Retrotransposon silencing by DNA methylation contributed to the evolution of placentation and genomic imprinting in mammals
Article first published online: 21 JUL 2010
© 2010 The Authors. Journal compilation © 2010 Japanese Society of Developmental Biologists
Development, Growth & Differentiation
Special Issue: Epigenetics
Volume 52, Issue 6, pages 533–543, August 2010
How to Cite
Kaneko-Ishino, T. and Ishino, F. (2010), Retrotransposon silencing by DNA methylation contributed to the evolution of placentation and genomic imprinting in mammals. Development, Growth & Differentiation, 52: 533–543. doi: 10.1111/j.1440-169X.2010.01194.x
- Issue published online: 21 JUL 2010
- Article first published online: 21 JUL 2010
- Received 21 February 2010; revised 23 May 2010; accepted 23 May 2010.
- genomic imprinting;
- mammalian evolution;
The evolution of two mammalian-specific traits, viviparous reproduction with a placenta and genomic imprinting, have been addressed by multiple studies of two retrotransposon derived, mammalian-specific genes. These gene targeting experiments in mice, together with recent comparative genomic analyses among three mammalian groups, suggest that extremely rare events; namely exaptations from retrotransposons, made crucial contributions to the establishment and diversification of mammals via placental formation. We propose that nearly neutral evolution, as well as Darwinian evolution (natural selection), plays an important role in the exaptation process. Comparative genomic analysis of various imprinted regions has also revealed that an imprinting control element essential for parent-of-origin specific monoallelic expression of imprinted genes emerged in each of the imprinted regions, possibly by the insertion of exogenous DNAs, such as retrotransposons. In both cases, DNA methylation in germ cells must have been of critical importance to repress the exogenous DNAs inserted into the genomes of mammalian ancestors. We propose that the ability of germ line DNA methylation enabled the emergence of certain mammalian-specific features during the course of evolution.