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Updated: May 22, 2025

Detection of Ligand-activated G Protein-coupled Receptor Internalization by Confocal Microscopy
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Duplicated TLRs Possess Sub- and Neo-Functionalization to Broaden Their Ligand Recognition in Crucian Carp (Carassius

Yihui Fan1,2, Miaomiao Wu2,3, Caijiao Dai1,2

  • 1Department of Aquatic Animal Medicine, College of Fisheries, Huazhong Agricultural University, Wuhan, People's Republic of China.

European Journal of Immunology
|March 12, 2025
PubMed

Insights

Crucian carp Toll-like receptors (TLRs) show unique immune responses. Gene duplication and new functions in TLR3 and TLR5 help fish detect diverse pathogens, enhancing aquatic immune defense.

Area of Science:

  • Immunology
  • Genomics
  • Evolutionary Biology

Background:

  • Toll-like receptors (TLRs) are vital for innate immunity, recognizing pathogen-associated molecular patterns.
  • Teleost fish exhibit distinct TLR expression and function compared to mammals.
  • Understanding fish TLRs is crucial for aquaculture and aquatic ecosystem health.

Purpose of the Study:

  • To identify and characterize the Toll-like receptor (TLR) gene family in crucian carp (Carassius auratus).
  • To investigate the expression patterns and functional roles of crucian carp TLRs in immune response.
  • To explore the evolutionary adaptations of TLRs in fish immunity.

Main Methods:

  • Phylogenetic analysis to determine TLR family structure and relationships.
  • mRNA expression profiling to assess TLR responses to pathogens and ligands.
  • Functional assays to study the sensing capabilities and dimerization of specific TLRs (CaTLR3, CaTLR5).

Main Results:

  • The crucian carp TLR family comprises 25 members across six subfamilies.
  • Most TLRs displayed varied expression patterns upon challenge with different pathogens or ligands.
  • Duplicated CaTLR3 and CaTLR5 exhibited cross-sensing of poly (I:C) and flagellin, activating immune responses.
  • CaTLR3b, not CaTLR3a, homodimerizes to detect flagellin, with S310 identified as a key binding site.

Conclusions:

  • The expansion and functional diversification of TLR genes in crucian carp enhance pathogen recognition capabilities.
  • Sub- and neo-functionalization of duplicated TLRs represent an evolutionary strategy for fish immunity in aquatic environments.
  • These findings provide insights into the molecular mechanisms of fish immune defense against diverse pathogens.
Keywords:
TLR3cross‐sensecrucian carpdsRNAflagellin

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