13 research outputs found
Telomere Length as a Quantitative Trait: Genome-Wide Survey and Genetic Mapping of Telomere Length-Control Genes in Yeast
Telomere length-variation in deletion strains of Saccharomyces cerevisiae was used to identify genes and pathways that regulate telomere length. We found 72 genes that when deleted confer short telomeres, and 80 genes that confer long telomeres relative to those of wild-type yeast. Among identified genes, 88 have not been previously implicated in telomere length control. Genes that regulate telomere length span a variety of functions that can be broadly separated into telomerase-dependent and telomerase-independent pathways. We also found 39 genes that have an important role in telomere maintenance or cell proliferation in the absence of telomerase, including genes that participate in deoxyribonucleotide biosynthesis, sister chromatid cohesion, and vacuolar protein sorting. Given the large number of loci identified, we investigated telomere lengths in 13 wild yeast strains and found substantial natural variation in telomere length among the isolates. Furthermore, we crossed a wild isolate to a laboratory strain and analyzed telomere length in 122 progeny. Genome-wide linkage analysis among these segregants revealed two loci that account for 30%–35% of telomere length-variation between the strains. These findings support a general model of telomere length-variation in outbred populations that results from polymorphisms at a large number of loci. Furthermore, our results laid the foundation for studying genetic determinants of telomere length-variation and their roles in human disease
Identification of a negative feedback loop in biological oxidant formation fegulated by 4-hydroxy-2-(E)-nonenal
4-Hydroxy-2-(E)-nonenal (4-HNE) is one of the major lipid peroxidation product formed during oxidative stress. At high concentrations, 4-HNE is cytotoxic and exerts deleterious effects that are often associated with the pathology of oxidative stress-driven disease. Alternatively, at low concentrations it functions as a signaling molecule that can activate protective pathways including the antioxidant Nrf2-Keap1 pathway. Although these biphasic signaling properties have been enumerated in many diseases and pathways, it has yet to be addressed whether 4-HNE has the capacity to modulate oxidative stress-driven lipid peroxidation. Here we report an auto-regulatory mechanism of 4-HNE via modulation of the biological oxidant nitric oxide (NO). Utilizing LPS-activated macrophages to induce biological oxidant production, we demonstrate that 4-HNE modulates NO levels via inhibition of iNOS expression. We illustrate a proposed model of control of NO formation whereby at low concentrations of 4-HNE a negative feedback loop maintains a constant level of NO production with an observed inflection at approximately 1 µM, while at higher 4-HNE concentrations positive feedback is observed. Further, we demonstrate that this negative feedback loop of NO production control is dependent on the Nrf2-Keap1 signaling pathway. Taken together, the careful regulation of NO production by 4-HNE argues for a more fundamental role of this lipid peroxidation product in normal physiology
Bryonolic Acid Transcriptional Control of Anti-inflammatory and Antioxidant Genes in Macrophages in Vitro and in Vivo
Bryonolic acid (BA) (<b>1</b>) is a naturally occurring
triterpenoid
with pleiotropic properties. This study characterizes the mechanisms
mediating the anti-inflammatory and antioxidant activities of BA and
validates the utility of BA as a tool to explore the relationships
between triterpenoid structure and activity. BA reduces the inflammatory
mediator NO by suppressing the expression of the inflammatory enzyme
inducible nitric oxide synthase (iNOS) in LPS-activated RAW 264.7
macrophage cells. In addition, BA robustly induces the antioxidant
protein heme oxygenase-1 (HO-1) in vitro and in vivo in an Nrf2-dependent
manner. Further analyses of Nrf2 target genes reveal selectivity for
the timing and level of gene induction by BA in treated macrophages
with distinct patterns for Nrf2-regulated antioxidant genes. Additionally,
the distinct expression profile of BA on Nrf2 target genes relative
to oleanolic acid suggests the importance of the triterpenoid scaffold
in dictating the pleiotropic effects exerted by these molecules
Sir2 suppresses transcription-mediated displacement of Mcm2-7 replicative helicases at the ribosomal DNA repeats.
Repetitive DNA sequences within eukaryotic heterochromatin are poorly transcribed and replicate late in S-phase. In Saccharomyces cerevisiae, the histone deacetylase Sir2 is required for both transcriptional silencing and late replication at the repetitive ribosomal DNA arrays (rDNA). Despite the widespread association between transcription and replication timing, it remains unclear how transcription might impinge on replication, or vice versa. Here we show that, when silencing of an RNA polymerase II (RNA Pol II)-transcribed non-coding RNA at the rDNA is disrupted by SIR2 deletion, RNA polymerase pushes and thereby relocalizes replicative Mcm2-7 helicases away from their loading sites to an adjacent region with low nucleosome occupancy, and this relocalization is associated with increased rDNA origin efficiency. Our results suggest a model in which two of the major defining features of heterochromatin, transcriptional silencing and late replication, are mechanistically linked through suppression of polymerase-mediated displacement of replication initiation complexes
Telomere Blots of Mutants with Short and Long Telomeres
<p>Short (A) and long (B) telomeres. Every other lane (unlabeled) presents
DNA isolated from wild-type cells.</p
Epistatic Analysis of Telomere Length among <i>TLM</i> Genes
<div><p>(A) Telomerase is required for increased telomere length in long telomere
mutants. This shows telomere length of single <i>tlc1,
tlm,</i> and double <i>tlc1 tlm</i> mutants 20 doublings
after germination of <i>TLC1/tlc1 TML/tlm</i> heterozygous
diploids. Telomere length of double <i>tlc1 tlm</i> mutants is
similar to telomere length of <i>tlc1</i> single mutants.</p><p>(B) VPS genes and NMD genes participate in separate telomere-maintenance
pathways. VSP genes (e.g., <i>VPS34, VPS15</i>) are epistatic
with KU telomere-capping pathway (e.g., <i>YKU70</i>), and NMD
genes (e.g., <i>NAM7</i>) have synthetic telomere phenotype
with the lack of <i>YKU70.</i></p></div