Auxin response, but not its polar transport, plays a role in hydrotropism of Arabidopsis roots

Plants are sessile in nature, and need to detect and respond to many environmental cues in order to regulate their growth and orientation. Indeed, plants sense numerous environmental cues and respond via appropriate tropisms, and it is widely accepted that auxin plays an important role in these responses. Recent analyses using Arabidopsis have emphasized the importance of polar auxin transport and differential auxin responses to gravitropism. Even so, the involvement of auxin in hydrotropism remains unclear. To clarify whether or not auxin is involved in the hydrotropic response, Arabidopsis seedlings were treated with inhibitors of auxin influx (3-chloro-4-hydroxyphenylacetic acid), efflux (1-naphthylphthalemic acid and 2,3,5-triiodobenzoic acid), and response (p-chlorophenoxyisobutylacetic acid), and their effects were examined on both hydrotropic and gravitropic responses. In agreement with previous reports, gravitropism was inhibited by all the chemicals tested. By contrast, only an inhibitor of the auxin response (p-chlorophenoxyisobutylacetic acid) reduced hydrotropism, whereas inhibitors for influx or efflux of auxin had no effect. These results suggest that auxin response, apart from its polar transport, plays a definite role in hydrotropic response, and will evoke a new concept for the auxin-mediated regulation of tropisms.     

Possible function of caudal nuclear pocket: degradation of nucleoproteins by ubiquitin-proteasome system in rat spermatids and human sperm.

Many temporarily functioning proteins are generated during the replacement of nucleoproteins in the nuclei of late spermatids and seem to be degraded in the nucleus. This study was designed to clarify the involvement of the ubiquitin-proteasome degradation system in the nucleus of rat developing spermatids. Thus, we studied the nuclear distribution of polyubiquitinated proteins (pUP) and proteasome in spermiogenic cells and sperm using postembedding immunoelectron microscopy. We divided the nuclear area of late spermatids into two regions: (1) a dense area composed of condensed chromatin and (2) a nuclear pocket in the neck region. The latter was located in the caudal nuclear region and was surrounded by redundant nuclear envelope. We demonstrated the presence of pUP in the dense area and nuclear pocket, proteasome in the nuclear pocket, and clear spots in the dense area of rat spermatids. Using quantitative analysis of immunogold labeling, we found that fluctuation of pUP and proteasome levels in late spermatogenesis was mostly synchronized with disappearance of histones and transitional proteins reported previously. In the nuclei of human sperm, pUP was detected in the dense area, whereas proteasome was in the nuclear vacuoles and clear spots. These results strongly suggest that pUP occur in the dense nuclear area of developing spermatids and that the ubiquitin-proteasome system is more actively operational in the nuclear pocket than dense area. Thus, the nuclear pocket might be the degradation site for temporarily functioning proteins generating during condensation of chromatin in late spermatids.     

Fiber-modified adenovirus vectors decrease liver toxicity through reduced IL-6 production

Adenovirus (Ad) vectors are one of the most commonly used viral vectors in gene therapy clinical trials. However, they elicit a robust innate immune response and inflammatory responses. Improvement of the therapeutic index of Ad vector gene therapy requires elucidation of the mechanism of Ad vector-induced inflammation and cytokine/chemokine production as well as development of the safer vector. In the present study, we found that the fiber-modified Ad vector containing poly-lysine peptides in the fiber knob showed much lower serum IL-6 and aspartate aminotransferase levels (as a maker of liver toxicity) than the conventional Ad vector after i.v. administration, although the modified Ad vector showed higher transgene production in the liver than the conventional Ad vector. RT-PCR analysis showed that spleen, not liver, is the major site of cytokine, chemokine, and IFN expression. Splenic CD11c(+) cells were found to secret cytokines. The tissue distribution of Ad vector DNA showed that spleen distribution was much reduced in this modified Ad vector, reflecting reduced IL-6 levels in serum. Liver toxicity by the conventional Ad vector was reduced by anti-IL-6R Ab, suggesting that IL-6 signaling is involved in liver toxicity and that decreased liver toxicity of the modified Ad vector was due in part to the reduced IL-6 production. This study contributes to an understanding of the biological mechanism in innate immune host responses and liver toxicity toward systemically administered Ad vectors and will help in designing safer gene therapy methods that can reduce robust innate immunity and inflammatory responses.     

Fibroblast growth factor receptor 3 kinase domain mutation increases cortical progenitor proliferation via mitogen-activated protein kinase activation

We have previously shown that mice carrying the K644E kinase domain mutation in fibroblast growth factor receptor 3 (Fgfr3) (EIIa;Fgfr3(+/K644E)) have enlarged brains with increased proliferation and decreased apoptosis of the cortical progenitors. Despite its unique rostral-low caudal-high gradient expression in the cortex, how Fgfr3 temporally and spatially influences progenitor proliferation is unknown. In vivo BrdU labelling now showed that progenitor proliferation was 10-46% higher in the EIIa;Fgfr3(+/K644E) cortex compared with wild type during embryonic day 11.5 (E11.5)-E13.5. The difference in proliferation between the EIIa;Fgfr3(+/K644E) and wild-type cortices was the greatest in the caudal cortex at E12.5 and E13.5. Inhibition of mitogen-activated or extracellular signal-regulated protein kinase (MEK) in vitro at E11.5 reduced the proliferation rate of the EIIa;Fgfr3(+/K644E) cortical progenitors to similar levels observed in the wild type, indicating that the majority of the increase in cell proliferation caused by the Fgfr3 mutation is mitogen-activated protein kinase (MAPK) pathway-dependent at this stage. In addition, elevated levels of Sprouty were observed in the EIIa;Fgfr3(+/K644E) telencephalon at E14.5, indicating the presence of negative feedback that may have suppressed further MAPK activation. We suggest that temporal activation of MAPK is largely responsible for cell proliferation caused by the Fgfr3 mutation during early stages of cortical development.     

Potassium bromate treatment predominantly causes large deletions, but not GC>TA transversion in human cells

Potassium bromate (KBrO(3)) is strongly carcinogenic in rodents and mutagenic in bacteria and mammalian cells in vitro. The proposed genotoxic mechanism for KBrO(3) is oxidative DNA damage. KBrO(3) can generate high yields of 8-hydroxydeoxyguanosine (8OHdG) DNA adducts, which cause GC>TA transversions in cell-free systems. In this study, we investigated the in vitro genotoxicity of KBrO(3) in human lymphoblastoid TK6 cells using the comet (COM) assay, the micronucleus (MN) test, and the thymidine kinase (TK) gene mutation assay. After a 4h treatment, the alkaline and neutral COM assay demonstrated that KBrO(3) directly yielded DNA damages including DNA double strand breaks (DSBs). KBrO(3) also induced MN and TK mutations concentration-dependently. At the highest concentration (5mM), KBrO(3) induced MN and TK mutation frequencies that were over 30 times the background level. Molecular analysis revealed that 90% of the induced mutations were large deletions that involved loss of heterozygosity (LOH) at the TK locus. Ionizing-irradiation exhibited similar mutational spectrum in our system. These results indicate that the major genotoxicity of KBrO(3) may be due to DSBs that lead to large deletions rather than to 8OHdG adducts that lead to GC>TA transversions, as is commonly believed. To better understand the genotoxic mechanism of KBrO(3), we analyzed gene expression profiles of TK6 cells using Affymetrix Genechip. Some genes involved in stress, apoptosis, and DNA repair were up-regulated by the treatment of KBrO(3). However, we could not observe the similarity of gene expression profile in the treatment of KBrO(3) to ionizing-irradiation as well as oxidative damage inducers.     

Two distinct human POM121 genes: requirement for the formation of nuclear pore complexes

Pom121 is one of the integral membrane components of the nuclear pore complex (NPC) in vertebrate cells. Unlike rodent cells carrying a single POM121 gene, human cells possess multiple POM121 gene loci on chromosome 7q11.23, as a consequence of complex segmental-duplications in this region during human evolution. In HeLa cells, two "full-length" Pom121 are transcribed and translated by two distinct genetic loci. RNAi experiments showed that efficient depletion of both Pom121 proteins significantly reduces assembled NPCs on nuclear envelope. Pom121-depletion also induced clustering of NPCs, indicating its role on maintenance of NPC structure/organization.     

Two mutations convert mammalian xanthine oxidoreductase to highly superoxide-productive xanthine oxidase

Reactive oxygen species are generated by various systems, including NADPH oxidases, xanthine oxidoreductase (XOR) and mitochondrial respiratory enzymes, and contribute to many physiological and pathological phenomena. Mammalian xanthine dehydrogenase (XDH) can be converted to xanthine oxidase (XO), which produces both superoxide anion and hydrogen peroxide in a molar ratio of about 1:3, depending upon the conditions. Here, we present a mutant of rat XOR that displays mainly XO activity with a superoxide:hydrogen peroxide production ratio of about 6:1. In the mutant, tryptophan 335, which is a component of the amino acid cluster crucial for switching from the XDH to the XO conformation, was replaced with alanine, and phenylalanine 336, which modulates FAD's redox potential through stacking interactions with the flavin cofactor, was changed to leucine. When the mutant was expressed in Sf9 cells, it was obtained in the XO form, and dithiothreitol treatment only partially restored the pyridine nucleotide-binding capacity. The crystal structure of the dithiothreitol-treated mutant at 2.3 Angstroms resolution showed the enzyme's two subunits to be quite similar, but not identical: the cluster involved in conformation-switching was completely disrupted in one subunit, but remained partly associated in the other one. The chain trace of the active site loop in this mutant is very similar to that of the bovine XO form. These results are consistent with the idea that the XDH and XO forms of the mutant are in an equilibrium that greatly favours the XO form, but the equilibrium is partly shifted towards the XDH form upon incubation with dithiothreitol.     

Mechanisms of plasmin-catalyzed inactivation of factor VIII: a crucial role for proteolytic cleavage at Arg336 responsible for plasmin-catalyzed factor VIII inactivation

Plasmin not only functions as a key enzyme in the fibrinolytic system but also directly inactivates factor VIII and other clotting factors such as factor V. However, the mechanisms of plasmin-catalyzed factor VIII inactivation are poorly understood. In this study, levels of factor VIII activity increased approximately 2-fold within 3 min in the presence of plasmin, and subsequently decreased to undetectable levels within 45 min. This time-dependent reaction was not affected by von Willebrand factor and phospholipid. The rate constant of plasmin-catalyzed factor VIIIa inactivation was approximately 12- and approximately 3.7-fold greater than those mediated by factor Xa and activated protein C, respectively. SDS-PAGE analysis showed that plasmin cleaved the heavy chain of factor VIII into two terminal products, A1(37-336) and A2 subunits, by limited proteolysis at Lys(36), Arg(336), Arg(372), and Arg(740). The 80-kDa light chain was converted into a 67-kDa subunit by cleavage at Arg(1689) and Arg(1721), identical to the pattern induced by factor Xa. Plasmin-catalyzed cleavage at Arg(336) proceeded faster than that at Arg(372), in contrast to proteolysis by factor Xa. Furthermore, breakdown was faster than that in the presence of activated protein C, consistent with rapid inactivation of factor VIII. The cleavages at Arg(336) and Lys(36) occurred rapidly in the presence of A2 and A3-C1-C2 subunits, respectively. These results strongly indicated that cleavage at Arg(336) was a central mechanism of plasmin-catalyzed factor VIII inactivation. Furthermore, the cleavages at Arg(336) and Lys(36) appeared to be selectively regulated by the A2 and A3-C1-C2 domains, respectively, interacting with plasmin.     

Prevalence and genetic properties of Salmonella enterica serovar typhimurium definitive phage type 104 isolated from Rattus norvegicus and Rattus rattus house rats in Yokohama City, Japan

Salmonella enterica serovar Typhimurium was isolated from the intestinal contents of Rattus rattus and Rattus norvegicus house rats captured at two buildings, designated buildings J and YS, in Yokohama City, Japan. From October 1997 to September 1998, 52 of 339 (15.3%) house rats were found to carry Salmonella serovar Typhimurium definitive phage type 104 (DT104). In building J, 26 of 161 (16.1%) house rats carried DT104 over the 1-year study period, compared to 26 of 178 (14.6%) rats in building YS. The isolation rates of DT104 from R. rattus and R. norvegicus were similar in the two buildings. Most DT104 strains from building J (24 of 26) showed resistance to ampicillin, chloramphenicol, streptomycin, sulfisoxazole, and tetracycline and contained both the 1.0- and 1.2-kbp integrons, carrying genes pse1, pasppflo-like, aadA2, sulI, and tet(G). All DT104 strains from building YS were resistant to ampicillin and sulfisoxazole, and had the 1.2-kbp integron carrying pse1 and sulI. Cluster analysis of pulsed-field gel electrophoresis patterns of BlnI-digested DT104 DNAs showed that 22 of 26 DT104 strains from building J and 24 of 26 strains from building YS could be grouped into separate clusters each specific for the building origin. These results indicated that DT104 strains were prevalent in house rat colonies in each building and suggest that house rats may play an important role in the epidemiology of DT104.