No abstract

To probe the one-dimensional nature of single-wall carbon nanotubes (SWNTs) in bulk samples, we have devised a simple method for generating fibers of aligned SWNTs. We measured polarization-dependent Raman spectra on the oriented fibers. Contrary to what is expected from their theoretically assigned vibration-mode symmetries, all the Raman line intensities are observed to decrease in nearly equal amounts for the 647.1 nm laser excitation polarized perpendicular to the fiber axis versus that polarized parallel to the fiber axis. The effect is explained as a loss of resonance Raman scattering for the perpendicular polarization case.

As major determinants of cell shape and polarity, microtubules are required to have suitable rigidity. However, our knowledge of the mechanical properties of microtubules is far from satisfactory. We report here a new method of measuring the flexural rigidity of a single microtubule by direct buckling using the optical trapping technique. Microtubule buckling was induced by applying a small longitudinal compressing force through an optically trapped microsphere that was firmly attached to the microtubule. Three ways of estimating the flexural rigidity of a continuous slender rod, one from the observed critical load of buckling and two from deflected lengths and angles of bending, yielded values which agreed well when applied to the analysis of buckling microtubules. Unexpectedly, we found that the rigidity was not constant as expected but was dependent on microtubule length. This length dependency explains the discrepancies among reported values of microtubule flexural rigidity measured by different methods. Comparing microtubules of identical lengths, microtubules assembled with brain-derived associated proteins (4 x 10(-23) Nm2 at around 10 microns in length) were four times more rigid than those assembled from purified tubulin and stabilized with taxol (1 x 10(-23) Nm2).

We used direct buckling force measurements with optical traps to determine the flexural rigidity of individual microtubules bound to polystyrene beads. To optimize the accuracy of the measurement, we used two optical traps and antibody-coated beads to manipulate each microtubule. We then applied a new analytical model assuming nonaxial buckling. Paclitaxel-stabilized microtubules were polymerized from purified tubulin, and the average microtubule rigidity was calculated as 2.0 x 10(-24) Nm2 using this novel microtubule buckling system. This value was not dependent on microtubule length. We also measured the rigidity of paclitaxel-free microtubules, and obtained the value of 7.9 x 10(-24) Nm2, which is nearly four times that measured for paclitaxel-stabilized microtubules.

a b s t r a c tAlthough microRNAs (miRNAs) are involved in many biological processes, the mechanisms whereby miRNAs regulate osteoblastic differentiation are poorly understood. Here, we found that BMP-4-induced osteoblastic differentiation of bone marrow-derived ST2 stromal cells was promoted and repressed after transfection of sense and antisense miR-210, respectively. A reporter assay demonstrated that the activin A receptor type 1B (AcvR1b) gene was a target for miR-210. Furthermore, inhibition of transforming growth factor-b (TGF-b)/activin signaling in ST2 cells with SB431542 promoted osteoblastic differentiation. We conclude that miR-210 acts as a positive regulator of osteoblastic differentiation by inhibiting the TGF-b/activin signaling pathway through inhibition of AcvR1b.

No abstract

We believe that we have developed the narrowest optical-fiber Raman probe ever reported, 600 microm in total diameter, that can be inserted into coronary arteries. The selection of suitable optical fibers, filters, and a processing method is discussed. Custom-made filters attached to the front end of a probe eliminate the background Raman signals of the optical fiber itself. The experimental evaluation of various optical fibers is carried out for the selection of suitable fibers. Measurement of the Raman spectra of an atherosclerotic lesion of a rabbit artery in vitro demonstrates the excellent performance of the micro-Raman probe.

Library on a glass slide: A variety of small molecules, including complex natural products, are introduced to glass slides using a photoaffinity reaction (see picture). The small molecules retain the inherent ability to interact with the relevant binding proteins. Importantly, this immobilization procedure does not require a specific functional group, and can be applied for use with a diverse small‐molecule library.