Studies on the function of the NGFIC subfamily of nuclear receptors in adipose tissue.

The NGFIB family of nuclear receptors consists of three members: Nurrl, nur77 and NOR-1. Genes from this family are classified as immediate early genes in that they are rapidly and transiently induced by a variety of stimuli, including neurotransmitters, growth factors, cAMP and fatty acids. Although identified as having no putative ligand binding domain, regulation of these nuclear receptors may be at the level of phosphorylation or RXR heterodimerisation. Nurrl and nur77 are expressed in adipose tissue at levels greater than in liver, spleen, lung and kidney, in both human and mouse tissue. During adipogenesis in both 3T3-L1 cells and primary sub-cutaneous murine preadipocytes, there is induction of Nurrl and nur77 expression between 60 and 120 minutes after which expression subsides. Using different protocols to induce differentiation it was demonstrated that isobutylmethylxanthine (IBMX), a phosphodiesterase inhibitor which elevates intracellular cAMP, was a critical requirement for inducing the transient Nurrl expression as well as adipogenesis. In order to investigate the effect of Nurrl expression in adipogenesis, an adenovirus mediated over-expression system was employed. Over-expression of Nurrl resulted in a decrease in adipogenesis, as well as decreases in the expression of PPARy and C/EBPa. Examination of adipocyte morphology illustrated that cells over-expressing Nurrl had less lipid accumulation, as assessed by Oil red O and by confocal microscopy. Furthermore mRNA analysis of adipocyte markers showed reduced levels of Hormone Sensitive Lipase (HSL), CD36 and Perilipin expression. In addition, the effect on adipocyte function, namely lipolysis and glucose uptake, was also investigated. Results suggest that Nurrl does not significantly alter glucose uptake but does elevate lipolysis. Subsequent to the findings above, microarray analysis has been performed on control and Nurrl over-expressing 3T3-L1 cells at two time points (72hrs and 192hrs), post differentiation. Analysis of the microarray data confirmed the earlier findings on adipogenesis and has identified a number of additional pathways, in which Nurrl would appear to play a role, namely - NO pathway, steroidogenesis and cytokine/prostaglandin regulation. Preliminary work has been performed with siRNA to knock-down the gene expression of Nurrl in order to investigate potential consequences on adipogenesis. In conclusion, a supposed role for Nurrl has been demonstrated in adipogenesis and lipid accumulation and also adipocyte secretory and metabolic function, with implications for insulin resistance at the adipocyte level

The Effect of wake Turbulence Intensity on Transition in a Compressor Cascade

Direct numerical simulations of separating flow along a section at midspan of a low-pressure V103 compressor cascade with periodically incoming wakes were performed. By varying the strength of the wake, its influence on both boundary layer separation and bypass transition were examined. Due to the presence of small-scale three-dimensional fluctuations in the wakes, the flow along the pressure surface undergoes bypass transition. Only in the weak-wake case, the boundary layer reaches a nearly-separated state between impinging wakes. In all simulations, the flow along the suction surface was found to separate. In the simulation with the strong wakes, separation is intermittently suppressed as the periodically passing wakes managed to trigger turbulent spots upstream of the location of separation. As these turbulent spots convect downstream, they locally suppress separation. © 2014 Springer Science+Business Media Dordrecht

Formation of a Propeller Structure by a Moonlet in a Dense Planetary Ring

The Cassini spacecraft discovered a propeller-shaped structure in Saturn's A ring. This propeller structure is thought to be formed by gravitational scattering of ring particles by an unseen embedded moonlet. Self-gravity wakes are prevalent in dense rings due to gravitational instability. Strong gravitational wakes affect the propeller structure. Here, we derive the condition for formation of a propeller structure by a moonlet embedded in a dense ring with gravitational wakes. We find that a propeller structure is formed when the wavelength of the gravitational wakes is smaller than the Hill radius of the moonlet. We confirm this formation condition by performing numerical simulations. This condition is consistent with observations of propeller structures in Saturn's A ring.Comment: 12 pages, 4 figures. Accepted for publication in ApJ Letter

Angular 21 cm Power Spectrum of a Scaling Distribution of Cosmic String Wakes

Cosmic string wakes lead to a large signal in 21 cm redshift maps at redshifts larger than that corresponding to reionization. Here, we compute the angular power spectrum of 21 cm radiation as predicted by a scaling distribution of cosmic strings whose wakes have undergone shock heating.Comment: 13 pages, 6 figures; v2: minor modifications, journal versio

Helical motion of magnetic flux tubes in the solar atmosphere

Photospheric granulation may excite transverse kink pulses in anchored vertical magnetic flux tubes. The pulses propagate upwards along the tubes with the kink speed, while oscillating wakes are formed behind the wave front in a stratified atmosphere. The wakes oscillate at the kink cut-off frequency of stratified medium and gradually decay in time. When two or more consecutive kink pulses with different polarizations propagate in the same thin tube, then the wakes corresponding to different pulses may superimpose. The superposition sets up helical motions of magnetic flux tubes in the photosphere/chromosphere as seen by recent Hinode movies. The energy carried by the pulses is enough to heat the solar chrmosphere/corona and accelerate the solar wind.Comment: Accepted in ApJ

The 21 cm Signature of Shock Heated and Diffuse Cosmic String Wakes

The analysis of the 21 cm signature of cosmic string wakes is extended in several ways. First we consider the constraints on $G\mu$ from the absorption signal of shock heated wakes laid down much later than matter radiation equality. Secondly we analyze the signal of diffuse wake, that is those wakes in which there is a baryon overdensity but which have not shock heated. Finally we compare the size of these signals compared to the expected thermal noise per pixel which dominates over the background cosmic gas brightness temperature and find that the cosmic string signal will exceed the thermal noise of an individual pixel in the Square Kilometre Array for string tensions $G\mu > 2.5 \times 10^{-8}$.Comment: 10 pages, 4 figures, Appendix added, version published in JCA