Metabolic oscillations on the circadian time scale in Drosophila cells lacking clock genes. Drosophila melanogaster

Circadian rhythms are cell-autonomous biological oscillations with a period of about 24 hours. Current models propose that transcriptional feedback loops are the primary mechanism for the generation of circadian oscillations1. In these models, Drosophila S2 cells are generally regarded as ‘non-rhythmic’ cells, as they do not express several canonical circadian components2,3. Using an unbiased multi-omics approach, we made the surprising discovery that Drosophila S2 cells do in fact display widespread daily rhythms. Transcriptomics and proteomics analyses revealed that hundreds of genes and their products, and in particular metabolic enzymes, are rhythmically expressed in a 24-hour cycle. Metabolomics analyses extended these findings and demonstrated that central carbon metabolism and amino acid metabolism are the principal pathways regulated in a rhythmic fashion. We thus demonstrate that 24-hour metabolic oscillations, coupled to gene expression cycles, take place in eukaryotic cells without the contribution of any known circadian regulators. Overall design: RNA-Seq time courses over 57 h sampled at 3 h interval in Drosophila S2 cells at a constant temperature of 25C or 28C.