201 research outputs found

    A general theory of intertemporal decision-making and the perception of time

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    Animals and humans make decisions based on their expected outcomes. Since relevant outcomes are often delayed, perceiving delays and choosing between earlier versus later rewards (intertemporal decision-making) is an essential component of animal behavior. The myriad observations made in experiments studying intertemporal decision-making and time perception have not yet been rationalized within a single theory. Here we present a theory-Training--Integrated Maximized Estimation of Reinforcement Rate (TIMERR)--that explains a wide variety of behavioral observations made in intertemporal decision-making and the perception of time. Our theory postulates that animals make intertemporal choices to optimize expected reward rates over a limited temporal window; this window includes a past integration interval (over which experienced reward rate is estimated) and the expected delay to future reward. Using this theory, we derive a mathematical expression for the subjective representation of time. A unique contribution of our work is in finding that the past integration interval directly determines the steepness of temporal discounting and the nonlinearity of time perception. In so doing, our theory provides a single framework to understand both intertemporal decision-making and time perception.Comment: 37 pages, 4 main figures, 3 supplementary figure

    Enhancing the anti-angiogenic action of histone deacetylase inhibitors

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    <p>Abstract</p> <p>Background</p> <p>Histone deacetylase inhibitors (HDACIs) have many effects on cancer cells, such as growth inhibition, induction of cell death, differentiation, and anti-angiogenesis, all with a wide therapeutic index. However, clinical trials demonstrate that HDACIs are more likely to be effective when used in combination with other anticancer agents. Moreover, the molecular basis for the anti-cancer action of HDACIs is still unknown. In this study, we compared different combinations of HDACIs and anti-cancer agents with anti-angiogenic effects, and analysed their mechanism of action.</p> <p>Results</p> <p>Trichostatin A (TSA) and Ī±-interferon (IFNĪ±) were the most effective combination across a range of different cancer cell lines, while normal non-malignant cells did not respond in the same manner to the combination therapy. There was a close correlation between absence of basal p21<sup>WAF1 </sup>expression and response to TSA and IFNĪ± treatment. Moreover, inhibition of p21<sup>WAF1 </sup>expression in a p21<sup>WAF1</sup>-expressing breast cancer cell line by a specific siRNA increased the cytotoxic effects of TSA and IFNĪ±. <it>In vitro </it>assays of endothelial cell function showed that TSA and IFNĪ± decreased endothelial cell migration, invasion, and capillary tubule formation, without affecting endothelial cell viability. TSA and IFNĪ± co-operatively inhibited gene expression of some pro-angiogenic factors: vascular endothelial growth factor, hypoxia-inducible factor 1Ī± and matrix metalloproteinase 9, in neuroblastoma cells under hypoxic conditions. Combination TSA and IFNĪ± therapy markedly reduced tumour angiogenesis in neuroblastoma-bearing transgenic mice.</p> <p>Conclusion</p> <p>Our results indicate that combination TSA and IFNĪ± therapy has potent co-operative cytotoxic and anti-angiogenic activity. High basal p21<sup>WAF1 </sup>expression appears to be acting as a resistance factor to the combination therapy.</p

    The Angola Gyre is a hotspot of dinitrogen fixation in the South Atlantic Ocean

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    Ā© The Author(s), 2022. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Marshall, T., Granger, J., Casciotti, K. L., Dahnke, K., Emeis, K.-C., Marconi, D., McIlvin, M. R., Noble, A. E., Saito, M. A., Sigman, D. M., & Fawcett, S. E. The Angola Gyre is a hotspot of dinitrogen fixation in the South Atlantic Ocean. Communications Earth & Environment, 3(1), (2022): 151, https://doi.org/10.1038/s43247-022-00474-x.Biological dinitrogen fixation is the major source of new nitrogen to marine systems and thus essential to the oceanā€™s biological pump. Constraining the distribution and global rate of dinitrogen fixation has proven challenging owing largely to uncertainty surrounding the controls thereon. Existing South Atlantic dinitrogen fixation rate estimates vary five-fold, with models attributing most dinitrogen fixation to the western basin. From hydrographic properties and nitrate isotope ratios, we show that the Angola Gyre in the eastern tropical South Atlantic supports the fixation of 1.4ā€“5.4 Tg N.aāˆ’1, 28-108% of the existing (highly uncertain) estimates for the basin. Our observations contradict model diagnoses, revealing a substantial input of newly-fixed nitrogen to the tropical eastern basin and no dinitrogen fixation west of 7.5ĖšW. We propose that dinitrogen fixation in the South Atlantic occurs in hotspots controlled by the overlapping biogeography of excess phosphorus relative to nitrogen and bioavailable iron from margin sediments. Similar conditions may promote dinitrogen fixation in analogous ocean regions. Our analysis suggests that local iron availability causes the phosphorus-driven coupling of oceanic dinitrogen fixation to nitrogen loss to vary on a regional basis.This work was supported by the South African National Research Foundation (114673 and 130826 to T.M., 115335, 116142 and 129320 to S.E.F.); the US National Science Foundation (CAREER award, OCE-1554474 to J.G., OCE-1736652 to D.M.S. and K.L.C., OCE-05-26277 to K.L.C.); the German Federal Agency for Education and Research (DAAD-SPACES 57371082 to T.M.); the Royal Society (FLAIR fellowship to S.E.F.); and the University of Cape Town (T.M., J.G., S.E.F.). The authors also recognize the support of the South African Department of Science and Innovationā€™s Biogeochemistry Research Infrastructure Platform (BIOGRIP)

    MmeI: a minimal Type II restriction-modification system that only modifies one DNA strand for host protection

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    MmeI is an unusual Type II restriction enzyme that is useful for generating long sequence tags. We have cloned the MmeI restriction-modification (R-M) system and found it to consist of a single protein having both endonuclease and DNA methyltransferase activities. The protein comprises an amino-terminal endonuclease domain, a central DNA methyltransferase domain and C-terminal DNA recognition domain. The endonuclease cuts the two DNA strands at one site simultaneously, with enzyme bound at two sites interacting to accomplish scission. Cleavage occurs more rapidly than methyl transfer on unmodified DNA. MmeI modifies only the adenine in the top strand, 5ā€²-TCCRAC-3ā€². MmeI endonuclease activity is blocked by this top strand adenine methylation and is unaffected by methylation of the adenine in the complementary strand, 5ā€²-GTYGGA-3ā€². There is no additional DNA modification associated with the MmeI R-M system, as is required for previously characterized Type IIG R-M systems. The MmeI R-M system thus uses modification on only one of the two DNA strands for host protection. The MmeI architecture represents a minimal approach to assembling a restriction-modification system wherein a single DNA recognition domain targets both the endonuclease and DNA methyltransferase activities
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