The Effects of Digitoxin on the Differential Expression of the Sodium-Potassium Pump in Oncopeltus fasciatus

Abstract

The widespread adaptations and duplications of the sodium-potassium pump (Na+,K+-ATPase), specifically the α1 subunit, provides a natural platform for examining the effects of cardenolides on the expression of ATPα1 duplicates in insects. Oncopeltus fasciatus, or the large milkweed bug, has four copies of ATPα1 with differing amounts of insensitivity to cardenolides depending on the number of mutations they have. To determine if there is a diet specific plasticity in the expression of ATPα1, I conducted a feeding assay using digitoxin, a nonpolar cardenolide. Although I did not find a difference between groups that consumed digitoxin (and methanol) soaked sunflower seeds and groups that did not, my results did show that there is a tissue specific differential expression of ATPα1; more insensitive copies were expressed in the gut while more sensitive copies were expressed in the head. In addition, my differential expression analyses of the O. fasciatus genome across the digitoxin (and methanol), methanol, and control groups showed that there were seven genes that were expressed more in the digitoxin group than in the others, notably CG3097, which functions as a metallocarboxypeptidase. My results also showed one gene, Gasp, that was under expressed in both digitoxin (and methanol) and methanol groups which indicated that methanol influences the expression of chitin binding. As both important to cancer treatments and to the better understanding of the complex intrinsic genetic interactions with external factors, cardenolides and the adaptations of Na+,K+-ATPase to these toxins in insects warrant further study.