Magnetic field topology of the RS CVn star II Pegasi

The dynamo processes in cool active stars generate complex magnetic fields responsible for prominent surface stellar activity and variability at different time scales. For a small number of cool stars magnetic field topologies were reconstructed from the time series of spectropolarimetric observations using the Zeeman Doppler imaging (ZDI) method. In this study we follow a long-term evolution of the magnetic field topology of the RS CVn binary star II Peg. We collected high-resolution circular polarisation observations of II Peg using the SOFIN spectropolarimeter at the Nordic Optical Telescope. These data cover 12 epochs spread over 7 years. A multi-line diagnostic technique in combination with a new ZDI code is applied to interpret these observations. Magnetic inversions using these data reveals evolving magnetic fields with typical local strengths of 0.5-1.0 kG and complex topologies. Despite using a self-consistent magnetic and temperature mapping technique, we do not find a clear correlation between magnetic and temperature features in the ZDI maps. Neither do we confirm the presence of persistent azimuthal field rings found in other RS CVn stars. Reconstruction of the magnetic field topology of II Peg reveals significant evolution of both the surface magnetic field structure and the extended magnetospheric field geometry. From 2004 to 2010 the total field energy drastically declined and the field became less axisymmetric. This also coincided with the transition from predominantly poloidal to mainly toroidal field topology. A qualitative comparison of the ZDI maps of II Peg with the prediction of dynamo theory suggests that the magnetic field in this star is produced mainly by the turbulent alpha^2 dynamo rather than the solar alphaOmega dynamo. Our results do not show a clear active longitude system, nor is there an evidence of the presence of an azimuthal dynamo wave.Comment: 20 pages, 10 figures; accepted for publication in Astronomy & Astrophysic

Targeting Glycolysis with Epigallocatechin-3-Gallate Enhances the Efficacy of Chemotherapeutics in Pancreatic Cancer Cells and Xenografts.

Pancreatic cancer is a complex disease, in need of new therapeutic approaches. In this study, we explored the effect and mechanism of action of epigallocatechin-3-gallate (EGCG), a major polyphenol in green tea, alone and in combination with current chemotherapeutics on pancreatic cancer cell growth, focusing on glycolysis metabolism. Moreover, we investigated whether EGCG's effect is dependent on its ability to induce reactive oxygen species (ROS). EGCG reduced pancreatic cancer cell growth in a concentration-dependent manner and the growth inhibition effect was further enhanced under glucose deprivation conditions. Mechanistically, EGCG induced ROS levels concentration-dependently. EGCG affected glycolysis by suppressing the extracellular acidification rate through the reduction of the activity and levels of the glycolytic enzymes phosphofructokinase and pyruvate kinase. Cotreatment with catalase abrogated EGCG's effect on phosphofructokinase and pyruvate kinase. Furthermore, EGCG sensitized gemcitabine to inhibit pancreatic cancer cell growth in vitro and in vivo. EGCG and gemcitabine, given alone, reduced pancreatic tumor xenograft growth by 40% and 52%, respectively, whereas the EGCG/gemcitabine combination reduced tumor growth by 67%. EGCG enhanced gemcitabine's effect on apoptosis, cell proliferation, cell cycle and further suppressed phosphofructokinase and pyruvate kinase levels. In conclusion, EGCG is a strong combination partner of gemcitabine reducing pancreatic cancer cell growth by suppressing glycolysis

Epigallocatechin-3-Gallate (EGCG) Suppresses Pancreatic Cancer Cell Growth, Invasion, and Migration partly through the Inhibition of Akt Pathway and Epithelial-Mesenchymal Transition: Enhanced Efficacy when Combined with Gemcitabine.

Most pancreatic cancers are usually diagnosed at an advanced stage when they have already metastasized. Epigallocatechin-3-gallate (EGCG), a major polyphenolic constituent of green tea, has been shown to reduce pancreatic cancer growth, but its effect on metastasis remains elusive. This study evaluated the capacity of EGCG to inhibit pancreatic cancer cell migration and invasion and the underlying mechanisms. EGCG reduced pancreatic cancer cell growth, migration, and invasion in vitro and in vivo. EGCG prevented "Cadherin switch" and decreased the expression level of TCF8/ZEB1, β-Catenin, and Vimentin. Mechanistically, EGCG inhibited the Akt pathway in a time-dependent manner, by suppressing IGFR phosphorylation and inducing Akt degradation. Co-treatment with catalase or N-Acetyl-L-cysteine did not abrogate EGCG's effect on the Akt pathway or cell growth. Moreover, EGCG synergized with gemcitabine to suppress pancreatic cancer cell growth, migration, and invasion, through modulating epithelial-mesenchymal transition markers and inhibiting Akt pathway. In summary, EGCG may prove beneficial to improve gemcitabine sensitivity in inhibiting pancreatic cancer cell migration and invasion, to some extent through the inhibition of Akt pathway and epithelial-mesenchymal transition

First measurement of the magnetic field on FK Com and its relation to the contemporaneous starspot locations

In this study we present simultaneous low-resolution longitudinal magnetic field measurements and high-resolution spectroscopic observations of the cool single giant FK Com. The variation of the magnetic field over the rotational period of 2.4 days is compared with the starspot location obtained using Doppler imaging techniques, V-band photometry and V-I colours. The chromospheric activity is studied simultaneously with the photospheric activity using high resolution observations of the Halpha, Hbeta and Hgamma line profiles. Both the maximum (272 +/- 24 G) and minimum (60 +/- 17 G) in the mean longitudinal magnetic field, , are detected close to the phases where cool spots appear on the stellar surface. A possible explanation for such a behaviour is that the active regions at the two longitudes separated by 0.2 in phase have opposite polarities.Comment: 10 Pages, 11 figures (quality of Figures 7,8 and 10 reduced), accepted for publication in MNRA

The effect of steroids on GPR54 and GnRH neurons in the postpubertal male mouse [abstract]

Abstract only availableA novel neuropeptide, kisspeptin, binds to the receptor GPR54, to influence the initiation and regulation of puberty in mammals. It appears that the activation of GPR54 stimulates the release of gonadotropin releasing hormone (GnRH) from specialized neurons, resulting in the activation of the reproductive system. To further understand the role of the kisspeptin system in GnRH secretion, levels of GPR54 and GnRH mRNA were compared in hypothalamic tissue before, during, and after puberty in male mice. In addition, the expression of GPR54 and GnRH mRNA was examined after castration with or without steroid replacement in postpubertal males. Transgenic male mice that express green fluorescent protein (GFP) were used at 20, 30, and 60 days postnatal (PND). Some postnatal mice were gonadectomized (GDX), and half received testosterone (T) replacement. RNA was isolated from the septum and the basal hypothalamus (areas known to contain GnRH neurons), reverse transcribed, and subjected to real-time, quantitative PCR. Levels of mRNA were compared between GDX and GDX+T, as well as at each of the three ages. Relative amounts of mRNA from GPR54 and GnRH were compared with a housekeeping gene, RPII, using standard curves. Preliminary data suggests that the amount of GPR54 mRNA in hypothalamic tissue is unchanged at the ages studied (p<0.892), although we need to increase the number of mice studied at each age. However, the levels of GnRH mRNA in hypothalamic tissue do increase, although not significantly, with age and the pubertal transition (p<0.112). In postpubertal mice, the relative amount of GnRH mRNA is greater than GPR54 mRNA. Thus, data indicate that there is a decrease in GPR54 mRNA when compared to GnRH mRNA (p<0.05) during the pubertal transition. Studies that examine the effect of steroids on GPR54 and GnRH mRNA expression are currently in progress.Life Sciences Undergraduate Research Opportunity Progra

Stellar activity as noise in exoplanet detection I. Methods and application to solar-like stars and activity cycles

The detection of exoplanets using any method is prone to confusion due to the intrinsic variability of the host star. We investigate the effect of cool starspots on the detectability of the exoplanets around solar-like stars using the radial velocity method. For investigating this activity-caused "jitter" we calculate synthetic spectra using radiative transfer, known stellar atomic and molecular lines, different surface spot configurations, and an added planetary signal. Here, the methods are described in detail, tested and compared to previously published studies. The methods are also applied to investigate the activity jitter in old and young solar-like stars, and over a solar-like activity cycles. We find that the mean full jitter amplitude obtained from the spot surfaces mimicking the solar activity varies during the cycle approximately between 1 m/s and 9 m/s. With a realistic observing frequency a Neptune mass planet on a one year orbit can be reliably recovered. On the other hand, the recovery of an Earth mass planet on a similar orbit is not feasible with high significance. The methods developed in this study have a great potential for doing statistical studies of planet detectability, and also for investigating the effect of stellar activity on recovered planetary parameters.Comment: Accepted to MNRA

Kisspeptin, GPR54, and GnRH neurons: Interactions in the male mouse [abstract]

Abstract only availableFaculty Mentor: Dr. M. Cathleen Kovarik, Veterinary Biomedical SciencesA novel neuropeptide, kisspeptin, binds to the receptor GPR54, to influence the initiation and regulation of puberty in mammals. It appears that the activation of GPR54 stimulates the release of gonadotropin releasing hormone (GnRH) from specialized neurons, resulting in the activation of the reproductive system. To further understand the role of the kisspeptin system in GnRH secretion, levels of GPR54 and GnRH mRNA were compared in hypothalamic tissue before, during, and after puberty in male mice. Transgenic male mice that express green fluorescent protein (GFP) in their GnRH neurons were used at 20 (prepubertal), 30 (pubertal) and 60 (postpubertal) days postnatal. RNA was isolated from brain areas known to contain GnRH neurons. Isolated RNA was reverse transcribed and will be subjected to real-time, quantitative PCR. Relative amounts of mRNA from GPR54 and GnRH will be compared with a housekeeping gene, RPII using standard curves at each of the three ages. Currently, we have used real-time PCR to detect amplicons, of approximately 60 base pairs, for each group down to the attogram (10-18) level. We have also determined that the ABI 7000 machine and SYBR- green as a detector are optimal for our purposes. We are currently performing PCRs for each of the three genes of interest. Amounts of GPR54 and GnRH in older animals will be expressed relative to amounts from the 20 day postnatal animals. Similar techniques will be used to study the expression of GPR54 and GnRH mRNA at the level of the single GnRH neuron, as well as the effect of steroids on the system

Doppler images of II Pegasi for 2004-2010

Aims. We study the spot activity of II Peg during the years 2004-2010 to determine long- and short-term changes in the magnetic activity. In a previous study, we detected a persistent active longitude, as well as major changes in the spot configuration occurring on a timescale of shorter than a year. The main objective of this study is to determine whether the same phenomena persist in the star during these six years of spectroscopic monitoring. Methods. The observations were collected with the high-resolution SOFIN spectrograph at the Nordic Optical Telescope. The temperature maps were calculated using a Doppler imaging code based on Tikhonov regularization. Results. We present 12 new temperature maps that show spots distributed mainly over high and intermediate latitudes. In each image, 1-3 main active regions can be identified. The activity level of the star is clearly lower than during our previous study for the years 1994-2002. In contrast to the previous observations, we detect no clear drift of the active regions with respect to the rotation of the star. Conclusions. Having shown a systematic longitudinal drift of the spot-generating mechanism during 1994-2002, the star has clearly switched to a low-activity state for 2004-2010, during which the spot locations appear more random over phase space. It could be that the star is near to a minimum of its activity cycle.Comment: Accepted for publication in Astron. and Astrophys., 8 pages, 5 figure