A Toll receptor from Chinese shrimp Fenneropenaeus chinensis is responsive to Vibrio anguillarum infection

Toll-like receptors (TLRs) are an evolutionarily ancient family of pattern recognition receptors (PRRs), playing a crucial role in innate immune responses. Here we present a Toll homolog from Chinese shrimp Fenneropenaeus chinensis, designated FcToll. The full-length cDNA of FcToll is 4115 bp including a poly A-tail of 16 bp, encoding a putative protein of 931 amino acids. The predicted protein consists of an extracellular domain with a potential signal peptide, 16 leucine-rich repeats (LRR), two LRR-C-terminal (LRR-CT) motifs, and two LRR-N-terminal (LRR-NT) motifs, followed by a transmembrane segment of 23 amino acids, and a cytoplasmic Toll/Interleukin-1R (TIR) domain of 139 residues. Genomic structure of FcToll gene contains five exons and four introns. Phylogenetic analysis revealed that it belongs to insect-type invertebrate Toll family. Transcripts of FcToll gene were constitutively expressed in various tissues, with predominant level in lymphoid organ. Real-time PCR assays demonstrated that expression patterns of FcToll were distinctly modulated after bacterial or viral stimulation, with significant enhancement after 5 h post-Vibrio anguillarum challenge but markedly reduced levels immediately after white spot syndrome virus (WSSV) exposure. These results suggest that FcToll might be involved in innate host defense, especially against the pathogen V. anguillarum.