ABSTRACT: Background Antennae of fruit flies are the major organs responsible for detecting environmental volatiles, e.g., egg-laying substrates. An adult antenna contains many sensilla full of olfactory sensory neurons, where olfactory receptor (Or) genes are expressed. Each sensory neuron only expresses up to three receptors, making it difficult to estimate expression levels by conventional methods. In this study, we applied Illumina RNA sequencing (RNA-seq) to study the expression levels of Or and other genes in fly antennae. Results RNA from approximately 1,200 pairs of adult antennae from each sex of Drosophila melanogaster was used to obtain the antennal transcriptome of each sex. We detected approximately 12,000 genes expressed in antennae of either sex. The most highly expressed genes included pheromone-binding genes, transmembrane transporter genes, and sensory reception genes. Among the 61 annotated Or genes, we observed 53 and 54 genes (approximately 90%) expressed (fragments per kilobase of exon per million fragments mapped (FPKM) > 0.05) in male and female antennae, respectively; approximately 25 genes were expressed with FPKM > 15. Compared to previous studies, which extracted RNA from the whole body or head and used microarrays, antenna-specific transcriptomes obtained by RNA-seq provided more reliable estimates of gene expression levels and revealed many lowly expressed genes. Ninty-one genes, including one odorant-binding protein (Obp) gene and four Or genes, were differentially expressed between male and female antennae. These sexually biased genes were enriched on the X chromosome and showed enrichment in different gene ontology categories for male and female flies. The present and previous data together suggest that a gene family with putative immune response functions is related to pheromone detection and involved in the courtship behavior of male flies. Conclusions Tissue-specific RNA-seq is powerful for detecting lowly expressed genes. Our study provides new insight into the expression of olfactory-related genes in Drosophila antennae.ophila sechellia relies exclusively on the fruits of Morinda citrifolia, which are toxic to most insects, including its sibling species D. melanogaster and D. simulans. Although several odorant binding protein (Obp) genes and olfactory receptor (Or) genes were suggested to be associated with the D. sechellia host shift, a broad view of how chemosensory genes have contributed to this shift is still lacking. We therefore studied the antennal transcriptomes, the main organ responsible for detecting food resource and oviposition, of D. sechellia and its two sibling species. We wanted to know whether gene expression, particularly chemosensory genes, has diverged between D. sechellia and its two sibling species. Using a very stringent definition of differential gene expression, we found 147 genes (including 11 chemosensory genes) were up-regulated while only 81 genes (including 5 chemosensory genes) were down-regulated in D. sechellia. Interestingly, Obp50a exhibited the highest up-regulation, a ~100 fold increase, and Or85c – previously reported to be a larva-specific gene– showed ~20 fold up-regulation in D. sechellia. Furthermore, Ir84a, proposed to be associated with male courtship behavior, is significantly up-regulated in D. sechellia. We also found expression divergence in most of the receptor gene families between D. sechellia and the two sibling species. Our observations suggest that the host shift of D. sechellia is associated with expression profile divergence in all chemosensory gene families and is achieved mostly by up-regulation of chemosensory genes.the evolutionary behaviour of Polycomb group proteins, their recruitment factors and their underlying sequences by performing ChIP-seq analysis in 4-5 different Drosophila species (GSE60428) and HiC analysis in Drosophila melanogaster. We demonstrate an extremely high conservation of Polycomb repressive domains across Drosophila species We validate few cases of PRE divergence that shows that cis-driven PRE evolution is a rare event. We further show that PHO recruitment to Polycomb domains is evolutionarily robust to motif changes and that PRC1 stabilizes binding of its key recruiter
