No description available.

Diss. (sammanfattning) Göteborg : Göteborgs universitet, 2007. / Härtill 4 uppsatser.

<p> Gulonolactone oxidase enzyme is important in the final stage of ascorbic acid biosynthesis. Gulonolactone oxidase is encoded by the Gulo gene. Most animals, such as mice, have the Gulo gene, through which they produce ascorbic acid from glucose, while humans, guinea pigs and primate animals carry a non functional Gulo gene. Ascorbic acid plays an important role in many biological processes. However, it is primarily essential as an antioxidant. Ascorbic acid protects genomic DNA from free radicals resulting from oxidative stress that might otherwise cause a variety of diseases such as cancer or heart disease. This thesis focuses on investigating the role of ascorbic acid in the elimination of oxidative stress-induced mutagenesis.</p> <p> To investigate how vitamin C decreases level of the DNA mutation frequency and protects DNA from free radicals, knockout Gulo and Big Blue mice were used as models to determine the ability of vitamin C to minimize oxidative stress. The Big Blue mice carry the cll gene which is a reporter gene through which DNA mutation rate can be detected in any part of body. Therefore, we generated double transgenic mice which are Gulo deficient or a Big Blue background. Homozygote Gulo cll positive (Gulo-/- cll+) were obtained by crossing heterozygote Gulo cll Positive and homozygote Gulo mice. Five Gulo-/-cll mice were placed under vitamin C deficient diet and another five were supplemented with vitamin C. DNA mutation frequency was analyzed in the two groups. There were no significant differences in mutation frequencies between homozygote Gulo-/- cll mice on vitamin C deficient diet and homozygote Gulo-/- cll+ mice fed vitamin C rich diet. One treatment mouse showed increased frequency in mutations but a second did not. Further tests can be done on other treated knockout mice to identify the mutation types generated by oxidative stress in the absence of vitamin C.</p> / Thesis / Master of Science (MSc)

Diss. (sammanfattning) Uppsala : Sveriges lantbruksuniv., 2007. / Härtill 3 uppsatser.

Thesis (Ph. D.)--Virginia Commonwealth University, 2009. / Prepared for: Dept. of Health and Human Performance. Title from resource description page. Includes bibliographical references.

Submitted by Michele Mologni (mologni@unoeste.br) on 2017-06-13T13:30:56Z No. of bitstreams: 1 Viviane Cacefo.pdf: 1556310 bytes, checksum: 3f9d8dc2ff4a08b8acc2ec7e1a731117 (MD5) / Made available in DSpace on 2017-06-13T13:30:56Z (GMT). No. of bitstreams: 1 Viviane Cacefo.pdf: 1556310 bytes, checksum: 3f9d8dc2ff4a08b8acc2ec7e1a731117 (MD5) Previous issue date: 2017-02-17 / C4 plants have been classified into three groups based on the enzymes used to decarboxylate C4 acids in the bundle sheath: NADP-ME, NAD-ME and PEPCK subtypes. Numerous molecular, biochemical and physiological evidences indicate that C4 plants could exhibit a certain degree of flexibility in the use of the three established decarboxylation mechanisms, depending on environmental factors. In this context, the objective of this work was to evaluate the modulation of the pathways of decarboxylation of the C4 photosynthesis in sugarcane (NADP-ME specie) under water deficit. The experiment was realized with two genotypes - RB92579 (tolerant to water deficit) and SP80-3280 (susceptible to water deficit) submitted to four treatments: control (normal conditions of water supply), moderate stress (-1,5 to -1,8 MPa), severe stress (below -2,0 MPa) and recovery (48 hours after rehydration). Leaf water potential, leaf gas exchange and biomass production were measured for the physiological characterization of the plants. Changes in the transcriptional responses of genes encoding C4-cycle enzymes (NADP-ME, NAD-ME, PEPCK, AspAT, AlaAT, PEPC, NADP-MDH and PPDK) and the activities of the enzymes NADP-ME, NAD-ME, PEPCK, AspAT and AlaAT were analyzed by RT-qPCR and spectrophotometry, respectively. Under water deficit conditions the genotypes SP80-3280 was more sensitive to drought stress in terms of increased loss of above ground biomass and lower leaf water potential. It also showed less capacity of photosynthetic recovery following rehydration compared to the tolerant genotypes RB92579. The analysis of transcriptionals and of the activities of enzymes involved in the C4 photosynthetic pathway showed that sugarcane uses the PEPCK pathway as a decarboxylation mechanism in addition to the NADP-ME, which was more evident under water deficit conditions for both the drought tolerant and susceptible genotypes. Finally, the results here obtained, together with the existing information, do not support the established classification of sugarcane (Saccharum spp.) as a classical NADP-ME C4 subtype, but instead should be considered as a NADP-ME + PEPCK species. / As plantas C4 são classificadas em três grupos de acordo com as enzimas utilizadas para descarboxilação de ácidos C4 na bainha dos feixes vasculares: subtipos NADP-ME, NAD-ME e PEPCK. Inúmeras evidências moleculares, bioquímicas e fisiológicas indicam que plantas C4 podem exibir certo nível de flexibilidade na utilização dos três mecanismos de descarboxilação, dependendo de fatores ambientais. Neste contexto, o objetivo deste trabalho foi avaliar a modulação das vias de descarboxilação da fotossíntese C4 em cana-de-açúcar (espécie NADP-ME) sob déficit hídrico. O experimento foi realizado com dois genótipos - RB92579 (tolerante ao déficit hídrico) e SP80-3280 (suscetível ao déficit hídrico) submetidos a quatro tratamentos: controle (condições normais de suprimento de água), estresse moderado (-1,5 a -1,8 MPa), estresse severo (abaixo de -2,0 MPa) e recuperação (48 hrs após a reidratação). Foram realizadas análises de potencial de água foliar, trocas gasosas foliares e biomassa para caracterização fisiológica das plantas. As alterações nas respostas transcricionais dos genes codificadores de enzimas do ciclo C4 (NADP-ME, NAD-ME, PEPCK, AspAT, AlaAT, PEPC, NADP-MDH e PPDK) e atividades das enzimas NADP-ME, NAD-ME, PEPCK, AspAT e AlaAT, foram analisadas por RT-qPCR e espectrofotometria, respectivamente. Em condições de déficit hídrico, o genótipo SP80-3280 foi mais sensível ao estresse por seca em termos de aumento da perda de biomassa e menor potencial de água foliar. Também mostrou menor capacidade de recuperação fotossintética após reidratação do que o genótipo tolerante RB92579. As análises transcricionais e das atividades das enzimas envolvidas na via fotossintética C4 mostraram que a cana-de-açúcar utiliza a via PEPCK como mecanismo de descarboxilação, além da NADP-ME, mais evidente em condições de déficit hídrico tanto para genótipos tolerantes à seca como para suscetíveis. Finalmente, os resultados aqui obtidos, juntamente com a informação existente, não suportam a classificação estabelecida da cana-de-açúcar (Saccharum spp.) como um subtipo C4 NADP-ME clássico, mas considerá-la como uma espécie NADP-ME + PEPCK.

After almost two decades of research on direct repression by p53, I provide evidence that the transcription factor p53 solely acts as an activator of transcription. I evaluate the prominent models of transcriptional regulation by p53 based on a computational meta-analysis of genome-wide data. With this tool at hand, the major contradiction how p53 binding can result in activation of one target gene and repression of another is resolved. In contrast to most current models, solely genes activated by p53 are found to be enriched for p53 binding. Meta-analysis of large-scale data is unable to confirm reports on directly repressed p53 target genes and does not support models of direct repression. Consequently, as supported by experimental data, p53 is not a direct repressor of transcription, but solely activates its target genes. Moreover, models based on interference of p53 with activating transcription factors are also not supported by the meta-analysis. As an alternative to these models, the meta-analysis leads to the conclusion that p53 represses transcription indirectly by activation of the p53-p21- DREAM/RB pathway. Thus, results of the meta-analysis support only two models, namely activation by direct binding of p53 to target genes and repression through activating the p53-p21-DREAM/RB pathway.

No description available.