SUMMARY To define the C. elegans aging process at the molecular level, we used DNA microarray experiments to identify a set of 1294 age-regulated genes and found that the GATA transcription factors ELT-3, ELT-5, and ELT-6 are responsible for age regulation of a large fraction of these genes. Expression of elt-5 and elt-6 increases during normal aging, and both of these GATA factors repress expression of elt-3, which shows a corresponding decrease in expression in old worms. elt-3 regulates a large number of downstream genes that change expression in old age, including ugt-9, col-144, and sod-3. elt-5(RNAi) and elt-6(RNAi) worms have extended longevity, indicating that elt-3, elt-5, and elt-6 play an important functional role in the aging process. These results identify a transcriptional circuit that guides the rapid aging process in C. elegans and indicate that this circuit is driven by drift of developmental pathways rather than accumulation of damage.

Streptococcus strain V4051 is motile in the presence of glucose. The cells move steadily along smooth paths (run), jump about briefly with little net displacement (twiddle), and then run in new directions. They stop swimming when deprived of glucose. These cells become motile when an electrical potential or a pH gradient is imposed across the membrane. Starved cells suspended in a potassium-free medium respond to the addition of valinomycin b a brief period of vigorous twiddling. They also twiddle, although less vigorously, when the external pH is lowered. Valinomycin-induced twiddling occurs in the absence of external alkali or alkaline earth cations and without significant net synthesis of ATP. When a chemoattractant is .added to cells swimming in the presence of ,1ucose, twiddles are transiently suppressed, and the cells run or a time. Similarly, when starved cells are suspended in a potassium-free medium containing both valinomycin and an attractant, many cells initially run rather than twiddle. We conclude that the flagella are driven by a protonmotive force. Chemiosmotic energy coupling, as originally proposed by Mitchell (14), is involved in the function of a number of bacterial transport systems, in oxidative phosphorylation, and in pyridine nucleotide transhydrogenation (for reviews see refs. 5 and 6). We undertook the experiments reported here to determine whether bacterial motility is also powered by the proton movements that constitute the primary energy currency of Mitchell's theory. Our results confirm and extend those of Larsen et al. (7) Cells. Streptococcus strain V4051 (11) was grown at 340 in KTY-glucose medium (19) and harvested in early logarithmic phase at a cell density of 0.15 mg of dry weight per ml. Preparative steps were done at room temperature (22-24°). The cells from 20 ml of culture were trapped on a Millipore nitrocellulose filter (25 mm diameter, 0.45 Am pore size) and washed three times with 5 ml of 100 mM potassium phosphate (pH 7.5). They were resuspended very gently and washed twice by centrifugation in 5 ml of the desired final buffer. A concentrated stock of cells (25-50 mg dry weight per ml) was kept at room temperature and used within 3 hr.Motility. The motion of the cells was judged by eye or recorded with a Polaroid camera (type 107 film) using a phase contrast microscope (Nikon S-Ke, 30-W tungsten lamp, magnification 200X). When the camera was used, a programmed shutter (Vincent 26XOAOX5) placed between the microscope condenser and stage generated a series of 20-msec exposures. This is a variation of the motility-track method of Macnab and Koshland (20). Cells were diluted 1:1000 from the concentrated stock into the medium in which motility was to be tested, and the mixture was drawn by vacuum into the viewing chamber (21). All observations were made at room temperature.Protonmotive Force. The protonmotive force, the work per unit charge required to move a proton from the outside to the inside of the cell, is given by Ap = AAt-2.3(RT/F)ApH, [1] in which At is t...

We have followed by eye and with the tracking microscope the rotational behavior of E. coli tethered to coverslips by their flagella. The cells change their directions of rotation at random, on the average, about once a second. When an attractant is added or a repellent is subtracted, they spin clockwise (as viewed through the coverslip, i.e., along the flagellum toward the body) for many seconds, then counter-clockwise for many seconds, and then gradually resume their normal mode of behavior. The time interval between the onset of the stimulus and the clockwise to counter-clockwise transition is a linear function of the change in receptor occupancy. The cells adapt slowly at a constant rate to the addition of an attractant or the subtraction of a repellent. They adapt rapidly to the subtraction of an attractant or the addition of a repellent. Responses to mixed stimuli can be analyzed in terms of one equivalent stimulus.longer than the mean run length (3). The mean run length must be shorter than a few seconds, or changes in direction will be dominated by rotational diffusion (1).The results described here suggest that E. coli has found the optimum solution. As the concentration of an attractant increases, the cell adapts slowly at a constant rate. As the concentration decreases, it adapts rapidly. The time spans over which comparisons are made differ depending on whether the bacterium is moving up or down the gradient.The measurements were made by exposing cells tethered to coverslips by their flagella (6) to varying concentrations of attractants and/or repellents (7) and by monitoring the changes in the direction of their rotation by eye or with the tracking microscope (8).The swimming pattern of Escherichia coli resembles a three-dimensional random walk. A cell moves along a relatively straight path (runs), stops and jiggles about (twiddles), and then runs again (1). Twiddles occur at random, about once a second; they generate changes in direction which are nearly random (1, 2). The chemotactic behavior of a cell can be characterized in terms of a single parameter, the probability per unit time that a twiddle will occur. When the cell swims up a spatial gradient of an attractant, the probability that a twiddle will occur is somewhat smaller than it is in an isotropic solution; when it swims down the gradient, the probability is about the same as it is in an isotropic solution (1); thus, the cell drifts up the gradient by increasing the lengths of runs which are favorable. The same asymmetry is observed when cells are exposed to temporal gradients generated by the enzymatic synthesis or destruction of an attractant; as the concentration of the attractant increases, twiddles occur less frequently; as it decreases, they occur about as often as they do in the absence of a stimulus (3). When a large amount of attractant is suddenly added, the cells swim without twiddling for several minutes and then gradually resume their normal mode of behavior; when the attractant is diluted out, they twiddle more freq...

We have performed a whole-genome analysis of changes in gene expression during aging in C. elegans that provides a molecular description of C. elegans senescence.

SummaryOxidative stress has been hypothesized to play a role in normal aging. The response to oxidative stress is regulated by the SKN-1 transcription factor, which also is necessary for intestinal development in Caenorhabditis elegans. Almost a thousand genes including the antioxidant and heat-shock responses, as well as genes responsible for xenobiotic detoxification were induced by the oxidative stress which was found using transcriptome analysis. There were also 392 down-regulated genes including many involved in metabolic homeostasis, organismal development, and reproduction. Many of these oxidative stress-induced transcriptional changes are dependent on SKN-1 action; the induction of the heat-shock response is not. When RNAi to inhibit genes was used, most had no effect on either resistance to oxidative stress or longevity; however two SKN-1-dependent genes, nlp-7 and cup-4, that were up-regulated by oxidative stress were found to be required for resistance to oxidative stress and for normal lifespan. nlp-7 encodes a neuropeptide-like protein, expressed in neurons, while cup-4 encodes a coelomocyte-specific, ligand-gated ion channel. RNAi of nlp-7 or cup-4 increased sensitivity to oxidative stress and reduced lifespan. Among down-regulated genes, only inhibition of ent-1, a nucleoside transporter, led to increased resistance to oxidative stress; inhibition had no effect on lifespan. In contrast, RNAi of nhx-2, a Na + ⁄ H + exchanger, extended lifespan significantly without affecting sensitivity to oxidative stress. These findings showed that a transcriptional shift from growth and maintenance towards the activation of cellular defense mechanisms was caused by the oxidative stress; many of these transcriptional alterations are SKN-1 dependent.

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Hormesis has emerged as an important manipulation for the study of aging. Although hormesis is manifested in manifold combinations of stress and model organism, the mechanisms of hormesis are only partly understood. The increased stress resistance and extended survival caused by hormesis can be manipulated to further our understanding of the roles of intrinsic and induced stress resistance in aging. Genes of the dauer/insulin/insulin-like signaling (IIS) pathway have well-established roles in aging in Caenorhabditis elegans. Here, we discuss the role of some of those genes in the induced stress resistance and induced life extension attributable to hormesis. Mutations in three genes (daf-16, daf-18, and daf-12) block hormetically induced life extension. However, of these three, only daf-18 appears to be required for a full induction of thermotolerance induced by hormesis, illustrating possible separation of the genetic requirements for stress resistance and life extension. Mutations in three other genes of this pathway (daf-3, daf-5, and age-1) do not block induced life extension or induced thermotolerance; daf-5 mutants may be unusually sensitive to hormetic conditions.

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