Differential inhibition of postnatal brain,spinal cord and body growth by a growth hormone antagonist

Background  

Growth hormone (GH) plays an incompletely understood role in the development of the central nervous system (CNS). In this study, we use transgenic mice expressing a growth hormone antagonist (GHA) to explore the role of GH in regulating postnatal brain, spinal cord and body growth into adulthood. The GHA transgene encodes a protein that inhibits the binding of GH to its receptor, specifically antagonizing the trophic effects of endogenous GH.     

Direct observation of shear-induced orientational phase coexistence in a lyotropic system using a modified x-ray surface forces apparatus

The second generation x-ray surface forces apparatus (XSFA-II) allows for the first time simultaneous in situ small-angle x-ray scattering and surface force measurements. We have used the XSFA-II to monitor shear-induced orientational transitions in a lyotropic model lubricant system. Upon applying small shear amplitudes (approximately 20 micrometer) to a relatively thick (approximately 800 micrometer) film, we observed evidence for the formation of an orientational boundary layer at the shearing surface. Time-resolved x-ray diffraction revealed the gradual transition to shear-favored orientation by growth of the boundary layer.     

Unconventional salt trend from soft to stiff in single neurofilament biopolymers

We present persistence length measurements on neurofilaments (NFs), an intermediate filament with protruding side arms, of the neuronal cytoskeleton. Tapping mode atomic force microscopy enabled us to visualize and trace at subpixel resolution photoimmobilized NFs, assembled at various subunit protein ratios, thereby modifying the side-arm length and chain density charge distribution. We show that specific polyampholyte sequences of the side arms can form salt-switchable intrafilament attractions that compete with the net electrostatic and steric repulsion and can reduce the total persistence length by half. The results are in agreement with present X-ray and microscopy data yet present a theoretical challenge for polyampholyte interchain interactions.     

Cationic liposome-nucleic acid complexes: liquid crystal phases with applications in gene therapy

Cationic liposome (CL) carriers of nucleic acids are primarily studied because of their applications in gene delivery and gene silencing with CL-DNA and CL-siRNA (short-interfering RNA) complexes, respectively, and their implications to ongoing clinical gene therapy trials worldwide. A series of synchrotron-based small-angle-x-ray scattering studies, dating back to 1997, has revealed that CL-nucleic acid complexes spontaneously assemble into distinct novel liquid crystalline phases of matter. Significantly, transfection efficiency (TE; a measure of expression of an exogenous gene that is transferred into the cell by the lipid carrier) has been found to be dependent on the liquid crystalline structure of complexes, with lamellar complexes showing strong dependence on membrane charge density (σ(M)) and non-lamellar complexes exhibiting TE behavior independent ofσ(M). The review describes our current understanding of the structures of different liquid crystalline CL-nucleic acid complexes including the recently described gyroid cubic phase of CL-siRNA complexes used in gene silencing. It further makes apparent that the long-term goal of developing optimized liquid crystalline CL-nucleic acid complexes for successful medical applications requires a comprehensive understanding of the nature of the interactions of distinctly structured complexes with cell membranes and events leading to release of active nucleic acids within the cell cytoplasm.     

Two-dimensional packing of short DNA with nonpairing overhangs in cationic liposome-DNA complexes: from Onsager nematics to columnar nematics with finite-length columns

We report the formation of liquid crystalline (LC) phases of short double-stranded DNA with nonpairing (nonsticky) overhangs, confined between two-dimensional (2D) lipid bilayers of cationic liposome-DNA complexes. In a landmark study (Science2007, 318, 1276), Nakata et al. reported on the discovery of strong end-to-end stacking interactions between short DNAs (sDNAs) with blunt ends, leading to the formation of 3D nematic (N) and columnar LC phases. Employing synchrotron small-angle X-ray scattering, we have studied the interplay between shape anisotropy-induced and DNA end-to-end interaction-induced N ordering for 11, 24, and 48 bp sDNA rods with single-stranded oligo-thymine (T) overhangs modulating the end-to-end interactions. For suppressed stacking interactions with 10-T overhangs, the volume fraction of sDNA at which the 2D isotropic (I)-to-N transition occurs for 24 and 48 bp sDNA rods depended on their length-to-width (L/D) shape anisotropy, qualitatively consistent with Onsager's theory for the entropic alignment of rigid rods. As the overhang length is reduced from 10 to 5 and 2 T for 24 and 48 bp sDNA, the N-to-I transition occurs at lower volume fractions, indicating the onset of some degree of end-to-end stacking interactions. The 11 bp sDNA rods with 5- and 10-T overhangs remain in the I phase, consistent with their small shape anisotropy (L/D ≈ 1.9) below the limit for Onsager LC ordering. Unexpectedly, in contrast to the behavior of 24 and 48 bp sDNA, the end-to-end interactions between 11 bp sDNA rods with 2-T overhangs set in dramatically, and a novel 2D columnar N phase (N(C)) with finite-length columns formed. The building blocks of this phase are comprised of 1D stacks of (on average) four 11 bp DNA-2T rods with an effective L(stacked)/D ≈ 8.2. Our findings have implications for the DNA-directed assembly of nanoparticles on 2D platforms via end-to-end interactions and in designing optimally packed LC phases of short anisotropic biomolecules (such as peptides and short-interfering RNAs) on nanoparticle membranes, which are used in gene silencing and chemical delivery.     

Direct imaging of aligned neurofilament networks assembled using in situ dialysis in microchannels

We report a technique to produce aligned neurofilament networks for direct imaging and diffraction studies using in situ dialysis in a microfluidic device. The alignment is achieved by assembling neurofilaments from protein subunits confined within microchannels. Resulting network structure was probed by polarized optical microscopy and atomic force microscopy, which confirmed a high degree of protein alignment inside the microchannels. This technique can be expanded to facilitate structural studies of a wide range of filamentous proteins and their hierarchical assemblies under varying assembly conditions.     

Fusion around the barrier for 7Li+12C

Fusion cross-sections for the ⁷Li + ¹²C reaction have been measured at energies above the Coulomb barrier by the direct detection of evaporation residues. The heavy evaporation residues with energies below 3 MeV could not be separated out from the α-particles in the spectrum and hence their contribution was estimated using statistical model calculations. The present work indicates that suppression of fusion cross-sections due to the breakup of ⁷Li may not be significant for ⁷Li + ¹²C reaction at energies around the barrier.