Imprinting in mammals

1 ABSTRACT Genomic imprinting is a form of epigenetic regulation that results in gene expression from a single allele in a parent-of-origin manner. It is a form of monoallelic gene expression, another forms of monoallelic expression are X chromosome inactivation and stochastic monoallelic gene expression, so-called allelic exclusion. Imprinting affects expression of many genes which regulate growth and development. Disruption of imprinting leads to some diseases, such as Prader-Willie and Angelman syndromes, Russel-Silver and Beckwith- Wiedemann syndromes, transient neonatal diabetes, persistent hyperinsulinemic hypoglycemia of infancy and pseudehypoparathyroidism. Disruption of imprinting is implicated at some types of embryonic cancers. Imprinted genes are arranged in clusters and the expression in these domains is regulated by imprinting control regions (ICRs). Expression of imprinted genes is a complex process which underlies a strict regulatory mechanisms. DNA methylation and histone modifications are included in a molecular mechanism of imprinting. The methylation imprints are established during gametogenesis and are maintained during lifetime. Methylation marks at ICRs are essential for activity of genes localized in a cluster. Additional regulatory mechanism contributing to imprinting is non- coding...