Characterization of Arabidopsis decapping proteins AtDCP1 and AtDCP2, which are essential for post-embryonic development

Although decapping is an important process in eukaryotic mRNA turnover, little is known about this process in plants. Here, we identified Arabidopsis thaliana decapping proteins AtDCP1 and AtDCP2 and showed that (I) AtDCP2 is an active decapping enzyme, (II) AtDCP1 interacts with itself, (III) AtDCP1 and AtDCP2 are localized to cytoplasmic foci (putative Arabidopsis processing body), and (IV) AtDCP1 and AtDCP2 are essential for post-embryonic development. Our findings provide new insights into the role of decapping-dependent mRNA turnover.     

Work behaviors of artificial muscle based on cation driven polypyrrole

A soft actuator mimicking natural muscles (artificial muscle) has been developed using a flexible conducting polymer of polypyrrole films, which were driven by electrical stimulus in a saline solution. The work characteristics were studied under various load stresses and found to behave like natural muscles. The artificial muscles shrunk and stiffened by the positive electrical stimulus by 2-3% at the maximum force of 5 MPa, and relaxed by application of negative voltages. At larger load stresses, the artificial muscle shrunk slowly as natural muscles do. The driving current also lasted longer at larger loads, indicating that the muscle sensed the magnitude of the load stress. During contraction of the muscle, the conversion efficiency from the electrical input and mechanical output energies was estimated to be around 0.06%. The maximum volumetric work was approximately estimated to be 100 kJ m(-3). These figures are unexpectedly small compared with those of natural muscles.     

Mutagenic and nonmutagenic bypass of DNA lesions by Drosophila DNA polymerases dpoleta and dpoliota

cDNA sequences were identified and isolated that encode Drosophila homologues of human Rad30A and Rad30B called drad30A and drad30B. Here we show that the C-terminal-truncated forms of the drad30A and drad30B gene products, designated dpoletaDeltaC and dpoliotaDeltaC, respectively, exhibit DNA polymerase activity. dpoletaDeltaC and dpoliotaDeltaC efficiently bypass a cis-syn-cyclobutane thymine-thymine (TT) dimer in a mostly error-free manner. dpoletaDeltaC shows limited ability to bypass a 6-4-photoproduct ((6-4)PP) at thymine-thymine (TT-(6-4)PP) or at thymine-cytosine (TC-(6-4)PP) in an error-prone manner. dpoliotaDeltaC scarcely bypasses these lesions. Thus, the fidelity of translesion synthesis depends on the identity of the lesion and on the polymerase. The human XPV gene product, hpoleta, bypasses cis-syn-cyclobutane thymine-thymine dimer efficiently in a mostly error-free manner but does not bypass TT-(6-4)PP, whereas Escherichia coli DNA polymerase V (UmuD'(2)C complex) bypasses both lesions, especially TT-(6-4)PP, in an error-prone manner (Tang, M., Pham, P., Shen, X., Taylor, J. S., O'Donnell, M., Woodgate, R., and Goodman, M. F. (2000) Nature 404, 1014-1018). Both dpoletaDeltaC and DNA polymerase V preferentially incorporate GA opposite TT-(6-4)PP. The chemical structure of the lesions and the similarity in the nucleotides incorporated suggest that structural information in the altered bases contribute to nucleotide selection during incorporation opposite these lesions by these polymerases.     

Polyamine cytotoxicity in the presence of bovine serum amine oxidase

The toxicity of extracellular spermine, determined in the presence of fetal calf serum, was studied using three cell lines: FM3A, L1210, and NIH3T3 cells. Amine oxidase in fetal calf serum produces aminodialdehyde generating acrolein spontaneously, H(2)O(2), and ammonia from spermine. Spermine toxicity was prevented by aldehyde dehydrogenase, but not by catalase. Similar concentrations of spermine and acrolein were needed to produce toxicity. Other aldehydes (formaldehyde, acetaldehyde, and propionaldehyde) and hydrogen peroxide were less toxic than acrolein. Spermidine and 3-aminopropanal, which produces acrolein, also exhibited severe cytotoxicity. The degree of cytotoxicity of spermine, spermidine, and 3-aminopropanal was nearly parallel with the amount of acrolein produced from each compound. Thus, it was deduced that acrolein is a major toxic compound produced from polyamines (spermine and spermidine) by amine oxidase.     

Hydrogen peroxide induces Src family tyrosine kinase-dependent activation of Xenopus eggs

Fertilization is accompanied by a rapid and transient calcium release in eggs, which is required for the onset of zygotic developmental program or 'egg activation'. Recently, it was found that Src family tyrosine kinase (SFK)-dependent phospholipase C (PLC) activity is necessary for the calcium transience in fertilized Xenopus eggs. The present study demonstrates that hydrogen peroxide (H2O2) stimulates protein-tyrosine phosphorylation in Xenopus eggs, which occurs primarily in the egg cortex of the animal hemisphere as revealed by indirect immunofluorescence study. Egg SFK was found to be upregulated by H2O2 while the SFK-specific inhibitor PP1 effectively blocked H2O2-induced tyrosine phosphorylation. As in fertilized eggs, PLCgamma, but not Shc, was tyrosine-phosphorylated in H2O2-treated eggs. H2O2 also caused inositol 1,4,5-trisphosphate (IP3) production and sustained calcium release. After limited application of H2O2, elevated SFK activity and tyrosine phosphorylation were quickly reversed. Under such conditions, eggs showed cortical contraction and dephosphorylation of p42 MAP kinase, both of which are indicative of egg activation. These egg activation events, as well as H2O2-induced IP3 production and calcium release, were sensitive to PP1 and PLC inhibitor U-73122. Together, the present study demonstrated that H2O2 can mimic, at least in part, early events of Xenopus egg activation that require an SFK-dependent PLC pathway.     

Inhibitory effects of fluvastain and its metabolites on the formation of several reactive oxygen species

We investigated the inhibitory effects of fluvastain (FV) and its metabolites (M-2, M-3, M-4, M-5, and M-7) on the formation of several reactive oxygen species (ROS), such as singlet oxygen (1O2), superoxide anion (O2-), hydroxy radical (*OH), hypochlorite ion (OCL-), and linoleic acid peroxide (LOO*). Inhibitory effects of pravastatin (PV), simvastatin (SV), probucol (PR) and alpha-tocopherol (TOC) were also tested. The inhibitory effects of 5-hydroxy FV (M-2) and 6-hydroxy FV (M-3) on the formation of 1O2, O2-, *OH, and OCL- were strongest. Scavenging of 1O2 by M-4, M-5, (+)-FV, and (-)-FV was also noted. The inhibitory effects of (+)-FV on the formation of 1O2 were comparable to those of (-)-FV, PV, SV, PR and M-7 had little or no inhibitory effect on the formation of several ROS. In conclusion, FV and its metabolites, particulary M-2 and M-3, have the potential to protect against oxidative stress mediated by several ROS.