Targeted disruption of the gene encoding DNA ligase IV leads to lethality in embryonic mice

DNA ligase IV is the most recently identified member of a family of enzymes joining DNA strand breaks in mammalian cell nuclei [1] and [2]. The enzyme occurs in a complex with the XRCC4 gene product [3], an interaction mediated via its unique carboxyl terminus [4] and [5]. Cells lacking XRCC4 are hypersensitive to ionising radiation and defective in V(D)J recombination [3] and [6], implicating DNA ligase IV in the pathway of nonhomologous end-joining (NHEJ) of DNA double-strand breaks mediated by XRCC4, the Ku70/80 heterodimer and the catalytic subunit of DNA-dependent protein kinase (DNA-PKcs) in mammalian cells (reviewed in [7]). The phenotype of a null mutant of the Saccharomyces cerevisiae DNA ligase IV homologue indicates that the enzyme is non-essential and functions in yeast NHEJ [8], [9] and [10]. Unlike other mammalian DNA ligases for which cDNAs have been characterised, DNA ligase IV is encoded by an intronless gene (LIG4). Here, we show that targeted disruption of LIG4 in the mouse leads to lethality associated with extensive apoptotic cell death in the embryonic central nervous system. Thus, unlike Ku70/80 and DNA-PKcs [11], [12], [13] and [14], DNA ligase IV has an essential function in early mammalian development.     

Factors affecting calculation of nutritional induces for foliage-fed insects: an experimental approach

To determine how nutritional indices for insects fed leaves are affected by the experimental conditions and the physiology of the plant material, we used larvae of the buckmoth, Hemileuca lucina Hy. Ed. (Saturniidae) and their hostplant Spiraea latifolia Ait. Bork (Rosaceae). Under experimental conditions identical to those used to determine larval nutritional indices, we found that the age of leaves (new versus mature) significantly affected their metabolism and water loss, but simulated herbivory did not directly affect leaf metabolism. Over a 6-day test, nitrogen concentration showed an initial increase followed by a gradual decline, and was higher in new leaves compared to mature leaves. New leaves increased in protein concentration and then gradually returned to the initial level, whereas mature leaves changed little over the 6-day test. These changes in percent nitrogen and protein may largely reflect the disproportional changes in non-nitrogenous materials. Solitary and grouped larvae had similar growth rates on new leaves, but they differed on mature leaves. Deliberate manipulation of larvae during the course of an experiment significantly reduced relative growth rates by increasing duration of the stadium rather than by decreasing biomass gained. Two methods of estimating larval gut contents at mid-stadium were compared: weight of frass produced and weight of digestive tract and contents. After the end of the 4-day test period used to determine nutritional indices, the digestive tracts with food accounted for 10.8% of the larval dry weight. Larval frass produced in 24 h after the end of the test period comprised 9.3% of the larval dry weight. Correction factors for plant metabolism changed nutritional indices by 1 to 8%, while those for larval gut contents altered indices by 2 to 15%.     

Quantitative trait loci for lodging resistance in a segregating wheat×spelt population

 Lodging can strongly affect both the grain yield and the quality of wheat. Lodging represents a quantitative trait and is difficult to assess on a phenotypic basis. Marker-assisted selection (MAS) could therefore become an important tool in breeding for lodging resistance. In this study, we mapped and characterised quantitative trait loci (QTLs) for lodging resistance, as well as morphological traits correlated with lodging, in a segregating population of 226 recombinant inbred lines derived from the cross of the lodging-resistant wheat variety Forno with the susceptible spelt variety Oberkulmer. Lodging, plant height, leaf width, leaf-growth habit, culm stiffness, culm swinging, culm thickness, days to ear emergence and days to flowering were assessed in field trials at two locations in 1996 and at one location in 1997. Additionally, at one location weight and length parameters were also assessed. Plant height and culm stiffness explained 77% of the phenotypic variance of lodging in a multiple regression model over all three environments. QTL analysis of lodging and morphological parameters was based on a genetic map containing 230 loci with 23 linkage groups (2469 cM). With the method of composite interval mapping nine QTLs for lodging resistance were detected, explaining 63% of the phenotypic variance in a simultaneous fit. Seven of these QTLs coincided with QTLs for morphological traits, reflecting the correlations between these traits and lodging. In our population the most efficient way to improve lodging resistance would be by a combination of indirect selection on plant height and culm stiffness together with MAS on the two QTLs for lodging resistance which did not coincide with QTLs for morphological traits. Received: 3 August 1998 / Accepted: 28 November 1998     

1981～2000年陕西省植被净初级生产力时空变化

为阐明陕西省植被净初级生产力(NPP)变化的整体状况,应用以遥感观测数据驱动的GLO-PEM模式模拟估计的NPP数据,对陕西省1981~2000年间的地表植被净初级生产力的空间分布及时间序列变化进行了综合分析.研究结果表明:(1)20年来,陕西省年NPP变化范围为687~858 g/(m2?a),平均值为749 g/(m2?a);(2)陕西省年平均NPP在波动中缓慢上升,NPP年增长幅度为3.248 2 g/(m2?a);(3)陕西省年平均NPP分布总体呈现从南到北递减的趋势,长城沿线风沙区NPP在200~400 g/(m2?a)之间,是陕西省NPP最低的地区;关中中东部NPP较高,大部在800 g/(m2?a)以上,NPP在1 200 g/(m2?a)以上的面积约占1/3,是全省NPP的高值区;(4)陕西省NPP基本不变(NPP变化百分率在-10%~10%之间)的面积占54.7%,NPP变化百分率增加10%以上的面积占40.5%,NPP变化百分率降低10%以下的面积仅占4.8%;(5)占陕西省总面积的77.3%的区域NPP变化不显著(P>0.05),NPP增加极显著(P<0.01)的区域占8.3%,增加显著(P<0.05)的区域占13.8%,NPP降低显著(P<0.05)和降低极显著(P<0.01)占0.7%.     

Effect of group size on parasitism in a natural population of the Baltimore checkerspot Euphydryas phaeton

Summary The effect of group size of early instars on parasitism of Euphydryas phaeton (Nymphalidae) was examined. Different numbers of larvae were stocked per web to determine the effect of group size on parasitism. Larval aggregations of moderate size (the size occurring naturally) had the least parasitism. Larger larval groups had a disproportionately high rate of parasitism. The major larval parasitoids located vulnerable larvae within webs, instead of attacking larvae available on the outside of webs. Parasitism rates were similar for larvae of damaged and undamaged webs, a consequence of the behavior and location of larvae in the webs. Lower limit to group size was a function of facilitation of larval numbers in reaching the first feeding site, the top of the host plant. Feeding facilitation by larval aggregations was not a factor in larval survival or growth.     

Novel zinc-based fixative for high quality DNA, RNA and protein analysis

We have developed a reliable, cost-effective and non-toxic fixative to meet the needs of contemporary molecular pathobiology research, particularly in respect of RNA and DNA integrity. The effects of 25 different fixative recipes on the fixed quality of tissues from C57BL/6 mice were investigated. Results from IHC, PCR, RT–PCR, RNA Agilent Bioanalyser and Real-Time PCR showed that a novel zinc-based fixative (Z7) containing zinc trifluoroacetate, zinc chloride and calcium acetate was significantly better than the standard zinc-based fixative (Z2) and neutral buffered formalin (NBF) for DNA, RNA and protein preservation. DNA sequences up to 2.4kb in length and RNA fragments up to 361bp in length were successfully amplified from Z7 fixed tissues, as demonstrated by PCR, RT–PCR and Real-Time PCR. Total protein analysis was achieved using 2-D gel electrophoresis. In addition, nucleic acids and proteins were very stable over a 6–14-month period. This improved, non-toxic and economical tissue fixative could be applied for routine use in pathology laboratories to permit subsequent genomic/proteomic studies.     

The Genome Sequence of a Type ST239 Methicillin-Resistant Staphylococcus aureus Isolate from a Malaysian Hospital

We report the genome sequence of a healthcare-associated MRSA type ST239 clone isolated from a patient with septicemia in Malaysia. This clone typifies the characteristics of ST239 lineage, including resistance to multiple antibiotics and antiseptics.     

Can the growth–differentiation balance hypothesis be tested rigorously?

The growth–differentiation balance (GDB) hypothesis (as elaborated by Herms and Mattson) provides a framework for examining the impact of a resource gradient on the constant tradeoff between growth and differentiation in cells and tissues of plants, in particular with the consequences for plant defense. The GDB hypothesis, which is the most mature of the hypotheses of plant defensive levels, has not been tested directly. Examination of the requirements for a rigorous test indicates that, like the other hypotheses of plant defense, it cannot be tested directly. Furthermore, rigorously testing the primary derivative hypotheses, while possible, would require considerable methodological effort, on a scale not previously attempted for tests of plant defense, which is likely to discourage researchers, and understandably so, even though the GDB hypothesis warrants methodical investigation due to its potential explanatory power. Although farther removed from the abstract model (i.e. the GDB framework), other derivative hypotheses can be tested, but doing so will require thoughtful consideration and acknowledgement of that. Study of a few carefully chosen systems (i.e. plant species) may provide considerable insight and potentially useful refinement of the GDB framework.