Evolutionary significance of gene expression divergence

Area of Science:

• Evolutionary biology
• Genomics
• Molecular evolution

Background:

• Large-scale studies suggest gene expression divergence may be neutral regarding fitness.
• The evolution of gene expression patterns and levels is a key area in understanding mammalian evolution.

Purpose of the Study:

• To test the hypothesis that gene expression evolution is predominantly neutral.
• To compare gene sequence divergence with gene expression divergence in mammals.
• To evaluate models of neutral evolution versus selective constraint in gene expression.

Main Methods:

• Comparative analysis of mammalian gene sequence and gene expression divergence.
• Testing correlations between gene expression changes and sequence divergence.
• Relative rate tests on orthologous gene sets (human-mouse-rat).

Main Results:

• Gene expression levels correlate with sequence divergence (purifying selection), but tissue-specific profiles do not.
• Divergence in gene expression levels and profiles is lower for orthologs than random gene pairs, indicating selective constraint.
• Clock-like evolution observed for sequence divergence and, to a lesser extent, expression levels, but not tissue-specific profiles.

Conclusions:

• Gene expression divergence is influenced by selective constraint, inconsistent with purely neutral evolution.
• A neutral component likely exists, especially in tissues with low or irrelevant gene expression.
• Evidence suggests both purifying and potentially positive Darwinian selection shape gene expression evolution.