Castillo Bravo, Paula Andrea (2015-12). Short Neuropeptide F Receptor in the Worker Brain of the Red Imported Fire Ant (Solenopsis invicta Buren) and Methodology for RNA Interference. Master's Thesis.
Thesis
The red imported fire ant (Solenopsis invicta Buren) is one of the worst invasive species in the United States. Investigating their physiology to understand its molecular basis could lead to the discovery of new gene targets for fire ant control. Neuropeptides are involved in the regulation of important physiological processes, and in insects the short neuropeptide F (sNPF) plays an important role as regulator of feeding, and involved in mechanisms of nutrient sensing, growth and reproduction. This study is focused into unveiling the physiological role of the sNPF and its receptor (sNPFR) in fire ants. In workers, we found a total of nine clusters of immunoreactive-sNPFR cells located near important neuropiles in the brain. These sNPFR-expressing cells are sensitive to the presence/absent of brood, perhaps in correlation with changes in the nutritional status of the colony. Also, these cell clusters are differentially expressed among worker subcastes, suggesting the sNPF/sNPFR pathway could be associated with mechanisms of division of labor. To discover where sNPF is synthesized, we attempted to localize the sNPF-expressing cells in the brain of queens and workers through in situ hybridization, unfortunately without success; thus, the site of synthesis of sNPF in the brain still remains unknown. Finally, we tried to elucidate the role of the sNPFR in social context by silencing its gene expression trough feeding of dsRNA using small laboratory colonies. We found differential effects when delivering the sNPFR-dsRNA through heat-killed dsRNA-producing bacteria or by delivering dsRNA purified from these bacterial cultures. Also, the type of food used as carrier and the concentration of dsRNA were crucial for gene silencing success. Our results showed that feeding a large concentration of dsRNA in liquid and solid foods is required to induce RNAi in the queen midgut; and that the silencing of the sNPFR in this organ did not induce mortality in these queens, but instead it appears to increase larval mortality. In summary, our results are consistent with the sNPF/sNPFR signaling pathway in fire ants being involved in the regulation of division of labor and in sensing the nutritional status, and suggest its function is fundamental for larval development.
