Project summary The gut microbiome is a dense, complex community of microbes associated with maintaining health in not only the gastrointestinal tract, but also other organs in the human body. Large shifts that disrupt microbial homeostasis are linked to digestive diseases, but diurnally rhythmic fluctuations in microbial populations are associated with good gut health. Therefore, it is of critical importance to delineate the microbial and temporal cues that control intestinal homeostasis to uncover the mechanisms that separate the beneficial and detrimental effects of microbial flux. These discoveries have the potential to reveal novel targets urgently needed for treating colitis, a digestive disease for which a cure remains unknown. We performed a time-course transcriptomics screen and single-cell transcriptomic analyses from mouse colon and identified a new intestinal gene associated with the secretory epithelial lineage that exhibited both rhythmic and microbiota-dependent expression. Mice lacking this protein had a thinner mucus layer compared to wild-type mice, and were not only more susceptible to DSS colitis, but also displayed delayed recovery after DSS cessation. Our preliminary results implicate host circadian clock and gut microbiome in this phenotype, but specifics of the upstream temporal and microbial signals that activate this gene, as well its downstream function in mucus production, remain completely unknown. Therefore, we hypothesize that the host circadian clock and gut microbiome regulates mucus production in the large intestine through a newly identified temporal and microbially regulated gene to protect the host from infectious and chemical colitis. To test this hypothesis, two specific aims are proposed. In Aim 1, we will identify specific microbiota members and metabolites and investigate circadian clock-dependent regulation that activate mucus production. In Aim 2, we will characterize the function of our novel protein plays in mucus production by comparing mucus secretion, permeability, and composition in wild-type and knockout mice. Successful completion of this proposal will identify a previously undefined mucosal protein that integrates temporal and microbial cues to regulate mucus production and protects the host against chemical and infectious colitis. This innovative project will additionally expand my training to include key methods and concepts in microbiota, chronobiology, and mucosal immunology. Altogether, the research and training plan proposed will facilitate a better understanding of the role the microbiome and circadian clock in modulating host immunity, while preparing me for a future career as an independent investigator studying the role the circadian clock and microbiome play in aggravating digestive diseases.