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11.
The short-wavelength (blue) light sensitivity of human circadian, neurobehavioral, neuroendocrine, and neurophysiological responses is attributed to melanopsin. Whether melanopsin is the sole factor in determining the efficacy of a polychromatic light source in driving nonvisual responses, however, remains to be established. Monochromatic (λ(max) 437, 479, and 532 nm administered singly and in combination with 479 nm light) and polychromatic (color temperature: 4000 K and 17000 K) light stimuli were photon matched for their predicted ability to stimulate melanopsin, and their capacity to affect nocturnal melatonin levels, auditory reaction time, and subjective alertness and mood was assessed. Young, healthy male participants aged 18-35 yrs (23.6?±?3.6 yrs [mean?±?SD]; n=12) participated in 12 overnight sessions that included an individually timed 30-min nocturnal light stimulus on the rising limb of the melatonin profile. At regular intervals before, during, and after the light stimulus, subjective mood and alertness were verbally assessed, blood samples were taken for analysis of plasma melatonin levels, and an auditory reaction time task (psychomotor vigilance task; PVT) was performed. Proc GLM (general linear model) repeated-measures ANOVA (analysis of variance) revealed significantly lower melatonin suppression with the polychromatic light conditions (4000 and 17000 K) compared to the "melanopsin photon-matched" monochromatic light conditions (p.05). In contrast, subjective alertness was significantly lower under the 479 nm monochromatic light condition compared to the 437 and 532 nm monochromatic and both polychromatic light conditions. The alerting responses more reflected the total photon content of the light stimulus. The demonstration that the melatonin suppression response to polychromatic light was significantly lower than predicted by the melanopsin photosensitivity function suggests this function is not the sole consideration when trying to predict the efficacy of broadband lighting. The different spectral sensitivity of subjective alertness and melatonin suppression responses may imply a differential involvement of the cone photopigments. An analysis of the photon densities in specific wavelength bands for the polychromatic lights used in this and the authors' previous study suggests the spectral composition of a polychromatic light source, and particularly the very short-wavelength content, may be critical in determining response magnitude for the neuroendocrine and neurobehavioral effects of nocturnal light. 相似文献
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The murid rodent subfamily Sigmodontinae contains 79 genera which are
distributed throughout the New World. The time of arrival of the first
sigmodontines in South America and the estimated divergence time(s) of the
different lineages of South American sigmodontines have been controversial
due to the lack of a good fossil record and the immense number of extant
species. The "early-arrival hypothesis" states that the sigmodontines must
have arrived in South America no later than the early Miocene, at least 20
MYA, in order to account for their vast present-day diversity, whereas the
"late-arrival hypothesis" includes the sigmodontines as part of the
Plio-Pleistocene Great American Interchange, which occurred approximately
3.5 MYA. The phylogenetic relationships among 33 of these genera were
reconstructed using mitochondrial DNA (mtDNA) sequence data from the ND3,
ND4L, arginine tRNA, and ND4 genes, which we show to be evolving at the
same rate. A molecular clock was calibrated for these genes using published
fossil dates, and the genetic distances were estimated from the DNA
sequences in this study. The molecular clock was used to estimate the dates
of the South American sigmodontine origin and the main sigmodontine
radiation in order to evaluate the "early-" and "late-arrival" scenarios.
We estimate the time of the sigmodontine invasion of South America as
between approximately 5 and 9 MYA, supporting neither of the scenarios but
suggesting two possible models in which the invading lineage was either (1)
ancestral to the oryzomyines, akodonts, and phyllotines or (2) ancestral to
the akodonts and phyllotines and accompanied by the oryzomyines. The
sigmodontine invasion of South America provides an example of the advantage
afforded to a lineage by the fortuitous invasion of a previously
unexploited habitat, in this case an entire continent.
相似文献
15.
Multiple duplications of yeast hexose transport genes in response to selection in a glucose-limited environment 总被引:11,自引:2,他引:9
When microbes evolve in a continuous, nutrient-limited environment, natural
selection can be predicted to favor genetic changes that give cells greater
access to limiting substrate. We analyzed a population of baker's yeast
that underwent 450 generations of glucose-limited growth. Relative to the
strain used as the inoculum, the predominant cell type at the end of this
experiment sustains growth at significantly lower steady-state glucose
concentrations and demonstrates markedly enhanced cell yield per mole
glucose, significantly enhanced high-affinity glucose transport, and
greater relative fitness in pairwise competition. These changes are
correlated with increased levels of mRNA hybridizing to probe generated
from the hexose transport locus HXT6. Further analysis of the evolved
strain reveals the existence of multiple tandem duplications involving two
highly similar, high- affinity hexose transport loci, HXT6 and HXT7.
Selection appears to have favored changes that result in the formation of
more than three chimeric genes derived from the upstream promoter of the
HXT7 gene and the coding sequence of HXT6. We propose a genetic mechanism
to account for these changes and speculate as to their adaptive
significance in the context of gene duplication as a common response of
microorganisms to nutrient limitation.
相似文献
16.
Translocations for conservation often involve species limited to relict distributions. However, uncertainty can exist regarding the ability of source individuals to acclimatise following a shift to a distant location. We investigated the ability of captive-reared juvenile tuatara (Sphenodon punctatus) of Cook Strait stock (41°S) to adjust to outdoor, predator-protected pens within Orokonui Ecosanctuary (45 °S). We examined potential basking and within burrow temperatures, the influence of temperature on emergence, and growth rates in comparison with other locations. Tuatara at Orokonui reached their preferred temperature when basking over summer, and burrows provided protection from freezing over winter. Emergence was temperature-dependent and essentially ceased during winter. Growth rates of Orokonui-held juveniles were within the range for four other captive-rearing facilities and faster than for wild juveniles from a Cook Strait population. As all Orokonui-held juveniles have survived and grown we conclude that the climate at this southern location is suitable to consider a free-release. 相似文献
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Enezi J Revell V Brown T Wynne J Schlangen L Lucas R 《Journal of biological rhythms》2011,26(4):314-323
Photoreception in the mammalian retina is not restricted to rods and cones but extends to a small number of intrinsically photosensitive retinal ganglion cells expressing the photopigment melanopsin. These mRGCs are especially important contributors to circadian entrainment, the pupil light reflex, and other so-called nonimage-forming (NIF) responses. The spectral sensitivity of melanopsin phototransduction has been addressed in several species by comparing responses to a range of monochromatic stimuli. The resultant action spectra match the predicted profile of an opsin:vitamin A-based photopigment (nomogram) with a peak sensitivity (λ(max)) around 480 nm. It would be most useful to be able to use this spectral sensitivity function to predict melanopsin's sensitivity to broad-spectrum, including "white," lights. However, evidence that melanopsin is a bistable pigment with an intrinsic light-dependent bleach recovery mechanism raises the possibility of a more complex relationship between spectral quality and photoreceptor response. Here, we set out to empirically determine whether simply weighting optical power at each wavelength according to the 480-nm nomogram and integrating across the spectrum could predict melanopsin sensitivity to a variety of polychromatic stimuli. We show that pupillomotor and circadian responses of mice relying solely on melanopsin for their photosensitivity (rd/rd cl) can indeed be accurately predicted using this methodology. Our data therefore suggest that the 480-nm nomogram may be employed as the basis for a new photometric measure of light intensity (which we term "melanopic") relevant for melanopsin photoreception. They further show that measuring light in these terms predicts the melanopsin response to light of divergent spectral composition much more reliably than other methods for quantifying irradiance or illuminance currently in widespread use. 相似文献
19.
Background
Digital polymerase chain reaction (dPCR) is an increasingly popular technology for detecting and quantifying target nucleic acids. Its advertised strength is high precision absolute quantification without needing reference curves. The standard data analytic approach follows a seemingly straightforward theoretical framework but ignores sources of variation in the data generating process. These stem from both technical and biological factors, where we distinguish features that are 1) hard-wired in the equipment, 2) user-dependent and 3) provided by manufacturers but may be adapted by the user. The impact of the corresponding variance components on the accuracy and precision of target concentration estimators presented in the literature is studied through simulation.Results
We reveal how system-specific technical factors influence accuracy as well as precision of concentration estimates. We find that a well-chosen sample dilution level and modifiable settings such as the fluorescence cut-off for target copy detection have a substantial impact on reliability and can be adapted to the sample analysed in ways that matter. User-dependent technical variation, including pipette inaccuracy and specific sources of sample heterogeneity, leads to a steep increase in uncertainty of estimated concentrations. Users can discover this through replicate experiments and derived variance estimation. Finally, the detection performance can be improved by optimizing the fluorescence intensity cut point as suboptimal thresholds reduce the accuracy of concentration estimates considerably.Conclusions
Like any other technology, dPCR is subject to variation induced by natural perturbations, systematic settings as well as user-dependent protocols. Corresponding uncertainty may be controlled with an adapted experimental design. Our findings point to modifiable key sources of uncertainty that form an important starting point for the development of guidelines on dPCR design and data analysis with correct precision bounds. Besides clever choices of sample dilution levels, experiment-specific tuning of machine settings can greatly improve results. Well-chosen data-driven fluorescence intensity thresholds in particular result in major improvements in target presence detection. We call on manufacturers to provide sufficiently detailed output data that allows users to maximize the potential of the method in their setting and obtain high precision and accuracy for their experiments.Electronic supplementary material
The online version of this article (doi:10.1186/1471-2105-15-283) contains supplementary material, which is available to authorized users. 相似文献20.
Y Deng J Zhao D Sakurai KM Kaufman JC Edberg RP Kimberly DL Kamen GS Gilkeson CO Jacob RH Scofield CD Langefeld JA Kelly ME Alarcón-Riquelme BIOLUPUS GENLES Networks JB Harley TJ Vyse BI Freedman PM Gaffney KM Sivils JA James TB Niewold RM Cantor W Chen BH Hahn EE Brown PROFILE BP Tsao 《Arthritis research & therapy》2012,14(Z3):A5