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Sex chromosome inactivation is essential epigenetic programming in male germ cells. However, it remains largely unclear how epigenetic silencing of sex chromosomes impacts the evolution of the mammalian genome. We recently demonstrated that male sex chromosome inactivation is highly conserved between humans and mice and has an impact on the genetic evolution of human sex chromosomes. Our analyses suggest that male sex chromosome inactivation has impacted multiple aspects of the evolutionary history of mammalian sex chromosomes: amplification of copy number, retrotranspositions, acquisition of de novo genes, and acquisition of different expression profiles. We propose that the epigenetic silencing mechanism impacts the genetic evolution of sex chromosomes and contributed to speciation and reproductive diversity in mammals. We further investigate the epigenetic impacts on sex chromosome evolution.
Figure 2 - Evolutional impacts of postmeiotic silencing. (A) Evolutional history of escape genes from postmeiotic silencing in the course of mammalian evolution. Genes in Lists A-F are displayed in Table S8. Stars denote the acquisition timing of de novo genes. Mya: million years ago. (B) Distribution of Ka/Ks values of X-linked escape genes and non-escape genes (listed in Table S9) along the length of the X chromosome. Ka/Ksvalues are calculated between humans and mice. Sin et al Genome Res 2012 22: 827-836.
Sin, H. S., and Namekawa, S. H. The great escape: active genes on inactive sex chromosomes and their evolutionary implications. Epigenetics. Sep;8(9):887-92. 2013
Sin, H. S., Ichijima, Y., Koh, E.,Namiki, M., and Namekawa, S. H.* Human post meiotic sex chromatin and its impact on sex chromosome evolution. Genome Res. 2012 May;22(5):827-36.
Payer, B.,* Lee, J. T., and Namekawa, S. H.* X-inactivation and X-reactivation: Epigenetic hallmarks of mammalian reproduction and pluripotent stem cells. Hum Genet. 2011 Aug;130(2):265-80.
Namekawa, S. H. and Lee, J. T. XY and ZW: is meiotic sex chromosome inactivation the rule in evolution? PLoS Genet. 2009 May;5(5):e1000493.
Namekawa, S. H., VandeBerg, J. L., McCarrey, J. R., and Lee, J. T. Sex chromosome silencing in the marsupial male germ line. Proc Natl Acad Sci U S A. 2007 Jun 5;104(23):9730-5.
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