Dataset Information

Molecular evolution of the insect chemoreceptor gene superfamily in Drosophila melanogaster.

ABSTRACT: The insect chemoreceptor superfamily in Drosophila melanogaster is predicted to consist of 62 odorant receptor (Or) and 68 gustatory receptor (Gr) proteins, encoded by families of 60 Or and 60 Gr genes through alternative splicing. We include two previously undescribed Or genes and two previously undescribed Gr genes; two previously predicted Or genes are shown to be alternative splice forms. Three polymorphic pseudogenes and one highly defective pseudogene are recognized. Phylogenetic analysis reveals deep branches connecting multiple highly divergent clades within the Gr family, and the Or family appears to be a single highly expanded lineage within the superfamily. The genes are spread throughout the Drosophila genome, with some relatively recently diverged genes still clustered in the genome. The Gr5a gene on the X chromosome, which encodes a receptor for the sugar trehalose, has transposed from one such tandem cluster of six genes at cytological location 64, as has Gr61a, and all eight of these receptors might bind sugars. Analysis of intron evolution suggests that the common ancestor consisted of a long N-terminal exon encoding transmembrane domains 1-5 followed by three exons encoding transmembrane domains 6-7. As many as 57 additional introns have been acquired idiosyncratically during the evolution of the superfamily, whereas the ancestral introns and some of the older idiosyncratic introns have been lost at least 48 times independently. Altogether, these patterns of molecular evolution suggest that this is an ancient superfamily of chemoreceptors, probably dating back at least to the origin of the arthropods.

SUBMITTER: Robertson HM

PROVIDER: S-EPMC304115 | biostudies-literature | 2003 Nov

REPOSITORIES: biostudies-literature

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Molecular evolution of the insect chemoreceptor gene superfamily in Drosophila melanogaster.

Robertson Hugh M HM Warr Coral G CG Carlson John R JR

Proceedings of the National Academy of Sciences of the United States of America 20031107

The insect chemoreceptor superfamily in Drosophila melanogaster is predicted to consist of 62 odorant receptor (Or) and 68 gustatory receptor (Gr) proteins, encoded by families of 60 Or and 60 Gr genes through alternative splicing. We include two previously undescribed Or genes and two previously undescribed Gr genes; two previously predicted Or genes are shown to be alternative splice forms. Three polymorphic pseudogenes and one highly defective pseudogene are recognized. Phylogenetic analysis ...[more]

PMID: 14608037

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Project description:Constitutive heterochromatin is a ubiquitous and still unveiled component of eukaryotic genomes, within which it comprises large portions. Although constitutive heterochromatin is generally considered to be transcriptionally silent, it contains a significant variety of sequences that are expressed, among which about 300 single-copy coding genes have been identified by genetic and genomic analyses in the last decades. Here, we report the results of the evolutionary analysis of Yeti, an essential gene of Drosophila melanogaster located in the deep pericentromeric region of chromosome 2R. By FISH, we showed that Yeti maintains a heterochromatin location in both D. simulans and D. sechellia species, closely related to D. melanogaster, while in the more distant species e.g., D. pseudoobscura and D. virilis, it is found within euchromatin, in the syntenic chromosome Muller C, that corresponds to the 2R arm of D. melanogaster chromosome 2. Thus, over evolutionary time, Yeti has been resident on the same chromosomal element, but it progressively moved closer to the pericentric regions. Moreover, in silico reconstruction of the Yeti gene structure in 19 Drosophila species and in 5 non-drosophilid dipterans shows a rather stable organization during evolution. Accordingly, by PCR analysis and sequencing, we found that the single intron of Yeti does not undergo major intraspecies or interspecies size changes, unlike the introns of other essential Drosophila heterochromatin genes, such as light and Dbp80. This implicates diverse evolutionary forces in shaping the structural organization of genes found within heterochromatin. Finally, the results of dS - dN tests show that Yeti is under negative selection both in heterochromatin and euchromatin, and indicate that the change in genomic location did not affected significantly the molecular evolution of the gene. Together, the results of this work contribute to our understanding of the evolutionary dynamics of constitutive heterochromatin in the genomes of higher eukaryotes.

Project description:Sexually dimorphic phenotypes are thought to largely result from sex differences in gene expression, and genes with sex-biased expression have been well characterized in adults of many species. Although most sexual dimorphisms manifest in adults, many result from sex-specific developmental trajectories, implying that juveniles may exhibit significant levels of sex-biased expression. However, it is unclear how much sex-biased expression occurs before reproductive maturity and whether preadult sex-biased genes should exhibit the same evolutionary dynamics observed for adult sex-biased genes. In order to understand the continuity, or lack thereof, and evolutionary dynamics of sex-biased expression throughout the life cycle, we examined sex-biased genes in pre-gonad tissue of two preadult stages and compared them with the adult gonad of Drosophila melanogaster. We found that the majority of the genome is sex-biased at some point in the life cycle, with some genes exhibiting conserved sex-biased expression and others displaying stage-specific sex bias. Our results also reveal a far more complex pattern of evolution for sex-biased genes throughout development. The most rapid evolutionary divergence occurred in genes expressed only in larvae within each sex, compared with continuously expressed genes. In females-but not males-this pattern appeared to be due to relaxed purifying selection in larva-limited genes. Furthermore, genes that retained male bias throughout life evolved more rapidly than stage-specific male-biased genes, due to stronger purifying selection in stage-specific genes. However, female-biased genes that were specific to larvae evolved most rapidly, a pattern that could not be definitively attributed to differences in adaptive evolution or purifying selection, suggesting that pleiotropic constraints on protein-coding sequences can arise when genes are broadly expressed across developmental stages. These results indicate that the signature of sex-specific selection can be detected well before reproductive maturity and is strongest during development.

Dataset Information

Molecular evolution of the insect chemoreceptor gene superfamily in Drosophila melanogaster.

Publications

Molecular evolution of the insect chemoreceptor gene superfamily in Drosophila melanogaster.

Similar Datasets

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