Quantitation and Analysis of the Formation of HO-Endonuclease Stimulated Chromosomal Translocations by Single-Strand Annealing in Saccharomyces cerevisiae

Genetic variation is frequently mediated by genomic rearrangements that arise through interaction between dispersed repetitive elements present in every eukaryotic genome. This process is an important mechanism for generating diversity between and within organisms^1-3. The human genome consists of approximately 40% repetitive sequence of retrotransposon origin, including a variety of LINEs and SINEs⁴. Exchange events between these repetitive elements can lead to genome rearrangements, including translocations, that can disrupt gene dosage and expression that can result in autoimmune and cardiovascular diseases⁵, as well as cancer in humans^6-9.Exchange between repetitive elements occurs in a variety of ways. Exchange between sequences that share perfect (or near-perfect) homology occurs by a process called homologous recombination (HR). By contrast, non-homologous end joining (NHEJ) uses little-or-no sequence homology for exchange^10,11. The primary purpose of HR, in mitotic cells, is to repair double-strand breaks (DSBs) generated endogenously by aberrant DNA replication and oxidative lesions, or by exposure to ionizing radiation (IR), and other exogenous DNA damaging agents. In the assay described here, DSBs are simultaneously created bordering recombination substrates at two different chromosomal loci in diploid cells by a galactose-inducible HO-endonuclease (Figure 1). The repair of the broken chromosomes generates chromosomal translocations by single strand annealing (SSA), a process where homologous sequences adjacent to the chromosome ends are covalently joined subsequent to annealing. One of the substrates, his3-Δ3'', contains a 3'' truncated HIS3 allele and is located on one copy of chromosome XV at the native HIS3 locus. The second substrate, his3-Δ5'', is located at the LEU2 locus on one copy of chromosome III, and contains a 5'' truncated HIS3 allele. Both substrates are flanked by a HO endonuclease recognition site that can be targeted for incision by HO-endonuclease. HO endonuclease recognition sites native to the MAT locus, on both copies of chromosome III, have been deleted in all strains. This prevents interaction between the recombination substrates and other broken chromosome ends from interfering in the assay. The KAN-MX-marked galactose-inducible HO endonuclease expression cassette is inserted at the TRP1 locus on chromosome IV. The substrates share 311 bp or 60 bp of the HIS3 coding sequence that can be used by the HR machinery for repair by SSA. Cells that use these substrates to repair broken chromosomes by HR form an intact HIS3 allele and a tXV::III chromosomal translocation that can be selected for by the ability to grow on medium lacking histidine (Figure 2A). Translocation frequency by HR is calculated by dividing the number of histidine prototrophic colonies that arise on selective medium by the total number of viable cells that arise after plating appropriate dilutions onto non-selective medium (Figure 2B). A variety of DNA repair mutants have been used to study the genetic control of translocation formation by SSA using this system^12-14.     

Myrmecochorous dispersal distances: a world survey

Abstract. Myrmecochorous dispersal distances are reviewed; the seed dispersal curve generated by ants shows a characteristic peak at short distances and a long tail, a shape suited to small densities of safe sites. Mean global distance is of 0.96 m (n= 2524) with a range of 0.01–77 m. Data have been broken down by geography (Northern hemisphere v. Southern hemisphere), taxonomy (ant subfamilies) and ecology (vegetation: sclerophyllous v. mesophyllous). Although a statistical difference exists between dispersal curves from the Northern hemisphere and the Southern hemisphere, this may be an artefact of lack of data from mesophyllous myrmecochores from this hemisphere. The four ant subfamilies do show also numerical differences but could not be subjected to statistical analysis. A difference between the shape of dispersal curve for sclerophyllous myrmecochores and mesophyllous myrmecochores has also been detected. We hypothesize that this difference is related to the myrmecological communities from both types of vegetation: dispersing ants from sclerophyllous vegetation would have smaller nest densities and/or bigger foraging areas than dispersing ants from mesic environments.     

Temperate forests of the southern hemisphere

The much higher proportion of sea to land in the southern hemisphere creates conditions favouring temperate rain forest on west-facing coasts, so that forests dominated by Nothofagus spp. and southern conifers in Araucariaceae and Podocarpaceae have survived since Cretaceous times. By contrast only Australia preserves to any significant extent forests of a xeromorphic character in drier areas. During the progressive desiccation of the Tertiary era, the prevalent nutrient deficiency in Australian soils led to the evolution of xeromorphic forests of a pronouncedly sclerophyll type in which many elements were inherently fire-resistant. Such forests were enabled to withstand the intensification of burning following the arrival of early man, with selection for the more highly fire-resistant elements such as Eucalyptus which became widely dominant. In other land areas of the southern hemisphere fire has largely destroyed the drier forests.     

Landscape Transformations and loss of Atlantic Forests: challenges for conservation

Regions of intense fragmentation and landscape transformation can indicate patterns of conversion of forest areas in space and time, challenging the resilience of ecosystems and driving the degradation of natural resources. In this study, we analyzed the dynamics of use, loss, and gain of Atlantic forests in the southern region of Bahia State in the last thirty-four years (1985–2019) based on pre and post-implementation of forest production policies. The area has ecological, historical, and cultural importance, and is the most conserved portion of the Atlantic Forest in northeastern Brazil. From the remote sensing products of the MapBiomas Project and spatial analyses of land use and forests, we evaluated a conflicted region that has 751 km of coastline and seventy municipalities. Our results indicate a degraded landscape, with 59% of the territory occupied by anthropogenic activities and intense fragmentation. The planting of eucalyptus forests and pasture stood out as landscape modifiers. The results show a loss of 328,595 ha of Atlantic Forest in the period under study, with a large part of this area being replaced by planted forests of Eucalyptus sp derivated the policies economics of the sector. It is urgent to consider the recovery of the Atlantic domain, prioritizing the capacity of ecosystems, especially in the Decade of Restoration.     

从墓砖上的手掌印纹看两广东汉至南朝陶工的体质特征

墓砖表面的手掌印纹是陶工在制砖过程中有意将手掌纹印于砖体表面而形成的一种印记,是一种特殊的文化现象。现代法医学、指纹学和痕检学研究表明,手部形态与人的基本体质信息密切相关。本文通过运用上述学科业已成熟的研究方法,对两广地区出土东汉至南朝的手掌印纹砖进行收集、观察和测量,在此基础上,获得了东汉至南朝两广地区陶工群体丰富的体质人类学数据,而后对手印纹行为主体的性别、年龄、利手、身高、体质量和体型特征等六个方面进行了分析,推断陶工群体是以青壮年男性为主的结构,有少量未成年人和女性,大部分陶工与现代两广人差异不大,身高和体质量均为中等,体态敦实。该研究为了解这一时期岭南地区陶工群体的组织结构和生产状况提供了新的视角。     

青藏高原杨属化石概述

杨属是北半球温带森林生态系统中一个重要的乔木属。文中概述了青藏高原古近纪和新近纪的杨属化石记录,并根据最新的地层学和年代学数据,对化石的时代进行厘定。化石记录显示杨属在青藏高原最早出现于始新世最晚期。在渐新世和中新世杨属在青藏高原的南部和北部都有较多的化石,但在高原中部尚未见记录。青藏高原具有杨属的化石植物群大多数都是温带落叶阔叶的河岸植被,进一步证实杨属在其演化历史早期就偏好温带近河岸的环境。青藏高原北部的早渐新世植物群中杨属多样性较高,并占据显著优势,表明这一地区在杨属早期分化中具有重要作用。     

Climate and density influence annual survival and movement in a migratory songbird

Assessing the drivers of survival across the annual cycle is important for understanding when and how population limitation occurs in migratory animals. Density‐dependent population regulation can occur during breeding and nonbreeding periods, and large‐scale climate cycles can also affect survival throughout the annual cycle via their effects on local weather and vegetation productivity. Most studies of survival use mark–recapture techniques to estimate apparent survival, but true survival rates remain obscured due to unknown rates of permanent emigration. This is especially problematic when assessing annual survival of migratory birds, whose movement between breeding attempts, or breeding dispersal, can be substantial. We used a multistate approach to examine drivers of annual survival and one component of breeding dispersal (habitat‐specific movements) in a population of American redstarts (Setophaga ruticilla) over 11 years in two adjacent habitat types. Annual survival displayed a curvilinear relation to the Southern Oscillation Index, with lower survival during La Niña and El Niño conditions. Although redstart density had no impact on survival, habitat‐specific density influenced local movements between habitat types, with redstarts being less likely to disperse from their previous year's breeding habitat as density within that habitat increased. This finding was strongest in males and may be explained by conspecific attraction influencing settlement decisions. Survival was lowest in young males, but movement was highest in this group, indicating that apparent survival rates were likely biased low due to permanent emigration. Our findings demonstrate the utility of examining breeding dispersal in mark–recapture studies and complement recent work using spatially explicit models of dispersal probability to obtain greater accuracy in survival estimates.     

抗南方水稻黑条矮缩病水稻光温敏核不育系的筛选和鉴定

对东乡野生稻(Oryza rufipogon Griff.)3个生态群落株系及协青早B//协青早B/东乡野生稻的BC1F6株系进行了南方水稻黑条矮缩病抗性鉴定,筛选出抗性较好的种质资源。利用筛选到的协青早B//协青早B/东乡野生稻抗性株系,与光温敏核不育系C47S杂交转育,鉴定筛选到6份抗性较好的光温敏核不育系,为选育抗南方水稻黑条矮缩病的两系杂交稻组合奠定了材料基础;同时研究发现,来源于东乡野生稻的对南方水稻黑条矮缩病的抗性可能由数量性状基因控制。