Developmental exposure to the herbicide atrazine causes defects in intestinal morphogenesis Julia Grzymkowski: Graduate Student (firstname.lastname@example.org) Nanette Nascone-Yoder (email@example.com) North Carolina State University The herbicide atrazine (ATR) has been experimentally and epidemiologically associated with structural birth defects in multiple organ systems; however, the mechanism by which ATR disrupts organogenesis is unknown. We have found that Xenopus (frog) embryos exposed to this environmental toxicant exhibit intestinal malrotation, a common human birth defect. In addition, ATR-exposed intestines are shorter, suggesting that ATR perturbs the process of tissue elongation. Consistent with this idea, immunostaining of ATR-exposed guts revealed severe abnormalities in cell shape, polarization and epithelial architecture, indicative of a failure to execute the cell rearrangement events that drive intestine elongation. As an herbicide, ATR inhibits the photosynthetic electron transport chain (ETC) in chloroplasts, leading to the overproduction of reactive oxygen species (ROS) in plants. However, ATR has also been shown to elicit oxidative stress and dysregulate metabolism in mammalian cell culture and adult animal models, suggesting that ATR-induced intestinal defects may be a result of mitochondrial ETC inhibition. Indeed, ATR exposure increased total levels of ROS within the embryo. Importantly, the intestinal shortening and malrotation phenotypes exhibited by ATR can be rescued after pretreatment with an antioxidant. Moreover, RNA sequencing analysis of control and ATR exposed intestines revealed an enrichment for pathways involved in metabolism and the oxidative stress response. Finally, metabolomic profiles reveal changes in glycolysis/gluconeogenesis and TCA cycle metabolites after ATR exposure. Our results reveal a potentially novel mechanism of action of ATR on intestinal development and suggest that oxidative stress and metabolic dysfunction may underlie the etiology of a common birth defect.