Genome reshuffling of the copia element in an inbred line of Drosophila melanogaster

Mobile genetic elements are found in the genomes of many organisms, and because of their effects on genes and their ability to induce chromosomal rearrangements they are an important source of genetic variability. Transposition rates are usually found to be low, estimated at around 10(-3) per generation. Higher rates of transposition are observed, however, in crosses between certain strains of Drosophila melanogaster ('hybrid dysgenesis'), which can lead to a dramatic rearrangement of many mobile elements ('transposition bursts'). We have studied the chromosomal distribution of mdg-1 and copia mobile elements in 17 highly inbred lines of D. melanogaster, after 69 generations of sib-mating. Most lines show no changes, but one showed a complete reshuffling of the copia element. We conclude that the transpositions of the copia element in this line occurred rapidly in a few generations. This phenomenon, distinct from 'transposition bursts' in that only copia elements are involved, may account for the instability sometimes observed in inbred lines and may be important in creating genetic variability in highly homozygous populations.     

Learning and memory mutations impair acoustic priming of mating behaviour in Drosophila

The courtship song in Drosophila melanogaster has two components, a low-frequency hum and a train of pulses with a species-specific interpulse interval (IPI) of 30-40 ms(1,2). The IPIs oscillate rhythmically, with periods between 50 and 60 s in wild-type males(3). When females are stimulated with artificial songs in the presence of courting but silent (wingless) males, the 'pulse song' and its oscillation can enhance mating success(4?6). If separated males and females are first simultaneously primed with invariant 34-ms IPIs, their subsequent mating success is improved(7). However, exclusive prestimulation of females leads to faster mating only when the hum component of the song is applied, not constant 34-ms IPIs(5). We have re-examined these findings by testing whether prior exposure of females to a rhythmic pulse song speeds up subsequent mating performance. We report here that it does. Furthermore, learning and memory mutations(8), expressed in the females to whom songs are being played, either 'block' or attenuate the effectiveness of acoustical priming.     

Complete replacement of mitochondrial DNA in Drosophila

The introduction of foreign mitochondria or mitochondrial DNA into a cell is a useful technique for clarifying the molecular mechanisms responsible for the maintenance of mitochondria. Novel combinations of mitochondrial and nuclear genomes have been studied in mammalian cells in culture and in yeast. In Drosophila, we have recently constructed heteroplasmic flies possessing both endogenous mitochondrial DNA and foreign mitochondrial DNA by intra- and interspecific transplantation of germ plasm. During the maintenance of these heteroplasmic lines, flies of D. melanogaster are produced that no longer possess their own mitochondrial DNA but retain the foreign mitochondrial DNA from D. mauritiana. .These flies are fertile and the foreign mitochondrial DNA is stably maintained in their offspring. Here we report the complete replacement of endogenous mitochondrial DNA with that from another multicellular species. Molecular and genetic analysis of this replacement in Drosophila should provide new insight into the functional interaction between nuclear and organelle genomes.     

Adaptive evolution of non-coding DNA in Drosophila

A large fraction of eukaryotic genomes consists of DNA that is not translated into protein sequence, and little is known about its functional significance. Here I show that several classes of non-coding DNA in Drosophila are evolving considerably slower than synonymous sites, and yet show an excess of between-species divergence relative to polymorphism when compared with synonymous sites. The former is a hallmark of selective constraint, but the latter is a signature of adaptive evolution, resembling general patterns of protein evolution in Drosophila. I estimate that about 40-70% of nucleotides in intergenic regions, untranslated portions of mature mRNAs (UTRs) and most intronic DNA are evolutionarily constrained relative to synonymous sites. However, I also use an extension to the McDonald-Kreitman test to show that a substantial fraction of the nucleotide divergence in these regions was driven to fixation by positive selection (about 20% for most intronic and intergenic DNA, and 60% for UTRs). On the basis of these observations, I suggest that a large fraction of the non-translated genome is functionally important and subject to both purifying selection and adaptive evolution. These results imply that, although positive selection is clearly an important facet of protein evolution, adaptive changes to non-coding DNA might have been considerably more common in the evolution of D. melanogaster.     

Taq酶体外合成DNA时模板错位机制的探讨

利用Taq DNA聚合酶体外合成DNA过程中,当反应体系中缺少与模板链互补配对的dNTP底物时,产物合成并不会在底物缺失位点处终止,聚合反应继续进行.为研究此复制缺陷现象,设计一系列模板用于DNA体外酶促合成.除了已知的碱基错配机制,笔者发现存在另一种"模板错位"机制,即模板中与底物非Watson-Crick互补配对的碱基位点首先进行收缩滑动,形成模板bulge结构后再继续进行酶促合成反应.这项研究有助于提高DNA样品合成保真度以及继续深入探索体外DNA合成的详细机制.     

Genetic dissection of monoamine neurotransmitter synthesis in Drosophila

The biogenic monoamine neurotransmitters octopamine, dopamine and serotonin have been detected in nervous tissue from many insects. We report here that intact Drosophila melanogaster brains, when incubated with the radioactive amino acids tyrosine and tryptophan, synthesized and accumulated labelled monoamines. In two mutant strains monoamine synthesis was abnormal. The per o mutation abolishes the normal circadian rhythm. Brains from per o flies, when incubated in tritiated tyrosine, accumulated one-third as much labelled octopamine as did brains from wild-type flies, but had normal dopamine and serotonin synthesis. In contrast, dopa decarboxylase (Ddc) mutations decreased dopamine and serotonin synthesis but did not affect octopamine synthesis. These results suggest that there are two different aromatic amino acid decarboxylases in Drosophila brains, one that decarboxylates L-dopa and 5-hydroxytryptophan and another that decarboxylates tyrosine. Direct measurement of L-dopa, 5-hydroxytryptophan and tyrosine decarboxylase activities in the different strains confirmed this suggestion.     

粉末颗粒在混粉电火花加工中作用机理研究

混粉电火花加工在小脉冲能量下可稳定进行,良好的加工效果主要归因于工作液煤油中粉末颗粒.从粉末颗粒在放电间隙中引起的电场畸变入手,运用W agner模型,分析计算了粉末颗粒对放电间隙和工作液复合介电系数的影响,结果表明放电间隙和工作液的复合介电系数均有所增大,但放电间隙的增大程度更高,于是得出了混粉电火花加工放电过程稳定性提高的根本原因,即混粉电火花加工时的极间等效电容较常规电火花加工时大大减小,对加工过程的影响程度减弱.相关的实验结果与分析计算值相一致,证明了理论分析的正确性.     

超细颗粒声场流态化机理研究

在内径为56 mm的声场流化床中,以超细颗粒二氧化硅为实验物料,在声压水平为90～105 dB系统内考察了声波对超细颗粒流化行为和聚团尺寸的影响,并根据粘性颗粒聚团在流化床中的能量平衡分析,建立了能量平衡模型.结果表明,当声压级大于100 dB时,声波可以有效地消除节涌、抑制沟流、降低临界流化速度、减小聚团尺寸,显著地改善超细颗粒的流化质量.声场强度越大,颗粒聚团的直径越小.     

超细颗粒声场流态化机理研究

在内径为56mm的声场流化床中,以超细颗粒二氧化硅为实验物料,在声压水平为90～105dB系统内考察了声波对超细颗粒流化行为和聚团尺寸的影响,并根据粘性颗粒聚团在流化床中的能量平衡分析,建立了能量平衡模型。结果表明,当声压级大于100dB时,声波可以有效地消除节涌、抑制沟流、降低临界流化速度、减小聚团尺寸,显著地改善超细颗粒的流化质量。声场强度越大,颗粒聚团的直径越小。