Microvilli are found on the surface of many cell types, including the mammalian oocyte, where they are thought to act in initial contact of sperm and oocyte plasma membranes. CD9 is currently the only oocyte protein known to be required for sperm-oocyte fusion. We found CD9 is localized to the oocyte microvillar membrane using transmission electron microscopy (TEM). Scanning electron microscopy (SEM) showed that CD9 null oocytes, which are unable to fuse with sperm, have an altered length, thickness and density of their microvilli. One aspect of this change in morphology was quantified using TEM by measuring the radius of curvature at the microvillar tips. A small radius of curvature is thought to promote fusibility and the radius of curvature of microvillar tips on CD9 wild-type oocytes was found to be half that of the CD9 null oocytes. We found that oocyte CD9 co-immunoprecipitates with two Ig superfamily cis partners, EWI-2 and EWI-F, which could have a role in linking CD9 to the oocyte microvillar actin core. We also examined latrunculin B-treated oocytes, which are known to have reduced fusion ability, and found altered microvillar morphology by SEM and TEM. Our data suggest that microvilli may participate in sperm-oocyte fusion. Microvilli could act as a platform to concentrate adhesion/fusion proteins and/or provide a membrane protrusion with a low radius of curvature. They may also have a dynamic interaction with the sperm that serves to capture the sperm cell and bring it into close contact with the oocyte plasma membrane.

Antibody inhibition and alpha6beta1 ligand binding experiments indicate that the egg integrin alpha6beta1 functions as a receptor for sperm during gamete fusion; yet, eggs null for the alpha6 integrin exhibit normal fertilization. Alternative integrins may be involved in sperm-egg binding and fusion and could compensate for the absence of alpha6beta1. Various beta1 integrins and alphav integrins are present on mouse eggs. Some of these integrins are also reported to be receptors for ADAMs, which are expressed on sperm. Using alpha3 integrin null eggs, we found that the alpha3beta1 integrin was not essential for sperm-egg binding and fusion. Oocyte-specific, beta1 integrin conditional knockout mice allowed us to obtain mature eggs lacking all beta1 integrins. We found that the beta1 integrin null eggs were fully functional in fertilization both in vivo and in vitro. Furthermore, neither anti-mouse beta3 integrin function-blocking monoclonal antibody (mAb) nor alphav integrin function-blocking mAb inhibited sperm binding to or fusion with beta1 integrin null eggs. Thus, function of beta3 or alphav integrins does not seem to be involved in compensating for the absence of beta1 integrins. These results indicate that none of the integrins known to be present on mouse eggs or to be ADAM receptors are essential for sperm-egg binding/fusion, and thus, egg integrins may not play the role in gamete fusion previously attributed to them.

High-pressure structures of disilane (Si 2 H 6 ) are investigated extensively by means of first-principles density functional theory and a random structure-searching method. Three metallic structures with P-1, Pm-3m, and C2∕c symmetries are found, which are more stable than those of XY 3 -type candidates under high pressure. Enthalpy calculations suggest a remarkably wide decomposition (Si and H 2 ) pressure range below 135 GPa, above which three metallic structures are stable. Perturbative linear-response calculations for Pm-3m disilane at 275 GPa show a large electron-phonon coupling parameter λ of 1.397 and the resulting superconducting critical temperature beyond the order of 10 2 K. metallization | new phase | solid disilane I t is known that the highest superconductive critical temperature (T c ) found for a conventional superconductor is 39 K for MgB 2 (1) at ambient pressure. Cuprate superconductors have much higher critical temperatures. The cuprate superconductor discovered has a critical temperature of 93 K (2), and mercury-based cuprates have critical temperatures in excess of 130 K. Pressure causes extraordinary changes in materials and modifies their properties. This often provides a path for synthesis of novel materials. Applying BCS theory to hypothetic metallic hydrogen, Ashcroft realized that it is a conventional superconductor with a very high-T c (3). A T c of the order of 10 2 K was further proposed under very strong compression by quantitative calculations (4). This value compares favorably with those in cuprate superconductors. However, hydrogen remains insulating up to extremely high pressures, at least up to about 342 GPa (5).It was recently predicted that group IVa hydrides would also present a high superconducting critical temperature, while becoming metallic at lower pressures due to chemical precompression (6). Theoretical (7-12) and experimental (13-15) studies of silane, and theoretical studies of germane (16) and stannane (17, 18), have investigated possible metallization and superconducting phase transitions at high pressures. Indeed, the theoretical studies on germane and stannane have predicted very high T c of 64 K at 220 GPa (16) and 80 K at 120 GPa (17), respectively. These results sufficiently encouraged us to prompt studies on a wider range of hydrides to confirm the prediction (6). Disilane containing a large fraction (3∕4) of H atoms is also an important hydrogen-rich compound and leads to interesting properties under high pressure. Furthermore, it is more readily available for experimental studies because of the higher boiling and melting points than silane, germane, and stannane. However, studies on disilane are very scarce.Here, we have explored the crystal structures of disilane in a wide pressure range from 50 to 400 GPa, and three favored structures, i.e., P-1, Pm-3m, and C2∕c, are found above 135 GPa. Remarkably, the large T c of 80 K at 200 GPa for P-1 and 139 K at 275 GPa for Pm-3m are predicted by quantitative calculations. Up to now, the superconductive T c of...

The structural transformations occurring to water from low-density (LDW) to high-density (HDW) regimes have been studied by Brillouin scattering for the first time at temperatures up to 453 K and at pressures up to the solidification point. At ambient temperature (293 K) a discontinuity in pressure response of the sound velocity is observed. Furthermore, there are evident breaks in the linear behavior of log10 C11 versus log10(rho/rho0) when pressure increases up to 0.29, 0.21, and 0.19 GPa at the temperature of 293, 316, and 353 K, respectively. It is supposed to indicate the structural transition from LDW to HDW, and the possible transition boundary between LDW and HDW is in good agreement with the molecular-dynamics simulation.

Based on an ab initio evolutionary algorithm, a novel carbon polymorph with an orthorhombic Cmcm symmetry is predicted, named as C carbon, which has the lowest enthalpy among the previously proposed cold-compressed graphite phases.