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81.
Estimates are made of the number of potential marriage partners available for unmarried men and women, by age, in Great Britain in 1991 and how this varies across local districts. The preferences of men and women in relation to partner ages are taken into account in the estimates. Average partner supply declines by age for women and increases with age for men. Marriage markets differ between local areas but the differentiation is not as substantial as in many other aspects of local demography and is a good deal less than the variation that occurs through time. Young women and older men have advantageous marriage markets almost everywhere while young men and older women are at a disadvantage in almost all areas. 相似文献
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Regot S Macia J Conde N Furukawa K Kjellén J Peeters T Hohmann S de Nadal E Posas F Solé R 《Nature》2011,469(7329):207-211
Ongoing efforts within synthetic and systems biology have been directed towards the building of artificial computational devices using engineered biological units as basic building blocks. Such efforts, inspired in the standard design of electronic circuits, are limited by the difficulties arising from wiring the basic computational units (logic gates) through the appropriate connections, each one to be implemented by a different molecule. Here, we show that there is a logically different form of implementing complex Boolean logic computations that reduces wiring constraints thanks to a redundant distribution of the desired output among engineered cells. A practical implementation is presented using a library of engineered yeast cells, which can be combined in multiple ways. Each construct defines a logic function and combining cells and their connections allow building more complex synthetic devices. As a proof of principle, we have implemented many logic functions by using just a few engineered cells. Of note, small modifications and combination of those cells allowed for implementing more complex circuits such as a multiplexer or a 1-bit adder with carry, showing the great potential for re-utilization of small parts of the circuit. Our results support the approach of using cellular consortia as an efficient way of engineering complex tasks not easily solvable using single-cell implementations. 相似文献
85.
Roppolo D De Rybel B Tendon VD Pfister A Alassimone J Vermeer JE Yamazaki M Stierhof YD Beeckman T Geldner N 《Nature》2011,473(7347):380-383
Polarized epithelia are fundamental to multicellular life. In animal epithelia, conserved junctional complexes establish membrane diffusion barriers, cellular adherence and sealing of the extracellular space. Plant cellular barriers are of independent evolutionary origin. The root endodermis strongly resembles a polarized epithelium and functions in nutrient uptake and stress resistance. Its defining features are the Casparian strips, belts of specialized cell wall material that generate an extracellular diffusion barrier. The mechanisms localizing Casparian strips are unknown. Here we identify and characterize a family of transmembrane proteins of previously unknown function. These 'CASPs' (Casparian strip membrane domain proteins) specifically mark a membrane domain that predicts the formation of Casparian strips. CASP1 displays numerous features required for a constituent of a plant junctional complex: it forms complexes with other CASPs; it becomes immobile upon localization; and it sediments like a large polymer. CASP double mutants display disorganized Casparian strips, demonstrating a role for CASPs in structuring and localizing this cell wall modification. To our knowledge, CASPs are the first molecular factors that are shown to establish a plasma membrane and extracellular diffusion barrier in plants, and represent a novel way of epithelial barrier formation in eukaryotes. 相似文献
86.
Many proteins are translocated through the SecY channel in bacteria and archaea and through the related Sec61 channel in eukaryotes. The channel has an hourglass shape with a narrow constriction approximately halfway across the membrane, formed by a pore ring of amino acids. While the cytoplasmic cavity of the channel is empty, the extracellular cavity is filled with a short helix called the plug, which moves out of the way during protein translocation. The mechanism by which the channel transports large polypeptides and yet prevents the passage of small molecules, such as ions or metabolites, has been controversial. Here, we have addressed this issue in intact Escherichia coli cells by testing the permeation of small molecules through wild-type and mutant SecY channels, which are either in the resting state or contain a defined translocating polypeptide chain. We show that in the resting state, the channel is sealed by both the pore ring and the plug domain. During translocation, the pore ring forms a 'gasket-like' seal around the polypeptide chain, preventing the permeation of small molecules. The structural conservation of the channel in all organisms indicates that this may be a universal mechanism by which the membrane barrier is maintained during protein translocation. 相似文献
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Serge M. Candéias Justyna Mika Paul Finnon Tom Verbiest Rosemary Finnon Natalie Brown Simon Bouffler Joanna Polanska Christophe Badie 《Cellular and molecular life sciences : CMLS》2017,74(23):4339-4351
While the biological effects of high-dose-ionizing radiation on human health are well characterized, the consequences of low-dose radiation exposure remain poorly defined, even though they are of major importance for radiological protection. Lymphocytes are very radiosensitive, and radiation-induced health effects may result from immune cell loss and/or immune system impairment. To decipher the mechanisms of effects of low doses, we analyzed the modulation of the T-cell receptor gene repertoire in mice exposed to a single low (0.1 Gy) or high (1 Gy) dose of radiation. High-throughput T-cell receptor gene profiling was used to visualize T-lymphocyte dynamics over time in control and irradiated mice. Radiation exposure induces “aging-like” effects on the T-cell receptor gene repertoire, detectable as early as 1 month post-exposure and for at least 6 months. Surprisingly, these effects are more pronounced in animals exposed to 0.1 Gy than to 1 Gy, where partial correction occurs over time. Importantly, we found that low-dose radiation effects are partially due to the hematopoietic stem cell impairment. Collectively, our findings show that acute low-dose radiation exposure specifically results in long-term alterations of the T-lymphocyte repertoire. 相似文献
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Several habitat evaluation procedures have been developed for bighorn sheep. However, none of these procedures specifically addresses the Rocky Mountain subspecies nor analyzes both the quantity and quality of potential bighorn habitat with regard to minimum viable population (MVP) criteria. This bighorn habitat evaluation procedure combines (1) a quantitative assessment of bighorn range to determine if there are adequate quantities of resources to support an MVP of bighorn sheep, and (2) a qualitative assessment of a range to predict the probable density of bighorns the range can support. Extensive literature review, intensive bighorn research, and a modeling tool, pattern recognition (PATREC), facilitate critical analysis of proposed bighorn reintroduction sites. The resultant stepwise approach to bighorn habitat evaluation enhances the ability of wildlife biologists to make timely and accurate bighorn habitat assessments. 相似文献
90.
Tom Olliff Roy Renkin Craig McClure Paul Miller Dave Price Dan Reinhart Jennifer Whipple 《西北部美国博物学家》2011,61(3)
The number of documented exotic plants in Yellowstone National Park has increased from 85 known in 1986 to over 185 today. Exotic plants are substantially impacting the parks natural and cultural resources and are a high management priority. We have adopted an integrated weed management approach with regard to exotic vegetation, emphasizing prevention, education, early detection and eradication, control, and, to a lesser degree, monitoring. The program involves over 140 staff with program expenditures averaging approximately $190,000 annually. Prevention actions include requiring approved gravel on construction projects; banning hay in the backcountry and allowing transport of only certified weed-seed-free hay through Yellowstone; requiring construction equipment to be pressurecleaned prior to entering the park; and native species revegetation after road, housing, and other construction projects have disturbed ground. Over 4500 acres, primarily along roadsides and in developed areas, are surveyed annually in early detection efforts with emphasis placed on eradicating small, new infestations of highly invasive species such as sulfur cinquefoil ( Potentilla recta L.) and leafy spurge ( Euphorbia esula L.). Control efforts focus on about 30 priority species, such as spotted knapweed ( Centaurea maculosa Lam.), oxeye daisy ( Chrysanthemum leucanthemum L.), and hoary cress ( Cardaria draba [L.] Desv.) using chemical, mechanical, and cultural techniques. A total of 2027 acres were treated during 1998, whereas control efforts for 12 species occurred on 2596 acres during the previous 3-year period, 1995-1997. Strong and expanding partnerships with other federal, state, and local agencies and private companies contribute to management efforts within the park. Future program goals emphasize increases in base funding to ensure continued weed management efforts as well as expanding survey, monitoring, and reclamation efforts. Ultimately, a more rigorous assessment of program effectiveness is desired. 相似文献