Knockdown-Induced Fasting Phenotypes in Flatworms: Insights into Underlying Mechanisms of Feeding Behavior

The intestine is a multifunctional organ responsible for digestion, nutrient absorption, metabolic regulation, and innate immunity. In flatworms, recent studies have highlighted the importance of intestine-enriched genes expressed strongly in cells of the digestive tract. These genes are not only involved in digestion, nutrient uptake, transport, metabolism, and feeding behavior, but also in the modulating dynamics of stem cells (neoblasts). In Macrostomum lignano, the molecular mechanisms regulating interaction between digestive and neural processes remain poorly understood, as in other free-living flatworms. Therefore, identifying the genes required for intestinal integrity and feeding behavior is essential for understanding the underpinning mechanisms. In this study, we examined intestine-enriched candidate genes predicted to be involved in cell differentiation and maintenance of the intestine in M. lignano and whether the knockdown of these genes affects other tissues' functioning. Using RNAi-mediated gene silencing, we identified four genes (kri1, wbp2nl, Mlig-tuf1, and Mlig-tuf2) whose knockdown causes pronounced phenotypes, including reduced feeding, fasting behavior, decreased body size and cell proliferation, low reproduction, and altered expression of an intestine-specific apob promoter. We have characterized their roles in intestinal homeostasis and neoblast dynamics and discussed potential mechanisms linking gene disruption to changes in feeding behavior.