Evidence for evolving Toll-IL-1 receptor-containing adaptor molecule function in vertebrates.

Area of Science:

• Immunology
• Evolutionary Biology
• Molecular Biology

Background:

• Toll-IL-1R-containing adaptor molecule 1 (TICAM1) is crucial for Toll-like receptor (TLR) signaling in mammals, mediating NF-kappaB and IFN-beta production.
• TICAM1 activates NF-kappaB via TNFR-associated factor 6 and receptor-interacting protein 1, and IFN regulatory factor 3/7 for IFN-beta induction.

Purpose of the Study:

• To identify and characterize the zebrafish TICAM1 ortholog and elucidate its role in NF-kappaB and type I IFN activation.
• To investigate the functional consequences of sequence divergence between zebrafish and mammalian TICAM1.

Main Methods:

• Sequence, phylogenetic, and syntenic analyses to identify zebrafish TICAM1.
• Functional assays to assess NF-kappaB and IFN activation by zebrafish TICAM1.
• Interaction studies with known mammalian TICAM1 binding partners.

Main Results:

• A zebrafish TICAM1 ortholog was identified, exhibiting sequence divergence from mammalian counterparts.
• Zebrafish TICAM1 activates zebrafish type I IFN independently of IFN regulatory factor 3/7.
• NF-kappaB activation by zebrafish TICAM1 relies on interaction with receptor-interacting protein 1, not TNFR-associated factor 6.
• Comparative genomics suggests TICAM1 and TICAM2 evolved from a common ancestor, with TICAM2 lost in teleosts.

Conclusions:

• Zebrafish TICAM1 has evolved distinct mechanisms for activating innate immune responses compared to mammals.
• These findings highlight the functional evolution of the TICAM1-dependent TLR pathway in vertebrates.
• The study provides novel insights into the divergence of immune signaling pathways in fish.