Human mitochondrial ribosomes can switch structural tRNAs - but when and why?

High resolution cryoEM of mammalian mitoribosomes revealed the unexpected presence of mitochondrially encoded tRNA as a structural component of mitochondrial large ribosomal subunit (mt-LSU). Our previously published data identified that only mitochondrial (mt-) tRNA(Phe) and mt-tRNA(Val) can be incorporated into mammalian mt-LSU and within an organism there is no evidence of tissue specific variation. When mt-tRNA(Val) is limiting, human mitoribosomes can integrate mt-tRNA(Phe) instead to generate a translationally competent monosome. Here we discuss the possible reasons for and consequences of the observed plasticity of the structural mt-tRNA integration. We also indicate potential direction for further research that could help our understanding of the mechanistic and evolutionary aspects of this unprecedented system.This work was supported by the Wellcome Trust under Grant 096919/Z/11/Z and Medical Research Council UK under Grant MC_U105697135

Technologie bioresorbowalnych wyrobów medycznych – opracowane w wyniku realizacji projektu kluczowego „Biodegradowalne wyroby włókniste”

Pod koniec 2008 r. rozpoczęto realizację projektu kluczowego pt. „Biodegradowalne wyroby włókniste”, POIG 01.03.01–00– 007/08 o akronimie BIOGRATEX. Projekt jest współfinansowany z funduszy strukturalnych w ramach Programu Operacyjnego Innowacyjna Gospodarka. Celem głównym projektu jest opracowanie innowacyjnych rozwiązań technologicznych, niezbędnych dla poszerzenia oferty wyrobów włóknistych produkowanych z użyciem polimerów biodegradowalnych, w większości pozyskiwanych z surowców odnawialnych, kierowanych nie tylko do sektora włókienniczego, ale również dla rolnictwa i medycyny. Celem niniejszej publikacji jest przedstawienie opisu trzech technologii odnoszących się do wyrobów przeznaczonych do zastosowań w medycynie regeneracyjnej. Opisano technologię formowania włókien z roztworu polimeru będącego kopolimerem L-laktydu i glikolidu (PGLA), którego syntezę opracowano w ramach projektu. Kolejna technologia dotyczy materiałów nanowłóknistych wytwarzanych metodą elektroprzędzenia z roztworu polimeru PGLA oraz z roztworu mieszaniny polimerów PGLA i hydroksymaślanu (PHB). Oba roztwory polimeru w DMSO przędziono z dodatkiem hydroksyapatytu (HAp). Wytworzony materiał włóknisty zaprojektowano do stosowania przy regeneracji tkanki kostnej, jako materiał osteokonduktywny, osteoinduktywny i bioresorbowalny. Trzecia opisana technologia odnosi się do wytwarzania prototypów bioresorbowalnych protez naczyń krwionośnych z PGLA o średnicach poniżej 6 mm. Przedstawiono możliwość zastosowania techniki elektroprzędzenia ze stopu polimeru wraz z wprowadzeniem dodatkowego procesu stabilizacji termicznej do wytwarzania struktur 3D o małych średnicach

Rho-stimulated contractility drives the formation of stress fibers and focal adhesions

Activated rhoA, a ras-related GTP-binding protein, stimulates the appearance of stress fibers, focal adhesions, and tyrosine phosphorylation in quiescent cells (Ridley, A.J., and A. Hall, 1992. Cell. 70:389-399). The pathway by which rho triggers these events has not been elucidated. Many of the agents that activate rho (e.g., vasopressin, endothelin, lysophosphatidic acid) stimulate the contractility of smooth muscle and other cells. We have investigated whether rho's induction of stress fibers, focal adhesions, and tyrosine phosphorylation is the result of its stimulation of contractility. We demonstrate that stimulation of fibroblasts with lysophosphatidic acid, which activates rho, induces myosin light chain phosphorylation. This precedes the formation of stress fibers and focal adhesions and is accompanied by increased contractility. Inhibition of contractility by several different mechanisms leads to inhibition of rho-induced stress fibers, focal adhesions, and tyrosine phosphorylation. In addition, when contractility is inhibited, integrins disperse from focal adhesions as stress fibers and focal adhesions disassemble. Conversely, upon stimulation of contractility, diffusely distributed integrins are aggregated into focal adhesions. These results suggest that activated rho stimulates contractility, driving the formation of stress fibers and focal adhesions and elevating tyrosine phosphorylation. A model is proposed to account for how contractility could promote these events

Towards understanding the ordering behavior of hard needles: New analytical solutions in one dimension

We re-examine the ordering behavior of a one-dimensional fluid of freely rotating hard needles, where the centers of mass of the particles are restricted to a line. Analytical equations are obtained for the equation of state, order parameter and orientational correlation functions using the transfer-matrix method if some simplifying assumptions are applied for either the orientational freedom or the contact distance between two needles. The two-state Zwanzig model accounts for the orientational ordering, but it produces unphysical pressure at high densities and there is no orientational correlation. The four-state Zwanzig model gives reasonable results for orientational correlation function, but the pressure is still poorly represented at high densities. In the continuum limit, apart from the orientational correlation length it is managed to reproduce all relevant bulk properties of the hard needles using an approximate formula for the contact distance. The results show that the orientational correlation length diverges at zero and infinite pressures. The high density behavior of needles is not resolved.Comment: 21 pages, 3 figure

Rap1b is required for normal platelet function and hemostasis in mice

Rap1b, an abundant small GTPase in platelets, becomes rapidly activated upon stimulation with agonists. Though it has been implicated to act downstream from G protein–coupled receptors (GPCRs) and upstream of integrin αIIbβ3, the precise role of Rap1b in platelet function has been elusive. Here we report the generation of a murine rap1b knockout and show that Rap1b deficiency results in a bleeding defect due to defective platelet function. Aggregation of Rap1b-null platelets is reduced in response to stimulation with both GPCR-linked and GPCR-independent agonists. Underlying the defective Rap1b-null platelet function is decreased activation of integrin αIIbβ3 in response to stimulation with agonists and signaling downstream from the integrin αIIbβ3. In vivo, Rap1b-null mice are protected from arterial thrombosis. These data provide genetic evidence that Rap1b is involved in a common pathway of integrin activation, is required for normal hemostasis in vivo, and may be a clinically relevant antithrombotic therapy target

Notes sur la pathologie spontanée du chien de laboratoire. 2e note : Hématome de la Rate

Présentation d’un cas d’hématome splénique, chez le Chien. Discussion de ses implications en chirurgie expérimentale et en médecine et chirurgie canines

Fabrication of Plga/Hap and Plga/Phb/Hap Fibrous Nanocomposite Materials for Osseous Tissue Regeneration

The study presents the manufacturing of nanofibrous structures as osteoconductive, osteoinductive materials for osseous tissue regeneration. The fibrous structures were obtained by electrospinning of poly(l-lactide-coglicolide) (PLGA) with addition of hydroxyapatite (HAp) and of a blend of PLGA with polyhydroxybutyrate with HAp added. The polymers used in the experiment were synthesised by an innovative method with a zirconium catalyst. First, the optimal electrospinning process parameters were selected. For the characterisation of the obtained osseous tissue reconstruction materials, the physical, macroscopic, functional, mechanical and thermal properties as well as crystallinity index were studied. The study of the radiation sterilisation influence on average molar mass, thermal and mechanical properties was made in order to analyse the degradation effect

Tyrosine phosphorylation is involved in reorganization of the actin cytoskeleton in response to serum or LPA stimulation

Tyrosine phosphorylation is known to regulate the formation of focal adhesions in cells adhering to extracellular matrix (ECM). We have investigated the possible involvement of tyrosine phosphorylation and the focal adhesion kinase (FAK) in the cytoskeletal changes induced by serum or lysophosphatidic acid (LPA) in quiescent Swiss 3T3 fibroblasts. As shown previously by others, quiescent cells stimulated with serum or LPA reveal a rapid reappearance of focal adhesions and stress fibers. Here we show that this is accompanied by an increase in phosphotyrosine in focal adhesions and specifically an increase in the tyrosine phosphorylation of FAK. The LPA-stimulated reappearance of focal adhesions and stress fibers is blocked by inhibitors of phospholipase C but not by pertussis toxin (PTX), indicating that this LPA signaling pathway is mediated by phospholipase C activation and does not involve PTX-sensitive G proteins. In the absence of serum or LPA, these cytoskeletal effects and the tyrosine phosphorylation of FAK can be mimicked by sodium orthovanadate in conjunction with hydrogen peroxide, agents that inhibit protein tyrosine phosphatases and thereby elevate levels of phosphotyrosine. Two tyrosine kinase inhibitors, erbstatin and genistein block both the serum-induced tyrosine phosphorylation of FAK and the assembly of focal adhesions and stress fibers. Two other tyrosine kinase inhibitors, tyrphostins 47 and 25, previously shown to inhibit FAK, failed to prevent FAK phosphorylation or the reassembly of focal adhesions and stress fibers in response to serum. However, these inhibitors did prevent FAK phosphorylation and cytoskeletal assembly in response to lysophosphatidic acid (LPA), one component of serum previously shown to stimulate assembly of focal adhesions and stress fibers. Our findings suggest that the response to serum is complex and that although FAK phosphorylation is important, other tyrosine kinases may also be involved

GRSF1 regulates RNA processing in mitochondrial RNA granules.

Various specialized domains have been described in the cytosol and the nucleus; however, little is known about compartmentalization within the mitochondrial matrix. GRSF1 (G-rich sequence factor 1) is an RNA binding protein that was previously reported to localize in the cytosol. We found that an isoform of GRSF1 accumulates in discrete foci in the mitochondrial matrix. These foci are composed of nascent mitochondrial RNA and also contain RNase P, an enzyme that participates in mitochondrial RNA processing. GRSF1 was found to interact with RNase P and to be required for processing of both classical and tRNA-less RNA precursors. In its absence, cleavage of primary RNA transcripts is abnormal, leading to decreased expression of mitochondrially encoded proteins and mitochondrial dysfunction. Our findings suggest that the foci containing GRSF1 and RNase P correspond to sites where primary RNA transcripts converge to be processed. We have termed these large ribonucleoprotein structures "mitochondrial RNA granules.