Transcriptome analysis of Drosophila melanogaster third instar larval ring glands points to novel functions and uncovers a cytochrome p450 required for development

In Drosophila melanogaster larvae the ring gland is a control center that orchestrates major developmental transitions. It is a composite organ, consisting of the prothoracic gland, the corpus allatum and the corpora cardiaca, each of which synthesizes and secretes a different hormone. Until now, the ring gland’s broader developmental roles beyond endocrine secretion have not been explored. RNA sequencing and analysis of a new transcriptome resource from D. melanogaster wandering third instar larval ring glands has provided a fascinating insight into the diversity of developmental signalling in this organ. We have found strong enrichment of expression of two gene pathways not previously associated with the ring gland: immune response and fatty acid metabolism. We have also uncovered strong expression for many uncharacterized genes. Additionally, RNA interference against ring gland-enriched cytochrome p450s Cyp6u1 and Cyp6g2 produced a lethal ecdysone deficiency and a juvenile hormone deficiency respectively, flagging a critical role for these genes in hormone synthesis. This transcriptome provides a valuable new resource for investigation of roles played by the ring gland in governing insect development. Overall design: Investigation of genome-wide expression in the third instar larval ring gland of two strains: Celera and Armenia-14. Three biological replicates were examined. For differential expression analysis, duplicate RNA-seq reads for the third instar larval central nervous system were obtained from the modMINE database (accession: SRX029398) [i.e., third-party re-analysis].