Toll-like receptors landscape in Takifugu fasciatus: Dynamic responses to Aeromonas hydrophila, poly I:C, and Ichthyophthirius multifiliis challenge

Abstract

Toll like receptors (TLRs) are essential for host defense, recognizing pathogen-associated molecular patterns (PAMPs) from infectious agents. However, limited information is available on TLRs in Takifugu fasciatus, a model species for comparative genomics and aquaculture. This study identified twelve T. fasciatus TLR genes, mapping them across nine chromosomes. Phylogenetic analysis revealed that the TfTLRs share orthologs from five vertebrate subfamilies, excluding the TLR4 subfamily. Gene synteny analysis confirmed the conservation of neighboring genes of TfTLRs within Neoteleostei, validating our annotation of TfTLRs. RT-PCR analysis showed ubiquitous expression of all TfTLRs across nine tissues, underscoring their role in immune homeostasis. Furthermore, RT-qPCR analysis showed significant expression changes in TfTLR2, TfTLR3, TfTLR5m, TfTLR5s and TfTLR8 in response to Aeromonas hydrophilia infection in vivo, while TfTLR3, TfTLR5m, TfTLR22, and TfTLR23 were responsive to poly I:C both in vivo and in vitro. In contrast, no significant TfTLRs expression changes were observed upon Ichthyophthirius multifiliis infection, suggesting their distinct roles in pathogens recognition. These findings deepen our understanding of TLR function in teleosts, providing valuable insights for future immune research in fish species.