Genomic imprinting is an Epigenetic phenomenon where certain genes are expressed exclusively from the maternal or paternal copy, not both. This selective silencing or activation, guided by parent-of-origin, is crucial for proper Development and stable Gene Expression patterns, without altering the underlying DNA sequence.
Unlike typical Mendelian Inheritance where both copies of a gene contribute to the phenotype, imprinted genes maintain a memory of their parental origin. This 'imprint' is established during Gametogenesis in the germline and is maintained throughout somatic cell divisions, leading to monoallelic expression where only one of the two alleles is active.
The molecular mechanisms underlying genomic imprinting primarily involve DNA Methylation and Histone Modification at specific genomic regions known as Imprinting Control Regions (ICRs). These epigenetic marks differentiate the maternal and paternal alleles, leading to the transcriptional silencing of one allele while the other remains active. For instance, a gene might only be expressed if inherited from the mother, or conversely, only if inherited from the father. These marks are reset in the germline of the next generation, ensuring parent-of-origin-specific imprinting is re-established.
Genomic imprinting plays a critical role in Embryogenesis, placental formation, and postnatal growth and metabolism. Proper dosage of imprinted genes is vital, as errors in imprinting can lead to severe developmental disorders and diseases. Examples of human disorders associated with disrupted imprinting include Prader-Willi Syndrome and Angelman Syndrome, which arise from deletions or epigenetic defects on Chromosome 15. These conditions highlight the delicate balance maintained by correct imprinting and its profound impact on human health.
