100mg/kg, at 3 different time points. Results: IPF derived fibroblasts had more distinct organisation of fibrous matrix filaments on the cell surface and between adjacent cells by SEM. Both control and IPF lung fibroblasts expressed transcripts for lysyl oxidase (LOX), LOXL1, LOXL2, LOXL3, LOXL4 and transglutaminase (TG) 2. IPF derived matrix increased expression of LOXL3 and TG2 transcripts, LOXL3 protein and TGase activity. Other cross linking enzymes were unchanged. To assess if IPF matrix affected fibroblast accumulation, I measured fibroblast adhesion, proliferation by MTT and EDU assays, and apoptosis by cleaved caspase 3, cleaved PARP and TUNEL assay on the different matrices. IPF matrix enhanced proliferation over control matrix in response to PDGF-BB. To determine if this pro-proliferative effect was dependent upon aberrant cross-linking we generated ECM from normal and IPF fibroblasts treated with cystamine dihydrochloride (TG2 inhibitor) or β-amino-proprionitrile (LOX family inhibitor). The enhanced fibroblast proliferation seen on IPF matrix was reduced close to levels of normal matrix by each cross link inhibitor. There was no effect on apoptosis induced by either FAS ligand or staurosporine when cells were seeded onto IPF or control matrix suggesting IPF ECM does not protect seeded fibroblasts from apoptosis. Bleomycin showed a trend towards increasing total lung hydroxyproline at day 24, 34 and 44 post administration however this was not statistically significant. Administration of cystamine at 40mg/kg/day showed no effect on total lung hydroxyproline. At day 34 post Bleomycin, cystamine administration showed a trend towards decreasing total lung hydroxyproline however again this was not statistically significant. Conclusions: The data supports the hypothesis that IPF derived matrix is structurally and functionally different from normal matrix. This results in enhanced fibroblast proliferation, adhesion and increased cross linking activity by effects on gene transcription. Inhibition of matrix cross-linking reduced this enhanced fibroblast adhesion and proliferation. Administration of cystamine dihydrochloride via IP injection for ten consecutive days at 100mg/kg/day in the Bleomycin model showed a trend towards decreasing total lung hydroxyproline

Molecular brakes regulating mTORC1 activation in skeletal muscle following synergist ablation

The goal of the current work was to profile positive (mTORC1 activation, autocrine/paracrine growth factors) and negative [AMPK, unfolded protein response (UPR)] pathways that might regulate overload-induced mTORC1 (mTOR complex 1) activation with the hypothesis that a number of negative regulators of mTORC1 will be engaged during a supraphysiological model of hypertrophy. To achieve this, mTORC1- IRS-1/2 signaling, BiP/CHOP/IRE1, and AMPK activation were determined in rat plantaris muscle following synergist ablation (SA). SA resulted in significant increases in muscle mass of 4% per day throughout the 21 days of the experiment. The expression of the insulin-like growth factors (IGF) were high throughout the 21st day of overload. However, IGF signaling was limited, since IRS-1 and -2 were undetectable in the overloaded muscle from day 3 to day 9. The decreases in IRS-1/2 protein were paralleled by increases in GRB10 Ser501/503 and S6K1 Thr389 phosphorylation, two mTORC1 targets that can destabilize IRS proteins. PKB Ser473 phosphorylation was higher from 3– 6 days, and this was associated with increased TSC2 Thr939 phosphorylation. The phosphorylation of TSC2 Thr1345 (an AMPK site) was also elevated, whereas phosphorylation at the other PKB site, Thr1462, was unchanged at 6 days. In agreement with the phosphorylation of Thr1345, SA led to activation of AMPK1 during the initial growth phase, lasting the first 9 days before returning to baseline by day 12. The UPR markers CHOP and BiP were elevated over the first 12 days following ablation, whereas IRE1 levels decreased. These data suggest that during supraphysiological muscle loading at least three potential molecular brakes engage to downregulate mTORC1. m

Mutations in the Drosophila melanogaster gene three rows permit aspects of mitosis to continue in the absence of chromatid segregation

We have cloned the three rows (thr) gene, by a combination of chromosome microdissection and P element tagging. We describe phenotypes of embryos homozygous for mutations at the thr locus. Maternal mRNA and protein appear to be sufficient to allow 14 rounds of mitosis in embryos homozygous for thr mutations. However, a small percentage of cells in syncytial blastoderm stage thr embryos sink into the interior of the embryo as if they have failed to divide properly. Following cellularisation all cells complete mitosis 14 normally. All cells become delayed at mitosis 15 with their chromosomes remaining aligned on the spindle in a metaphase-like configuration, even though both cyclins A and B have both been degraded. As cyclin B degradation occurs at the metaphase-anaphase transition, subsequent to the microtubule integrity checkpoint, the delay induced by mutations at the thr locus defines a later point in mitotic progression. Chromosomes in the cells of thr embryos do not undertake anaphase separation, but remain at the metaphase plate. Subsequently they decondense. A subset of nuclei go on to replicate their DNA but there is no further mitotic division

Phagocytosis-Dependent Ketogenesis in Retinal Pigment Epithelium

Daily, the retinal pigment epithelium (RPE) ingests a bolus of lipid and protein in the form of phagocytized photoreceptor outer segments (OS). The RPE, like the liver, expresses enzymes required for fatty acid oxidation and ketogenesis. This suggests that these pathways play a role in the disposal of lipids from ingested OS, as well as providing a mechanism for recycling metabolic intermediates back to the outer retina. In this study, we examined whether OS phagocytosis was linked to ketogenesis. We found increased levels of β-hydroxybutyrate (β-HB) in the apical medium following ingestion of OS by human fetal RPE and ARPE19 cells cultured on Transwell inserts. No increase in ketogenesis was observed following ingestion of oxidized OS or latex beads. Our studies further defined the connection between OS phagocytosis and ketogenesis in wild-type mice and mice with defects in phagosome maturation using a mouse RPE explant model. In explant studies, the levels of β-HB released were temporally correlated with OS phagocytic burst after light onset. In the Mreg-/- mouse where phagosome maturation is delayed, there was a temporal shift in the release of β-HB. An even more pronounced shift in maximal β-HB production was observed in the Abca4-/- RPE, in which loss of the ATP-binding cassette A4 transporter results in defective phagosome processing and accumulation of lipid debris. These studies suggest that FAO and ketogenesis are key to supporting the metabolism of the RPE and preventing the accumulation of lipids that lead to oxidative stress and mitochondrial dysfunction. © 2017 by The American Society for Biochemistry and Molecular Biology, Inc

Phagocytosis-Dependent Ketogenesis in Retinal Pigment Epithelium

Daily, the retinal pigment epithelium (RPE) ingests a bolus of lipid and protein in the form of phagocytized photoreceptor outer segments (OS). The RPE, like the liver, expresses enzymes required for fatty acid oxidation and ketogenesis. This suggests that these pathways play a role in the disposal of lipids from ingested OS, as well as providing a mechanism for recycling metabolic intermediates back to the outer retina. In this study, we examined whether OS phagocytosis was linked to ketogenesis. We found increased levels of β-hydroxybutyrate (β-HB) in the apical medium following ingestion of OS by human fetal RPE and ARPE19 cells cultured on Transwell inserts. No increase in ketogenesis was observed following ingestion of oxidized OS or latex beads. Our studies further defined the connection between OS phagocytosis and ketogenesis in wild-type mice and mice with defects in phagosome maturation using a mouse RPE explant model. In explant studies, the levels of β-HB released were temporally correlated with OS phagocytic burst after light onset. In the Mreg−/− mouse where phagosome maturation is delayed, there was a temporal shift in the release of β-HB. An even more pronounced shift in maximal β-HB production was observed in the Abca4−/− RPE, in which loss of the ATP-binding cassette A4 transporter results in defective phagosome processing and accumulation of lipid debris. These studies suggest that FAO and ketogenesis are key to supporting the metabolism of the RPE and preventing the accumulation of lipids that lead to oxidative stress and mitochondrial dysfunction