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Genomic imprinting is a genetic phenomenon involved in the control of a small proportion of genes in the genome, where the allele that is expressed is determined solely on which parent contributes it.
Overview
In diploid organisms somatic cells possess two copies of the genome. Each autosomal gene is therefore represented by two copies, or alleles, with one copy inherited from each parent at fertilization. For the vast majority of autosomal genes, expression may occur from either allele. However, a small proportion (<1%) of genes are imprinted, meaning that expression occurs from only one allele. The expressed allele is dependent upon its parental origin. For example, the gene encoding insulin-like growth factor II (IGF2/Igf2) is only expressed from the allele inherited from the father (DeChiara et al., 1991). A somatic cell is generally taken to mean any cell forming the body of an organism: the word somatic is derived from the Greek word sÅma (σώμα), meaning body. Somatic cells, by definition, are not germline cells. ...
In biology the genome of an organism is the whole hereditary information of an organism that is encoded in the DNA (or, for some viruses, RNA). ...
For other meanings of this term, see gene (disambiguation). ...
An allele is any one of a number of alternative forms of the same gene occupying a given locus (position) on a chromosome. ...
Categories: Biology stubs ...
Discovery of Imprinted Genes Genomic imprinting was first described in the insect Pseudococcus nipae (Schrader. 1921). In Pseudococcids or mealybugs (Homoptera, Coccoidea) both the male and female develop from a fertilized egg. In females, all chromosomes remain euchromatic and functional. In embryos destined to become males, one haploid set of chromosomes becomes hetrochromatinized after the sixth cleavage division and remains so in most tissues; males are thus functionally haploid (Brown and Nur. 1964; Hughes-Schrader. 1948; Nur. 1990). Mealybugs are a pest that often affect plants. ...
Imprinted Genes in Mammals Experimental manipulation of mouse embryos in the early 1980's showed that normal development requires the contribution of both the maternal and paternal genomes. Gynogenetic embryos (containing two female genomes) show relatively normal embryonic development, but poor placental development. In contrast, androgenetic embryos (containing two male genomes) show very poor embryonic development but normal placental development. Further investigation identified that these phenotypes were the result of unbalanced imprinted gene expression (Barton et al., 1984; McGrath and Solter, 1984).
The gynogenetic embryos have twice the normal level of maternally expressed genes, and completely lack expression of paternally expressed genes, whereas the reverse is true for androgenetic embryos. It is now known that there are approximately 80 imprinted genes in humans and mice, many of which are involved in embryonic and placental growth and development (Isles and Holland, 2005; Morison et al., 2005; Reik and Lewis, 2005; Wood and Oakey, 2006).
No naturally occurring cases of parthenogenesis exist in mammals because of imprinted genes. Experimental manipulation of a paternal methylation imprint controlling the Igf2 gene has, however, recently allowed the creation of rare individual mice with two maternal sets of chromosomes - but this is not a true parthenogenote. Hybrid offspring of two species may exhibit unusual growth due to the novel combination of imprinted genes.[1] It has been suggested that this article or section be merged into Asexual reproduction. ...
Genetic Mapping of Imprinted Genes At the same time as the generation of the gynogenetic and androgenetic embryos discussed above, mouse embryos were also being generated that contained only small regions that were derived from either a paternal or maternal source (Cattanach and Kirk, 1985; McLaughlin et al., 1996). The generation of a series of such uniparental disomies, which together span the entire genome, allowed the creation of an imprinting map.[2] Those regions which when inherited from a single parent result in a discernable phenotype contain imprinted gene(s). Further research showed that within these regions there were often numerous imprinted genes (Bartolomei and Tilghman 1997), around 80% of imprinted genes are found in clusters such as these, called imprinted domains, suggesting a level of co-ordinated control (Reik and Walter 2001).
What is an Imprint? Imprinting is a dynamic process. It must be possible to erase and re-establish the imprint through each generation. The nature of the imprint must therefore be epigenetic (modifications to the structure of the DNA rather than the sequence). In germline cells the imprint is erased, and then re-established according to the sex of the individual; i.e. in the developing sperm, a paternal imprint is established, whereas in developing oocytes, a maternal imprint is established. This process of erasure and reprogramming is necessary such that the current imprinting status is relevant to the sex of the individual. There are two major mechanisms that are involved in establishing the imprint; these are DNA methylation and histone modifications. Epigenetic inheritance is the transmission of information from a cell or multicellular organism to its descendants without that information being encoded in the nucleotide sequence of the gene. ...
Reprogramming refers to erasure and reestablishment of DNA methylation during mammalian development. ...
DNA methylation is a type of chemical modification of DNA that can be inherited without changing the DNA sequence. ...
Schematic representation of the assembly of the core histones into the nucleosome. ...
Regulation The grouping of imprinted genes within clusters allows them to share common regulatory elements, such as non-coding RNAs and differentially methylated regions (DMRs). When these regulatory elements control the imprinting of several genes in a given region, they are known as imprinting control regions (ICR). The expression of non-coding RNAs, such as Air on mouse chromosome 17 and KCNQ1OT1 on human chromosome 11p15.5, have been shown to be essential for the imprinting of genes in their corresponding regions.
Differentially methylated regions are generally segments of DNA rich in cytosine and guanine nucleotides, with the cytosine nucleotides methylated on one copy but not on the other. Contrary to expectation, methylation does not necessarily mean silencing; instead, the effect of methylation depends upon the default state of the region.
Functions of Imprinted Genes The control of expression of specific genes by genomic imprinting is unique to placental mammals (eutherians and marsupials). Imprinting of whole chromosomes has been reported in mealybugs (Brown and Nur. 1964; Hughes-Schrader. 1948; Schrader 1921; Nur. 1990) and the fungus gnat (Sciara) (Metz. 1938). Some genes have also been reported to be imprinted in flowering plants (Alleman and Doctor, 2000; Reik and Walter, 2001). This page is a candidate for speedy deletion, because: If you disagree with its speedy deletion, please explain why on its talk page or at Wikipedia:Speedy deletions. ...
Orders Superorder Ameridelphia Didelphimorphia Paucituberculata Superorder Australidelphia Microbiotheria Dasyuromorphia Peramelemorphia Notoryctemorphia Diprotodontia Marsupials are mammals in which the female typically has a pouch (called the marsupium, from which the name Marsupial derives) in which it rears its young through early infancy. ...
Mealybugs are a pest that often affect plants. ...
Fungus gnats are small, dark, short-lived flies, of the families Sciaridae and Mycetophilidae (order Diptera), whose larvae feed on plant roots or fungi and aid in the decomposition of organic matter. ...
The majority of imprinted genes in mammals have been found to have roles in the control of embryonic growth and development, including development of the placenta (Isles and Holland 2005; Tycko and Morison 2002). Other imprinted genes are involved in post-natal development, with roles affecting suckling and metabolism (Constancia et al., 2004; Tycko and Morison, 2002).
The Parental Conflict Hypothesis Perhaps the most widely accepted explanation for the occurrence of genomic imprinting is the “parental conflict hypothesis” (Moore and Haig 1991). The hypothesis states that the inequality between parental genomes due to imprinting is a result of the differing interests of each parent. The father is more interested in the growth of his offspring, at the expense of the mother, whose priority is to conserve resources for her own survival whilst providing sufficient nourishment to the fetus and for subsequent litters. Hence, paternally expressed genes tend to be growth promoting whereas maternally expressed genes tend to be growth limiting (Moore and Haig 1991).
Problems with imprinting Imprinting may cause problems in cloning, with clones having DNA that is not methylated in the correct position. It is possible that this is due to a lack of time for reprogramming to be completely achieved. When a nucleus is added to an egg during somatic cell nuclear transfer, the egg starts dividing in minutes, as compared to the days or months it takes for reprogramming during embryonic development. If time is the responsible factor, it may be possible to delay cell division in clones, giving time for proper reprogramming to occur. Cloning is the process of creating an identical copy of something. ...
Methylation is a term used in the chemical sciences to denote the attachment or substitution of a methyl group on various substrates. ...
The eukaryotic cell nucleus. ...
In genetics and developmental biology, somatic cell nuclear transfer (SCNT) is a laboratory technique for creating an ovum with a donor nucleus (see process below) . It can be used in embryonic stem cell research, or in regenerative medicine where it is sometimes referred to therapeutic cloning. ...
It has been suggested that embryology be merged into this article or section. ...
An allele of the "callipyge" (from the Greek for "beautiful buttocks"), or CLPG, gene in sheep produces large buttocks consisting of muscle with very little fat. The large-buttocked phenotype only occurs when the allele is present on the copy of chromosome 18 inherited from a sheep's father and is not on the copy of chromosome 18 inherited from that sheep's mother.[3] Species See text. ...
Examples
Prader-Willi and Angelman Syndrome Several genetic diseases that map to 15q11 (band 11 of the long arm of chromosome 15) in humans are due to abnormal imprinting. This region is differently imprinted in maternal and paternal chromosomes, and both imprintings are needed for normal development. It is possible for an individual to fail to inherit a properly imprinted 15q11 from one parent, as a result either of deletion of the 15q11 region from that parent's chromosome 15 or, less frequently, of uniparental disomy (in which both copies have been taken from the other parent's genes). A genetic disorder or a clinical phenotype. ...
Uniparental disomy (UPD) occurs when a person receives two copies of a chromosome, or part of a chromosome, from one parent and no copies from the other parent. ...
Prader-Willi Syndrome is a genetic disorder, in which seven genes (or some subset thereof) on chromosome 15 are missing or unexpressed (chromosome 15q partial deletion) on the paternal chromosome. ...
Hypotonia is a condition of abnormally low muscle tone (the amount of tension or resistance to movement in a muscle), often involving reduced muscle strength. ...
Hypogonadism is a medical term for a defect of the reproductive system which results in lack of function of the gonads (ovaries or testes). ...
Angelman Syndrome (AS) is a rare neuro-genetic disorder named after an English pediatrician, Dr. Harry Angelman, who first described the syndrome in 1965. ...
Fred Ward as Earl Bassett in the 1990 film Tremors. ...
Laughing Child Laughter is the biological reaction of humans to moments or occasions of humor: an outward expression of amusement. ...
Photographs from the 1862 book Mécanisme de la Physionomie Humaine by Guillaume Duchenne. ...
NOEY2 NOEY2 is located on chromosome 1 in humans. It is maternally imprinted. Researchers have found that its lack of expression relates to ovarian and breast cancers; in 41% of breast and ovarian cancers the protein transcribed by NOEY2 is not expressed. This leads scientists to believe that it is a tumor suppressor gene[4]- a gene that helps to prevent cancer by stopping uncontrolled cell growth. Therefore, if a person inherits both chromosomes from the mother, the gene will not be expressed and the individual is put at a greater risk for breast and ovarian cancer. NOEY2 is a gene located on chromosome 1 in humans. ...
A tumor suppressor gene is a gene that reduces the probability that a cell in a multicellular organism will turn into a tumor cell. ...
See also Hormonal imprinting (HI) is a biological phenomenon which takes place at the first encounter between a hormone and its developing receptor in the critical periods of life (in unicellulars during the whole life) and determines the later signal transduction capacity of the cell. ...
Bookmarking is a biological phenomenon believed to function as an epigenetic mechanism for transmitting cellular memory of the pattern of gene expression in a cell through mitosis to its daughter cells. ...
In Biology, while the subject of genetics focuses on how organisms can inherit traits by inheriting genes from their parent(s), which encode information for cell function as sequences of DNA, epigenetics is sometimes used to refer to additional methods of biological inheritance that do not directly relate to the...
References
Scientific Journals Bartolomei, M. S. and Tilghman, S. M. 1997. Genomic imprinting in mammals. Annu Rev Genet 31, pp. 493-525
Barton, S. C. et al. 1984. Role of paternal and maternal genomes in mouse development. Nature 311(5984), pp. 374-376.
Brown S.W. and Nur U. 1964. Heterochromatic chromosomes in the coccids. Science 145, pp 130-136.
Cattanach, B. M. and Kirk, M. 1985. Differential activity of maternally and paternally derived chromosome regions in mice. Nature 315(6019), pp. 496-498
Constancia, M. et al. 2004. Resourceful imprinting. Nature 432(7013), pp. 53-57
DeChiara, T. M. et al. 1991. Parental imprinting of the mouse insulin-like growth factor II gene. Cell 64(4), pp. 849-859
Hughes-Schrader, S. 1948. Cytology of Coccids (Coccoidea-Homoptera). Adv. Genet. 2, pp127-203.
Isles, A. R. and Holland, A. J. 2005. Imprinted genes and mother-offspring interactions. Early Hum Dev 81(1), pp. 73-77.
McGrath, J. and Solter, D. 1984. Completion of mouse embryogenesis requires both the maternal and paternal genomes. Cell 37(1), pp. 179-183.
McLaughlin, K. J. et al. 1996. Mouse embryos with paternal duplication of an imprinted chromosome 7 region die at midgestation and lack placental spongiotrophoblast. Development 122(1), pp. 265-270.
Metz, C.W. 1938. Chromosome behavior, inheritance and sex determination in Sciara. Am. Nat. 72, pp. 485-520.
Moore, T. and Haig, D. 1991. Genomic imprinting in mammalian development: a parental tug-of-war. Trends Genet 7(2), pp. 45-49
Morison, I. M. et al. 2005. A census of mammalian imprinting. Trends Genet 21(8), pp. 457-465.
Nur, U. (1990). Heterochromatization and euchromatization of whole genome in scale insects (Coccoidea:Homoptera). Development Suppl. 29-34.
Reik, W. and Lewis, A. 2005. Co-evolution of X-chromosome inactivation and imprinting in mammals. Nat Rev Genet 6(5), pp. 403-410.
Reik, W. and Walter, J. 2001. Genomic imprinting: parental influence on the genome. Nat Rev Genet 2(1), pp. 21-32.
Schrader, F. 1921. The chromosomes of Pseudococcus nipae. Biol Bull. 40, pp 259-270.
Tycko, B. and Morison, I. M. 2002. Physiological functions of imprinted genes. J Cell Physiol 192(3), pp. 245-258
Wood, A.J. and Oakey, R.J. 2006. Genomic Imprinting in Mammals: Emerging Themes and Established Theories. PLoS Genetics 2(11), e147.
Websites - ^ http://www.hhmi.org/news/tilghman.html
- ^ http://www.mgu.har.mrc.ac.uk/research/imprinting/largemap.html
- ^ "The Legacy of Solid Gold", Genome News Network, May 7, 2001.
- ^ "NOEY2 (ARHI), an imprinted putative tumor suppressor gene in ovarian and breast carcinomas", The National Academy of Sciences, January 5, 1999.
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