The Discovery of a Debris Disk Around the DAV White Dwarf PG 1541+651

To search for circumstellar disks around evolved stars, we targeted roughly 100 DA white dwarfs from the Palomar Green survey with the Peters Automated Infrared Imaging Telescope (PAIRITEL). Here we report the discovery of a debris disk around one of these targets, the pulsating white dwarf PG 1541+651 (KX Draconis, hereafter PG1541). We detect a significant flux excess around PG1541 in the K-band. Follow-up near-infrared spectroscopic observations obtained at the NASA Infrared Telescope Facility (IRTF) and photometric observations with the warm Spitzer Space Telescope confirm the presence of a warm debris disk within 0.13-0.36 Rsun (11-32x the stellar radius) at an inclination angle of 60deg. At Teff = 11880 K, PG1541 is almost a twin of the DAV white dwarf G29-38, which also hosts a debris disk. All previously known dusty white dwarfs are of the DAZ/DBZ spectral type due to accretion of metals from the disk. High-resolution optical spectroscopy is needed to search for metal absorption lines in PG1541 and to constrain the accretion rate from the disk. PG1541 is only 55 pc away from the Sun and the discovery of its disk in our survey demonstrates that our knowledge of the nearby dusty white dwarf population is far from complete.Comment: MNRAS Letters, in pres

The Evolution of Compact Binary Star Systems

We review the formation and evolution of compact binary stars consisting of white dwarfs (WDs), neutron stars (NSs), and black holes (BHs). Binary NSs and BHs are thought to be the primary astrophysical sources of gravitational waves (GWs) within the frequency band of ground-based detectors, while compact binaries of WDs are important sources of GWs at lower frequencies to be covered by space interferometers (LISA). Major uncertainties in the current understanding of properties of NSs and BHs most relevant to the GW studies are discussed, including the treatment of the natal kicks which compact stellar remnants acquire during the core collapse of massive stars and the common envelope phase of binary evolution. We discuss the coalescence rates of binary NSs and BHs and prospects for their detections, the formation and evolution of binary WDs and their observational manifestations. Special attention is given to AM CVn-stars -- compact binaries in which the Roche lobe is filled by another WD or a low-mass partially degenerate helium-star, as these stars are thought to be the best LISA verification binary GW sources.Comment: 105 pages, 18 figure

Human Skeletal Muscle Possesses an Epigenetic Memory of Hypertrophy

It is unknown if adult human skeletal muscle has an epigenetic memory of earlier encounters with growth. We report, for the first time in humans, genome-wide DNA methylation (850,000 CpGs) and gene expression analysis after muscle hypertrophy (loading), return of muscle mass to baseline (unloading), followed by later hypertrophy (reloading). We discovered increased frequency of hypomethylation across the genome after reloading (18,816 CpGs) versus earlier loading (9,153 CpG sites). We also identified AXIN1, GRIK2, CAMK4, TRAF1 as hypomethylated genes with enhanced expression after loading that maintained their hypomethylated status even during unloading where muscle mass returned to control levels, indicating a memory of these genes methylation signatures following earlier hypertrophy. Further, UBR5, RPL35a, HEG1, PLA2G16, SETD3 displayed hypomethylation and enhanced gene expression following loading, and demonstrated the largest increases in hypomethylation, gene expression and muscle mass after later reloading, indicating an epigenetic memory in these genes. Finally, genes; GRIK2, TRAF1, BICC1, STAG1 were epigenetically sensitive to acute exercise demonstrating hypomethylation after a single bout of resistance exercise that was maintained 22 weeks later with the largest increase in gene expression and muscle mass after reloading. Overall, we identify an important epigenetic role for a number of largely unstudied genes in muscle hypertrophy/memory

The role of resveratrol on skeletal muscle cell differentiation and myotube hypertrophy during glucose restriction

Glucose restriction (GR) impairs muscle cell differentiation and evokes myotube atrophy. Resveratrol treatment in skeletal muscle cells improves inflammatory-induced reductions in skeletal muscle cell differentiation. We therefore hypothesised that resveratrol treatment would improve muscle cell differentiation and myotube hypertrophy in differentiating C2C12 myoblasts and mature myotubes during GR. Glucose restriction at 0.6 g/L (3.3 mM) blocked differentiation and myotube hypertrophy versus high-glucose (4.5 g/L or 25 mM) differentiation media (DM) conditions universally used for myoblast culture. Resveratrol (10 μM) treatment increased SIRT1 phosphorylation in DM conditions, yet did not improve differentiation when administered to differentiating myoblasts in GR conditions. Resveratrol did evoke increases in hypertrophy of mature myotubes under DM conditions with corresponding elevated Igf-I and Myhc7 gene expression, coding for the ‘slow’ type I MYHC protein isoform. Inhibition of SIRT1 via EX-527 administration (100 nM) also reduced myotube diameter and area in DM conditions and resulted in lower gene expression of Myhc 1, 2 and 4 coding for ‘intermediate’ and ‘faster’ IIx, IIa and IIb protein isoforms, respectively. Resveratrol treatment did not appear to modulate phosphorylation of energy-sensing protein AMPK or protein translation initiator P70S6K. Importantly, in mature myotubes, resveratrol treatment was able to ameliorate reduced myotube growth in GR conditions over an acute 24-h period, but not over 48–72 h. Overall, resveratrol evoked myotube hypertrophy in DM conditions while favouring ‘slower’ Myhc gene expression and acutely ameliorated impaired myotube growth observed during glucose restriction

Occurrence of the autofluorescent pigment lipofuscin in polar crustaceans and its potential as age marker

The lack of reliable methods for age determination often complicates the determination of individual age which is a fundamental parameter for estimating growth in population dynamics. In crustaceans, the quantification of the autofluorescent age pigment lipofuscin has recently revealed more promising results in boreal and tropical species than traditional methods. The presence of morphological lipofuscin and its possible application as an age marker in polar species was assessed in brain sections of five Arctic and five Antarctic species comprising decapods, amphipods and a euphausiid. Lipofuscin granules were located using confocal fluorescence microscopy and quantified (as % lipofuscin area fraction) from digital images. The pigment was found in 94 of 100 individuals and in all ten species, and granules occurred in easily detectable amounts in five species. Two scavenging amphipod species, the Antarctic Waldeckia obesa and the Arctic Eurythenes gryllus, revealed the most conspicuous and numerous granules. There was a broad, though weak, correlation with individual body size within a species, but not with absolute body size of one species compared to another. In larvae of the decapod Chorismus antarcticus, lipofuscin accumulation was quantified over the first four months after larval release. Factors potentially influencing lipofuscin formation and their relevance for polar species are discussed. Factors explaining the pronounced differences in lipofuscin content between species for the moment remain unknown. The possibility for application of morphological lipofuscin as an index of age is encouraging for those investigated species with a sufficient accumulation rate of the pigment, and further studies will therefore be conducted

A photoswitchable GPCR-based opsin for presynaptic inhibition

Optical manipulations of genetically defined cell types have generated significant insights into the dynamics of neural circuits. While optogenetic activation has been relatively straightforward, rapid and reversible synaptic inhibition has proven more elusive. Here, we leveraged the natural ability of inhibitory presynaptic GPCRs to suppress synaptic transmission and characterize parapinopsin (PPO) as a GPCR-based opsin for terminal inhibition. PPO is a photoswitchable opsin that couples to Gi/o signaling cascades and is rapidly activated by pulsed blue light, switched off with amber light, and effective for repeated, prolonged, and reversible inhibition. PPO rapidly and reversibly inhibits glutamate, GABA, and dopamine release at presynaptic terminals. Furthermore, PPO alters reward behaviors in a time-locked and reversible manner in vivo. These results demonstrate that PPO fills a significant gap in the neuroscience toolkit for rapid and reversible synaptic inhibition and has broad utility for spatiotemporal control of inhibitory GPCR signaling cascades

Alkali metals in white dwarf atmospheres as tracers of ancient planetary crusts

White dwarfs that accrete the debris of tidally disrupted asteroids1 provide the opportunity to measure the bulk composition of the building blocks, or fragments, of exoplanets2. This technique has established a diversity of compositions comparable to what is observed in the Solar System3, suggesting that the formation of rocky planets is a generic process4. The relative abundances of lithophile and siderophile elements within the planetary debris can be used to investigate whether exoplanets undergo differentiation5, yet the composition studies carried out so far lack unambiguous tracers of planetary crusts6. Here we report the detection of lithium in the atmospheres of four cool (<5,000 K) and old (cooling ages of 5–10 Gyr ago) metal-polluted white dwarfs, of which one also displays photospheric potassium. The relative abundances of these two elements with respect to sodium and calcium strongly suggest that all four white dwarfs have accreted fragments of planetary crusts. We detect an infrared excess in one of the systems, indicating that accretion from a circumstellar debris disk is ongoing. The main-sequence progenitor mass of this star was 4.8 ± 0.2 M⊙, demonstrating that rocky, differentiated planets may form around short-lived B-type stars