Role of a sea anemone (Nematostella vectensis) toll-like receptor in pathogen detection, development, and activation of NF-kappaB signaling
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In organisms from insects to vertebrates, Toll-like receptors (TLRs) are primary pathogen detectors that activate downstream pathways, specifically those that direct expression of innate immune effector genes. TLRs also have roles in development in many species. The sea anemone Nematostella vectensis is a useful cnidarian model to study the origins of TLR signaling because its genome encodes a single TLR and homologs of many downstream signaling components, including the NF-κB pathway. In this dissertation, the single N. vectensis TLR (Nv-TLR) is characterized. It is demonstrated that Nv-TLR can activate canonical NF-κB signaling in human cells, the intracellular TIR domain of Nv-TLR can interact with human TLR adapter proteins MAL and MYD88, and the TIR domain of Nv-TLR is required for NF-κB activation. It is shown that the coral pathogen Vibrio coralliilyticus causes a rapidly lethal disease in N. vectensis and that heat-inactivated V. coralliilyticus and bacterial flagellin can activate a reconstituted Nv-TLR-to-NF-κB pathway in human cells. By immunostaining of anemones, Nv-TLR is shown to be expressed in a subset of cnidocytes and many of these Nv-TLR-positive cells also express Nv-NF-κB. Additionally, the nematosome, which is a Nematostella-specific multicellular structure, expresses Nv-TLR, many innate immune pathway homologs, and can engulf V. coralliilyticus. Morpholino knockdown indicates that Nv-TLR also has an essential role during early embryonic development. The characterization of this primitive TLR and identification of a bacterial pathogen for N. vectensis reveal ancient TLR functions and provide a novel model for studying the molecular basis of cnidarian disease and immunity.