Genetic Imprinting Based in Histone Proteins, Essay Example

Genetic imprinting is defined as the process in which expression of the proteins of gene copy is altered depending on whether the baby inherits it from father or mother. Some genes, or some chromosomes or even their segments are stamped with memory of the parent from whom it originated .Thus cells of a child show whether the origin of the chromosome is maternal or paternal. The phenomenon is also called parent-of-origin gene expression. This is due to the fact that the expression of a gene depends upon the parent who passed on the gene. Several mechanisms have been proposed to explain the process of imprinting. In these mechanisms the gene is believed to be “stamped” such that expression of the genetic information inherited is modified depending on whether it was passed to the baby via the sperm or egg. Such modifications determine the expression or suppression of the genetic information found in the gene copy.

It has been suggested that genetic imprinting might owe its cause to parental conflict of the genes where both maternal and paternal genes carry similar genetic information hence necessitating the partial expression of one of the pairs of genes the imprinting can be as a result of the modification of the DNA structure itself or of the histone proteins that package the DNA (Haig 7). Another argument is the fact that genetic imprinting was a biological mechanism to protect the genes from interference from viral and oncogenic genes that might have permeated the gene pool. The other argument is based on the survival needs of the species where both the maternal and paternal genes try to outdo each other and survive the transcription process. Studies have identified several histone modifications that affect the expression of the genes .Histone modifications and DNA methylation is therefore important in maintaining imprinting.

Histones are the packaging unit proteins for the DNA molecules. The modification of these histones therefore affects the manner in which the proteins genes are expressed (Lenninger 49).Genetic imprints result when DNA or the histone proteins that package DNA are modified. One type of epigenetic modification (DNA methylation) is evident in mammals. For histone proteins several modifications exist including methylation, phosphorylation, acetylation ubiquitylation and summoylation. Modification can also be achieved by having the histone proteins replaced by variant histones which have specific functions.

Genomic imprinting is determined by epigenetic modification of genes so that transcription of a gene is altered while ensuring the actual gene sequence is not changed. Genomic imprinting therefore results in the expression one copy of the relevant imprinted gene in an embryo.  In the case of paternally imprinted genes, the allele from the father le is modified epigenetically to prevent transcription and hence ensuring expression of one allele which is the copy inherited from the mother. The opposite is true for maternally imprinted genes, where paternally inherited copy is expressed. The fact that particular genes are  expressed differentially according to this phenomenon of parent- of -origin gene expression , means that during development the parental genomes are not equivalent  functionally (Surani 1998). Two main mechanisms through which the methylation of DNA can prevent gene transcription have been proposed. The first of these is where by the methyl group interfere with transcription directly by preventing binding of particular transcription factors to the methylated DNA (Iguchi-Ariga & Schaffner 1989)..

The second mechanism occurs when methyl-binding domain proteins (MBDs) bind to methylated DNA. Imprinting affects neuronal chromatin structure since they influence the manner in which the overall arrangement of the DNA molecules on the chromatin is set. The chromatin structure is affected in such areas as these nuclease sensitivity, and nuclear matrix association, it also affects the H4 and H3 differential histone acetylation, and also the presence near CpG-island genes which are rich in G bases and homologous chromosome association. On the converse imprinted antisense RNA transcripts DNA replication in asynchronous manner. Despite all this much as these factors may help to maintain the imprinted domains in body cells or become sequential events resulting  to differential packaging of chromatin on the 2 alleles, roles each plays in establishing the imprint in germ cells  after fertilization is yet to be established.

Genomic imprinting is important for regulating normal gene expression patterns in an individual however some errors sometimes may result in inappropriate gene repression or transcription. Genomic imprinting plays a critical role in fetal growth and development. This is because imprinting of certain genes provide mechanisms of regulation on gene expression and hence on the growth of babies especially growth during pregnancy. It is therefore a major and important aspect of genetic variability and development. The role it plays in perpetuation of the species as well as their preservation is in major focus especially in the currently age where the study of genomics and proteomics has taken centre stage in genetic studies. The focus is more heightened by the fact that genetic cloning has taken a whole new dimension (Ferguson 28).

Works Cited

Ferguson Smith, Epigenomics. Washington:  Springer Science 2009

Iguchi-Ariga SM & Schaffner W. Genes and Development.  Chicago: Penguin books 1989.

Lenniger A. Principles of Biochemistry. New York: W H Freeman publishers. 2005.

Moore, T. “Genomic imprinting in mammalian development: a parental tug-of-war”. Trends in Genetics 7. February 1991. Retrieved 2008-07-01http://linkinghub.elsevier.com/retrieve/pii/0168-9525(91)90230-N.

Surani MA.  Imprinting and the initiation of gene silencing in the germ line. 1998. 07 October 2009 .[CrossRef][Web of Science][Medline]