Differential response to paraquat induced oxidative stress in two rice cultivars on antioxidants and chlorophyll a fluorescence

The responses of antioxidative system and photosystem II photochemistry of rice (Oryza sativa L.) to paraquat induced oxidative stress were investigated in a chilling-tolerant cultivar Xiangnuo no. 1, and a chilling-susceptible cultivar, IR-50. Electrolyte leakage and malondialdehyde (MDA) content of Xiangnuo no. 1 were little affected by paraquat, but they increased in IR-50. After paraquat treatment, superoxide dismutase (SOD) activity remained high in Xiangnuo no. 1, while it declined in IR-50. Activities of catalase (CAT), ascorbate peroxidase (APX) and glutathione reductase (GR) declined with oxidative stress in both cultivars, but Xiangnuo no. 1 had higher GR activity than IR-50. Under paraquat induced oxidative stress, ascorbic acid (AsA) and reduced glutathione (GSH) concentrations remained high in Xiangnuo no. 1, but decreased in IR-50. The results indicated that higher activities of SOD and GR and higher contents of AsA and GSH in Xiangnuo no. 1 under paraquat induced oxidative stress were associated with its tolerance to paraquat, while paraquat induced damage to IR-50 was related to decreased activities of SOD, APX and GR and contents of AsA and GSH. F _v/F _m, Φ _PSII, and qP remained high in Xiangnuo no. 1, while they decreased greatly in IR-50 under paraquat induced oxidative stress.     

Generation of two modified mouse alleles of the Hic1 tumor suppressor gene

HIC1 (hypermethylated in cancer 1) is a tumor suppressor gene located on chromosome 17p13.3, a region frequently hypermethylated or deleted in human neoplasias. In mouse, Hic1 is essential for embryonic development and exerts an antitumor role in adult animals. Since Hic1-deficient mice die perinatally, we generated a conditional Hic1 null allele by flanking the Hic1-coding region by loxP sites. When crossed to animals expressing Cre recombinase in a cell-specific manner, the Hic1 conditional mice will provide new insights into the function of Hic1 in developing and mature tissues. Additionally, we used gene targeting to replace sequence-encoding amino acids 186-893 of Hic1 by citrine fluorescent protein cDNA. We demonstrate that the distribution of Hic1-citrine fusion polypeptide corresponds to the expression pattern of wild-type Hic1. Consequently, Hic1-citrine "reporter" mice can be used to monitor the activity of the Hic1 locus using citrine fluorescence.     

Chlorophyll b reduction during senescence of barley seedlings

During senescence of flowering plants, only breakdown products derived from chlorophyll a were detected although  b disappears, too (Matile et al., 1996, Plant Physiol 112: 1403–1409). We investigated the possibility of chlorophyll b reduction during dark-induced senescence of barley (Hordeum vulgare L.) leaves. Plastids isolated from senescing leaves were lysed and incubated with NADPH. We found 7¹-hydroxy-chlorophyll a, 7¹-hydroxy-chlorophyllide a, and, after incubation with Zn-pheophorbide b, also Zn-7¹-hydroxy-pheophorbide a, indicating activity of chlorophyll(ide) b reductase. The highest activity was found at day 2 of senescence when chlorophyll breakdown reached its highest rate. Chlorophyllase reached its highest activity under the same conditions only at days 4–6 of senescence. Based on the chlorophyll b reductase activity of plastids at day 2.5 of senescence (=100%), the bulk of activity (83%) was found in the thylakoids and only traces (5%) in the envelope fraction. Chlorophyll b reduction is considered to be an early and obligatory step of chlorophyll b breakdown. Received: 22 February 1999 / Accepted: 24 March 1999     

MiRNA-181b suppresses IGF-1R and functions as a tumor suppressor gene in gliomas

MicroRNAs (miRNAs) are single-stranded, 18- to 23-nt RNA molecules that function as regulators of gene expression. Previous studies have shown that microRNAs play important roles in human cancers, including gliomas. Here, we found that expression levels of miR-181b were decreased in gliomas, and we identified IGF-1R as a novel direct target of miR-181b. MiR-181b overexpression inhibited cell proliferation, migration, invasion, and tumorigenesis by targeting IGF-1R and its downstream signaling pathways, PI3K/AKT and MAPK/ERK1/2. Overexpression of IGF-1R rescued the inhibitory effects of miR-181b. In clinical specimens, IGF-1R was overexpressed, and its protein levels were inversely correlated with miR-181b expression. Taken together, our results indicate that miR-181b functions in gliomas to suppress growth by targeting the IGF-1R oncogene and that miR-181b may serve as a novel therapeutic target for gliomas.     

DNA variants in the human RAB3A gene are not associated with autism

Mutation screening of the RAB3A gene in 47 individuals with autism provided no evidence that DNA variants in this gene are associated with autism. Since Rab3a constitutive knockout mice react to novel stimuli with hyperactivity, a further search for association of RAB3A DNA variants with other neurobehavioral disorders such as attention deficit/hyperactivity disorder appears justified.     

Regulation of cyp26a1 on Th17 cells in mouse peri‐implantation

Cytochrome P450 26A1 (cyp26a1) is expressed in the mouse uterus during peri‐implantation. The repression of this protein is closely associated with a reduction in implantation sites, suggesting a specific role for cyp26a1 in pregnancy and prompting questions concerning how a metabolic enzyme can generate this distinct outcome. To explore the effective downstream targets of cyp26a1 and confirm if its role in peri‐implantation depends on its metabolic substrate RA (retinoic acid), we characterized the changes in the peripheral blood, spleen and uterine implantation sites using the cyp26a1 gene vaccine constructed before. Flow cytometry results showed a significant increase in CD4⁺RORγt⁺ Th17 cells in both the peripheral blood and spleen in the experimental group. The expression of RORγt and IL‐17 presented the Th17 cells reduction in uterus followed by the suppression of cyp26a1 expression. For greater certainty, cyp26a1 antibody blocking model and RNA interference model were constructed to determine the precise target immune cell group. High performance liquid chromatography results showed a significant increase in uterine at‐RA followed by the immunization of cyp26a1 gene vaccine. Both the ascertain by measuring RARα protein levels in peri‐implantation uterus after gene vaccine immunization and researches using the specific agonist and antagonist against RARα suggested that RARα may be the main RA receptor for signal transduction. These results provided more evidence for the signal messenger role of RA in cyp26a1 regulation from the other side. Here, we showed that the cyp26a1‐regulated Th17 cells are dependent on at‐RA signalling, which is delivered through RARα in mouse peri‐implantation.     

Satiation-dependent, intra-cohort variations in prey size selection of young roach (Rutilus rutilus)

The tolerance to freezing and thawing of Leucodon sciuroides, a moss growing in mountainous areas of the Mediterranean (south-east Spain), was investigated by means of CO₂ gas exchange, modulated chlorophyll (Chl) a fluorescence and pigment analysis by high-performance liquid chromatography. Evidence is presented for freezing-induced decreases in CO₂ fixation that enhance non-radiative dissipation of absorbed light energy, a process which protects the photosynthetic apparatus. The photosynthetic apparatus of L. sciuroides remained fully recuperable after freezing, as indicated by the recovery of photosynthetic CO₂ fixation and Chl fluorescence parameters to pre-freezing values during thawing. The rapid recovery of photosynthesis activity during thawing in L. sciuroides suggests that this moss is capable of tolerating freeze-thaw cycles in a manner similar to that found at higher latitudes or in the Antarctic. The resistance of the photosynthetic apparatus of this moss to freezing might be achieved, at least partially, through the employment of dissipative pathways, such as non-radiative dissipation of absorbed light energy. Received: 4 June 1998 / Accepted: 15 February 1999     

DNA sequence analysis of the defective interfering particles of bacteriophage f1.

Restriction mapping and nucleotide sequence analysis of several defective, interfering particles of bacteriophage f1 are described. These particles contain the nucleotide sequences corresponding to the carboxyl terminus of gene IV and the amino-terminus of gene II and the intergenic space between them. Tandem duplication of a portion of this intergenic space generates defective particles with novel nucleotide sequences not found in wild-type f1. This duplication is shown to contain the origin of complementary strand synthesis. Our results suggest that the duplication occurs at the site of gene II protein action, i.e. the origin of viral strand synthesis. A model is presented for the generation of these duplications in defective particles.