Chromatin accessibility, not 5mC methylation covaries with partial dosage compensation in crows

Area of Science:

• Evolutionary genetics
• Epigenetics
• Comparative genomics

Background:

• Genetic sex determination systems face challenges with sex chromosome dosage imbalance.
• Male heterogametic systems use epigenetic mechanisms for dosage compensation.
• Female heterogametic systems exhibit partial dosage compensation, with underlying mechanisms unclear.

Purpose of the Study:

• Investigate the mechanisms of partial dosage balance and compensation in female heterogametic systems.
• Quantify gene expression and epigenetic regulation in Eurasian crows.
• Determine the role of chromatin accessibility and DNA methylation in dosage regulation.

Main Methods:

• Gene expression profiling in male and female Eurasian crows.
• Chromatin accessibility analysis using ATAC-seq.
• 5mC methylation profiling.

Main Results:

• Female crows showed upregulation of Z-linked genes, correlating with increased Z chromosome chromatin accessibility.
• 5mC methylation was tissue- and sex-specific but not directly related to gene dosage.
• Upregulation was spread across the Z chromosome, without localized regulatory centers.

Conclusions:

• Partial dosage balance in female heterogametic systems is driven by chromosome-wide epigenetic control of the Z chromosome.
• Differential chromatin accessibility is a key mediator of this epigenetic regulation.
• Findings provide insights into the evolution of sex determination and dosage compensation.