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1.
《DNA Repair》2017
Double-strand breaks (DSBs) are among the most lethal DNA lesions, and a variety of pathways have evolved to manage their repair in a timely fashion. One such pathway is homologous recombination (HR), in which information from an undamaged donor site is used as a template for repair. Although many of the biochemical steps of HR are known, the physical movements of chromosomes that must underlie the pairing of homologous sequence during mitotic DSB repair have remained mysterious. Recently, several groups have begun to use a variety of genetic and cell biological tools to study this important question. These studies reveal that both damaged and undamaged loci increase the volume of the nuclear space that they explore after the formation of DSBs. This DSB-induced increase in chromosomal mobility is regulated by many of the same factors that are important during HR, such as ATR-dependent checkpoint activation and the recombinase Rad51, suggesting that this phenomenon may facilitate the search for homology. In this perspective, we review current research into the mobility of chromosomal loci during HR, as well as possible underlying mechanisms, and discuss the critical questions that remain to be answered. Although we focus primarily on recent studies in the budding yeast, Saccharomyces cerevisiae, examples of experiments performed in higher eukaryotes are also included, which reveal that increased mobility of damaged loci is a process conserved throughout evolution. 相似文献
2.
We compare the performances of local and global rules for smoothingparameter choice, in terms of asymptotic mean squared errorsof the resulting estimators. In some instances there is surprisinglylittle to choose between local and global approaches; our analysisidentifies contexts where the differences are small or large.This work motivates development of smoothing rules that forma half-way house between local and global smoothing.There, interpolation provides a basis for partial local smoothing.A key result shows that interpolation on even a coarse gridcan produce a very good approximation to full local smoothing.Our theoretical and numerical results lead us to suggest linearinterpolation of a bandwidth obtained by integral approximationson discrete intervals. 相似文献
3.
Elisa Villa Aleksander S. Alekseev James E. Barrick Darwin R. Boardman Alexandra V. Djenchuraeva Beate Fohrer Holger Forke Natalya V. Goreva Philip H. Heckel Tatiana N. Isakova Olga Kossovaya Lance L. Lambert María-Luisa Martínez-Chacn Carlos A. Mndez Tamara I. Nemyrovska Svetlana Remizova Elias Samankassou Luis C. Snchez de Posada Katsumi Ueno Greg Wahlman David M. Work 《Palaeoworld》2009,18(2-3):114-119
Studies carried out for more than 10 years by the Task Group to establish GSSPs at the base of the Moscovian–Kasimovian and Kasimovian–Gzhelian boundaries have resulted in the proposal that the level at which the conodont species Idiognathodus simulator (Ellison, 1941) first appears be selected to mark the base of the Gzhelian Stage. This expands this eastern European chronostratigraphic unit to a global scale.I. simulator (sensu Barrick et al., 2008) has been identified so far in Midcontinent and eastern North America, the Moscow and Donets basins and southern Urals of eastern Europe, and in south-central China. Correlation of this level based on this species and other conodont species can be reinforced in some areas by ammonoid and fusulinid data. 相似文献
4.
We investigated the relationship between eggsize variation and (a) egg hatching success, (b) chick survival to fledging and
recruitment, and (c) adult female survival, over 12 years in the lesser snow goose (Anser caerulescens caerulescens). By comparing the means and variances of egg size for successful and unsuccessful eggs, our aim was to assess the relative
fitness of eggs of different sizes and to determine the type of selection operating on egg size in this species. As both egg
size and reproductive success vary with age in the lesser snow goose we controlled for the effects of female age. Egg-size
variation is very marked in this population, varying by up to 52% for eggs hatching successfully. However, there was no relationship
between egg size and post-hatching survival of goslings to fledging or recruitment, either within or between broods, pooling
across years. Egg size varied significantly between successful and unsuccessful clutches in only 2 of 33 individual year comparisons.
First-laid eggs surviving to onset of incubation, and eggs hatching successfully, were on average larger than unsuccessful
eggs, but this was probably due to the confounding effects of female age-specific and sequence-specific egg survival. Variance
of egg size differed significantly between successful and unsuccessful eggs in only 3 of 24, and 0 of 21, individual year
comparisons for pre- and post-hatching survival respectively. We therefore found little evidence for a relationship between
egg-size variation and offspring fitness, or for strong directional, normalising or diversifying selection operating on egg
size, in the lesser snow goose. In addition, there was only weak support for the hypothesis that egg-size variation is maintained
by temporal variation in selection pressure (sensu Ankney and Bisset 1973). It is likely that egg-size variation represents the pleiotropic expression of alleles affecting
more general physiological or metabolic processes. While this does not rule out the existence of alleles with more direct
effects on egg size we suggest that their contribution to heritable egg size is small. 相似文献
5.
Differing effects of thermal stress on coral fertilization and early embryogenesis in four Indo Pacific species 总被引:1,自引:0,他引:1
Coral reefs are expected to be severely impacted by rising seawater temperatures associated with climate change. The fertilization
and early embryogenesis of four reef-building coral species representing three Indo-Pacific families were examined in a series
of laboratory experiments where temperatures were increased up to 5–6°C at ambient. High levels of fertilization and normal
embryogenesis were observed for Favites abdita, Favites chinensis and Mycedium elephantotus at temperatures to 32°C (+5°C) and embryos developed normally until the 5th cell cleavage. Acropora millepora was the only species to be affected by higher temperatures, exhibiting significantly reduced fertilization and a higher frequency
of embryonic abnormalities at 32°C (+4°C), and fertilization ceased altogether at 34°C (+6°C). Early cell cleavage rates increased
with temperature up to 32°C for all species. 相似文献
6.
Extensive economic growth, tourism activities and over-exploitation of resources have become the common causes of environmental degradation in Langkawi. The sudden development leap resulting from UNESCO's recognition of Langkawi Archipelago as a Global Geopark in 2007, leads to continuous conflicts between enhancing environmental protection and meeting tourism and development needs. Environmental sensitivity evaluation is a basis upon which the concept of environmentally sensitive areas (ESAs) can be practised in order to protect the environment, regulate development activities and promote sustainable land use planning. This study embarks on evaluating and classifying environmental sensitivity as well as comparing different ESA approaches applicable for land use planning in Langkawi. A GIS-based integrated evaluation model was performed on two assessment sets (Set A and Set B) using a standard grading system and weights determined with analytic hierarchy process (AHP) method. Of these sets, the former consists of selected indicators from the Malaysian integrated ESA instrument while the latter are derived from previous eco-environmental studies conducted in China. The projected final ESA maps of Langkawi indicate spatial distribution of four environmental sensitivity classes. More highly and moderately sensitive areas are observed in Set A, accounting for 339.15 km2 or 72.24% of the total land area compared to Set B with only 259.04 km2 or 55.18% respectively. The results also reveal large proportion of low sensitivity areas in Set A, covering areas of 117.42 km2 (25.01%). In contrast, more areas with non-sensitivity are widely distributed in Set B, occupying areas of 123.02 km2 (26.20%). Taking into consideration the natural and cultural characteristics of the islands, it is suggested that Set A is a better approach to portray current environmental concerns and to coordinate future land use planning as well as fits Langkawi's aspiration in becoming a sustainable, world-class Global Geopark. This study provides beneficial information and opportunity for reasonable rearrangement of zoning and development guidelines and strategies within sensitivity areas. It promotes effective utilization of the natural resources, minimizes negative tourism impacts and adequately highlights ecosystem functions to prosper local socio-economic growth. It also represents an early step for the design of universal ESA instruments to regulate local development activities and promote sustainable land use planning in vulnerable areas at global levels. 相似文献
7.
一个具暂时免疫且总人数可变的传染病动力学模型 总被引:10,自引:3,他引:7
建立了一个具常恢复率和接触率依赖于总人数的SIRS传染病动力学模型,讨论了系统平衡点的存在性和稳定性,对双线性传染率的特殊情形,给出了传染病平衡点的全局稳定性结论,推广和改进了已有的相应结果。 相似文献
8.
R. Pampanini 《Plant biosystems》2013,147(1):199-219
Abstract Bryophytes are excellent indicator organisms for monitoring environmental changes to which they could be more sensitive than vascular plants but our knowledge on their adaptation to alpine conditions is still very poor. Research programmes were set up to establish the ecological parameters for bryophyte distribution along the altitudinal gradient as well as for a better understanding of the population biology of alpine bryophytes. 相似文献
9.
Jenny Rooke 《Systems and synthetic biology》2013,7(3):67-72
Synthetic biology has the potential to contribute breakthrough innovations to the pursuit of new global health solutions. Wishing to harness the emerging tools of synthetic biology for the goals of global health, in 2011 the Bill & Melinda Gates Foundation put out a call for grant applications to “Apply Synthetic Biology to Global Health Challenges” under its “Grand Challenges Explorations” program. A highly diverse pool of over 700 applications was received. Proposed applications of synthetic biology to global health needs included interventions such as therapeutics, vaccines, and diagnostics, as well as strategies for biomanufacturing, and the design of tools and platforms that could further global health research. 相似文献
10.
Bryophyte biomass and diversity in tropical moist forests decrease dramatically from higher altitudes towards the lowlands. High respiratory carbon losses at high temperatures may partly explain this pattern, if montane species are unable to acclimatise their metabolic rates to lowland temperatures. We transplanted ten bryophyte species from two altitudes (1200 and 500 m a.s.l.) to lower (warmer) altitudes (500 m and sea level) in Panama. We studied short‐term temperature acclimation of CO2 exchange for 2.5 months, and survival and growth for 21 months following transplantation. Short‐term acclimation did not occur, and on a longer time scale mortality was highest and growth lowest in the transplanted samples. A few transplanted samples of most species, however, survived the whole experiment and finished with growth rates similar to controls. This recovery of growth rate suggests temperature acclimation, in spite of no measurable metabolic changes in smaller random samples. This acclimation even compensated for shorter periods of CO2 uptake due to more rapid drying. Nevertheless, these species are not abundant in lowland forests, perhaps due to dispersal or establishment limitation. The apparent heterogeneity of the acclimation potential within species may allow populations to adapt locally and avoid being forced uphill under climatic warming. 相似文献