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Imprinting and the Epigenetic Asymmetry between Parental Genomes

  1. Thomas Haaf

Published Online: 10 OCT 2011

DOI: 10.1002/3527600906.mcb.201100009

Encyclopedia of Molecular Cell Biology and Molecular Medicine

Encyclopedia of Molecular Cell Biology and Molecular Medicine

How to Cite

Haaf, T. 2011. Imprinting and the Epigenetic Asymmetry between Parental Genomes. Encyclopedia of Molecular Cell Biology and Molecular Medicine. .

Author Information

  1. Julius-Maximilians-University Würzburg, Institute of Human Genetics, Würzburg, Germany

Publication History

  1. Published Online: 10 OCT 2011

Abstract

Diploid organisms inherit a set of chromosomes from each parent. In contrast to Mendelian principles, according to which both parental alleles contribute equally to the phenotype, a small subset of genes in the mammalian genome is inherited in an inactive state from one parent, and in an active form from the other parent, thus conferring an epigenetic asymmetry on the two parental genomes. Many imprinted genes are involved in fetal and placental growth and/or tissue development. Genomic imprinting is regulated by DNA methylation and chromatin structure. Most imprinted genes are clustered with cis-acting imprinting control regions that carry parent-specific methylation patterns. These methylation imprints are established in the male or female germline, most likely because of a reproductive battle between the two sexes over the extraction of maternal resources for the offspring. The two germline epigenomes represent opposite parental interests and, therefore, must be reprogrammed after fertilization for somatic development. Genome-wide demethylation waves in the early embryo erase most germline methylation patterns, followed by de novo methylation and the establishment of somatic methylation patterns, which are identical on both parental alleles. Only imprinted genes escape this postzygotic reprogramming process and maintain their sex-specific epigenetic asymmetry in somatic cells. Their functional haploidy and complex regulation makes imprinted genes particularly susceptible to classical DNA sequence mutations and epigenetic errors. Apart from rare imprinting disorders, the dysregulation of imprinted genes has been linked to medical problems associated with assisted reproduction, pregnancy loss, cancer, neurodevelopmental and behavioral disorders, and various complex disease susceptibilities.

Keywords:

  • Chromatin;
  • Differentially methylated region (DMR);
  • DNA methylation;
  • Early embryogenesis (preimplantation development);
  • Epigenetics;
  • Epigenome;
  • Gametogenesis;
  • Germline;
  • Imprinting;
  • Imprinting control region (ICR); imprinting center (IC)