Eski İstanbul semtlerinin şiiri

Taha Toros Arşivi, Dosya No: 120-Saraylarİstanbul Kalkınma Ajansı (TR10/14/YEN/0033) İstanbul Development Agency (TR10/14/YEN/0033

Ran GTPase promotes oocyte polarization by regulating ERM (Ezrin/Radixin/Moesin) inactivation.

International audienceAsymmetric meiotic divisions in mammalian oocytes are driven by the eccentric positioning of the spindle, along with a dramatic reorganization of the overlying cortex, including a loss of microvilli and formation of a thick actin cap. Actin polarization relies on a Ran-GTP gradient centered on metaphase chromosomes; however, the downstream signaling cascade is not completely understood. In a recent study, we have shown that Ran promotes actin cap formation via the polarized activation of Cdc42. The related GTPase Rac is also activated in a polarized fashion in the oocyte cortex and co-localizes with active Cdc42. In other cells, microvilli collapse can be triggered by inactivation of the ERM (Ezrin/Radixin/Moesin) family of actin-membrane crosslinkers under the control of Rac. Accordingly, we show here that Ran-GTP promotes a substantial loss of phosphorylated ERMs in the cortex overlying the spindle in mouse oocytes. However, this polarized phospho-ERM exclusion zone was unaffected by Rac or Cdc42 inhibition. Therefore, we suggest that Ran activates two distinct pathways to regulate actin cap formation and microvilli disassembly in the polarized cortex of mouse oocytes. The possibility of a crosstalk between Rho GTPase and ERM signaling and a role for ERM inactivation in promoting cortical actin dynamics are also discussed

Bir Bodhisattva'nın hikayesi

Taha Toros Arşivi, Dosya No: 37-Kamuran-Sait-Hüsamettin-Işın-Babür-Asaf Halet Çeleb

Investigations in the ternary praseodymium–boron–carbon system: Solid-state phase diagram and structural chemistry

International audienceThe solid-state phase equilibrium in the Pr–B–C system was established using X-ray diffraction, scanning electron microscopy and electron probe microanalysis. The region up to 60 at % of Pr was studied at 1270 K, whereas the Pr-rich corner, due to the generally lower melting points, was investigated at 1070 K. Eleven ternary compounds were isolated. The existence of PrB2C2, Pr5B2C5, Pr5B4C5, Pr5B2C6, PrBC, and Pr10B9C12 was confirmed. Pr15B6C20 and Pr25B14C26 have been found only in arc-melted alloys. Three new ternary compounds were isolated, namely Pr2BC, ∼Pr4B3C13 and ∼Pr7B9C34. The monoclinic structure of Pr2BC was solved from X-ray single crystal data: space group C2/m (a = 13.088(1) Å, b = 3.6748(8) Å, c = 9.488(1) Å, β = 131.03(1)°, R1 = 0.035 (wR2 = 0.086) for 585 reflections with Io > 2σ (Io)). Additionally, the phase of Pr5B2C6 was analyzed showing a broad homogeneity range described by the formula Pr5(BC)x (7.5 ≤ x ≤ 9.3

Cross-cluster transition-metal bonding in oblato-nido dimetallaboranes unveiled by topological analysis

International audienceThe bonding situation for the oblato-nido dimetallaboranes (CpV)2B5H11 and ( Cp ∗ T ) 2 B 5 H 5 + x , where T = Ta, Cr, Mo, W, Re and Cp∗=C5Me5, was analyzed using the corresponding model series with Cp∗ replaced by the cyclopentadienyl C5Me5. The application of different bonding indicators revealed that both through-space and through-bond (via boron atoms of the ring) interactions account for a substantial metal-metal bon

The bacterial storage compound PHB protects <i>Artemia franciscana</i> from pathogenic <i>Vibrio campbellii</i>

Infections caused by luminescent vibrios can cause dramatic losses in aquaculture. These infections are often hard to treat with antibiotics because of the spread of resistant strains and therefore, alternative control strategies are urgently needed. We previously found that the short-chain fatty acid 3-hydroxybutyrate protects Artemia from pathogenic Vibrio campbellii. In this study, we investigated whether the homopolymer of the fatty acid, the well-known bacterial storage compound poly-3-hydroxybutyrate (PHB), could be used to protect the nauplii from the pathogen. A starvation experiment learned us that the addition of 1000mg.l-1 PHB particles (average diameter 30μm) to the culture water of starved Artemia nauplii significantly enhanced their survival. This indicated that the nauplii could obtain energy from the PHB. In order to provide the nauplii from energy, the PHB must have been at least partially degraded into water-soluble products (i.e. 3-hydroxybutyrate monomers and oligomers). Subsequently, an in vivo challenge test was performed with the PHB particles and Artemia nauplii challenged to Vibrio campbellii LMG21363. The addition of the PHB particles (at 100mg.l-1 and 1000mg l-1) to the Artemia culture water together with the pathogen significantly enhanced the survival of the infected nauplii. A complete protection (no significant difference in survival with uninfected nauplii) was observed at the highest concentration. If the PHB particles were added 1 day after the addition of the pathogen, a similar but less pronounced effect was noticed. In a second in vivo challenge test, we investigated the effect of the addition of a PHBaccumulating Brachymonas denitrificans strain on the survival of infected nauplii. The strain, added either untreated or pasteurised at 107CFU ml-1, completely protected the nauplii from the pathogen if it had a high PHB content (32% of the VSS). No protection was observed if the strain had a low PHB content

Addition and elimination reactions of \H2\ in ruthenaborane clusters: A computational study

International audienceRuthenaborane clusters have been modelled by performing density functional theory calculations using the \B3LYP\ functional. The calculations gain insights into hydrogen storage and the H-H bond activation by ruthenaboranes. To study the nature of the chemical bond of \H2\ molecules attached to ruthenaboranes, we carried out structural optimizations for different ruthenaborane clusters and determined transition state structures for their hydrogenation addition/elimination reactions. Calculations of the reaction pathways yielded different transition-state structures involving molecular hydrogen bonded to the cluster or formation of metal hydrides. The H-H bond of \H2\ seems to be activated by the ruthenaborane clusters as activation energies of 24-42 kcal/mol were calculated for the \H2\ addition reaction. The calculated Gibbs free energy for the \H2\ addition reaction is 14-27 kcal/mol. The calculated activation energies and the molecular structures of the [(C5Me5)Ru2B10H16], [(C5Me5)Ru2B8H14] and [(C5Me5)Ru2B8H12] clusters with different degree of hydrogenation are compared. The mechanisms of the \H2\ addition and elimination reactions of the studied clusters suggest that they might be useful as hydrogen storage materials due to their ability to activate the H-H bond. They also serve as an example of the ability of hypoelectronic metallaboranes to reversibly or irreversibly bind hydrogen

Structural, electronic and magnetic properties of some early vs late transition dimetallaborane clusters - A theoretical investigation

International audienceThe strength of DFT methods in analyzing the electronic and magnetic properties of a series of dimetallaboranes of varied stoichiometry and architectural core, namely M2B3, M2B4 and M2B5 with both early- and late-transition metals is demonstrated. In particular, the observed 1H and 11B chemical shifts of most of the studied compounds are reproduced with a good accuracy of a few ppm at the DFT-GIAO BP86/TZ2P/SC level for the compounds with first-row transition metal elements and at the B3LYP/TZ2P/SO level for those with second- and third-row transition metal elements. This allows structural applications in elucidating the number and the location of bridging hydrogen atoms in experimentally poorly characterized metallaboranes such as (Cp*Cr)2B4H