Spontaneous excision of a large composite transposable element of Drosophila melanogaster

The TE1 family of transposable elements (TEs) of Drosophila consists of unusually large transposons, cytologically visible in larval polytene chromosomes as one or more bands. They are composite elements, as their termini consist of foldback (FB) sequences which are themselves transposable. The location of FB elements at the termini of transposable elements suggests that these sequences have a direct role in the genetic instability of TEs. To investigate the structural and phenotypic consequence of TE excision, we have cloned genomic DNA required for the expression of the no-ocelli (noc) gene of Drosophila; this gene has been mutated by the insertion of TE146, a member of the TE1 family carrying six polytene chromosome bands including functional copies of the white (w+) and roughest (rst+) genes. As reported here, our experiments indicate that the spontaneous excision of TE146, which results in the loss of the w+ and rst+ markers, can occur either as a single-step event or following a partial internal deletion. In either case, the end product is an imprecise excision in which a residual portion of the element, varying in size from 3 to 10 kilobases (kb), is left at the insertion site. These residual sequences share homology with the FB family. Furthermore, despite their imprecise nature, all these spontaneous excisions restore a wild-type noc+ phenotype.     

岷江上游花椒地/林地边界土壤水分分布及影响域

在岷江上游干旱河谷区选取典型的花椒地,林地边界,利用TDR仪测定干旱条件下和雨后0-15cm表土层水分体积分数,刻画沿样带梯度土壤水分分布以及不同时段土壤水分变化,同时用移动窗口法判定土壤水分的边界影响域。结果表明,在干旱河谷区土壤水分体积分数较低并沿样带存在明显的变化,从林地到边界到花椒地土壤水分体积分数基本呈“V”字型变化;而在林地和花椒地内部,水分体积分数呈“W”型波动。干旱时土壤水分体积分数日间变化不大,而雨后水分体积分数逐日递减。土壤水分的影响域在雨后可达14m,干旱时为8m。     

Cloning of human telomeres by complementation in yeast

Telomeres confer stability on chromosomes by protecting them from degradation and recombination and by allowing complete replication of the end. They are genetically important as they define the ends of the linkage map. Telomeres of lower eukaryotes contain short repeats consisting of a G-rich and a C-rich strand, the G-rich strand running 5'-3' towards the telomere and extending at the end. Telomeres of human chromosomes share characteristics with those of lower eukaryotes including sequence similarity as detected by cross-hybridization. Telomeric repeats from many organisms can provide telomere function in yeast. Here we describe a modified yeast artificial chromosome (YAC) vector with only one telomere which we used to clone human telomeres by complementation in yeast. YACs containing human telomeres were identified by hydridization to an oligonucleotide of the trypanosome telomeric repeat. A subcloned human fragment from one such YAC is immediately subtelomeric on at least one human chromosome.     

A dynamic role for the mushroom bodies in promoting sleep in Drosophila

The fruitfly, Drosophila melanogaster, exhibits many of the cardinal features of sleep, yet little is known about the neural circuits governing its sleep. Here we have performed a screen of GAL4 lines expressing a temperature-sensitive synaptic blocker shibire(ts1) (ref. 2) in a range of discrete neural circuits, and assayed the amount of sleep at different temperatures. We identified three short-sleep lines at the restrictive temperature with shared expression in the mushroom bodies, a neural locus central to learning and memory. Chemical ablation of the mushroom bodies also resulted in reduced sleep. These studies highlight a central role for the mushroom bodies in sleep regulation.     

Warming experiments underpredict plant phenological responses to climate change

Warming experiments are increasingly relied on to estimate plant responses to global climate change. For experiments to provide meaningful predictions of future responses, they should reflect the empirical record of responses to temperature variability and recent warming, including advances in the timing of flowering and leafing. We compared phenology (the timing of recurring life history events) in observational studies and warming experiments spanning four continents and 1,634 plant species using a common measure of temperature sensitivity (change in days per degree Celsius). We show that warming experiments underpredict advances in the timing of flowering and leafing by 8.5-fold and 4.0-fold, respectively, compared with long-term observations. For species that were common to both study types, the experimental results did not match the observational data in sign or magnitude. The observational data also showed that species that flower earliest in the spring have the highest temperature sensitivities, but this trend was not reflected in the experimental data. These significant mismatches seem to be unrelated to the study length or to the degree of manipulated warming in experiments. The discrepancy between experiments and observations, however, could arise from complex interactions among multiple drivers in the observational data, or it could arise from remediable artefacts in the experiments that result in lower irradiance and drier soils, thus dampening the phenological responses to manipulated warming. Our results introduce uncertainty into ecosystem models that are informed solely by experiments and suggest that responses to climate change that are predicted using such models should be re-evaluated.