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Median Lifespans (median + lifespan)

Distribution by Scientific Domains

Life Sciences	83%

Selected Abstracts

Effects of leaf emergence on leaf lifespan are independent of life form and successional status

AUSTRAL ECOLOGY, Issue 7 2008
ROGER J. DUNGAN
Abstract The longevity of a leaf is related to the benefit that the plant is able to derive from it. This benefit varies among seasons and as more leaves emerge, such that leaf lifespan can be limited by canopy position rather than physiological age. Using interval-censored failure time analysis, we investigate leaf lifespan for 34 Mediterranean species in a previously published dataset involving species with different life forms and functional strategies. Failure time regression models were used to determine leaf lifespan, and to investigate how these effects varied among species. Median lifespan estimated for each species with two methods differed by less than 10% on average, but varied from 0.02,19.5% depending on the shape of the underlying failure time distribution. Within shoots, later-emerging leaves had shorter lifespans for species with longer periods of leaf emergence, and the reverse was true for species with short emergence. Having accounted for the within-shoot effect, leaves emerging in spring had shorter lifespans, particularly herbaceous species, whereas the reverse was true woody species. These effects were consistent among life forms and successional stages, and consistent with theories of within-shoot translocation of resources following self-shading. [source]

Aging in inbred strains of mice: study design and interim report on median lifespans and circulating IGF1 levels

AGING CELL, Issue 3 2009
Rong Yuan
Summary To better characterize aging in mice, the Jackson Aging Center carried out a lifespan study of 31 genetically-diverse inbred mouse strains housed in a specific pathogen-free facility. Clinical assessments were carried out every 6 months, measuring multiple age-related phenotypes including neuromuscular, kidney and heart function, body composition, bone density, hematology, hormonal levels, and immune system parameters. In a concurrent cross-sectional study of the same 31 strains at 6, 12, and 20 months, more invasive measurements were carried out followed by necropsy to assess apoptosis, DNA repair, chromosome fragility, and histopathology. In this report, which is the initial paper of a series, the study design, median lifespans, and circulating insulin-like growth factor 1 (IGF1) levels at 6, 12, and 18 months are described for the first cohort of 32 females and 32 males of each strain. Survival curves varied dramatically among strains with the median lifespans ranging from 251 to 964 days. Plasma IGF1 levels, which also varied considerably at each time point, showed an inverse correlation with a median lifespan at 6 months (R = ,0.33, P = 0.01). This correlation became stronger if the short-lived strains with a median lifespan < 600 days were removed from the analysis (R = ,0.53, P < 0.01). These results support the hypothesis that the IGF1 pathway plays a key role in regulating longevity in mice and indicates that common genetic mechanisms may exist for regulating IGF1 levels and lifespan. [source]

Pathology is alleviated by doxycycline in a laminin-,2,null model of congenital muscular dystrophy

ANNALS OF NEUROLOGY, Issue 1 2009
Mahasweta Girgenrath PhD
Objective Congenital muscular dystrophy type 1A is an autosomal recessive disease that is caused by loss-of-function mutations in the laminin-,2 gene, and results in motor nerve and skeletal muscle dysfunction. In a previous study, we used genetic modifications to show that inappropriate induction of apoptosis was a significant contributor to pathogenesis in a laminin-,2,deficient mouse model of congenital muscular dystrophy type 1A. To identify a possible pharmacological therapy for laminin-,2 deficiency, we designed this study to determine whether treatment with minocycline or doxycycline, which are tetracycline derivatives reported to have antiapoptotic effects in mammals, would significantly increase lifespan and improve neuromuscular function in laminin-,2,deficient mice. Methods Mice that were homozygous for a targeted, inactivating mutation of the laminin-,2 gene were placed into control, minocycline-treated, or doxycycline-treated groups. Drug treatment began within 2 weeks of birth, and the progression of disease was followed over time using behavioral, growth, histological, and molecular assays. Results We found that treatment with either minocycline or doxycycline increased the median lifespan of laminin-,2,null mice from approximately 32 days to approximately 70 days. Furthermore, doxycycline improved postnatal growth rate and delayed the onset of hind-limb paralysis. Doxycycline-treated laminin-,2,deficient muscles had increased Akt phosphorylation, decreased inflammation, and decreased levels of Bax protein, terminal deoxynucleotidyltransferase,mediated dUTP nick end labeling,positive myonuclei, and activated caspase-3. Interpretation Doxycycline or other drugs with similar functional profiles may be a possible route to improving neuromuscular dysfunction caused by laminin-,2-deficiency. Ann Neurol 2008 [source]

Aging in inbred strains of mice: study design and interim report on median lifespans and circulating IGF1 levels

Consequences of insect herbivory on grape fine root systems with different growth rates

PLANT CELL & ENVIRONMENT, Issue 7 2007
T. L. BAUERLE
ABSTRACT Herbivory tolerance has been linked to plant growth rate where plants with fast growth rates are hypothesized to be more tolerant of herbivory than slower-growing plants. Evidence supporting this theory has been taken primarily from observations of aboveground organs but rarely from roots. Grapevines differing in overall rates of new root production, were studied in Napa Valley, California over two growing seasons in an established vineyard infested with the sucking insect, grape phylloxera (Daktulosphaira vitifoliae Fitch). The experimental vineyard allowed for the comparison of two root systems that differed in rates of new root tip production (a ,fast grower', Vitis berlandieri × Vitis rupestris cv. 1103P, and a slower-growing stock, Vitis riparia × Vitis rupestris cv. 101,14 Mgt). Each root system was grafted with a genetically identical shoot system (Vitis vinifera cv. Merlot). Using minirhizotrons, we did not observe any evidence of spatial or temporal avoidance of insect populations by root growth. Insect infestations were abundant throughout the soil profile, and seasonal peaks in phylloxera populations generally closely followed peaks in new root production. Our data supported the hypothesis that insect infestation was proportional to the number of growing tips, as indicated by similar per cent infestation in spite of a threefold difference in root tip production. In addition, infested roots of the fast-growing rootstock exhibited somewhat shorter median lifespans (60 d) than the slower-growing rootstock (85 d). Lifespans of uninfested roots were similar for the two rootstocks (200 d). As a consequence of greater root mortality of younger roots, infested root populations in the fast-growing rootstock had an older age structure. While there does not seem to be a trade-off between potential growth rate and relative rate of root infestation in these cultivars, our study indicates that a fast-growing root system may more readily shed infested roots that are presumably less effective in water and nutrient uptake. Thus, differences in root tip production may be linked to differences in the way plants cope with roots that are infested by sucking insects. [source]