Figure 4

Signaling pathways downstream of the Toll/TLRs. Pattern recognition, either indirectly or directly, by Toll/TLRs results in activation of NF-κB (vertebrates) or the Dif/Rel heterodimer (Drosophila) and thus transcription of appropriate immune response genes. At TRAF6, the classic Toll/TIR pathway (shown in the right branch) is linked to the JNK/p38 pathway (shown in the left branch) by the ECSIT protein, which acts as a regulator of MEKK-1 processing [35]. Components of both pathways downstream of Toll/TLRs are represented in the cnidarian datasets (Table 1). ECSIT may also act as a link between these and the TGF-b signaling pathway, since it forms complexes with BMP-pathway restricted Smads and is essential for regulation of the BMP-target gene Tlx2 [36]. All of the components of the TGF-b signaling pathway are also known from anthozoan cnidarians [13].