732 research outputs found
Transcriptional regulation of the IGF signaling pathway by amino acids and insulin-like growth factors during myogenesis in Atlantic salmon
The insulin-like growth factor signalling pathway is an important regulator of skeletal muscle growth. We examined the mRNA expression of components of the insulin-like growth factor (IGF) signalling pathway as well as Fibroblast Growth Factor 2 (FGF2) during maturation of myotubes in primary cell cultures isolated from fast myotomal muscle of Atlantic salmon (Salmo salar). The transcriptional regulation of IGFs and IGFBP expression by amino acids and insulin-like growth factors was also investigated. Proliferation of cells was 15% d(-1) at days 2 and 3 of the culture, increasing to 66% d(-1) at day 6. Three clusters of elevated gene expression were observed during the maturation of the culture associated with mono-nucleic cells (IGFBP5.1 and 5.2, IGFBP-6, IGFBP-rP1, IGFBP-2.2 and IGF-II), the initial proliferation phase (IGF-I, IGFBP-4, FGF2 and IGF-IRb) and terminal differentiation and myotube production (IGF2R, IGF-IRa). In cells starved of amino acids and serum for 72 h, IGF-I mRNA decreased 10-fold which was reversed by amino acid replacement. Addition of IGF-I and amino acids to starved cells resulted in an 18-fold increase in IGF-I mRNA indicating synergistic effects and the activation of additional pathway(s) leading to IGF-I production via a positive feedback mechanism. IGF-II, IGFBP-5.1 and IGFBP-5.2 expression was unchanged in starved cells, but increased with amino acid replacement. Synergistic increases in expression of IGFBP5.2 and IGFBP-4, but not IGFBP5.1 were observed with addition of IGF-I, IGF-II or insulin and amino acids to the medium. IGF-I and IGF-II directly stimulated IGFBP-6 expression, but not when amino acids were present. These findings indicate that amino acids alone are sufficient to stimulate myogenesis in myoblasts and that IGF-I production is controlled by both endocrine and paracrine pathways. A model depicting the transcriptional regulation of the IGF pathway in Atlantic salmon muscle following feeding is proposed.Publisher PDFPeer reviewe
Role fluidity: a grounded theory study of distributed leadership in business teams
This research explores the alternate viewpoint that designated followers often readily exercise leadership within business teams, outlining the social process of Role Fluidity, which explains the phenomenon. Negating the dualist perspective, the research argues for a more holistic approach for envisioning leadership
Diverse N-heterocyclic ring systems via aza-Heck cyclizations of <i>N</i>-(pentafluorobenzoyloxy)sulfonamides
Aza-Heck cyclizations initiated by oxidative addition of Pd(0)-catalysts into the N-O bond of N-(pentafluoro-benzoyloxy)sulfonamides are described. These studies, which encompass only the second class of aza-Heck reaction developed to date, provide direct access to diverse N-heterocyclic ring systems
Phasing of muscle gene expression with fasting-induced recovery growth in Atlantic salmon
Background: Many fish species experience long periods of fasting in nature often associated with seasonal reductions in water temperature and prey availability or spawning migrations. During periods of nutrient restriction, changes in metabolism occur to provide cellular energy via catabolic processes. Muscle is particularly affected by prolonged fasting as myofibrillar proteins act as a major energy source. To investigate the mechanisms of metabolic reorganisation with fasting and refeeding in a saltwater stage of Atlantic salmon (Salmo salar L.) we analysed the expression of genes involved in myogenesis, growth signalling, lipid biosynthesis and myofibrillar protein degradation and synthesis pathways using qPCR. Results: Hierarchical clustering of gene expression data revealed three clusters. The first cluster comprised genes involved in lipid metabolism and triacylglycerol synthesis (ALDOB, DGAT1 and LPL) which had peak expression 3-14d after refeeding. The second cluster comprised ADIPOQ, MLC2, IGF-I and TALDO1, with peak expression 14-32d after refeeding. Cluster III contained genes strongly down regulated as an initial response to feeding and included the ubiquitin ligases MuRF1 and MAFbx, myogenic regulatory factors and some metabolic genes. Conclusion: Early responses to refeeding in fasted salmon included the synthesis of triacylglycerols and activation of the adipogenic differentiation program. Inhibition of MuRF1 and MAFbx respectively may result in decreased degradation and concomitant increased production of myofibrillar proteins. Both of these processes preceded any increase in expression of myogenic regulatory factors and IGF-I. These responses could be a necessary strategy for an animal adapted to long periods of food deprivation whereby energy reserves are replenished prior to the resumption of myogenesis.Publisher PDFPeer reviewe
Revisiting the Baryon Fractions of Galaxy Clusters: A Comparison with WMAP 3-year Results
The universal baryonic mass fraction (Omega_b/Omega_m) can be sensitively
constrained using X-ray observations of galaxy clusters. In this paper, we
compare the baryonic mass fraction inferred from measurements of the cosmic
microwave background with the gas mass fractions (f_gas) of a large sample of
clusters taken from the recent literature. In systems cooler than 4 keV, f_gas
declines as the system temperature decreases. However, in higher temperature
systems, f_gas(r500) converges to approx. (0.12 +/- 0.02)(h/0.72)^{-1.5}, where
the uncertainty reflects the systematic variations between clusters at r500.
This is significantly lower than the maximum-likelihood value of the baryon
fraction from the recently released WMAP 3-year results. We investigate
possible reasons for this discrepancy, including the effects of radiative
cooling and non-gravitational heating, and conclude that the most likely
solution is that Omega_m is higher than the best-fit WMAP value (we find
Omega_m = 0.36^{+0.11}_{-0.08}), but consistent at the 2-sigma level.
Degeneracies within the WMAP data require that sigma_8 must also be greater
than the maximum likelihood value for consistency between the data sets.Comment: 8 pages, 3 figures, MNRAS accepte
A Panoramic Halpha Imaging Survey of the z=0.4 cluster Cl0024.0+1652 with Subaru
We employ panoramic, multicolour (BRz') and narrow-band Halpha imaging of the
cluster Cl0024.0+1652 (z=0.39) from Subaru covering a ~30 arcmin field, to
determine cluster membership and star formation rates for a large sample of
galaxies across a wide field in the cluster, ~10 Mpc. We detect over 500
galaxies in narrow-band emission, with broad-band colours consistent with them
lying at z~0.39. Using this sample we determine the Halpha luminosity function
within the cluster and find that its form is approximately independent of local
density, and is consistent with that seen in the intermediate redshift field
population. This suggests that any density-dependent physical mechanisms which
alter the star formation rate must leave the Halpha luminosity function
unchanged; this is possible if the time-scale for star formation to cease
completely is short compared with a Hubble time. Such short time-scale
transformations are also supported by the presence of a population with
late-type morphologies but no detectable Halpha emission. The fraction of blue
galaxies, and the fraction of galaxies detected in Halpha, decreases strongly
with increasing galaxy density in a manner which is qualitatively similar to
that seen at lower redshifts. This trend is significantly steeper than the
trend with galaxy morphology observed from a panoramic Hubble Space Telescope
image of this cluster; this suggests that the physical mechanisms responsible
for transformations in morphology and star formation rates may be partially
independent. Finally, we compare our data with similar data on clusters
spanning a range of redshifts from 0.2<~z<~0.8 and find little evidence for a
trend in the total amount of star formation in clusters with redshift.Comment: 18 pages, 25 figures (of which 2 are provided in jpg format), uses
mn2e.cls. MNRAS in press, a small error in Fig.20 is fixed, Fig.5 and the
relevant text are updated with updated ISO catalo
Enantioselective Aza-Heck Cyclizations of N-(Tosyloxy)carbamates:Synthesis of Pyrrolidines and Piperidines
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