The progenitors of type Ia supernovae in the semidetached binaries with red giant donors

Context. The companions of the exploding carbon-oxygen white dwarfs (CO WDs) for producing type Ia supernovae (SNe Ia) are still not conclusively confirmed. A red-giant (RG) star has been suggested to be the mass donor of the exploding WD, named as the symbiotic channel. However, previous studies on the this channel gave a relatively low rate of SNe Ia. Aims. We aim to systematically investigate the parameter space, Galactic rates and delay time distributions of SNe Ia from the symbiotic channel by employing a revised mass-transfer prescription. Methods. We adopted an integrated mass-transfer prescription to calculate the mass-transfer process from a RG star onto the WD. In this prescription, the mass-transfer rate varies with the local material states. Results. We evolved a large number of WD+RG systems, and found that the parameter space of WD+RG systems for producing SNe Ia is significantly enlarged. This channel could produce SNe Ia with intermediate and old ages, contributing to at most 5% of all SNe Ia in the Galaxy. Our model increases the SN Ia rate from this channel by a factor of 5. We suggest that the symbiotic systems RS Oph and T CrB are strong candidates for the progenitors of SNe Ia.Comment: 8 pages, 6 figure

Overexpression of <i>HAL2</i> in <i>bdf1Δ</i> recovered its resistance to NaCl.

<p>5 µl aliquots of 10-fold serial dilutions of the mid-log phase cultures were spotted onto YPD plates and incubated at 30°C for 3 d.</p

The intracellular Na+ concentration in <i>bdf1Δ</i> was lower than that in wild type.

<p>Mid-log phase cells were grown for 5 h with or without 0.5 mol.L⁻¹ NaCl. The treated cells were washed with MgCl₂ and air dried. The dried cells were nitrified with nitric acid. The Na⁺ concentration was analyzed by atomic absorption spectrophotometry at 589 nm. Error bars denote standard deviation (SD). *P<0.05, **P<0.01 vs. wild type under the same treatment, ^# P<0.01 vs. <i>ena1Δ</i> under the same treatment, n = 3.</p

Deletion of <i>BDF1</i> reduced <i>HAL2</i> expression at both mRNA and protein levels.

<p>The mid-log phase cultures in YPD at 30°C were incubated for 45 min with or without 0.5 mol.L⁻¹ NaCl. (A) Relative fold-changes of <i>HAL2</i> mRNA were calculated against the wild type without NaCl treatment. Error bars denote standard deviation (SD). **P<0.01 vs. wild type under the same treatment, ^# P<0.01 vs. <i>bdf1Δ</i> under the same treatment, n = 3. (B) The Hal2p protein level was analyzed with whole cell protein by Western blot. β-tubulin was used as control. The polyclonal Hal2p antibody and anti-β-tubulin antisera were used in Western blot analysis.</p

<i>HAL2</i> overexpression affected ROS accumulation and partially affected the mitochondrial function.

<p>Mid-log phase cells were incubated for 45 min with or without 0.5 mol.L⁻¹ NaCl. ROS were detected by dihydrorhodamine 123. Mitochondrial membrane potential was measured with JC-1 (A) The ROS (B) and <i>Δ</i>φ (C) fluorescence values were quantified as the relative fluorescence intensity per strain by ImageJ software and averaged from ∼50 cells. Error bars denote standard deviation (SD). *P<0.05, **P<0.01 vs. strains without <i>HAL2</i> overexpression under the same treatment, n = 4. (D) 5 ul aliquots of 10-fold serial dilutions of the mid-log phage cultures were spotted onto YPG plates and incubated at 30°C for 3 d.</p

Salt sensitivity of <i>bdf1Δ</i> was not due to intracellular pAp or the lack of methionine.

<p>Cells grown to OD₆₀₀ = 0.2∼0.4 in SD medium were incubated at 30°C without or with different concentrations of NaCl for 4 h, or 0.1 mol.L⁻¹ LiCl for 2 h. The intracellular pAp concentration was determined as described in Materials and Methods (A–E). 5 ul aliquots of 10-fold serial dilutions of the mid-log phase cultures were spotted onto plates and incubated at 30°C for 3 d (F, G).</p

Hal2p Functions in Bdf1p-Involved Salt Stress Response in <i>Saccharomyces cerevisiae</i>

<div><p>The <i>Saccharomyces cerevisiae</i> Bdf1p associates with the basal transcription complexes TFIID and acts as a transcriptional regulator. Lack of Bdf1p is salt sensitive and displays abnormal mitochondrial function. The nucleotidase Hal2p detoxifies the toxic compound 3′ -phosphoadenosine-5′-phosphate (pAp), which blocks the biosynthesis of methionine. Hal2p is also a target of high concentration of Na⁺. Here, we reported that <i>HAL2</i> overexpression recovered the salt stress sensitivity of <i>bdf1Δ</i>. Further evidence demonstrated that <i>HAL2</i> expression was regulated indirectly by Bdf1p. The salt stress response mechanisms mediated by Bdf1p and Hal2p were different. Unlike <i>hal2Δ</i>, high Na⁺ or Li⁺ stress did not cause pAp accumulation in <i>bdf1Δ</i> and methionine supplementation did not recover its salt sensitivity. <i>HAL2</i> overexpression in <i>bdf1Δ</i> reduced ROS level and improved mitochondrial function, but not respiration. Further analyses suggested that autophagy was apparently defective in <i>bdf1Δ</i>, and autophagy stimulated by Hal2p may play an important role in recovering mitochondrial functions and Na⁺ sensitivity of <i>bdf1Δ</i>. Our findings shed new light towards our understanding about the molecular mechanism of Bdf1p-involved salt stress response in budding yeast.</p></div

Bdf1p regulated <i>HAL2</i> expression indirectly.

<p>The anti-Flag antibody was used for Bdf1p precipitation and IgG was used as a negative control. The promoter regions probed by ChIP correspond to nucleotides −200 to −1. Error bars denote standard deviation (SD). *P<0.05, **P<0.01 vs. wild type under the same treatment, n = 3.</p

Strains and plasmids used in this study.

<p>Strains and plasmids used in this study.</p

Iron Accumulates in Huntington’s Disease Neurons: Protection by Deferoxamine

<div><p>Huntington’s disease (HD) is a progressive neurodegenerative disorder caused by a polyglutamine-encoding CAG expansion in the huntingtin gene. Iron accumulates in the brains of HD patients and mouse disease models. However, the cellular and subcellular sites of iron accumulation, as well as significance to disease progression are not well understood. We used independent approaches to investigate the location of brain iron accumulation. In R6/2 HD mouse brain, synchotron x-ray fluorescence analysis revealed iron accumulation as discrete puncta in the perinuclear cytoplasm of striatal neurons. Further, perfusion Turnbull’s staining for ferrous iron (II) combined with transmission electron microscope ultra-structural analysis revealed increased staining in membrane bound peri-nuclear vesicles in R6/2 HD striatal neurons. Analysis of iron homeostatic proteins in R6/2 HD mice revealed decreased levels of the iron response proteins (IRPs 1 and 2) and accordingly decreased expression of iron uptake transferrin receptor (TfR) and increased levels of neuronal iron export protein ferroportin (FPN). Finally, we show that intra-ventricular delivery of the iron chelator deferoxamine results in an improvement of the motor phenotype in R6/2 HD mice. Our data supports accumulation of redox-active ferrous iron in the endocytic / lysosomal compartment in mouse HD neurons. Expression changes of IRPs, TfR and FPN are consistent with a compensatory response to an increased intra-neuronal labile iron pool leading to increased susceptibility to iron-associated oxidative stress. These findings, together with protection by deferoxamine, support a potentiating role of neuronal iron accumulation in HD. </p> </div