Molecular cloning and tissue distribution of the Toll receptor in the black tiger shrimp, Penaeus monodon

The black tiger shrimp (Penaeus monodon) is economically important in many parts of the world, including Thailand. Shrimp immunity is similar to that of other invertebrate organisms; it consists of an innate immunity system. Toll or Toll-like receptors (TLRs) play an essential role in recognizing the cleaved form of the cytokine Spatzle, which is processed by a series of proteolytic cascades activated by secreted recognition molecules. We isolated a full-length Toll receptor from P. monodon. The cloned full-length sequence of the PmToll cDNA consists of 4144 nucleotides, containing a 5'-UTR with 366 nucleotides, a 3'-terminal UTR with 985 nucleotides, with a classical polyadenylation signal sequence AATAAA, a poly A-tail with 27 nucleotides, and an open reading frame coding for 931 amino acids. The deduced amino acid sequence of PmToll is a typical type I membrane domain protein, characteristic of TLR functional domains. It includes a putative signal peptide, an extracellular domain consisting of leucine-rich repeats, flanked by cysteine-rich motifs, a single-pass transmembrane portion, and a cytoplasmic TLR domain. PmToll was expressed in all tissues tested, including gill, hemocytes, heart, hepatopancreas, lymphoid organs, muscle, nerve, pleopod, stomach, testis, and ovary. The deduced amino acid of PmToll is closely related to that of other shrimp Tolls, especially FcToll. Further studies elucidating the mechanism of action of Tolls will be of benefit for understanding the defense mechanisms of this economically important aquatic species.