Genetic characterization, cloning, and expression of Toll-like Receptor 1 mRNA Nile tilapia

Toll-like receptors (TLRs) are the most studied group of pathogen recognition receptor categories that detects infectious agents in vertebrates. Fish TLRs exhibit clear, distinct features, structure and a larger diversity than in other vertebrates. This study focused on identifying and detecting the structure of Oreochromis niloticus (Nile tilapia) Tolllike receptor-1 (TLR1|) as a model in freshwater bony fish. The full-length cDNA sequence of Oreochromis niloticus TLR1 mRNA was cloned. Cloning and sequence analysis revealed that the complete cDNA sequence of Oreochromis niloticus TLR1 consists of 2355 base pairs and encodes a polypeptide of 785 amino acids. The molecular analysis of the amino acid sequence indicated that Oreochromis niloticus TLR1 has the standard structural features and major components of amino acids of TLR family members, and is considered an orthologue to the vertebrate TLR1, not a paralogue. The translated amino acid analysis showed 96%, 88%, 85%, and 85% degrees of identity with Zebra Mbuna, Sea bass, Damsel fish, and Clownfish, respectively; and showed 66% identity t with electric eels and 61% with starlets. Phylogenetic analysis revealed that the Nile tilapia TLR1 is closely related to Larimichthys crocea, Epinephelus coioides, and Takifugu rubripes TLR1. Oreochromis niloticus TLR1 was expressed in the kidneys, brain, spleen, intestines, muscle, liver, gills, heart and skin. Quantitative RT-PCR showed differences in the expression levels between the tested tissues. In conclusion, this study is the first report (according to our knowledge) and provides a complete molecular and functional characterization of Oreochromis niloticus toll-like receptor 1, which is considered to be functionally orthologous to TLR1 in other species models. Key words: Oreochromis niloticus (Nile tilapia); transmembrane structure; fish; Toll-like receptor; TLR1; fish innate immunity