Imprinting in Genomes

It is a known fact that half of our chromosomes are obtained from our mother and the other half from our father. These chromosomes contain genes. Some of these genes are expressed only from one of the two inherited parental chromosomes which is known as genomic imprinting. Some imprinted genes are maternally inherited and some are paternal. This is one of the modes of gene regulation that mammalian genes utilize to control gene expression. Evidence exists for genomic imprinting to occur in plants as well.

One evidence for imprinting comes from experiments conducted in mice where mice embryos containing two maternal sets of chromosomes (both set of chromosomes from the mother and no contribution by the father) or vice versa were in viable.

Some imprinting disorders are identified in humans too. Loss of paternally inherited chromosome 15 results in Prader-Willi Syndrome (PWS) and loss of maternally inherited chromosome 15 delivers Angelman Syndromes (AS). Both the diseases are distinct neurological disorders.

All imprinted genes identified to date are expressed in the developing embryo, placenta and in the brain of the fetus and the newborn.

Imprinted genes in two parental chromosomes are tagged or marked for transcriptional machinery to distinguish them from non imprinted counterparts. These marks are known as epigenetic modifications that include DNA methylation and post translational modification of core histones. These modification alter chromatin structure and influence transcription.

One rather startling information suggests a higher percentage of imprinted disorders in people born via in vitro reproductive technologies. Research continues to reveal further insights into this exquisite mechanism of gene regulation.