Characterization of a honey bee Toll related receptor gene Am18w and its potential involvement in antimicrobial immune defense

Toll receptors are involved in intracellular signal transduction and initiation of insect antimicrobial immune responses. Here we report the isolation and characterization of a novel gene (Am18w) from honey bee Apis mellifera, which encodes for the Toll-like receptor and shares a striking 51.4% similarity with Bombyx mori 18-wheeler, 46.6% with Drosophila Toll-7 receptor and 42.5% with Drosophila 18-wheeler. The sequence analysis of the deduced 18W protein revealed a conserved Toll-Interleukin - Resistance signaling domain (TIR) characteristic of signal transducing receptors found in Toll and mammalian interleukin 1 (IL-1) receptors. The expression profiles of the honey bee Toll-like receptor gene Am18w were examined in all developmental stages, before and after immune challenge. Here we demonstrate that injection of a dsRNA probe into honey bee larvae successfully disrupts the endogenous mRNA of the target gene and allows us to examine the effects of Am18w gene silencing (RNAi) on the expression level of antimicrobial peptides.