250 research outputs found
Star formation history of KDG 61 and KDG 64 from spectroscopy and colour-magnitude diagrams
A study of two dE/dSph members of the nearby M 81 group of galaxies, KDG 61
and UGC 5442 = KDG 64, has been made. Direct Hubble Space Telescope (HST)
Advanced Camera for Surveys (ACS) images and integrated-light spectra of 6 m
telescope of Special Astrophysical Observatory of Russian Academy of Sciences
have been used for quantitative star formation history analysis. The
spectroscopic and colour-magnitude diagrams analysis gives consistent results.
These galaxies appear to be dominated by an old population (12-14 Gyr) of low
metallicity ([Fe/H]~-1.5). Stars of ages about 1 to 4 Gyr have been detected in
both galaxies. The later population shows marginal metal enrichment. We do not
detect any significant radial gradients in age or metallicity in these
galaxies. Our radial velocity measurement suggests that the HII knot on the
line-of-sight of KDG 61 is not gravitationally attached to the galaxy.Comment: 16 pages, 13 figures, accepted by MNRA
Kinematics and stellar population of NGC 4486A
NGC 4486A is a low-luminosity elliptical galaxy harbouring an edge-on nuclear
disk of stars and dust. It is known to host a super-massive black hole. We
study its large-scale kinematics and stellar population along the major axis to
investigate the link between the nuclear and global properties. We use
long-slit medium-resolution optical spectra that we fit against stellar
population models. The SSP-equivalent age is about 12 Gyr old throughout the
body of the galaxy, and its metallicity decreases from [Fe/H] = 0.18 near the
centre to sub-solar values in the outskirts. The metallicity gradient is -0.24
dex per decade of radius within the effective isophote. The velocity dispersion
is 132+-3 km/s at 1.3 arcsec from the centre and decreases outwards. The
rotation velocity reaches a maximum V_max >~ 115+-5 km/s at a radius 1.3 <
r_max < 2 arcsec. NGC\,4486A appears to be a typical low-luminosity elliptical
galaxy. There is no signature in the stellar population of the possible ancient
accretion/merging event that produced the disk.Comment: Astronomy and Astrophysics, in pres
The bacteriophage carrier state of Campylobacter jejuni features changes in host non-coding RNAs and the acquisition of new host-derived CRISPR spacer sequences
Incorporation of self-derived CRISPR DNA protospacers in Campylobacter jejuni PT14 occurs in the presence of bacteriophages encoding a CRISPR-like Cas4 protein. This
phenomenon was evident in carrier state infections where both bacteriophages and host are maintained for seemingly indefinite periods as stable populations following serial passage. Carrier state cultures of C. jejuni PT14 have greater aerotolerance in nutrient limited conditions, and may have arisen as an evolutionary response to selective
pressures imposed during periods in the extra-intestinal environment. A consequence of this is that bacteriophage and host remain associated and able to survive transition
periods where the chances of replicative success are greatly diminished. The majority of the bacteriophage population do not commit to lytic infection, and conversely the bacterial population tolerates low-level bacteriophage replication. We recently examined the effects of Campylobacter bacteriophage/C. jejuni PT14 CRISPR spacer acquisition using deep sequencing strategies of DNA and RNA-Seq to analyze carrier state cultures. This approach identified de novo spacer acquisition in C. jejuni PT14 associated with Class III Campylobacter phages CP8/CP30A but spacer acquisition was oriented toward the capture of host DNA. In the absence of bacteriophage predation the CRISPR spacers in uninfected C. jejuni PT14 cultures remain unchanged. A distinct preference was observed for incorporation of self-derived protospacers into the third spacer position of the C. jejuni PT14 CRISPR array, with the first and second spacers remaining fixed. RNA-Seq also revealed the variation in the synthesis of non-coding RNAs with the potential to bind bacteriophage genes and/or transcript sequences
Age and metallicity gradients in early-type galaxies: A dwarf to giant sequence
We studied the stellar populations of 40 early-type galaxies using medium
resolution long-slit spectroscopy along their major axes (and along the minor
axis for two of them), from 10^7 Msol to 10^12 Msol (-9.2 > M_B > -22.4 mag).
All the studied galaxies lie on the mass-metallicity and age-mass relations.
The transition type dwarfs deviate from the latter relation having younger mean
age, and the low-mass dwarf spheroidals have older ages, marking a
discontinuity in the relation, possibly due to selection effects.
In all mass regimes, the mean metallicity gradients are approximately -0.2
and the mean age gradients +0.1 dex per decade of radius. The individual
gradients are widely spread: and . We do not find evidence for a correlation
between the metallicity gradient and luminosity, velocity dispersion, central
age or age gradient. Likewise, we do not find a correlation between the age
gradient and any other parameter in bright early-type galaxies. In faint
early-types with mag, on the other hand, we find a
correlation between the age gradient and luminosity: the age gradient becomes
more positive for fainter galaxies.
We conclude that various physical mechanisms can lead to similar gradients
and that these gradients are robust against the environmental effects. In
particular, the gradients observed in dwarfs galaxies certainly survived the
transformation of the progenitors through tidal harassment or/and ram-pressure
stripping. The diversity of metallicity gradients amongst dwarf elliptical
galaxies may reflect a plurality of progenitors' morphologies. The dwarfs with
steep metallicity gradients could have originated from blue compact dwarfs and
those with flat profiles from dwarf irregulars and late type spirals.
(Abridged)Comment: 31 pages, 16 figures. Accepted for publications in MNRA
A unique isolated dwarf spheroidal galaxy at D=1.9 Mpc
We present a photometric and spectroscopic study of the unique isolated
nearby dSph galaxy KKR25. The galaxy was resolved into stars with HST/WFPC2
including old red giant branch and red clump. We have constructed a model of
the resolved stellar populations and measured the star formation rate and
metallicity as function of time. The main star formation activity period
occurred about 12.6 to 13.7 Gyr ago. These stars are mostly metal-poor, with a
mean metallicity [Fe/H]\sim -1 to -1.6 dex. About 60 per cent of the total
stellar mass was formed during this event. There are indications of
intermediate age star formation in KKR25 between 1 and 4 Gyr with no
significant signs of metal enrichment for these stars. Long-slit spectroscopy
was carried out using the Russian 6-m telescope of the integrated starlight and
bright individual objects in the galaxy. We have discovered a planetary nebula
(PN) in KKR25. This is the first known PN in a dwarf spheroidal galaxy outside
the Local Group. We have measured its oxygen abundance 12+log(O/H)=7.60+-0.07
dex and a radial velocity Vh=-79 km/s. We have analysed the stellar density
distribution in the galaxy body. The galaxy has an exponential surface
brightness profile with a central light depression. We discuss the evolutionary
status of KKR25, which belongs to a rare class of very isolated dwarf galaxies
with spheroidal morphology.Comment: Accepted to MNRAS. 11 figures, 7 table
Evolutionary history of the OmpR/IIIA family of signal transduction two component systems in Lactobacillaceae and Leuconostocaceae
<p>Abstract</p> <p>Background</p> <p>Two component systems (TCS) are signal transduction pathways which typically consist of a sensor histidine kinase (HK) and a response regulator (RR). In this study, we have analyzed the evolution of TCS of the OmpR/IIIA family in <it>Lactobacillaceae </it>and <it>Leuconostocaceae</it>, two families belonging to the group of lactic acid bacteria (LAB). LAB colonize nutrient-rich environments such as foodstuffs, plant materials and the gastrointestinal tract of animals thus driving the study of this group of both basic and applied interest.</p> <p>Results</p> <p>The genomes of 19 strains belonging to 16 different species have been analyzed. The number of TCS encoded by the strains considered in this study varied between 4 in <it>Lactobacillus helveticus </it>and 17 in <it>Lactobacillus casei</it>. The OmpR/IIIA family was the most prevalent in <it>Lactobacillaceae </it>accounting for 71% of the TCS present in this group. The phylogenetic analysis shows that no new TCS of this family has recently evolved in these <it>Lactobacillaceae </it>by either lineage-specific gene expansion or domain shuffling. Furthermore, no clear evidence of non-orthologous replacements of either RR or HK partners has been obtained, thus indicating that coevolution of cognate RR and HKs has been prevalent in <it>Lactobacillaceae</it>.</p> <p>Conclusions</p> <p>The results obtained suggest that vertical inheritance of TCS present in the last common ancestor and lineage-specific gene losses appear as the main evolutionary forces involved in their evolution in <it>Lactobacillaceae</it>, although some HGT events cannot be ruled out. This would agree with the genomic analyses of <it>Lactobacillales </it>which show that gene losses have been a major trend in the evolution of this group.</p
Crumbs 3b promotes tight junctions in an ezrin-dependent manner in mammalian cells
AMT-L is supported by the School of Biology, University of St Andrews. AMT-L, PAR and FJGM were funded by the Anonymous Trust, University of St Andrews. PAR is supported by the Melville Trust for the Care and Cure of Cancer. The mass spectrometry work was supported by the Wellcome Trust [grant number 094476/Z/10/Z], which funded the purchase of the TripleTOF 5600 mass spectrometer at the BSRC Mass Spectrometry and Proteomics Facility, University of St Andrews. The clinical study was supported by the Department of Pathology, Albert Einstein College of Medicine/ Montefiore Medical Center.Crumbs3 (CRB3) is a component of epithelial junctions that has been implicated in apical-basal polarity, apical identity, apical stability, cell adhesion and cell growth. CRB3 undergoes alternative splicing to yield two variants: CRB3a and CRB3b. Here, we describe novel data demonstrating that as with previous studies on CRB3a, CRB3b also promotes the formation of tight junctions. However, significantly we demonstrate that the 4.1-ezrin-radixin-moesin (FERM) binding motif (FBM) of CRB3b is required for CRB3b functionality and that ezrin binds to the FBM of CRB3b. Furthermore, we show that ezrin contributes to CRB3b functionality and the correct distribution of tight junction proteins. We demonstrate that both CRB3 isoforms are required for the production of functionally mature tight junctions and also the localization of ezrin to the plasma membrane. Finally, we demonstrate that reduced CRB3b expression in head and neck squamous cell carcinoma (HNSCC) correlates with cytoplasmic ezrin, a biomarker for aggressive disease, and show evidence that whilst CRB3a expression has no effect, low CRB3b and high cytoplasmic ezrin expression combined may be prognostic for HNSCC.PostprintPeer reviewe
Intra-strain elicitation and suppression of plant immunity by Ralstonia solanacearum type-III effectors in Nicotiana benthamiana
Effector proteins delivered inside plant cells are powerful weapons for bacterial pathogens, but this exposes the pathogen to potential recognition by the plant immune system. Therefore, the effector repertoire of a given pathogen must be balanced for a successful infection. Ralstonia solanacearum is an aggressive pathogen with a large repertoire of secreted effectors. One of these effectors, RipE1, is conserved in most R. solanacearum strains sequenced to date. In this work, we found that RipE1 triggers immunity in N. benthamiana, which requires the immune regulator SGT1, but not EDS1 or NRCs. Interestingly, RipE1-triggered immunity induces the accumulation of salicylic acid (SA) and the overexpression of several genes encoding phenylalanine-ammonia lyases (PALs), suggesting that the unconventional PAL-mediated pathway is responsible for the observed SA biosynthesis. Surprisingly, RipE1 recognition also induces the expression of jasmonic acid (JA)-responsive genes and JA biosynthesis, suggesting that both SA and JA may act cooperatively in response to RipE1. Finally, we found that RipE1 expression leads to the accumulation of glutathione in plant cells, which precedes the activation of immune responses. R. solanacearum secretes another effector, RipAY, which is known to inhibit immune responses by degrading cellular glutathione. Accordingly, we show that RipAY inhibits RipE1-triggered immune responses. This work shows a strategy employed by R. solanacearum to counteract the perception of its effector proteins by the plant immune system
Elliptical Galaxies and Bulges of Disk Galaxies: Summary of Progress and Outstanding Issues
This is the summary chapter of a review book on galaxy bulges. Bulge
properties and formation histories are more varied than those of ellipticals. I
emphasize two advances: 1 - "Classical bulges" are observationally
indistinguishable from ellipticals, and like them, are thought to form by major
galaxy mergers. "Disky pseudobulges" are diskier and more actively star-forming
(except in S0s) than are ellipticals. Theys are products of the slow
("secular") evolution of galaxy disks: bars and other nonaxisymmetries move
disk gas toward the center, where it starbursts and builds relatively flat,
rapidly rotating components. This secular evolution is a new area of galaxy
evolution work that complements hierarchical clustering. 2 - Disks of
high-redshift galaxies are unstable to the formation of mass clumps that sink
to the center and merge - an alternative channel for the formation of classical
bulges. I review successes and unsolved problems in the formation of
bulges+ellipticals and their coevolution (or not) with supermassive black
holes. I present an observer's perspective on simulations of dark matter galaxy
formation including baryons. I review how our picture of the quenching of star
formation is becoming general and secure at redshifts z < 1. The biggest
challenge is to produce realistic bulges+ellipticals and disks that overlap
over a factor of 10**3 in mass but that differ from each other as observed over
that whole range. Second, how does hierarchical clustering make so many giant,
bulgeless galaxies in field but not cluster environments? I argue that we rely
too much on AGN and star-formation feedback to solve these challenges.Comment: 46 pages, 10 postscript figures, accepted for publication in Galactic
Bulges, ed. E. Laurikainen, R. F. Peletier, & D. A. Gadotti (New York:
Springer), in press (2015
Snail Destabilizes Cell Surface Crumbs3a
Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/92424/1/tra1376.pd
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