30 pagesResident microbiotas can influence many aspects of host health and disease. Previous research by the Guillemin lab shows that in zebrafish and mice, gut microbiota promotes the expansion of insulin-producing beta cells in the pancreas through a secreted bacterial protein, beta-cell expansion factor A (BefA). This research investigates the role of microbiota, bacteria, and BefA protein to promote analogous insulin-producing cell (IPC) development in the fruit fly, Drosophila melanogaster. In Drosophila, 7 insulin-producing cells are present in each lobe of the larval brain. This research first established the effect of germ-free (GF) rearing on IPC numbers in Drosophila. The second and third aims tested if feeding flies BefA or if transgenic expression of BefA could restore insulin-producing cell numbers in germ-free flies. We compared the number of insulin-producing cells present in flies that were germ-free, conventionally reared (CV), germ-free and fed BefA protein, and germ-free flies with transgenic expression of BefA. Tissue-specific Dilp3:GAL4/UAS:GFP in all groups made insulin-producing cells visible after dissection and immunohistochemistry. Results showed that germ-free flies have fewer insulin-producing cells per brain lobe than conventional flies, indicating that microbiota is required for normal insulin-producing cell number and development. Further, germ-free larvae fed BefA protein showed a slight but significant increase in insulin-producing cells per lobe compared to conventional, indicating that BefA has the potential to rescue the effects of germ-free treatment. Transgenic expression of BefA, using the GAL4/UAS system, yielded a trending rescue of insulin-producing cells in germ-free flies, possibly due to lower levels of BefA produced through transgenic expression than via feeding. Results indicate that resident microbiota has a powerful effect on Drosophila metabolic pathways and fundamentally affects cell development, including cells in the gut-brain axis. This information can be used to direct research and treatment for diseases like diabetes, helps researchers better understand growth and development, and has implications for the microbiota’s effect on the brain. Future experiments include a developmental assay aimed at further investigating the properties of BefA and other similar bacterial proteins, including testing the hypothesis that BefA’s membrane permeabilizing properties induce insulin-producing cell expansion
