Sea anemone model has a single Toll-like receptor that can function in pathogen detection, NF-κB signal transduction, and development

Significance Toll-like receptors (TLR) are involved in pathogen recognition and defense in organisms from fruit flies to humans. Recent genomic evidence suggests that TLRs and their downstream signaling components are present in more basal phyla. We characterize a TLR in a sea anemone model and demonstrate its ability to activate NF-κB signaling when exposed to a bacterial pathogen and a known human TLR activator. Moreover, this TLR has an early developmental role in anemones. We also identify a primitive sea anemone organ that expresses components of the TLR–to–NF-κB pathway. These results demonstrate that TLRs have ancient roles in NF-κB signal transduction, pathogen detection, and development, thus providing molecular insights into how simple marine invertebrates may respond to pathogens.