Computational simulation of internal bone remodelling around dental implants: a sensitivity analysis

This study aimed to predict the distribution of bone trabeculae, as a density change per unit time, around a dental implant based on applying a selected mathematical remodelling model. The apparent bone density change as a function of the mechanical stimulus was the base of the applied remodelling model that describes disuse and overload bone resorption. The simulation was tested in a finite element model of a screw-shaped dental implant in an idealised bone segment. The sensitivity of the simulation to different mechanical parameters was investigated; these included element edge length, boundary conditions, as well as direction and magnitude of the implant loads. The alteration in the mechanical parameters had a significant influence on density distribution and model stability, in particular at the cortical bone region. The remodelling model could succeed to achieve trabeculae-like structure around osseointegrated dental implants. The validation of this model to a real clinical case is required.     

Isolation and characterization of three Mammalian orthoreoviruses from European bats

In recent years novel human respiratory disease agents have been described in South East Asia and Australia. The causative pathogens were classified as pteropine orthoreoviruses with strong phylogenetic relationship to orthoreoviruses of flying foxes inhabiting these regions. Subsequently, a zoonotic bat-to-human transmission has been assumed. We report the isolation of three novel mammalian orthoreoviruses (MRVs) from European bats, comprising bat-borne orthoreovirus outside of South East Asia and Australia and moreover detected in insectivorous bats (Microchiroptera). MRVs are well known to infect a broad range of mammals including man. Although they are associated with rather mild and clinically unapparent infections in their hosts, there is growing evidence of their ability to also induce more severe illness in dogs and man. In this study, eight out of 120 vespertilionid bats proved to be infected with one out of three novel MRV isolates, with a distinct organ tropism for the intestine. One isolate was analyzed by 454 genome sequencing. The obtained strain T3/Bat/Germany/342/08 had closest phylogenetic relationship to MRV strain T3D/04, isolated from a dog. These novel reoviruses provide a rare chance of gaining insight into possible transmission events and of tracing the evolution of bat viruses.     

Protection from Clostridium difficile toxin B-catalysed Rac1/Cdc42 glucosylation by tauroursodeoxycholic acid-induced Rac1/Cdc42 phosphorylation

Toxin A (TcdA) and toxin B (TcdB) are the major virulence factors of Clostridium difficile-associated diarrhoea (CDAD). TcdA and TcdB mono-glucosylate small GTPases of the Rho family, thereby causing actin re-organisation in colonocytes, resulting in the loss of colonic barrier function. The hydrophilic bile acid tauroursodeoxycholic acid (TUDCA) is an approved drug for the treatment of cholestasis and biliary cirrhosis. In this study, TUDCA-induced activation of Akt1 is presented to increase cellular levels of pS71-Rac1/Cdc42 in human hepatocarcinoma (HepG2) cells, showing for the first time that bile acid signalling affects the activity of Rho proteins. Rac1/Cdc42 phosphorylation, in turn, protects Rac1/Cdc42 from TcdB-catalysed glucosylation and reduces the TcdB-induced cytopathic effects in HepG2 cells. The results of this study indicate that TUDCA may prove useful as a therapeutic agent for the treatment of CDAD.     

A major locus expressed in the male gametophyte with incomplete penetrance is responsible for in situ gynogenesis in maize

In flowering plants, double fertilization occurs when the egg cell and the central cell are each fertilized by one sperm cell. In maize, some lines produce pollen capable of inducing in situ gynogenesis thereby leading to maternal haploids that originate exclusively from the female plant. In this paper, we present a genetic analysis of in situ gynogenesis in maize. Using a cross between non-inducing and inducing lines, we identified a major locus on maize chromosome 1 controlling in situ gynogenesis (ggi1, for gynogenesis inducer 1). Fine mapping of this locus was performed, and BAC physical contigs spanning the locus were identified using the rice genome as anchor. Genetic component analysis showed that (a) a segregation distortion against the inducer parent was present at this locus, (b) segregation resulted only from male deficiency and (c) there was a correlation between the rate of segregation distortion and the level of gynogenetic induction. In addition, our results showed that the genotype of the pollen determined its capacity to induce the formation of a haploid female embryo, indicating gametophytic expression of the character with incomplete penetrance. We propose the occurrence of a gametophytic-specific process which leads to segregation distortion at the ggi1 locus associated with gynogenetic induction with incomplete penetrance.     

A novel trehalose synthesizing pathway in the hyperthermophilic Crenarchaeon <Emphasis Type="Italic">Thermoproteus tenax</Emphasis>: the unidirectional TreT pathway

In the genome of the hyperthermophilic archaeon Thermoproteus tenax a gene (treS/P) encoding a protein with similarity to annotated trehalose phosphorylase (TreP), trehalose synthase (TreS) and more recently characterized trehalose glycosyltransferring synthase (TreT) was identified. The treS/P gene as well as an upstream located ORF of unknown function (orfY) were cloned, heterologously expressed in E. coli and purified. The enzymatic characterization of the putative TreS/P revealed TreT activity. However, contrary to the previously characterized reversible TreT from Thermococcus litoralis and Pyrococcus horikoshii, the T. tenax enzyme is unidirectional and catalyzes only the formation of trehalose from UDP (ADP)-glucose and glucose. The T. tenax enzyme differs from the reversible TreT of T. litoralis by its preference for UDP-glucose as co-substrate. Phylogenetic and comparative gene context analyses reveal a conserved organization of the unidirectional TreT and OrfY gene cluster that is present in many Archaea and a few Bacteria. In contrast, the reversible TreT pathway seems to be restricted to only a few archaeal (e.g. Thermococcales) and bacterial (Thermotogales) members. Here we present a new pathway exclusively involved in trehalose synthesis--the unidirectional TreT pathway--and discuss its physiological role as well as its phylogenetic distribution.     

Large-scale purification, dissociation and functional reassembly of the maltose ATP-binding cassette transporter (MalFGK2) of Salmonella typhimurium

The maltose ATP-binding cassette (ABC) transporter of Salmonella typhimurium is composed of a membrane-associated complex (MalFGK₂) and a periplasmic substrate binding protein. To further elucidate protein-protein interactions between the subunits, we have studied the dissociation and reassembly of the MalFGK₂ complex at the level of purified components in proteoliposomes. First, we optimized the yield in purified complex protein by taking advantage of a newly constructed expression plasmid that carries the malK, malF and malG genes in tandem orientation. Incorporated in proteoliposomes, the complex exhibited maltose binding protein/maltose-dependent ATPase activity with a V_max of 1.25 μmol P_i/min/mg and a K_m of 0.1 mM. ATPase activity was sensitive to vanadate and enzyme IIA^Glc, a component of the enterobacterial glucose transport system. The proteoliposomes displayed maltose transport activity with an initial rate of 61 nmol/min/mg. Treatment of proteoliposomes with 6.6 M urea resulted in the release of medium-exposed MalK subunits concomitant with the complete loss of ATPase activity. By adding increasing amounts of purified MalK to urea-treated proteoliposomes, about 50% of vanadate-sensitive ATPase activity relative to the control could be recovered. Furthermore, the phenotype of MalKQ140K that exhibits ATPase activity in solution but not when associated with MalFG was confirmed by reassembly with MalK-depleted proteoliposomes.     

Microsatellites in the genus Xiphophorus,developed in Xiphophorus montezumae

Species of the genus Xiphophorus (swordtails and platies) are of great interest for the study of evolution of sexually selected traits like the sword, which is an elongation of ventral fin rays of the male caudal fin, that has evolved in several species within this genus. The detection of 10 microsatellites within the genus Xiphophorus will enable studies about the correlation of this trait with sexual reproductive success of males possessing swords of different lengths. These microsatellites will also be useful in determining population structure and enable paternity analysis in these species, where sperm storage is widespread.