Drosophila Erecta Research Articles

Naturally occurring variation in copia expression is due to both element (cis) and host (trans) regulatory variation.

Significant differences in levels of copia [Drosophila long terminal repeat (LTR) retrotransposon] expression exist among six species representing the Drosophila melanogaster species complex (D. melanogaster, Drosophila mauritiana, Drosophila simulans, Drosophila sechellia, Drosophila yakuba, and Drosophila erecta) and a more distantly related species (Drosophila willistoni). These differences in expression are correlated with major size variation mapping to putative regulatory regions of the copia 5' LTR and adjacent untranslated leader region (ULR). Sequence analysis indicates that these size variants were derived from a series of regional duplication events. The ability of the copia LTR-ULR size variants to drive expression of a bacterial chloramphenicol acetyltransferase reporter gene was tested in each of the seven species. The results indicate that both element-encoded (cis) and host-genome-encoded (trans) genetic differences are responsible for the variability in copia expression within and between Drosophila species. This finding indicates that models purporting to explain the dynamics and distribution of retrotransposons in natural populations must consider the potential impact of both element-encoded and host-genome-encoded regulatory variation to be valid. We propose that interelement selection among retrotransposons may provide a molecular drive mechanism for the evolution of eukaryotic enhancers which can be subsequently distributed throughout the genome by retrotransposition.

Identification of a mariner element from the tsetse fly, Glossina palpalis palpalis.

In the present study, the polymerase chain reaction was used initially to demonstrate the presence of mariner sequences in seven species/subspecies of tsetse flies. DNA hybridization experiments show mariner sequences to be dispersed within the tsetse genome and that there are large variations in copy numbers among the various taxa. A genomic library was used to isolate and characterize a full-length mariner element from G. p. palpalis. The results indicate that this element is 1257 bp in length, flanked by two 32 bp inverted repeats differing at only one position, and belongs to the mellifera subfamily. The nucleotide sequence that is translated into a reading frame of 337 amino acids requires the introduction of two frame shifts and one stop codon to maximize sequence homology with a mariner element from Drosophila erecta. Based on this evidence, we conclude that the G. p. palpalis mariner element clearly represents a non-functional transposable element and that the protein product is not an active transposase.

Horizontal transmission, vertical inactivation, and stochastic loss of mariner-like transposable elements.

Horizontal transmission has been well documented as a major mechanism for the dissemination of mariner-like elements (MLEs) among species. Less well understood are mechanisms that limit vertical transmission of MLEs resulting in the "spotty" or discontinuous distribution observed in closely related species. In this article we present evidence that the genome of the common ancestor of the melanogaster species subgroup of Drosophila contained an MLE related to the mellifera (honey bee) subfamily. Horizontal transmission, approximately 3-10 MYA, is strongly suggested by the observation that the sequence of the MLE in Drosophila erecta is 97% identical in nucleotide sequence with that of an MLE in the cat flea, Ctenocephalides felis. The D. erecta MLE has a spotty distribution among species in the melanogaster subgroup. The element has a high copy number in D. erecta and D. orena, a moderate copy number in D. teissieri and D. yakuba, and was apparently lost ("stochastic loss") in the lineage leading to D. melanogaster, D. simulans, D. mauritiana, and D. sechellia. In D. erecta, most copies are concentrated in the heterochromatin. Two copies from D. erecta, denoted De12 and De19, were cloned and sequenced, and they appear to be nonfunctional ("vertical inactivation"). It therefore appears that the predominant mode of MLE evolution is vertical inactivation and stochastic loss balanced against occasional reinvasion of lineages by horizontal transmission.

Unusual variability of the Drosophila melanogaster ref(2)P protein which controls the multiplication of sigma rhabdovirus.

The ref(2)P gene of Drosophila melanogaster was identified by the discovery of two alleles, Po and Pp, respectively, permissive and restrictive for sigma rhabdovirus multiplication. A surprising variability of this gene was first noticed by the observation of size differences between the transcripts of permissive and restrictive alleles. In this paper, another restrictive allele, Pn, clearly distinct from Pp, is described: it exhibits a weaker antiviral effect than Pp and differs from Pp by its molecular structure. Five types of alleles were distinguished on the basis of their molecular structure, as revealed by S1 nuclease analysis of 17 D. melanogaster strains; three alleles were permissive and two restrictive. Comparison of the sequences of four haplotypes revealed numerous point mutations, two deletions (21 and 24 bp) and a complex event involving a 3-bp deletion, all affected the coding region. The unusual variability of the ref(2)P locus was confirmed by the high ratio of amino acid replacements to synonymous mutations (7:1), as compared to that of other genes, such as the Adh (2:42). Nevertheless, nucleotide sequence comparison with the Drosophila erecta ref(2)P gene shows that selective pressures are exerted to maintain the existence of a functional protein. The effects of this high variability on the ref(2)P protein are discussed in relation to its specific antiviral properties and to its function in D. melanogaster, where it is required for male fertility.

Informational redundancy of tRNA Ser4 and tRNA Ser7 genes in Drosophila melanogaster and evidence for intergenic recombination

Variant tRNA genes have been widely observed in multicellular eukaryotes. Recent biochemical studies have shown that some of them are expressed in a tissue- or a stage-specific manner. These findings would thus imply that certain modified tRNAs may be crucial for the development of the organism. Using Drosophila melanogaster as a model, we have taken a combined genetic and molecular approach to examine critically the possible biological functions of tRNA Ser 4,7 genes. We showed that at least 50% of the total templates can be deleted from the genome without inducing abnormal phenotypes such as Minute, or a decrease in viability. In addition, two of the tRNA Ser variant genes that are unique in sequence are also completely dispensable. This strongly implies that even though they may be expressed in vivo, they play no essential role in the development of the fruitfly. By comparison with some of the corresponding tRNA genes in another sibling species. Drosophila erecta, our results suggest strongly that the variants are products of non-reciprocal exchanges among the tRNA Ser 4,7 genes. Such intergenic recombination events may have a major influence in the concerted evolution of the two gene families.

Molecular cloning and partial sequence characterization of the duplicated amylase genes from Drosophila erecta

Summary - Previous studies have shown that the a-amylase gene is duplicated in each of the 8 species comprising the Drosophila melanogaster species subgroup. In this study, a genomic library in phage lambda was prepared from the DNA of 1 species member of this subgroup, D erecta. This gene library was screened with an amylase-specific probe from the closely-related species D melanogaster. One of the cross-hybridizing phage clones was isolated, insert fragments were sub-cloned into plasmid vectors, and the identity of the cloned locus was verified by DNA sequencing. The results confirm that this species contains 2 very similar copies of the amylase-coding sequence, as does D medanogaster. Within the amylase-coding region, there is a 3% sequence divergence between the 2 species; this value rises to 6% if we consider only silent sites within the coding region. Sequence divergence between D erecta and D melanogaster in the non-coding intergenic region is approximately 15%. These results constitute the first molecular sequence data available for protein-coding genes of D erecta. The data set allows us to calculate an estimated divergence time of more than 10 million years between the 2 species. This is consistent with the results of previous phylogenetic studies. Drosophila erecta / a-amylase / molecular evolution / gene conversion

Molecular cloning and partial sequence characterization of the duplicated amylase genes from Drosophila erecta

Molecular cloning and partial sequence characterization of the duplicated amylase genes from Drosophila erecta

An ultrastructural and histochemical study of the secretory granules in the salivary gland cells of the Drosophila melanogaster species subgroup: phylogenetic relationships and evolutionary aspects

The morphology of the secretory granules and the distribution of "neutral" complex carbohydrates in these structures of the larval salivary gland cells of six species belonging to the melanogaster subgroup of Drosophila were examined at the ultra-structural level. The secretory granules of each species show a unique morphology. The species of the melanogaster subgroup can be subdivided into two complexes (the melanogaster and the yakuba complexes) on the basis of the existence of filamentous or granular material in their secretory granules. In the former complex belong the species Drosophila melanogaster, Drosophila simulans, and Drosophila mauritiana, whose secretory granules consist mainly of filamentous material, and in the latter complex belong the species Drosophila yakuba, Drosophila teissieri, and Drosophila erecta, whose secretory granules consist of granular material. A phylogeny of the six species, in which D. erecta is regarded as the most primitive, is presented. It is proposed that the morphology of the secretory granules at the ultrastructural level, combined with the distribution of complex carbohydrates in them, can be used as an additional criterion for the classification of the Drosophila species.

Identical satellite DNA sequences in sibling species of Drosophila

The evolution of simple satellite DNAs was examined by DNA-DNA hybridization of ten Drosophila melanogaster satellite sequences to DNAs of the sibling species, Drosophila simulans and Drosophila erecta. Seven of these repeat types are present in tandem arrays in D. simulans and each of the ten sequences is repeated in D. erecta. In thermal melts, six of the seven satellite sequences in D. simulans and seven of the ten sequences in D. erecta melted within 1 deg.C of the corresponding values in D. melanogaster. The remaining sequences melted within 3 deg.C of the homologous hybrids. Therefore, there is little or no alteration in those satellite sequences held in common, despite a period of about ten million years since the divergence of D. melanogaster and D. simulans from a common ancestor. Simple satellite sequences appear to be more highly conserved than coding regions of the genome, on a per nucleotide basis. Since multiple copies of three satellite sequences could not be detected in D. simulans yet are present in D. erecta, a species more distantly related to D. melanogaster than is D. simulans, these sequences show discontinuities in evolution. There were major quantitative variations between species, showing that satellite DNAs are prone to massive amplification or diminution events over timespans as short as those separating sibling species. In D. melanogaster, these sequences amount to 21% of the genome but only 5% in D. simulans and 0.4% in D. erecta. There was a general trend of lower abundance with evolutionary distance for most satellites, suggesting that the amounts of different satellite sequences do not vary independently during evolution.