Imprinting (Mammals)


Genomic imprinting confers functional differences on parental genomes in mammals. This is due to germ line‐specific modifications of imprinted genes that regulate their parent of origin dependent expression in embryos.

Keywords: DNA methylation; imprinted genes; germ line; cis element

Figure 1.

Chromosomal regions in the mouse with imprinted genes. The overt phenotypic effects of the imprinted regions are indicated. Some genes recently identified are outside the genetically defined imprinted regions.

Figure 2.

A cluster of imprinted genes on the mouse distal chromosome 7. The domain consists predominantly of genes which display expression of the maternal allele. Evidence suggests that expression of Igf2 and H19 is linked mechanistically while other genes further upstream are regulated independently of the two genes. The figure also illustrates the key methylation difference on parental chromosomes.

Figure 3.

The key events associated with genomic reprogramming in the germline. The parental imprints are first erased in the male and female primordial germ cells as judged by demethylation of these loci. The homologous chromosomes thus attain an identical epigenetic state probably for the only time in the life of a mammal. The new imprints are germline‐specific and they are initiated during gametogenesis. This process is essentially complete by the time sperm and oocytes are formed. After fertilization, the new imprints are propagated during development and they can persist into adulthood. As a result, only one parental allele is expressed, resulting in the monoallelic expression of imprinted genes in appropriate cells.



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Further Reading

Barlow DP (1997) Competition – a common motif for the imprinting mechanism? EMBO Journal 16: 6899–6905.

Bartolomei MS and Tilghman SM (1997) Genomic imprinting in mammals. Annual Review of Genetics 31: 493–525.

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Lalande M (1996) Parental imprinting and human disease. Annual Review of Genetics 30: 173–195.

Reik W and Surani MA (eds) (1997) Genomic Imprinting: Frontiers in Molecular Biology. Oxford: IRL Press.

Reik W and Walter J (1998) Imprinting mechanisms in mammals. Current Opinion in Genetics and Development 8: 154–164.

Solter D (1988) Differential imprinting and expression of maternal and paternal genomes. Annual Review of Genetics 22: 127–146.

Tilghman MA (1999) The sins of the fathers and mothers: genomic imprinting in mammalian development. Cell 96: 185–193.

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Surani, M Azim(Apr 2001) Imprinting (Mammals). In: eLS. John Wiley & Sons Ltd, Chichester. [doi: 10.1038/npg.els.0001206]