Focal contacts organization in osteoblastic cells under microgravity and cyclic deformation conditions.

We compared quantitatively vinculin-related adhesion parameters in osteoblastic cells submitted to opposite mechanical stresses, i.e., low deformation and frequency strain regimens (stretch condition) and microgravity exposure (relaxed condition). Cyclic deformation induced a biphasic response comprising new focal contacts formation followed by their clustering in ROS cells. Microgravity exposure induced a reduction in focal contact number and clustering in ROS cells. We previously demonstrated that 1% cyclic deformations at 0.05 Hz during a daily 10 min episode over 7 days stimulated ROS 17/2.8 growth as compared to static culture whereas relaxed ROS proliferated similarly to static culture (BC). To evaluate whether the proliferation (stretch) or the survival (relaxed) status of ROS cells influences focal contact organization, we inhibited ERKs proliferative-dependent pathway. Inhibition of proliferation by PD98059 was overcome although not fully restored by stretch. Furthermore stretch-induced clustering of vinculin-positive contacts still occurs in the presence of ERKs inhibitor, whereas the increase in focal contact number is abolished. In conclusion, we showed that focal contacts are mechanoeffectors and that hyper-mechanical stimulation could up regulate focal contacts size as compared to hypo-mechanical that down regulate clusterization.     

3C 273: A review of recent results

3C 273 is the most extensively studied quasar both from the ground and from space. Recent satellite observations have given important information on the overall electromagnetic spectrum of 3C 273 in the -ray, X-ray, and UV ranges. The most salient results are: (i) the energy per decade of frequency emitted by 3C 273 is nearly constant between 6000 Å and 500 MeV and is 20 × 10⁴⁶ erg s^-1 for H = 50 km s^-1 Mpc^-1; (ii) there is no absorption in the soft X-ray range in contrast to the X-ray spectrum of Seyfert nuclei; (iii) the optical and UV spectra cannot be fitted by power-law spectra only, and the energy distribution in this range suggests that a substantial fraction of the energy in the UV is emitted as back-body radiation at 20 000 K. If the peculiar shape of the UV spectrum is indeed caused by black-body radiation, then an estimate of the energy emitted under this form is 2.5 × 10⁴⁶erg s^-1, corresponding to an optically thick disk of 10¹⁶ cm in diameter.The UV spectrum of 3C 273 shows absorption lines at zero redshift caused by interstellar matter in the disk and halo of our Galaxy. The strength of C iv 1550 in absorption indicates the presence of a hot outer region in the halo. Extragalactic objects with mostly continuous UV spectra, such as 3C 273, are very promising UV sources which allow us to observe the absorbing material over the entire line of sight throughout the galactic halo.