Independent evolution of Toll and related genes in insects and mammals

Toll and Toll-related proteins play an important role in antibacterial inna te immunity in insect, plants, and mammals. We present the first comprehens ive phylogenetic analyses of Toll-related genes from both insects and mamma ls. Drosophila melanogaster contains Toll and a highly homologous gene, Teh ao. The protein, Dm Tehao, comprises 795 amino acid residues and its cytopl asmic domain shares a striking 61% identity with Dm Toll. Two Toll homologu es were found in another dipteran of medical importance, Anopheles gambiae, a vector for human malaria. One Toll-like gene each was identified from Ae des aegypti and Glossina palpalis palpalis, vectors for yellow fever and tr ypanosomiasis, respectively. Phylogenetic analyses revealed separate cluste ring of Toll and related proteins from insects and mammals, suggesting inde pendent evolution of the Toll family of proteins and of innate immunity in arthropods and vertebrates. These results also provide new avenues to under standing the function of Toll proteins in insect innate immunity against ba cteria, fungi, and protozoans.