Characteristics of Imprinted Genes

Monoallelic expression :


This refers to the transcription of a gene from a single parental allele. Some imprinted genes are monoallelically expressed only in particular organ or tissue, and can be expressed from both parental alleles in other parts of the body.


Clustering of Imprinted genes into evolutionary conserved domains :
One of the hallmarks of imprinted genes is that many are evolutionary conserved domains are found in clusters throughout the genome. These clusters contain two or more imprinted genes over a region that can span 1 Mb or more. The genes in the clusters, which can be either maternally or paternally expressed, are jointly regulated through an imprinting control region (ICR). The ICRs exhibit parental-specific epigenetic modifications (DNA methylation and histone modifications) that govern their activity.


Parental – allele – specific methylation :
DNA can be modified by methyl groups that attach to cytosine residues within specific CpG (cytosine phosphate diester guanine) dinucleotide pairs. Methylation of a single parental allele is a hallmark of imprinted genes. This usually occurs across the CpG islands (generally at the 5’- end of the genes), and methylation of an allele usually correlates with its transcriptional inactivation.