Understanding the role of chromatin remodeling in the regulation of circadian transcription in Drosophila.

Circadian clocks enable organisms to anticipate daily changes in the environment and coordinate temporal rhythms in physiology and behavior with the 24-h day-night cycle. The robust cycling of circadian gene expression is critical for proper timekeeping, and is regulated by transcription factor binding, RNA polymerase II (RNAPII) recruitment and elongation, and post-transcriptional mechanisms. Recently, it has become clear that dynamic alterations in chromatin landscape at the level of histone posttranslational modification and nucleosome density facilitate rhythms in transcription factor recruitment and RNAPII activity, and are essential for progression through activating and repressive phases of circadian transcription. Here, we discuss the characterization of the BRAHMA (BRM) chromatin-remodeling protein in Drosophila in the context of circadian clock regulation. By dissecting its catalytic vs. non-catalytic activities, we propose a model in which the non-catalytic activity of BRM functions to recruit repressive factors to limit the transcriptional output of CLOCK (CLK) during the active phase of circadian transcription, while the primary function of the ATP-dependent catalytic activity is to tune and prevent over-recruitment of negative regulators by increasing nucleosome density. Finally, we divulge ongoing efforts and investigative directions toward a deeper mechanistic understanding of transcriptional regulation of circadian gene expression at the chromatin level

Stellar evolution from AGB to planetary nebulae

Proceedings of the International Astronomical Union, 2008, v. 4 n. S252, p. 197-203Planetary nebulae are formed by an interacting winds process where the remnant of the AGB wind is compressed and accelerated by a later-developed fast wind from the central star. One-dimensional dynamical models have successfully explained the multi-shell (bubble, shell, crown, haloes) structures and the kinematics of planetary nebulae. However, the origin of the diverse asymmetric morphology of planetary nebulae is still not understood. Recent observations in the visible, infrared, and the submillimeter have suggested that the AGB mass loss becomes aspherical in the very late stages, forming an expanding torus around the star. A fast, highly collimated wind then emerges in the polar directions and carves out a cavity in the AGB envelope to form a bipolar nebula. Newly discovered structures such as concentric arcs, 2-D rings, multiple lobes, and point-symmetric structures suggest that both the slow and fast winds may have temporal and directional variations, and precession can play a role in the shaping of planetary nebulae. In this paper, we review the latest observations of planetary nebulae and proto-planetary nebulae and discuss the various physical mechanisms (rotation, binary, magnetic field, etc) that could lead to the observed morphologies. © 2008 International Astronomical Union.published_or_final_versio

Synthesis of organic compounds in the circumstellar environment

Proceedings of the International Astronomical Union, 2008, v. 4 n. S251, p. 175-184Through the techniques of millimeter-wave and infrared spectroscopy, over 60 species of gas-phase molecules and a variety of inorganic and organic solids have been detected in the short phase of stellar evolution between the asymptotic giant branch and planetary nebulae. The chemical pathways that lead to the synthesis of complex organic compounds in such low-density environments are therefore important topics of astrochemistry. In this review, we summarize the observational evidence for the existence of complex aliphatic and aromatic compounds in these circumstellar environments, and discuss the nature of their possible carriers. Also discussed are a number of unidentified emission features which may also have an organic origin. The possible relations between these circumstellar organic matter with Solar System organic matter are explored. © 2008 International Astronomical Union.published_or_final_versio

SpS1-Infrared and submillimetre-wave spectroscopy as probes of stellar evolution

Vol. 5 - Highlights H15 (Highlights of Astronomy)published_or_final_versionThe 27th International Astronomical Union (IAU) General Assembly, Rio de Janeiro, Brazil, 3-4 August 2009. In IAU Proceedings, 2009, v. 5, p. 508-50

Complex organics in space from Solar System to distant galaxies

published_or_final_versio

SiO and H2O Maser Observations of Red Supergiants in Star Clusters Embedded in the Galactic Disk

We present the result of radio observations of red supergiants in the star cluster, Stephenson's #2, and candidates for red supergiants in the star clusters, Mercer et al. (2005)'s #4, #8, and #13, in the SiO and H$_2$O maser lines.The Stephenson's #2 cluster and nearby aggregation at the South-West contain more than 15 red supergiants. We detected one at the center of Stephenson's #2 and three in the south-west aggregation in the SiO maser line, and three of these 4 were also detected in the H2O maser line. The average radial velocity of the 4 detected objects is 96 km s^{-1}, giving a kinematic distance of 5.5 kpc, which locates this cluster near the base of the Scutum-Crux spiral arm. We also detected 6 SiO emitting objects associated with the other star clusters. In addition, mapping observations in the CO J=1--0 line toward these clusters revealed that an appreciable amount of molecular gas still remains around Stephenson's #2 cluster in contrast to the prototypical red-supergiant cluster, Bica et al.'s #122. It indicates that a time scale of gas expulsion differs considerably in individual clusters.Comment: high res. figures available at http://www.nro.nao.ac.jp/~lib_pub/report/data/no674.pdf. PASJ 62, No.2 (2010, April 25 issue) in pres

Molecular evolution from AGB stars to planetary nebulae

The late stages of stellar evolution from the Asymptotic Giant Branch (AGB) to planetary nebulae represent the most active phase of molecular synthesis in a star's life. Over 60 molecular species, including inorganics, organics, radicals, chains, rings, and molecular ions have been detected in the circumstellar envelopes of evolved stars. Most interestingly, complex organic compounds of aromatic and aliphatic structures are synthesized over very short time intervals after the end of the AGB. Also appeared during the post-AGB evolution are the unidentified 21 and 30 μm emission features, which are believed to originate from carbonaceous compounds. The circumstellar environment is an ideal laboratory for the testing of theories of chemical synthesis. The distinct spectral behavior among AGB stars, proto-planetary nebulae (PPN), and planetary nebulae (PN) and the short evolutionary time scales that separate these stages pose severe constraints on models. In this paper, we will present an observational summary of the chemical synthesis in the late stages of stellar evolution, discuss chemical and physical processes at work, and speculate on the possible effects these chemical products have on the Galaxy and the Solar System.published_or_final_versio

Delivery of complex organic compounds from planetary nebulae to the solar system

Special issue Papers from ESLAB 2008 Symposium Cosmic Cataclysms and LifeInfrared spectroscopic observations of planetary nebulae and proto-planetary nebulae have shown that complex organic compounds are synthesized in these objects over periods as short as a thousand years. These compounds are ejected into the interstellar medium and spread throughout the Galaxy. Evidence from meteorites has shown that these stellar grains have reached the Solar System, and may have showered the Earth during the heavy bombardment stage of the Early Earth. In this paper, we discuss the chemical structure of stellar organic grains and compare them to the organic matter found in meteorites, comets, asteroids, planetary satellites, and interplanetary particles. The possibility that the early Solar System was chemically enriched by organic compounds ejected from distant stars is presented. © Cambridge University Press 2009.published_or_final_versio