Patterns of Microsatellite Variability in the Drosophila Melanogaster Complex

Forty-seven microsatellite loci were amplified in Drosophila melanogaster, Drosophila simulans, Drosophila mauritiana and Drosophila sechellia. The two cosmopolitan species D. melanogaster and D. simulans were found to be the most variable ones, followed by D. mauritiana and D. sechellia. A model based clustering algorithm was applied to the population samples of D. melanogaster, D. simulans and D. sechellia. No evidence for population substructure was detected within species--most likely due to insufficient power. A Markov chain Monte Carlo method developed for demographic inference based on microsatellites provided unambiguous evidence for population contraction in D. melanogaster, D. simulans and D. sechellia, despite that the D. melanogaster and D. simulans population samples were of non-African origin and represented recently expanded populations.     

果蝇在肿瘤学研究中的优势及应用前景

果蝇作为研究人类疾病的模式生物, 与哺乳动物不仅在基本的生物学、生理学和神经系统机能等方面比较相似, 而且果蝇有其作为模式生物的独特优势。近年来的研究表明, 果蝇和人类在肿瘤发生信号通路等方面的保守性很高, 而且果蝇具有很强的遗传学可操作性, 是肿瘤学研究有效的模型之一, 可用于研究人类肿瘤发生、发展、转移等分子机制。文章综述了果蝇在肿瘤学研究中的优势、已建立的用于研究特定癌症的果蝇模型, 并对其在未来肿瘤学的研究方向进行展望, 以期为国内肿瘤学研究和抗肿瘤药物的研发提供参考。     

Promoter analysis of the Drosophila melanogaster gene encoding the pterin 4alpha-carbinolamine dehydratase.

Pterin-4alpha-carbinolamine dehydratase (PCD) is a key enzyme in the regeneration pathway of tetrahydrobiopterin. Previously, we isolated and reported the Drosophila melanogaster gene encoding PCD. In the present study, we isolated and characterized the Drosophila virilis gene encoding PCD. The Drosophila virilis PCD gene has two introns and an open reading frame to encode a protein of 101 amino acids. The amino acid sequence of Drosophila virilis PCD shows a 83% homology to that of the Drosophila melanogaster PCD protein. From the alignment of the nucleotide sequence in the 5'-flanking region of the Drosophila melanogaster and Drosophila virilis PCD genes, we found four conserved sequences. Using a transient transfection assay, we showed that one of the conserved sequences (-127 to approximately -115) is critical for expression, also the minimal promoter region between -127 and +51 is necessary for the efficient expression of Drosophila melanogaster PCD.     

Comparative and functional studies of Drosophila species invasion by the gypsy endogenous retrovirus.

Gypsy is an endogenous retrovirus of Drosophila melanogaster. Phylogenetic studies suggest that occasional horizontal transfer events of gypsy occur between Drosophila species. gypsy possesses infective properties associated with the products of the envelope gene that might be at the origin of these interspecies transfers. We report here the existence of DNA sequences putatively encoding full-length Env proteins in the genomes of Drosophila species other than D. melanogaster, suggesting that potentially infective gypsy copies able to spread between sexually isolated species can occur. The ability of gypsy to invade the genome of a new species is conditioned by its capacity to be expressed in the naive genome. The genetic basis for the regulation of gypsy activity in D. melanogaster is now well known, and it has been assigned to an X-linked gene called flamenco. We established an experimental simulation of the invasion of the D. melanogaster genome by gypsy elements derived from other Drosophila species, which demonstrates that these non- D. melanogaster gypsy elements escape the repression exerted by the D. melanogaster flamenco gene.     

生活中潜在诱变剂对果蝇存活率及遗传变异的影响

用紫外线、抗氧化剂、化妆品等多种生活中潜在的诱变剂处理野生型黑腹果蝇,观察果蝇的存活率及性状遗传变异情况,进而分析这些诱变剂对于果蝇的影响。实验结果表明,随紫外线照射时间的增加,果蝇生活力降低,子代果蝇突变率增加;随培养基中抗氧化剂浓度的增加,果蝇突变率与死亡率均呈上升趋势;不同化妆品也对果蝇造成了明显伤害,造成亲代个体死亡,后代出现突变型果蝇。     

Ecological and Genetic Interactions in Drosophila–parasitoids Communities: A Case Study with D. Melanogaster, D. Simulans and their Common Leptopilina Parasitoids in Southe-astern France

Drosophila species are attacked by a number of parasitoid wasps, which constitute an important factor of population regulation. Since Drosophila melanogaster and Drosophila simulans share common parasitoid species, their ecology and evolution can hardly be understood without considering parasitoids. After a short review of data available on Drosophila-parasitoid interactions involving D. melanogaster and D. simulans as hosts, we report field and laboratory experiments investigating the ecological role of Leptopilina parasitoids in Drosophila communities of southern France. Seasonal survey of species abundance shows that strong interspecific interactions occur at both tropic levels. D. simulans progressively replaces D. melanogaster in southern areas suggesting competitive displacement. Parasitoids are responsible for very high Drosophila mortality (up to 90% in some fruits). Field data emphasize the importance of selective pressure that parasitoids exert on Drosophila communities. The two Leptopilina parasites (L. heterotoma and L boulardi) have different local abundances, which vary in time, and they also compete for hosts. We show that parasitoids can mediate the coexistence of D. melanogaster and D. simulans in the laboratory, and thus may contribute to their puzzling coexistence in the field. Conversely, hosts exert selective pressures on parasitoids, and development on either D. melanogaster or D. simulans strongly affects fitness of adult wasps in a temperature-dependent fashion. Local variation in host species abundance and diversity could thus account for the genetic differentiation we observed in one parasitoid species. Despite laboratory studies cannot fully explain complex field situations, it is clear that the ecology and evolution of Drosophila populations and communities, especially D. melanogaster and D. simulans, are strongly constrained by parasitoids, which should receive more attention.     

Microfluidic tools for developmental studies of small model organisms –nematodes,fruit flies,and zebrafish

Studying the genetics of development with small model organisms such as the zebrafish (Danio Rerio), the fruit fly (Drosophila melanogaster), and the soil-dwelling nematode (Caenorhabditis elegans), provide unique opportunities for understanding related processes and diseases in humans. These model organisms also have potential for use in drug discovery and toxicity-screening applications. There have been sweeping developments in microfabrication and microfluidic technologies for manipulating and imaging small objects, including small model organisms, which allow high-throughput quantitative biological studies. Here, we review recent progress in microfluidic tools able to manipulate small organisms and project future directions and applications of these techniques and technologies.     

P transposable element in Drosophila melanogaster: horizontal transfer]

The P transposable element family in Drosophila melanogaster is responsible for the syndrome of hybrid dysgenesis which includes chromosomal rearrangements, male recombination, high mutability and temperature sensitive agametic sterility (called gonadal dysgenesis sterility). P element activity is controlled by a complex regulation system, encoded by the elements themselves, which keeps their transposition rate low within the strain bearing P elements and limits copy number by genome. A second regulatory mechanism, which acts on the level of RNA processing, prevents P mobility to somatic cells. The oldest available strains, representing most major geographical regions of the world, exhibited no detectable hybridization to the P-element. In contrast, all recently collected natural populations that were tested carried P-element sequences. The available evidence is consistent with the hypothesis of a worldwide P-element invasion of D. melanogaster during the past 30 years. Timing and direction of the invasion are discussed. The lack of P-element in older strains of Drosophila melanogaster as well as in the species must closely related to Drosophila melanogaster, suggests that P entered the Drosophila melanogaster genome recently, probably by horizontal transfer from an other species. The analysis of P-element elsewhere in the genus Drosophila reveals that several more distantly related species carried transposable elements with sequences quite similar to P. The species with the best-matching P-element is D. willistoni. A P-element from this species was found to match all but one of the 2907 nucleotides of the Drosophila melanogaster P-element. The phylogenic distributions and the likely horizontal transfers of the two other Drosophila transposable elements are discussed.     

An intron loss of Dfak gene in species of the Drosophila melanogaster subgroup and phylogenetic analysis

Drosophila focal adhesion kinase (Dfak) gene is a single-copy nuclear gene. Previous study revealed that Drosophila melanogaster and Drosophila simulans had lost an intron precisely within the tyrosine kinase (TyK) domain of this gene. However, this did not happen in several other Drosophila species, including Drosophila elegans, Drosophila ficusphila, Drosophila biarmipes, Drosophila jambulina, Drosophila prostipennis, Drosophila takahashii, and Drosophila pseudoobscura. In the current study, homologous sequences of Drosophila sechellia, Drosophila mauritiana, Drosophila yakuba, Drosophila teissieri, Drosophila santomea, and Drosophila erecta were amplified by polymerase chain reaction, and further sequencing analysis indicated that these species were missing a TyK domain intron, indicating they were closely related. The relationship of the D. melanogaster species group was reconstructed using TyK domain nucleotide sequences. The resulting phylogenetic tree revealed that these 8 species were the most related species in the melanogaster group. These results strongly support previously proposed classifications based on morphological and molecular data.     

Isolation, characterization, and localization of beta-tubulin genomic clones of three Drosophila montium subgroup species.

Genomic libraries were constructed from three Drosophila species, namely Drosophila auraria, Drosophila serrata, and Drosophila kikkawai, belonging to the Drosophila montium subgroup of the Drosophila melanogaster species group. Clones containing beta-tubulin specific sequences were isolated, characterized by restriction endonuclease digestions and Southern hybridizations, and mapped by in situ hybridization on the polytene chromosomes of the species studied. The distribution of the beta-tubulin loci was found to be similar in D. montium species and D. melanogaster.     

The spontaneous mutation rate in Drosophila simulans

The purpose of this investigation was to determine whether there exists a correlation in Drosophila between the spontaneous mutation rate and the amount of dispersed middle repetitive (mobile) DNA sequences. The amount of these sequences is 7 times less in Drosophila simulans as compared to Drosophila melanogaster. Therefore, if a correlation exists, the spontaneous mutation rate in Drosophila simulans should be 7 times lower than that in Drosophila melanogaster. We isolated an X-chromosome inversion after X-irradiation of wild-type Drosophila simulans males, that reduced crossing-over between white and forked, two X-linked visible markers, to less than 1%. This inversion was subsequently used to determine the sex-linked recessive lethal mutation rate in Drosophila simulans males of a laboratory strain marked with white. The frequency of these lethal mutations found is not different from that observed in Drosophila melanogaster males of laboratory strains.     

HeT-A_pi1, a piRNA target sequence in the Drosophila telomeric retrotransposon HeT-A, is extremely conserved across copies and species

The maintenance of the telomeres in Drosophila species depends on the transposition of the non-LTR retrotransposons HeT-A, TAHRE and TART. HeT-A and TART elements have been found in all studied species of Drosophila suggesting that their function has been maintained for more than 60 million years. Of the three elements, HeT-A is by far the main component of D. melanogaster telomeres and, unexpectedly for an element with an essential role in telomere elongation, the conservation of the nucleotide sequence of HeT-A is very low. In order to better understand the function of this telomeric retrotransposon, we studied the degree of conservation along HeT-A copies. We identified a small sequence within the 3' UTR of the element that is extremely conserved among copies of the element both, within D. melanogaster and related species from the melanogaster group. The sequence corresponds to a piRNA target in D. melanogaster that we named HeT-A_pi1. Comparison with piRNA target sequences from other Drosophila retrotransposons showed that HeT-A_pi1 is the piRNA target in the Drosophila genome with the highest degree of conservation among species from the melanogaster group. The high conservation of this piRNA target in contrast with the surrounding sequence, suggests an important function of the HeT-A_pi1 sequence in the co-evolution of the HeT-A retrotransposon and the Drosophila genome.     

Components Acting in Localization of Bicoid mRNA Are Conserved among Drosophila Species

Substantial insights into basic strategies for embryonic body patterning have been obtained from genetic analyses of Drosophila melanogaster. This knowledge has been used in evolutionary comparisons to ask if genes and functions are conserved. To begin to ask how highly conserved are the mechanisms of mRNA localization, a process crucial to Drosophila body patterning, we have focused on the localization of bcd mRNA to the anterior pole of the embryo. Here we consider two components involved in that process: the exuperantia (exu) gene, required for an early step in localization; and the cis-acting signal that directs bcd mRNA localization. First, we use the cloned D. melanogaster exu gene to identify the exu genes from Drosophila virilis and Drosophila pseudoobscura and to isolate them for comparisons at the structural and functional levels. Surprisingly, D. pseudoobscura has two closely related exu genes, while D. melanogaster and D. virilis have only one each. When expressed in D. melanogaster ovaries, the D. virilis exu gene and one of the D. pseudoobscura exu genes can substitute for the endogenous exu gene in supporting localization of bcd mRNA, demonstrating that function is conserved. Second, we reevaluate the ability of the D. pseudoobscura bcd mRNA localization signal to function in D. melanogaster. In contrast to a previous report, we find that function is retained. Thus, among these Drosophila species there is substantial conservation of components acting in mRNA localization, and presumably the mechanisms underlying this process.     

Hsp70 duplication in the Drosophila melanogaster species group: how and when did two become five?

To determine how the modern copy number (5) of hsp70 genes in Drosophila melanogaster evolved, we localized the duplication events that created the genes in the phylogeny of the melanogaster group, examined D. melanogaster genomic sequence to investigate the mechanisms of duplication, and analyzed the hsp70 gene sequences of Drosophila orena and Drosophila mauritiana. The initial two-to-four hsp70 duplication occurred 10--15 MYA, according to fixed in situ hybridization to polytene chromosomes, before the origin and divergence of the melanogaster and five other species subgroups of the melanogaster group. Analysis of more than 30 kb of flanking sequence surrounding the hsp70 gene clusters suggested that this duplication was likely a retrotransposition. For the melanogaster subgroup, Southern hybridization and an hsp70 restriction map confirmed the conserved number (4) and arrangement of hsp70 genes in the seven species other than D. melanogaster. Drosophila melanogaster is unique; tandem duplication and gene conversion at the derived cluster yielded a fifth hsp70 gene. The four D. orena hsp70 genes are highly similar and concertedly evolving. In contrast, the D. mauritiana hsp70 genes are divergent, and many alleles are nonfunctional. The proliferation, concerted evolution, and maintenance of functionality in the D. melanogaster hsp70 genes is consistent with the action of natural selection in this species.     

The Use of Yolk Protein Variations in Drosophila Species to Analyse the Control of Vitellogenesis

The yolk proteins of many insects, including Drosophila , are synthesised in the fat body of adult females and are transported through the haemolymph to be accumulated in the oocytes. We have used differences in the size and number of yolk polypeptides in different species of Drosophila to investigate the role of the ovary and of juvenile hormone in vitellogenesis.
The yolk proteins of eight species of Drosophila were compared with those of Drosophila melanogaster . Only Drosophila simulans had three yolk polypeptides of similar molecular weight to the three polypeptides in D. melanogaster and gave a high degree of cross reactivity with antibody raised against the yolk proteins of D. melanogaster . All other species had one to three bands on a sodium dodecyl sulphate gel representing the yolk polypeptides; they are between 44,000 and 49,500 daltons in molecular weight, showing weak cross reactivity with anti- D. melanogaster yolk antibody. Interspecies ovary transplants established that males of D. arizonensis and D.pseudoobscura which supported vitellogenesis of D. melanogaster ovaries, did so by permitting the implanted ovaries to synthesise their own yolk proteins. The synthetic juvenile hormone, ZR515, was unable to induce ovaries, which failed to develop in other species of males, to undergo vitellogenesis. In females, however, ZR515 was able to induce uptake of the yolk proteins of some of the species into the D. melanogaster donor ovaries, which had failed to develop in the absence of hormone. These interspecies differences in the yolk proteins have therefore been used to investigate the control of vitellogenesis and the role of juvenile hormone in this process in Drosophila .     

Drosophila virilis has long and highly polymorphic microsatellites

Comparative genomics is a powerful approach to inference of the dynamics of genome evolution. Most information about the evolution of microsatellites in the genus Drosophila has been obtained from Drosophila melanogaster. For comparison, we collected microsatellite data for the distantly related species Drosophila virilis. Screening about 0.5 Mb of nonredundant genomic sequence from GenBank, we identified 239 dinucleotide microsatellites. On average, D. virilis dinucleotides were significantly longer than D. melanogaster microsatellites (7.69 repeats vs. 6.75 repeats). Similarly, direct cloning of microsatellites resulted in a higher mean repeat number in D. virilis than in D. melanogaster (12.7 repeats vs. 12.2 repeats). Characterization of 11 microsatellite loci mapping to division 40-49 on the fourth chromosome of D. virilis indicated that D. virilis microsatellites are more variable than those of D. melanogaster.     

Lineage-specific expansion of the zinc finger associated domain ZAD

The zinc finger associated domain (ZAD), present in almost 100 distinct proteins, characterizes the largest subgroup of C2H2 zinc finger proteins in Drosophila melanogaster and was initially found to be encoded by arthropod genomes only. Here, we report that the ZAD was also present in the last common ancestor of arthropods and vertebrates, and that vertebrate genomes contain a single conserved gene that codes for a ZAD-like peptide. Comparison of the ZAD proteomes of several arthropod species revealed an extensive and species-specific expansion of ZAD-coding genes in higher holometabolous insects, and shows that only few ZAD-coding genes with essential functions in Drosophila melanogaster are conserved. Furthermore, at least 50% of the ZAD-coding genes of Drosophila melanogaster are expressed in the female germline, suggesting a function in oocyte development and/or a requirement during early embryogenesis. Since the majority of the essential ZAD coding genes of Drosophila melanogaster were not conserved during arthropod or at least during insect evolution, we propose that the LSE of ZAD-coding genes shown here may provide the raw material for the evolution of new functions that allow organisms to pursue novel evolutionary paths.