Rapid and repeated evolution of myosin copy number in threespine stickleback

Area of Science:

• Evolutionary genetics
• Genomics
• Comparative genomics

Background:

• Copy number variants (CNVs) are crucial in adaptive evolution and disease.
• Gene duplication is a major driver of evolutionary innovation.

Purpose of the Study:

• To investigate the role of gene copy number changes in adaptive divergence between marine and freshwater stickleback fish.
• To understand the mechanisms and evolutionary consequences of MYH3C gene family expansion.

Main Methods:

• Comparative genomics analysis of marine and freshwater stickleback populations.
• Identification and characterization of copy number variants (CNVs) in the MYH3C gene family.
• Analysis of MYH3C gene expression in skeletal muscle tissues.
• Investigation of duplication mechanisms, including microhomology-mediated break repair and non-allelic homologous recombination.

Main Results:

• Freshwater stickleback populations exhibit rapid and repeated expansion of the MYH3C gene family compared to marine populations.
• MYH3C copy number differences are maintained despite gene flow, indicating adaptive divergence.
• Copy number expansion involves tandem duplication of coding and regulatory regions on the sex chromosome.
• Elevated MYH3C copy number correlates with increased mRNA expression in skeletal muscle.
• Common MYH3C copy number variants include 3-, 4-, 5-, and 6-copy clusters.

Conclusions:

• CNVs, specifically MYH3C expansion, are key drivers of adaptive evolution in wild stickleback populations.
• The stickleback sex chromosome acts as a hotspot for adaptive CNV evolution.
• MYH3C copy number variation provides a model for studying rapid adaptation in response to environmental changes.