Characterization of Transferrin‐1 from Drosophila melanogaster

Abstract

Transferrins are secreted proteins that bind iron. Mammalian serum transferrin is involved in iron transport, while mammalian lactoferrin functions as an immune protein. Both proteins are thought to protect against oxidative stress. Insect transferrin is similar to both serum transferrin and lactoferrin, and its functions are not well characterized. Previous studies have demonstrated that insect transferrin can function as an immune protein, and limited data suggest that it may have a role in protection against oxidative stress and in iron transport. The goal of this study was to identify the functions of Drosophila melanogaster transferrin‐1 (DmTsf1). Our approach was to observe changes in DmTsf1 concentration in response to immune challenge, oxidative stress, metal stress, and dietary iron availability; test the antimicrobial activity of apo and holo forms of DmTsf1; and evaluate phenotypes associated with RNAi‐mediated knockdown of DmTsf1. We estimated the concentration of DmTsf1 in hemolymph to be 0.5 μM in larvae, 4 μM in adult females and 20 μM in adult males. We found that DmTsf1 concentration increased after inoculation of bacteria, and that DmTsf1 inhibited bacterial growth by sequestering iron. These findings indicate that DmTsf1 can protect flies against bacterial infection. In contrast to its response to immune challenge, DmTsf1 was not upregulated in response to paraquat‐induced oxidative stress, metal stress, or changes in dietary iron availability. We used genetic crosses to generate insects with strong or weak knockdown of DmTsf1 and observed that strong knockdown resulted in mortality in the early larval stages, while 75% knockdown resulted in insects that eclosed as normal‐looking adults. We found that knockdown of DmTsf1 had no effect on an insect's susceptibility to paraquat; therefore, DmTsf1 does not seem to protect flies from paraquat‐induced oxidative stress. Likewise, knockdown of DmTsf1 had no effect on the susceptibility of insects to a high iron diet. Additional experiments to test the effect of knockdown on susceptibility to iron‐induced oxidative stress are ongoing. Our findings demonstrate that DmTsf1 inhibits bacterial growth by iron sequestration, that it does not protect against at least some types of oxidative stress, and that it plays an essential but still unknown role in development.Support or Funding InformationNIH NGMS R37 GM041247, NSF IOS 1656388This abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.