Genomic imprinting is an epigenetic process in which the expression of certain genes is carried out depending on which parent the alleles came from. Inheritance of traits determined by imprinted genes is not according to Mendel . Imprinting is carried out by DNA methylation in promoters , as a result of which gene transcription is blocked. Usually imprinted genes form clusters in the genome . [1] Imprinting of certain genes in the genome is indicated for insects , mammals and flowering plants .
Overview
In diploid organisms, somatic cells carry two copies of the genome . Therefore, each autosomal gene is represented by two copies, alleles obtained from maternal and paternal organisms as a result of fertilization. For the predominant number of genes, expression occurs from both alleles simultaneously. However, in mammals, less than one percent of the genes are imprinted, that is, only one allele is expressed. [2] Which allele will be expressed depends on the gender of the parent organism that provided the allele. For example, for the IGF2 gene (insulin-like growth factor), only the allele inherited from the father is expressed. [3]
The word "imprinting" was first used to describe the phenomena observed in the insect Pseudococcus nipae . [4] In pseudococcids ( Homoptera, Coccoidea ), males and females develop from fertilized eggs. In females, all chromosomes remain euchromatin and function, while in males, one haploid set of chromosomes becomes heterochromatin after the sixth division of the zygote and remains so in most tissues, so males are functionally haploid. [5] [6] [7] In insects, imprinting events usually mean genome silencing in males and are therefore involved in sex determination processes. In mammals, genomic imprinting processes are involved in functional inequality between parental alleles of genes. [eight]
Discovery History
The first experiments, which detected differences in the chromosomes obtained from the father or from the mother, were carried out almost simultaneously by scientists working in Philadelphia [9] and Cambridge [10] , in 1984 .
Five years later, of Oxford hypothesized that paternal genes are responsible for placenta formation , and maternal genes are responsible for the differentiation of embryonic cells in the formation of tissues and organs. From this, he concluded that egg-laying and even marsupials should not have imprinting of paternal or maternal genes. This conclusion has been experimentally confirmed. [11] But Haig's studies explain only a few cases of imprinting. [12] [13]
Mechanism
Gene imprinting is carried out using the DNA methylation process. If for some reason imprinting does not work, this can lead to the appearance of genetic disorders (for example, Prader-Willi syndrome ). [14]
See also
- Epigenetics
- DNA methylation
Notes
- ↑ Nucleic acids: from A to Z / B. Appel [et al.]. - M .: Binom: Laboratory of Knowledge, 2013 .-- 413 p. - 700 copies. - ISBN 978-5-9963-0376-2 .
- ↑ Wilkinson, Lawrence S .; William Davies and Anthony R. Isles. Genomic imprinting effects on brain development and function (English) // Nature Reviews Neuroscience : journal. - 2007 .-- November ( vol. 8 , no. 11 ). - P. 832-843 . - DOI : 10.1038 / nrn2235 . - PMID 17925812 .
- ↑ DeChiara, Thomas M .; Elizabeth J. Robertson and Argiris Efstratiadis. Parental imprinting of the mouse insulin-like growth factor II gene (Eng.) // Cell : journal. - Cell Press 1991 .-- February ( vol. 64 , no. 4 ). - P. 849-859 . - PMID 1997210 .
- ↑ Schrader, Franz. The chromosomes in Pseudococcus nipæ (neopr.) // Biological Bullitin. - 1921. - May ( t. 40 , No. 5 ). - S. 259-270 . - DOI : 10.2307 / 1536736 .
- ↑ Brown, SW; U. Nur. Heterochromatic chromosomes in the coccids (English) // Science : journal. - 1964. - Vol. 145 . - P. 130-136 . - DOI : 10.1126 / science.145.3628.130 . - PMID 14171547 .
- ↑ Hughes-Schrader, S. Cytology of coccids (Coccoïdea-Homoptera) (neopr.) // Advances in Genetics. - 1948. - T. 35 , No. 2 . - S. 127—203 . - PMID 18103373 .
- ↑ Nur, U. Heterochromatization and euchromatization of whole genomes in scale insects (Coccoidea: Homoptera) (Eng.) // Dev. Suppl. : journal. - 1990. - P. 29-34 . - PMID 2090427 .
- ↑ Feil, Robert Feil; Frédéric Berger. Convergent evolution of genomic imprinting in plants and mammals (English) // Trends in Genetics : journal. - Cell Press 2007 .-- April ( vol. 23 , no. 4 ). - P. 192-199 . - DOI : 10.1016 / j.tig.2007.02.02.004 . - PMID 17316885 .
- ↑ McGrath J., Solter D. 1984. Completion of mouse embryogenesis requires both the maternal and paternal genomes. Cell 37: 179-183.
- ↑ Barton SC, Surami MAH, Norris ML 1984. Role of paternal and maternal genomes in mouse development. Nature 311: 374-376.
- ↑ Haig D., Westoby M. 1989. Parent-specific gene expression and the triploid endosperm. American Naturalist 134: 147-155.
- ↑ Hurst LD, McVean GT 1997. Growth effects of uniparental disomies and the conflict theory of genomic imprinting. Trends in Genetics 13: 436–443.
- ↑ Hurst LD 1997. Evolutionary theories of genomic imprinting. In: Reik W., Surani A. (eds), Genomic imprinting, p. 211-237. Oxford University Press, Oxford.
- ↑ Horsthemke B. 1997. Imprinting in the Prader-Willi / Angelman syndrome region on human chromosome 15. In: Reik W., Surani A. (eds), Genomic imprinting, p. 177-190. Oxford University Press, Oxford.