Alexis Rivas - Academia.edu (original) (raw)

Papers by Alexis Rivas

Jcr-journal of Clinical Rheumatology, 2006

Molecular and Cellular Biology, 2009

In the present study, we report that ubiquitin-mediated degradation of dMyc, the Drosophila homol... more In the present study, we report that ubiquitin-mediated degradation of dMyc, the Drosophila homologue of the human c-myc proto-oncogene, is regulated in vitro and in vivo by members of the casein kinase 1 (CK1) family and by glycogen synthase kinase 3␤ (GSK3␤). Using Drosophila S2 cells, we demonstrate that CK1␣ promotes dMyc ubiquitination and degradation with a mechanism similar to the one mediated by GSK3␤ in vertebrates. Mutation of ck1␣ or -or sgg/gsk3␤ in Drosophila wing imaginal discs results in the accumulation of dMyc protein, suggesting a physiological role for these kinases in vivo. Analysis of the dMyc amino acid sequence reveals the presence of conserved domains containing potential phosphorylation sites for mitogen kinases, GSK3␤, and members of the CK1 family. We demonstrate that mutations of specific residues within these phosphorylation domains regulate dMyc protein stability and confer resistance to degradation by CK1␣ and GSK3␤ kinases. Expression of the dMyc mutants in the compound eye of the adult fly results in a visible defect that is attributed to the effect of dMyc on growth, cell death, and inhibition of ommatidial differentiation.

Biochemistry, 2003

DNA-protein cross-links form when guanine undergoes a 1-electron oxidation in a flashquench exper... more DNA-protein cross-links form when guanine undergoes a 1-electron oxidation in a flashquench experiment, and the importance of reactive oxygen species, protein, and photosensitizer is examined here. In these experiments, a strong oxidant produced by oxidative quenching of a DNA-bound photosensitizer generates an oxidized guanine base that reacts with protein to form the covalent adduct. These cross-links are cleaved by hot piperidine and are not the result of reactive oxygen species, since neither a hydroxyl radical scavenger (mannitol) nor oxygen affects the yield of DNA-histone crosslinking, as determined via a chloroform extraction assay. The cross-linking yield depends on protein, decreasing as histone > cytochrome c > bovine serum albumin. The yield does not depend on the cytochrome oxidation state, suggesting that reduction of the guanine radical by ferrocytochrome c does not compete effectively with cross-linking. The photosensitizer strongly influences the cross-linking yield, which decreases in the order Ru(phen) 2 dppz 2+ [phen ) 1,10-phenanthroline; dppz ) dipyridophenazine] > Ru(bpy) 3 2+ [bpy ) 2,2′-bipyridine] > acridine orange > ethidium, in accordance with measured oxidation potentials. A long-lived transient absorption signal for ethidium dication in poly(dG-dC) confirms that guanine oxidation is inefficient for this photosensitizer. From a polyacrylamide sequencing gel of a 32 Plabeled 40-mer, all of these photosensitizers are shown to damage guanines preferentially at the 5′ G of 5′-GG-3′ steps, consistent with a 1-electron oxidation. Additional examination of ethidium shows that it can generate cross-links between histone and plasmid DNA (pUC19) and that the yield depends on the quencher. Altogether, these results illustrate the versatility of the flash-quench technique as a way to generate physiologically relevant DNA-protein adducts via the oxidation of guanine and expand the scope of such cross-linking reactions to include proteins that may associate only transiently with DNA.

Revista Medica De Chile, 2008

phenotype, has been demonstrated in animal models and clinical studies with IBD patients. CD and ... more phenotype, has been demonstrated in animal models and clinical studies with IBD patients. CD and UC predominantly behave with a Th 1 and Th 2 immune phenotype, respectively. Recently, an association between CD and Th 17 has been reported. The knowledge acquired from immunologic and molecular research will help to develop accurate diagnostic methods and efficient therapies (Rev Méd Chile 2008; 136: 367-75). (

Nature, 2010

The 1000 Genomes Project aims to provide a deep characterization of human genome sequence variati... more The 1000 Genomes Project aims to provide a deep characterization of human genome sequence variation as a foundation for investigating the relationship between genotype and phenotype. Here we present results of the pilot phase of the project, designed to develop and compare different strategies for genome-wide sequencing with high-throughput platforms. We undertook three projects: low-coverage whole-genome sequencing of 179 individuals from four populations; high-coverage sequencing of two mother-father-child trios; and exon-targeted sequencing of 697 individuals from seven populations. We describe the location, allele frequency and local haplotype structure of approximately 15 million single nucleotide polymorphisms, 1 million short insertions and deletions, and 20,000 structural variants, most of which were previously undescribed. We show that, because we have catalogued the vast majority of common variation, over 95% of the currently accessible variants found in any individual are present in this data set. On average, each person is found to carry approximately 250 to 300 loss-of-function variants in annotated genes and 50 to 100 variants previously implicated in inherited disorders. We demonstrate how these results can be used to inform association and functional studies. From the two trios, we directly estimate the rate of de novo germline base substitution mutations to be approximately 10-8 per base pair per generation. We explore the data with regard to signatures of natural selection, and identify a marked reduction of genetic variation in the neighbourhood of genes, due to selection at linked sites. These methods and public data will support the next phase of human genetic research.

Medicine and Science in Sports and Exercise, 2009

Virology, 1998

An increase of Hantavirus Pulmonary Syndrome (HPS) cases around a southwestern Argentina town and... more An increase of Hantavirus Pulmonary Syndrome (HPS) cases around a southwestern Argentina town and in persons living 1400 km away but in contact with those cases was detected during the spring of 1996. In order to evaluate person-to-person transmission we compared the homology of PCR-amplified viral sequences of 26 Argentine and Chilean cases. Sixteen of them were epidemiologically linked cases and had the same sequence (Epilink/96) in the S segment 3Ј noncoding region and in the M segment partial G1 and G2 region (a total of 1075 nucleotides). Contrarily, two geographical and contemporary but nonepidemiologically related cases differed from Epilink/96 in the compared regions. No significant differences, such as glycosylation or hydrophilic pattern, were found between Epilink/96 and the other sequences. Nucleotide and deduced amino acid sequence homologies between samples from southern Argentina and Chile ranged from 90.9 to 100% and 96.4 to 100%, respectively. Phylogenetic analysis revealed that all the analyzed southwestern viruses belong to the Andes lineage. Although human infection principally occurs via inhalation of contaminated rodent excreta, our results with Andes virus show the first direct genetic evidence of person-to-person transmission of a hantavirus.

Medicine and Science in Sports and Exercise, 2008

Biological Research, 2006

The orange color of tiger lily (Lolium lancifolium 'Splendens') flowers is due, primarily, to the... more The orange color of tiger lily (Lolium lancifolium 'Splendens') flowers is due, primarily, to the accumulation of two k-xanthophylls, capsanthin and capsorubin. An enzyme, known as capsanthin-capsorubin synthase (CCS), catalyzes the conversion of antheraxanthin and violaxanthin into capsanthin and capsorubin, respectively. We cloned the gene for capsanthin-capsorubin synthase (Llccs) from flower tepals of L. lancifolium by the rapid amplification of cDNA ends (RACE) with a heterologous non-degenerate primer that was based on the sequence of a gene for lycopene b-cyclase (lcyB). The full-length cDNA of Llccs was 1,785 bp long and contained an open reading frame of 1,425 bp that encoded a polypeptide of 474 amino acids with a predicted N-terminal plastid-targeting sequence. Analysis by reverse transcription-PCR (RT-PCR) revealed that expression of Llccs was spatially and temporally regulated, with expression in flower buds and flowers of L. lancifolium but not in vegetative tissues. Stable overexpression of the Llccs gene in callus tissue of Iris germanica, which accumulates several xanthophylls including violaxanthin, the precursor of capsorubin, resulted in transgenic callus whose color had changed from its normal yellow to red-orange. This novel red-orange coloration was due to the accumulation of two non-native k-xanthophylls, capsanthin and capsorubin, as confirmed by HPLC and ultraperformance liquid chromatographytandem mass spectrometry (UPLC-MS/MS) analysis with authentic standards. Cloning of the Llccs gene should advance our understanding of the molecular and genetic mechanisms of the biosynthesis of k-carotenoids in general and in the genus Lilium in particular, and will facilitate transgenic alterations of the colors of flowers and fruits of many plant species.

Guía Pedagógica y de Evaluación del Módulo: Reflexión sobre el pensamiento y quehacer humano (Fil... more Guía Pedagógica y de Evaluación del Módulo: Reflexión sobre el pensamiento y quehacer humano (Filosofía)