5,585 research outputs found
Identification of dividing, determined sensory neuron precursors in the mammalian neural crest
Sensory and autonomic neurons of the vertebrate peripheral nervous system are derived from the neural crest. Here we use the expression of lineage-specific transcription factors as a means to identify neuronal subtypes that develop in rat neural crest cultures grown in a defined medium. Sensory neurons, identified by expression of the POU-domain transcription factor Brn-3.0, develop from dividing precursors that differentiate within 2 days following emigration from the neural tube. Most of these precursors generate sensory neurons even when challenged with BMP2, a factor that induces autonomic neurogenesis in many other cells in the explants. Moreover, BMP2 fails to prevent expression of the sensory-specific basic helix-loop-helix (bHLH) transcription factors neurogenin1, neurogenin2 and neuroD, although it induces expression of the autonomic-specific bHLH factor MASH1 and the paired homeodomain factor Phox2a in other cells. These data suggest that there are mitotically active precursors in the mammalian neural crest that can generate sensory neurons even in the presence of a strong autonomic-inducing cue. Further characterization of the neurons generated from such precursors indicates that, under these culture conditions, they exhibit a proprioceptive and/or mechanosensory, but not nociceptive, phenotype. Such precursors may therefore correspond to a lineally (Frank, E. and Sanes, J. (1991) Development 111, 895-908) and genetically (Ma, Q., Fode, C., Guillemot, F. and Anderson, D. J. (1999) Genes Dev. 13, in press) distinct subset of early-differentiating precursors of large-diameter sensory neurons identified in vivo
Ultracompact X-ray Binaries in Globular Clusters: Variability of the Optical Counterpart of X1832-330 in NGC 6652
Evidence is emerging that the luminous X-ray sources in the cores of globular
clusters may often consist of, or perhaps even as a class be dominated by,
ultracompact (P < 1 hr) binary stars. To the two such systems already known, in
NGC 6624 and NGC 6712, we now add evidence for two more. We detect large
amplitude variability in the candidate optical counterpart for the X-ray source
in the core of NGC 6652. Although the available observations are relatively
brief, the existing Hubble Space Telescope data indicate a strong 43.6 min
periodic modulation of the visible flux of semi-amplitude 30%. Further,
although the orbital period of the source in NGC 1851 is not yet explicitly
measured, we demonstrate that previous correlations of optical luminosity with
X-ray luminosity and accretion disk size, strengthened by recent data, strongly
imply that the period of that system is also less than 1 hr. Thus currently
there is evidence that 4 of the 7 globular cluster X-ray sources with
constrained periods are ultracompact, a fraction far greater than that found in
X-ray binaries the field.Comment: 10 pages including 2 figures and 1 table. Accepted for publication in
The Astrophysical Journal Letter
Recommended from our members
Coking-Resistant Sub-Nano Dehydrogenation Catalysts: PtnSnx/SiO2 (n=4, 7)
We present a combined experimental/theoretical study of Pt/SiO and
PtSn/SiO (n = 4, 7) model catalysts for the endothermic
dehydrogenation of hydrocarbons, using the ethylene intermediate as a model
reactant. Supported pure Ptn clusters are found to be highly active toward
dehydrogenation of C2D4, quickly deactivating due to a combination of carbon
deposition and sintering, resulting in loss of accessible Pt sites. Addition of
Sn to Ptn clusters results in the complete suppression of C2D4 dehydrogenation
and carbon deposition, and also stabilizes the clusters against thermal
sintering. Theory shows that both systems have thermal access to a multitude of
cluster structures and adsorbate configurations that form a statistical
ensemble. While Pt4/SiO2 clusters bind ethylene in both di-sigma and pi-bonded
configurations, PtSn/SiO binds C2H4 only in the pi-mode, with
di-sigma bonding suppressed by a combination of electronic and geometric
features of the PtSn clusters. Dehydrogenation reaction profiles on the
accessible cluster isomers were calculated using the climbing image nudged
elastic band (CI-NEB) method
Recommended from our members
Preparation of Size- and Composition-Controlled PtnSnx/SiO2 (n=4, 7, 24) Bimetallic Model Catalysts with Atomic Layer Deposition
Particulate and water-soluble carbon measured in recent snow at Summit, Greenland
Water-soluble organic carbon (WSOC), waterinsoluble particulate organic carbon (WIOC), and particulate elemental carbon (EC) were measured simultaneously for the first time on the Greenland Ice Sheet in surface snow and in a 3-meter snow pit. Snow pit concentrations reveal that, on average, WSOC makes up the majority (89%) of carbonaceous species, followed by WIOC (10%) and EC (1%). The enhancement of OC relative to EC (ratio 99:1) in Greenland snow suggests that, along with atmospheric particulate matter, gaseous organics contribute to snow-phase OC. Comparison of summer surface snow concentrations in 2006 with past summer snow pit layers (2002 ā 2005) found a significant depletion in WSOC (20 ā 82%) and WIOC (46 ā 65%) relative to EC for 3 of the 4 years. The apparent substantial loss of WSOC and WIOC in aged snow suggests that post-depositional processes, such as photochemical reactions, need to be considered in linking ice core records of organics to atmospheric concentrations. Citation: Hagler, G. S. W., M. H. Bergin, E. A. Smith, J. E. Dibb, C. Anderson, and E. J. Steig (2007), Particulate and water-soluble carbon measured in recent snow at Summit, Greenland, Geophys. Res. Lett., 34, L16505, doi:10.1029/2007GL030110
Open access to novel dual flow chamber technology for in vitro cell mechanotransduction, toxicity and pharamacokinetic studies
<p>Abstract</p> <p>Background</p> <p>A major stumbling block for researchers developing experimental models of mechanotransduction is the control of experimental variables, in particular the transmission of the mechanical forces at the cellular level. A previous evaluation of state of the art commercial perfusion chambers showed that flow regimes, applied to impart a defined mechanical stimulus to cells, are poorly controlled and that data from studies in which different chambers are utilized can not be compared, even if the target stress regimes are comparable.</p> <p>Methods</p> <p>This study provides a novel chamber design to provide both physiologically-based flow regimes, improvements in control of experimental variables, as well as ease of use compared to commercial chambers. This novel design achieves controlled stresses through five gasket designs and both single- and dual-flow regimes.</p> <p>Results</p> <p>The imparted shear stress within the gasket geometry is well controlled. Fifty percent of the entire area of the 10 Ć 21 mm universal gasket (Gasket I, designed to impart constant magnitude shear stresses in the center of the chamber where outcome measures are taken), is exposed to target stresses. In the 8 mm diameter circular area at the center of the chamber (where outcome measures are made), over 92% of the area is exposed to the target stress (Ā± 2.5%). In addition, other gasket geometries provide specific gradients of stress that vary with distance from the chamber inlet. Bench-top testing of the novel chamber prototype shows improvements, in the ease of use as well as in performance, compared to the other commercial chambers. The design of the chamber eliminates flow deviations due to leakage and bubbles and allows actual flow profiles to better conform with those predicted in computational models.</p> <p>Conclusion</p> <p>The novel flow chamber design provides predictable and well defined mechanical forces at the surface of a cell monolayer, showing improvement over previously tested commercial chambers. The predictability of the imparted stress improves both experiment repeatability as well as the accuracy of inter-study comparisons. Carefully controlling the stresses on cells is critical in effectively mimicking <it>in vivo </it>situations. Overall, the improved perfusion flow chamber provides the needed resolution, standardization and <it>in vitro </it>model analogous to <it>in vivo </it>conditions to make the step towards greater use in research and the opportunity to enter the diagnostic and therapeutic market.</p
Recommended from our members
Rapidly expanding lake heatwaves under climate change
Lake heatwaves ā prolonged periods of hot surface water temperature in lakes ā have recently been shown to increase in intensity and duration, with numerous potential implications for aquatic ecosystems. However, an important physical attribute of lake heatwaves that has not yet been investigated is their spatial extent, and how it varies within a warming world. Here, we show that the spatial extent of lake heatwaves, defined as contiguous regions within a lake that simultaneously experience extreme warm conditions, is increasing in the largest group of freshwater lakes on Earth, The Laurentian Great Lakes. We show that the maximum spatial extent of lake heatwaves is sensitive to inter-annual variations in winter ice cover and the timing of stratification onset in spring. Notably, we find that a lengthening of the warm summer season and, in turn, an overall increase in surface water temperature, stimulates the development of larger lake heatwaves. On average, our results suggest that the mean spatial extent of lake heatwaves has increased two-fold since 1995. We anticipate this rapid expansion of lake heatwaves to have widespread implications for heat-related impacts on aquatic species
- ā¦