The evolution of X-linked genomic imprinting

Area of Science:

• Evolutionary genetics
• Genomics

Background:

• X-imprinting, the differential expression of X-linked genes based on parental origin, is a complex epigenetic phenomenon.
• Understanding the evolutionary pressures shaping X-imprinting is crucial for comprehending gene regulation and inheritance.

Purpose of the Study:

• To develop a quantitative genetic model to investigate the evolutionary forces driving X-imprinting.
• To compare the explanatory power of genomic conflict versus sex-specific selection on X-imprinting.

Main Methods:

• Development of a quantitative genetic model.
• Comparative analysis of two selection forces: genomic conflict (polygamy) and sex-specific selection.
• Inclusion of Y chromosome activity as a variable.

Main Results:

• Genomic conflict alone cannot fully explain X-imprinting, particularly maternal X gene silencing.
• Sex-specific selection can drive extreme gene expression modifications, including silencing of either maternal or paternal alleles.
• An active Y chromosome homologue leads to an autosomal-like imprinting pattern (active paternal, silenced maternal), but this is likely limited by mutation accumulation.

Conclusions:

• Sex-specific selection provides a more robust explanation for observed X-imprinting patterns than genomic conflict.
• Experimental data from mice and humans align better with predictions derived from sex-specific selection models.
• The evolutionary trajectory of X-imprinting is strongly influenced by differential selective pressures between sexes.