453 research outputs found
Physiology, development, and disease modeling in the Drosophila excretory system
The insect excretory system contains two organ systems acting in concert: the Malpighian tubules and the hindgut perform essential roles in excretion and ionic and osmotic homeostasis. For over 350 years, these two organs have fascinated biologists as a model of organ structure and function. As part of a recent surge in interest, research on the Malpighian tubules and hindgut of Drosophila have uncovered important paradigms of organ physiology and development. Further, many human disease processes can be modeled in these organs. Here, focusing on discoveries in the past 10 years, we provide an overview of the anatomy and physiology of the Drosophila excretory system. We describe the major developmental events that build these organs during embryogenesis, remodel them during metamorphosis, and repair them following injury. Finally, we highlight the use of the Malpighian tubules and hindgut as accessible models of human disease biology. The Malpighian tubule is a particularly excellent model to study rapid fluid transport, neuroendocrine control of renal function, and modeling of numerous human renal conditions such as kidney stones, while the hindgut provides an outstanding model for processes such as the role of cell chirality in development, nonstem cellâbased injury repair, cancer-promoting processes, and communication between the intestine and nervous system
The COS-Dwarfs Survey: The Carbon Reservoir Around sub-L* Galaxies
We report new observations of circumgalactic gas from the COS-Dwarfs survey,
a systematic investigation of the gaseous halos around 43 low-mass z 0.1
galaxies using background QSOs observed with the Cosmic Origins Spectrograph.
From the projected 1D and 2D distribution of C IV absorption, we find that C IV
absorption is detected out to ~ 0.5 R of the host galaxies. The C IV
absorption strength falls off radially as a power law and beyond 0.5 R,
no C IV absorption is detected above our sensitivity limit of ~ 50-100 m.
We find a tentative correlation between detected C IV absorption strength and
star formation, paralleling the strong correlation seen in highly ionized
oxygen for L~L* galaxies by the COS-Halos survey. The data imply a large carbon
reservoir in the CGM of these galaxies, corresponding to a minimum carbon mass
of 1.2 out to ~ 110 kpc. This mass is
comparable to the carbon mass in the ISM and more than the carbon mass
currently in stars of these galaxies. The C IV absorption seen around these
sub-L* galaxies can account for almost two-thirds of all > 100 m C IV
absorption detected at low z. Comparing the C IV covering fraction with
hydrodynamical simulations, we find that an energy-driven wind model is
consistent with the observations whereas a wind model of constant velocity
fails to reproduce the CGM or the galaxy properties.Comment: 18 Pages, 11 Figures, ApJ 796 13
The COS-Halos Survey: Physical Conditions and Baryonic Mass in the Low-Redshift Circumgalactic Medium
We analyze the physical conditions of the cool, photoionized (T
K) circumgalactic medium (CGM) using the COS-Halos suite of gas column density
measurements for 44 gaseous halos within 160 kpc of galaxies at . These data are well described by simple photoionization models, with
the gas highly ionized (n/n) by the
extragalactic ultraviolet background (EUVB). Scaling by estimates for the
virial radius, R, we show that the ionization state (tracked by the
dimensionless ionization parameter, U) increases with distance from the host
galaxy. The ionization parameters imply a decreasing volume density profile
n = (10)(R/R. Our derived
gas volume densities are several orders of magnitude lower than predictions
from standard two-phase models with a cool medium in pressure equilibrium with
a hot, coronal medium expected in virialized halos at this mass scale. Applying
the ionization corrections to the HI column densities, we estimate a lower
limit to the cool gas mass M
M for the volume within R R. Allowing for an
additional warm-hot, OVI-traced phase, the CGM accounts for at least half of
the baryons purported to be missing from dark matter halos at the 10
M scale.Comment: 19 pages, 12 Figures, and a 37-page Appendix with 36 additional
figures. Accepted to ApJ June 21 201
Tentative detection of the circumgalactic medium of the isolated low-mass dwarf galaxy WLM
We report a tentative detection of the circumgalactic medium (CGM) of WolfâLundmarkâMelotte (WLM), an isolated, low-mass (logM*/Mâ â 7.6), dwarf irregular galaxy in the Local Group (LG). We analyse an HST/COS archival spectrum of a quasar sightline (PHL2525), which is 45 kpc (0.5 virial radius) from WLM and close to the Magellanic Stream (MS). Along this sightline, two ion absorbers are detected in Si II, Si III, Si IV, C II, and C IV at velocities of âŒâ220 km sâ»Âč (Component v-220) and âŒâ150 km sâ»Âč (Component v-150). To identify their origins, we study the positionâvelocity alignment of the components with WLM and the nearby MS. Near the magellanic longitude of PHL2525, the MS-related neutral and ionized gas moves at âČâ190 km sâ»Âč, suggesting an MS origin for Component v-220, but not for Component v-150. Because PHL2525 passes near WLM and Component v-150 is close to WLMâs systemic velocity (âŒâ132 km sâ»Âč), it is likely that Component v-150 arises from the galaxyâs CGM. This results in a total Si mass in WLMâs CGM of M^(CGM)_(Si)âŒ(0.2â1.0)Ă10â” Mâ using assumption from other COS dwarf studies. Comparing M^(CGM)_(Si) to the total Si mass synthesized in WLM over its lifetime (âŒ1.3 Ă 10â” Mâ), we find âŒ3 perâcent is locked in stars, âŒ6 perâcent in the ISM, âŒ15â77 perâcent in the CGM, and the rest (âŒ14â76 perâcent) is likely lost beyond the virial radius. Our finding resonates with other COS dwarf galaxy studies and theoretical predictions that low-mass galaxies can easily lose metals into their CGM due to stellar feedback and shallow gravitational potential
The high-ion content and kinematics of low-redshift lyman limit systems
We study the high-ion content and kinematics of the circumgalactic medium around low-redshift galaxies using a sample of 23 Lyman limit systems (LLSs) at 0.08 < z < 0.93 observed with the Cosmic Origins Spectrograph on board the Hubble Space Telescope. In Lehner et al., we recently showed that low-z LLSs have a bimodal metallicity distribution. Here we extend that analysis to search for differences between the high-ion and kinematic properties of the metal-poor and metal-rich branches. We find that metal-rich LLSs tend to show higher O VI columns and broader O VI profiles than metal-poor LLSs. The total H I line width (Îv 90 statistic) in LLSs is not correlated with metallicity, indicating that the H I kinematics alone cannot be used to distinguish inflow from outflow and gas recycling. Among the 17 LLSs with O VI detections, all but two show evidence of kinematic sub-structure, in the form of O VI-H I centroid offsets, multiple components, or both. Using various scenarios for how the metallicities in the high-ion and low-ion phases of each LLS compare, we constrain the ionized hydrogen column in the O VI phase to lie in the range log N(H II) ~ 17.6-20. The O VI phase of LLSs is a substantial baryon reservoir, with M(high-ion) ~ 108.5-10.9 (r/150 kpc)2 M â, similar to the mass in the low-ion phase. Accounting for the O VI phase approximately doubles the contribution of low-z LLSs to the cosmic baryon budget.Department of HE and Training approved lis
Distinct responses to rare codons in select Drosophila tissues
Codon usage bias has long been appreciated to influence protein production. Yet, relatively few studies have analyzed the impacts of codon usage on tissue-specific mRNA and protein expression. Here, we use codon-modified reporters to perform an organism-wide screen in Drosophila melanogaster for distinct tissue responses to codon usage bias. These reporters reveal a cliff-like decline of protein expression near the limit of rare codon usage in endogenously expressed Drosophila genes. Near the edge of this limit, however, we find the testis and brain are uniquely capable of expressing rare codon-enriched reporters. We define a new metric of tissue-specific codon usage, the tissue-apparent Codon Adaptation Index (taCAI), to reveal a conserved enrichment for rare codon usage in the endogenously expressed genes of both Drosophila and human testis. We further demonstrate a role for rare codons in an evolutionarily young testis-specific gene, RpL10Aa. Optimizing RpL10Aa codons disrupts female fertility. Our work highlights distinct responses to rarely used codons in select tissues, revealing a critical role for codon bias in tissue biology
Reverberation Mapping of the Kepler-Field AGN KA1858+4850
KA1858+4850 is a narrow-line Seyfert 1 galaxy at redshift 0.078 and is among
the brightest active galaxies monitored by the Kepler mission. We have carried
out a reverberation mapping campaign designed to measure the broad-line region
size and estimate the mass of the black hole in this galaxy. We obtained 74
epochs of spectroscopic data using the Kast Spectrograph at the Lick 3-m
telescope from February to November of 2012, and obtained complementary V-band
images from five other ground-based telescopes. We measured the H-beta light
curve lag with respect to the V-band continuum light curve using both
cross-correlation techniques (CCF) and continuum light curve variability
modeling with the JAVELIN method, and found rest-frame lags of lag_CCF = 13.53
(+2.03, -2.32) days and lag_JAVELIN = 13.15 (+1.08, -1.00) days. The H-beta
root-mean-square line profile has a width of sigma_line = 770 +/- 49 km/s.
Combining these two results and assuming a virial scale factor of f = 5.13, we
obtained a virial estimate of M_BH = 8.06 (+1.59, -1.72) x 10^6 M_sun for the
mass of the central black hole and an Eddington ratio of L/L_Edd ~ 0.2. We also
obtained consistent but slightly shorter emission-line lags with respect to the
Kepler light curve. Thanks to the Kepler mission, the light curve of
KA1858+4850 has among the highest cadences and signal-to-noise ratios ever
measured for an active galactic nucleus; thus, our black hole mass measurement
will serve as a reference point for relations between black hole mass and
continuum variability characteristics in active galactic nuclei
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