Abstract
DNA methylation is a key epigenetic modification in vertebrate genomes known to be involved in the regulation of gene expression, X chromosome inactivation, genomic imprinting, chromatin structure, and control of transposable elements. DNA methylation is common to all eukaryote genomes, but we still lack a complete understanding of the variation in DNA methylation patterns on sex chromosomes and between the sexes in diverse species. To better understand sex chromosome DNA methylation patterns between different amniote vertebrates, we review literature that has analyzed the genome-wide distribution of DNA methylation in mammals and birds. In each system, we focus on DNA methylation patterns on the autosomes versus the sex chromosomes.
Highlights
Genetic sex determination is often accompanied by the presence of differentiated sex chromosomes
Is autosomal in marsupials, defining an X-added region (XAR) that was translocated to the sex chromosomes in the eutherian mammal ancestor (Figure 1a)
This is consistent with a model in which the acquisition of a novel testis-determining factor (TDF) was followed by the nearby accumulation of alleles that were beneficial to males on the proto-Y chromosome, increasing the likelihood of being inherited in males
Summary
Genetic sex determination is often accompanied by the presence of differentiated sex chromosomes. Therians (eutherians and marsupials) typically have an XX female/XY male sex chromosome system. The remainder of the human X is autosomal in marsupials (and is separate from the XCR in other vertebrates), defining an X-added region (XAR) that was translocated to the sex chromosomes in the eutherian mammal ancestor (reviewed in [4]) (Figure 1a). We outline the processes of sex chromosome evolution and dosage compensation and relate them to the DNA methylation patterns on different sex chromosome systems. To understand this relationship and its implications for a potential role in gene silencing, we review DNA methylation patternsGenes from birds through to mice.
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