Evolutionary history and functional characterization of Lj-TICAM-a and Lj-TICAM-b formed via lineage-specific tandem duplication in lamprey (Lampetra japonica).

Toll/interleukin-1 receptor domain-containing adaptor molecule (TICAM) genes respond to infections. We identified TICAM-a and TICAM-b in Lampetra japonica and investigated their evolutionary history and potential function via comparative genomics and molecular evolution analyses. They are arranged in tandem and evolved from a multi-exon to a single-exon structure. Lj-TICAM-a and Lj-TICAM-b might be the ancestral gene of the vertebrate TICAM genes. Lj-TICAM-b arose via a lamprey-specific tandem duplication event. Both genes are expressed in many tissues during an immune response, and exhibit different responses to peptidoglycan, indicating their functional divergence. Simultaneous overexpression of both proteins activated nuclear factor κB expression and co-immunoprecipitation assays indicated that they might form a complex for signal transduction. However, unlike in mammals, the TICAM-dependent signaling pathway in lamprey might rely on TRAF3 rather than on TRAF6. These results suggest that both Lj-TICAM-a and Lj-TICAM-b play a role in host defenses.