Molecular cloning and DNA binding characterization of DAF-16 orthologs from Ancylostoma hookworms

Abstract

Infective hookworm L3s encounter a host-specific signal during infection that re-initiates a suspended developmental pathway, resulting in development to the adult stage. This resumption of development in the host is analogous to recovery of developmentally arrested Caenorhabditis elegans dauer larvae in response to favorable environmental signals. Dauer recovery in C. elegans dauers and hookworm L3s is mediated by insulin-like signaling (ILS). A key output of ILS in C. elegans is the forkhead transcription factor DAF-16, which controls the expression of genes required for maintenance of the dauer stage. The similarity between recovery pathways of L3s and dauers suggests that DAF-16 functions similarly in hookworm L3 activation. To test this, orthologs of Ce-DAF-16 were isolated from the hookworms Ancylostoma caninum and Ancylostoma ceylanicum. The protein sequences of hookworm DAF-16 DNA binding domains were identical, and shared 94% identity with the b and c isoforms of Ce-DAF-16. Ac-DAF-16 expressed in HEK293 kidney cells bound strongly to the conserved DAF family binding element (DBE), but not to a random DNA sequence. Ac-DAF-16 was able to drive transcription of a reporter gene located downstream of six copies of the DBE in NIH3T3 cells under starved conditions. Addition of serum caused a decrease in reporter gene expression, indicating that DAF-16 is negatively regulated by growth factor stimulation. These data confirm the presence of DAF-16 orthologs in hookworms, and demonstrate that Ac-DAF-16 binds to and drives transcription from a conserved DAF-16 family DNA binding element.