The first Toll receptor from the triangle-shell pearl mussel Hyriopsis cumingii.

Toll receptor was first discovered in Drosophila and has an important function in the innate immunity of invertebrates. In this study, the Toll receptor HcToll1 from Hyriopsis cumingii with a full length of 3810 bp consisting of a 3687 bp ORF that encodes a total of 1228 amino acids protein was selected for further study. The HcToll1 protein consisted of a signal peptide, 17 LRR domains, 2 LRRCT domains, 1 LRRNT domain, 1 TM domain, and 1 TIR domain. Phylogenetic analysis results showed that HcToll1 was clustered in one group together with other mollusca tolls. RT-PCR analysis results showed that HcToll1 was expressed in all tested tissues such as hemocytes, hepatopancreas, gills, and mantle. qRT-PCR analysis results showed that HcToll1 expression was increased by the presence of Escherichia coli, Vibrio anguillarum, Staphyloccocus aureus, and White Spot Syndrome Virus (WSSV). Over-expression of HcTIR could up-regulate expression of drosomycin gene in Drosophila S2 cells. The results of our study indicated that HcToll1 is a functional Toll and it has an important function in the generation of innate immune responses of H. cumingii against microbial challenge.