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Positive selection and functional divergence after melanopsin gene duplication.

Changgui Dong1, Junpeng Zhang, Jian Qiao

  • 1Department of Pathophysiology, College of Veterinary Medicine, China Agricultural University, Beijing, China.

Biochemical Genetics
|September 29, 2011
PubMed
Summary

Melanopsin gene (Opn4) evolution reveals duplication before vertebrates and loss in mammals. Analysis shows purifying selection on Opn4m and positive selection on Opn4x, indicating functional divergence.

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Area of Science:

  • Evolutionary Biology
  • Genetics
  • Molecular Biology

Background:

  • Melanopsin (Opn4) is a light-sensitive opsin crucial for non-visual light responses.
  • Two forms, Opn4m and Opn4x, exist in vertebrates, but their evolutionary origins are unclear.
  • Understanding melanopsin gene duplication is key to deciphering vertebrate visual and circadian system evolution.

Purpose of the Study:

  • To elucidate the evolutionary history and duplication mechanisms of melanopsin (Opn4) genes.
  • To investigate the selective pressures acting on Opn4m and Opn4x during vertebrate evolution.
  • To provide a genetic basis for comparative functional studies of melanopsin variants.

Main Methods:

  • Phylogenetic analysis of melanopsin gene sequences across diverse vertebrate species.
  • Evolutionary computational analyses to detect selection pressures (purifying and positive selection).
  • Identification of positively selected amino acid sites to infer functional divergence.

Main Results:

  • The duplication of Opn4m and Opn4x predates vertebrate emergence.
  • Opn4x was subsequently lost in mammalian lineages.
  • Strong purifying selection acted on melanopsin evolution, while Opn4x experienced positive selection post-duplication, suggesting functional divergence.

Conclusions:

  • Vertebrate melanopsin genes exhibit significant evolutionary malleability.
  • Evidence suggests functional divergence between Opn4m and Opn4x due to altered functional constraints and positive selection on Opn4x.
  • This study provides a foundation for understanding the distinct roles of melanopsin paralogs in vertebrates.