Summary Background Many unicellular organisms age: as time passes, they divide more slowly and ultimately die. In budding yeast, asymmetric segregation of cellular damage results in aging mother cells and rejuvenated daughters. We hypothesize that the organisms in which this asymmetry is lacking, or can be modulated, may not undergo aging. Results We performed a complete pedigree analysis of microcolonies of the fission yeast Schizosaccharomyces pombe growing from a single cell. When cells were grown under favorable conditions, none of the lineages exhibited aging, which is defined as a consecutive increase in division time and increased death probability. Under favorable conditions, few cells died, and their death was random and sudden rather than following a gradual increase in division time. Cell death correlated with the inheritance of Hsp104-associated protein aggregates. After stress, the cells that inherited large aggregates aged, showing a consecutive increase in division time and an increased death probability. Their sisters, who inherited little or no aggregates, did not age. Conclusions We conclude that S. pombe does not age under favorable growth conditions, but does so under stress. This transition appears to be passive rather than active and results from the formation of a single large aggregate, which segregates asymmetrically at the subsequent cell division. We argue that this damage-induced asymmetric segregation has evolved to sacrifice some cells so that others may survive unscathed after severe environmental stresses.

Fusion of harmful aggregated proteins into larger clumps increases the asymmetry of segregation of damage at cell division, favoring the production of rejuvenated cells.

We assess whether reactive oxygen species production and resistance to oxidative stress might be causally involved in the exceptional longevity exhibited by the ocean quahog Arctica islandica. We tested this hypothesis by comparing reactive oxygen species production, resistance to oxidative stress, antioxidant defenses, and protein damage elimination processes in long-lived A islandica with the shorter-lived hard clam, Mercenaria mercenaria. We compared baseline biochemical profiles, age-related changes, and responses to exposure to the oxidative stressor tert-butyl hydroperoxide (TBHP). Our data support the premise that extreme longevity in A islandica is associated with an attenuated cellular reactive oxygen species production. The observation of reduced protein carbonyl concentration in A islandica gill tissue compared with M mercenaria suggests that reduced reactive oxygen species production in long-living bivalves is associated with lower levels of accumulated macromolecular damage, suggesting cellular redox homeostasis may determine life span. Resistance to aging at the organismal level is often reflected in resistance to oxidative stressors at the cellular level. Following TBHP exposure, we observed not only an association between longevity and resistance to oxidative stress-induced mortality but also marked resistance to oxidative stress-induced cell death in the longer-living bivalves. Contrary to some expectations from the oxidative stress hypothesis, we observed that A islandica exhibited neither greater antioxidant capacities nor specific activities than in M mercenaria nor a more pronounced homeostatic antioxidant response following TBHP exposure. The study also failed to provide support for the exceptional longevity of A islandica being associated with enhanced protein recycling. Our findings demonstrate an association between longevity and resistance to oxidative stress-induced cell death in A islandica, consistent with the oxidative stress hypothesis of aging and provide justification for detailed evaluation of pathways involving repair of free radical-mediated macromolecular damage and regulation of apoptosis in the world's longest-living non-colonial animal.

Modern industrial agriculture depends on high-density cultivation of genetically similar crop plants, creating favorable conditions for the emergence of novel pathogens with increased fitness in managed compared with ecologically intact settings. Here, we present the genome sequence of six strains of the cucurbit bacterial wilt pathogen Erwinia tracheiphila (Enterobacteriaceae) isolated from infected squash plants in New York, Pennsylvania, Kentucky, and Michigan. These genomes exhibit a high proportion of recent horizontal gene acquisitions, invasion and remarkable amplification of mobile genetic elements, and pseudogenization of approximately 20% of the coding sequences. These genome attributes indicate that E. tracheiphila recently emerged as a host-restricted pathogen. Furthermore, chromosomal rearrangements associated with phage and transposable element proliferation contribute to substantial differences in gene content and genetic architecture between the six E. tracheiphila strains and other Erwinia species. Together, these data lead us to hypothesize that E. tracheiphila has undergone recent evolution through both genome decay (pseudogenization) and genome expansion (horizontal gene transfer and mobile element amplification). Despite evidence of dramatic genomic changes, the six strains are genetically monomorphic, suggesting a recent population bottleneck and emergence into E. tracheiphila’s current ecological niche.

A cell can be viewed as a dynamic puzzle, where single pieces shuffle in space, change their conformation to fit different partners, and new pieces are generated while old ones are destroyed.Microscopy has become capable of directly observing the pieces of the puzzle, which are single molecules. Single-molecule microscopy in vivo provides new insights into the molecular processes underlying the physiology of a cell, allowing not only for visualizing how molecules distribute with nanometer resolution in the cellular environment, but also for characterizing their movement with high temporal precision. This approach reveals molecular behaviors normally invisible in ensemble measurements. Depending on the molecule, the process, and the cellular region studied, single Insight, innovation, integrationSingle molecule imaging in vivo provides new insights into the molecular processes in cells. This approach is important not only to map the distribution of single molecules inside the cell with high spatial resolution, but also to analyze the movement of these molecules and their interactions over time. Single molecule imaging in live cells reveals transient molecular interactions that cannot be identified by conventional biochemical methods. Moreover, single molecule imaging allows for direct measurements of parameters of molecular reactions, including the number of molecules, concentrations, reaction rate constants and diffusion coefficients. These parameters can be used in building mathematical models of intracellular processes.

Caesalpinia ferrea Mart ex Tul é uma espécie arbórea nativa do Brasil que ocorre no bioma Caatinga. Possui grande potencial medicinal e ornamental, além de sua madeira ser utilizada na construção civil e na carpintaria. Este estudo foi realizado com o objetivo de avaliar a eficiência de métodos para superação de dormência de sementes de C. ferrea. Foram aplicados os seguintes tratamentos pré germinativos: T1 -escarificação mecânica com lixa na extremidade oposta ao hilo; T2 -escarificação mecânica com lixa na extremidade junto ao hilo; T3 -escarificação mecânica na extremidade lateral da semente; T4 e T5 -imersão das sementes em água a 80 e a 100ºC, respectivamente; T6 -testemunha (sem qualquer pré tratamento). Foram avaliadas as seguintes variáveis: a percentagem de emergência, o índice de velocidade de emergência, o comprimento da parte aérea e da raiz principal, massa seca da parte aérea e do sistema radicular de plântulas. As sementes de C. ferrea apresentam dormência tegumentar. A escarificação mecânica na extremidade oposta ao hilo, ou próxima à região deste, proporciona a superação da dormência em sementes de C. ferrea. Palavras-chave: Pau ferro, propagação, germinação, escarificaçãoOvercoming of dormancy coats of Caesalpinia ferrea Mart ex Tul. seeds AB S TR ACTCaesalpinia ferrea is a tree species native to Brazil coming from Caatinga (dryland) biome. It has great medicinal and ornamental potential; its wood is used in construction and carpentry. This study aimed to evaluate the efficiency of methods to overcoming of dormancy Caesalpinia ferrea Mart. ex Tul. seed. The following pre-germinative treatments had been applied: T1 -mechanical scarification on the opposing extremity to hilum with sandpaper; T2 -mechanical scarification on the extremity next to hilum with sandpaper; T3 -mechanical scarification on the lateral region with sandpaper; T4 -immersion in water at 80ºC; T5 -immersion in water at 100ºC; T6 -control (no treatment). The emergency, emergency speed index, length of the aerial part and primary root, dry weight matter of the aerial part and root system were evaluated. The C. ferrea seeds they present tegument dormancy. Mechanical scarification and immersion in water at 80ºC are efficient methods to overcome dormancy in Caesalpinia ferrea.

Genetic instability, a heritable increase in the mutation rate, accelerates evolutionary adaptation 1 and is widespread in cancer 2,3 . In mammals, instability can arise from damaging both copies of genes involved in DNA metabolism and cell cycle regulation 4 or from inactivating one copy of a gene whose product is present in limiting amounts (haploinsufficiency 5 ), but determining the relative importance of these two mechanisms is difficult. In E. coli 6 , applying repeated, strong selection enriches for genetic instability. We used this approach to evolve genetic instability in diploid cells of the budding yeast, Saccharomyces cerevisiae and isolated clones with increased rates of point mutation, mitotic recombination, and chromosome loss. We identified candidate, heterozygous, instability-causing mutations and engineering these mutations, as heterozygotes, into the ancestral diploid strain caused genetic instability. Mutations that inactivate one copy of haploinsufficient genes are more common than those that dominantly alter the function of the mutated gene copy. The mutated genes are enriched for genes functioning in transport, protein quality control, and DNA metabolism, and reveal new targets for genetic instability 7-11 , including Reprints and permission information is available at www.nature.com/reprints.

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