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Weksberg Lab

Genetic imprinting and epigenetics

What is Genomic Imprinting?

Every cell in the body has two copies of genetic material, one copy that we inherit from our mother and one that we inherit from our father. Thus, a normal cell that has two copies of its genetic material and is called diploid.

Genes, which are segments of DNA that encode a sequence that can be first transcribed into RNA and then ultimately translated into a protein, are usually expressed (make RNA) from both copies (or alleles).

Both alleles are usually on or off at the same time. However, for a small percentage of genes, they are expressed from only one allele dependent on which parent they came from. These genes are said to be genomically imprinted. Genes that are imprinted are marked somehow in the germline and that mark is erased and reset every time it passes into a new generation. Thus, paternally imprinted genes remain paternally imprinted through successive generations even if the sex of the transmitting parent changes and the same is true for maternally imprinted genes.

There are currently more than 50 known imprinted human genes, but it is estimated that there are more than 200-300 such genes in the human genome many of which occur in clusters of greater than 1Mb in length.

(for an up-to-date catalogue of imprinted genes see: Imprinted Gene Catalogue)

What is Epigenetics?

Epigenetics refers to modification of genetic information not encoded in the DNA sequence of genomes. Epigenetics marks can change a gene expression pattern without a change in primary nucleotide sequence - without changing an A, C, G or T. Changes in gene expression often correspond with epigenetic changes such as methylation of DNA, changes in chromatin conformation (methylation, acetylation), and expression of non-coding RNAs.

Epigenetic regulation of gene expression is an important but poorly understood component of normal development and homeostasis. Disruption of normal epigenetic states in various genomic regions cause congenital malformations and predispose to a variety of childhood cancers. As well, for a large number of adult onset cancers, the high frequency of epigenetic errors has underscored the importance of studying this new type of gene regulation.

Further, epigenetic regulation has received considerable attention with the recent demonstration that assisted reproductive technologies (ART) may significantly increase the rate of epimutations and diseases such as Beckwith-Wiedemann syndrome (BWS), Angelman syndrome and even cancer. Our laboratory is interested in the epigenetic mechanisms that regulate genomic imprinting and how they can be disrupted.