The Synthesis and Function of the Peritrophic Matrix in Drosophila Melanogaster
Maintenance of functional barrier structures separating an organism from and regulating its interaction with the environment is critical for many aspects of fitness. Arguably, the most dynamic interface between an animal and its environment is the gut, as the organism must balance the primary functions, digestion and nutrient acquisition, with several homeostatic and defensive systems including pathogen defense, microbiome maintenance and stem cell renewal. Many animals secrete extracellular barrier structures along their guts to organize and modulate these interactions, including intestinal mucosal secretions in humans and a semi-permeable structure in insects called the peritrophic matrix (PM). In Drosophila, the PM is theorized to play an integral role in numerous gut processes, but to date, all studies are limited as there are no published lines of insects that completely lack a PM. Reported here are four genes, drd, mco4, cyp6a22 and cyp6t, that produce flies completely lacking a PM when knocked down. By manipulating temporal and spatial expression of drd, it was found constant adult expression of drd is necessary for PM formation, and this phenotype is separable from other drd gut phenotypes. drd, cyp6a22 and cyp6t are necessary for normal early adult immune activity and defecation while mco4 is not. Global mco4, cyp6a22 and cyp6t knockdowns do not phenocopy non-gut drd mutant phenotypes. The mco4 gene product displayed canonical laccase activity and mco4 knockdown flies were used to investigate the role of the PM in larval nutrient absorption and adult microbiome maintenance. mco4 knockdown larva develop and gain weight slower than wildtype larva and this defect is not due to food movement but rather digestive inefficiency. mco4 knockdown adult flies maintain a lower commensal bacterial load that can be abolished when stressed and conversely display a more active immune response and upregulated stem cell renewal activation. These data support a critical role for the PM in several essential Drosophila gut functions. mco4 knockdown flies provide an ideal genetic model for studying PM function and will be a valuable tool in future studies fine tuning observations reported here and exploring additional gut processes potentially modulated by the PM.