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Toll-Like Receptor Evolution in Birds: Gene Duplication, Pseudogenization, and Diversifying Selection.

Hana Velová1, Maria W Gutowska-Ding2, David W Burt3

  • 1Department of Zoology, Faculty of Science, Charles University, Prague, Czech Republic.

Molecular Biology and Evolution
|June 13, 2018
PubMed
Summary

Avian Toll-like receptors (TLRs) show diverse evolutionary paths, including gene duplication and loss. Selection pressures reveal key sites in TLRs likely shaped by host-pathogen interactions.

Keywords:
adaptive evolutionamino acid physicochemical propertiesconvergencepattern recognition receptorspositive selectionpseudogene

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Area of Science:

  • Immunology
  • Evolutionary Biology
  • Genomics

Background:

  • Toll-like receptors (TLRs) are crucial for innate immunity in vertebrates, recognizing pathogen-associated molecular patterns.
  • The avian TLR family comprises ten receptors, each with specific ligand-binding capabilities.

Purpose of the Study:

  • To investigate the evolutionary history and genetic variability of avian Toll-like receptors (TLRs).
  • To identify sites under selection and potential functional roles in avian immune responses.

Main Methods:

  • Comparative genomic analysis of TLRs across 63 bird species.
  • Identification of gene duplication, pseudogenization, and positive selection events.
  • Analysis of functionally relevant TLR regions and convergent evolution with mammals.

Main Results:

  • TLR1 gene duplication predates synapsid diversification; TLR7 duplicated independently in avian taxa.
  • TLR5 pseudogenization occurred multiple times; TLR5 and extracellular TLRs experienced stronger positive selection.
  • 84 positively selected sites showed significant amino acid property changes, with 54 sites showing convergent evolution with mammals.

Conclusions:

  • Avian TLR evolution is characterized by gene gain/loss and significant adaptive selection.
  • Specific TLR regions, particularly those facing the extracellular space, are shaped by host-pathogen coevolution.
  • This study provides insights into the molecular basis of avian immune defense and TLR evolution.