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MHC class I evolution; from Northern pike to salmonids.

U Grimholt1, M Lukacs2

  • 1Fish Research Group, Norwegian Veterinary Institute, Ullevaalsveien 68, 0454, Oslo, Norway. Unni.Grimholt@vetinst.no.

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|January 30, 2021
PubMed
Summary
This summary is machine-generated.

Salmonids possess unique Major Histocompatibility Complex class I (MHCI) gene duplications, distinct from Northern Pike, reflecting evolutionary adaptations in their immune systems. These duplications, particularly in the L lineage, suggest significant functional diversity in salmonids.

Keywords:
EvolutionMHC class INorthern pikePhylogenySalmonidsWhole genome duplication

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Area of Science:

  • Immunogenetics
  • Evolutionary Biology
  • Comparative Genomics

Background:

  • Salmonids are crucial farmed and wild species facing evolving environmental and pathogenic pressures.
  • Understanding their immune system, particularly Major Histocompatibility Complex (MHC) genes, is essential for health and management.
  • Classical MHC class I (MHCI) genes are vital for adaptive immunity, with salmonids possessing duplicate regions due to a whole genome duplication event.

Purpose of the Study:

  • To compare the gene organization and evolution of MHC class I gene sequences in salmonids and Northern Pike.
  • To investigate the impact of whole genome duplication events on MHCI gene evolution in salmonids.
  • To understand the diversification of MHCI lineages, including U, Z, and L, in salmonids.

Main Methods:

  • Comparative analysis of MHC class I gene sequences between salmonids and Northern Pike.
  • Phylogenetic analysis to trace the evolutionary history of MHCI gene duplications.
  • Examination of gene duplication patterns across different salmonid lineages (Ia, Ib, Z, U, L).

Main Results:

  • Salmonid MHCI gene duplicates (Ia, Ib, Z lineages) are not orthologous to Northern Pike sequences, indicating unique salmonid-specific duplications.
  • Both salmonids and Northern Pike show expanded U and Z lineage genes, but these duplications occurred independently.
  • Massive species-specific gene duplications in the L lineage occurred after the divergence of Oncorhynchus and Salmo.

Conclusions:

  • Salmonid MHCI evolution is characterized by unique gene duplications, distinct from basal relatives like Northern Pike.
  • The MHCIa and MHCIb regions in salmonids originated after their split from pike, predating the Oncorhynchus and Salmo divergence.
  • The extensive diversification of L lineage genes in salmonids suggests a broad range of functional roles and adaptations in their immune response.