Project description:The objective of this study was to explore the transcriptional basis of the holometabolous development of Danaus plexippus (the monarch butterfly), which we reasoned would lend insight into how complex life cycles evolve.
Project description:Seasonal adaptation to changes in light:dark regimes (i.e., photoperiod) allows organisms living at temperate latitudes to anticipate environmental change and adjust their physiology and behavior accordingly. The circadian system has been implicated in measurement and response to changes in photoperiod in nearly all animals studied so far (Saunders, 2011). The use of both traditional and non-traditional model insects with robust seasonal responses has recently genetically demonstrated the central role that clock genes play in photoperiodic response. Yet, the molecular pathways involved in insect photoperiodic responses remain largely unknown. Here, using the Eastern North American monarch butterfly (Reppert et al, 2016; Denlinger et al, 2017), we identified the vitamin A pathway as a novel pathway downstream of the circadian clock mediating insect photoperiod responsiveness. We found that interrupting clock function by disrupting circadian activation and repression abolishes photoperiodic responses in reproductive output, providing a functional link between clock genes and photoperiodic responsiveness in the monarch. Through transcriptomic approaches, we identified a molecular signature of seasonal-specific rhythmic gene expression in the brain, the organ known to function in photoperiodic reception in both Lepidoptera and some flies (Bowen et al, 1984; Saunders & Cymborowski, 1996). Among genes differentially expressed between both long and short photoperiods and between seasonal forms, several were belonging to the vitamin A pathway. The rhythmic expression of all of these genes was abolished in clock-deficient mutants. We also showed that a CRISPR/Cas9-mediated loss-of-function mutation in the pathway’s rate-limiting enzyme, ninaB1, impaired the monarch ability to respond to the photoperiod independently of visual function in the compound eye and without affecting circadian rhythms. Our finding that the vitamin A pathway is a key mediator of photoperiodic responses in insects could have broad implications for understanding the molecular mechanisms underlying photoperiodism.
Project description:Gut microbiome research is rapidly moving towards the functional characterization of the microbiota by means of shotgun meta-omics. Here, we selected a cohort of healthy subjects from an indigenous and monitored Sardinian population to analyze their gut microbiota using both shotgun metagenomics and shotgun metaproteomics. We found a considerable divergence between genetic potential and functional activity of the human healthy gut microbiota, in spite of a quite comparable taxonomic structure revealed by the two approaches. Investigation of inter-individual variability of taxonomic features revealed Bacteroides and Akkermansia as remarkably conserved and variable in abundance within the population, respectively. Firmicutes-driven butyrogenesis (mainly due to Faecalibacterium spp.) was shown to be the functional activity with the higher expression rate and the lower inter-individual variability in the study cohort, highlighting the key importance of the biosynthesis of this microbial by-product for the gut homeostasis. The taxon-specific contribution to functional activities and metabolic tasks was also examined, giving insights into the peculiar role of several gut microbiota members in carbohydrate metabolism (including polysaccharide degradation, glycan transport, glycolysis and short-chain fatty acid production). In conclusion, our results provide useful indications regarding the main functions actively exerted by the gut microbiota members of a healthy human cohort, and support metaproteomics as a valuable approach to investigate the functional role of the gut microbiota in health and disease.