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Evolution of gene expression in the Drosophila melanogaster subgroup

ABSTRACT: Little is known about broad patterns of variation and evolution of gene expression during any developmental process. Here we investigate variation in genome-wide gene expression among Drosophila simulans, Drosophila yakuba and four strains of Drosophila melanogaster during a major developmental transition-the start of metamorphosis. Differences in gene activity between these lineages follow a phylogenetic pattern, and 27% of all of the genes in these genomes differ in their developmental gene expression between at least two strains or species. We identify, on a gene-by-gene basis, the evolutionary forces that shape this variation and show that, both within the transcriptional network that controls metamorphosis and across the whole genome, the expression changes of transcription factor genes are relatively stable, whereas those of their downstream targets are more likely to have evolved. Our results demonstrate extensive evolution of developmental gene expression among closely related species. Keywords: other

ORGANISM(S): Drosophila simulans Drosophila yakuba Drosophila melanogaster

PROVIDER: GSE327 | GEO | 2003/03/05

SECONDARY ACCESSION(S): PRJNA85531

REPOSITORIES: GEO

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Project description:MicroRNAs (miRNAs) are endogenous RNA molecules that contribute to the regulation of gene expression post-transcriptionally. Recently, patterns of sequence evolution and evolutionary emergence of miRNAs have been analyzed in detail. However, the extent to which miRNA expression levels vary within and between species, the role of stabilizing selection versus other evolutionary mechanisms in shaping the temporal dynamics of these changes, and how this variation might unveil the interplay between miRNAs and mRNAs remain poorly understood. This is especially true during key developmental transitions involving miRNA regulation. Combining deep-sequencing with multi-species microarrays, we assayed miRNA expression levels immediately before (≥18BPF) and after (PF) the increase in steroid hormone ecdysone that triggers metamorphosis. We did so both at the intra- and interspecific levels in the Drosophila melanogaster species group. In contrast to their sequence conservation, ~25% of the analyzed miRNAs differed significantly in expression levels at ≥18BPF and/or PF across D. melanogaster strains. Additionally, ~33% showed modifications in their pattern of expression bias between developmental timepoints. Relative to the patterns of evolution, changes in miRNA abundance at PF accumulate linearly over evolutionary time while similar changes at ≥18BPF do not. Importantly, expression levels of ≥18BPF-enriched miRNAs are the most variable within and between species and therefore the least likely to evolve under stabilizing selection, especially as compared to non-developmentally enriched miRNAs. Overall, functional attributes such as expression ubiquity are more tightly associated with lower levels of miRNA expression polymorphism at PF than at ≥18BPF. Furthermore, ≥18BPF- and PF-enriched miRNAs showed opposite patterns of covariation in expression with mRNAs, which was found to denote the type of regulatory relationship between miRNA and mRNA. By focusing on the miRNA expression levels at the onset of metamorphosis, our results have unveiled contrasting functional patterns of evolutionary divergence during ontogeny.

Project description:Early embryogenesis is a unique developmental stage where genetic control of development is handed off from mother to zygote. Yet the contribution of this transition to the evolution of gene expression is poorly understood. Here we study two aspects of gene expression specific to early embryogenesis in Drosophila: sex-biased gene expression prior to the onset of canonical X chromosomal dosage compensation, and the contribution of maternally supplied mRNAs. We sequenced mRNAs from individual unfertilized eggs, precisely staged and sexed blastoderm embryos and compared levels between D. melanogaster, D. yakuba, D. pseudoobscura and D. virilis. First, we find that mRNA content is highly conserved for a given stage and that studies relying on pooled embryos may systematically overstate the degree of gene expression divergence. Unlike studies done on larvae and adults, where most species show a larger proportion of genes with male-biased expression, we find that transcripts in Drosophila embryos are largely female-biased in all species, likely due to incomplete dosage compensation prior to the activation of the canonical dosage compensation mechanism. The divergence of sex-biased gene expression across species is observed to be often due to a decrease of expression, the most drastic example of which is the overall reduction of male expression from the neo-X chromosome in D. pseudoobscura, leading to a pervasive female-bias on this chromosome. We see no evidence for a faster evolution of expression on the X chromosome in embryos (no “faster X” effect), unlike in adults and contrary to a previous study on pooled non-sexed embryos. Finally, we find that most genes are conserved in regard to their maternal or zygotic origin of transcription, and present evidence that differences in maternal contribution to the blastoderm transcript pool may be due to species-specific divergence of transcript degradation rates We sequenced mRNA from D. melanogaser, D. yakuba, D. pseudoobscura and D. virilis single unfertilized eggs (1 to 2 per species) and from both single female and male embryos (3 per sex per species).

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Evolution of gene expression in the Drosophila melanogaster subgroup

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