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Scientists discover imprinted gene on chromosome 19: A gene that defies classic laws of inheritance may prove key in combatting certain cancers

By Marko Djuranovic, Duke Chronicle

9 January 2001: University researchers have offered further proof that the classic laws of genetic inheritance taught in biology classes may not apply to all aspects of the human genome after all.

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In a study to be published in the upcoming issue of the journal Genomics, Medical Center researchers have found an "imprinted" gene-the Peg3 gene-on human chromosome 19.

An imprinted gene is expressed depending on whether it has been inherited from the mother or the father. This contradicts Gregor Mendel's centuries-old model of inheritance, where phenotype is regulated solely by the dominance or recessiveness of alleles.

Professor of radiation oncology and the study's principal investigator Randy Jirtle explained that imprinted genes are more susceptible to a loss of function than normal genes because they only have one working copy of the allele.

"So you need only one 'hit,' one mutation, to knock them out," said Jirtle.

Lead author of the study and research associate in radiation oncology Susan Murphy also pointed out that some types of cancer, like ovarian and gliomas, have been linked with defects in the region of chromosome 19 where the imprinted gene has been located.

The gene, then, or other still-undiscovered imprinted genes like it on chromosome 19, may be involved in cancer.

But Murphy said that since no one has reported the existence of imprinted genes in this chromosome until now, research has not been done to either prove or disprove the possibility.

While previous studies have located as many as 40 imprinted genes on chromosomes 7, 11 and 15, this is the first time an imprinted gene has been found on chromosome 19. And if past experience offers any indication, researchers believe there are more such genes to be found.

"[Imprinted genes] are found in clusters," said Jirtle. "Finding imprinted genes is like finding a mushroom-when you find one, you know you'll find more."

The prevailing scientific theory states that imprinting evolved over 100 million years ago as a result of competition between the male and the female on the manner of resource allocation during their offspring's growth.

Also involved with the study was Andrew Wylie, a research associate funded by AstraZeneca Pharmaceuticals Ltd., from Cheshire, UK. Since regions of the gene with differential chemical modifications have been correlated with the presence of imprinted genes, Wylie was brought into the research team to assist with the process of identifying the imprinting status of a gene.

The Peg3 gene has been found to play a role in cellular and behavioral functions such as growth and maternal nurturing-previous studies have linked disruptions in this gene to defects in maternal nurturing.

Female mice inheriting a faulty copy of this gene from their fathers were reported to have such serious nurturing shortcomings that their offspring died as a result.

Although the researchers were very careful about jumping to any premature conclusions, they did point out that if the function of the Peg3 gene in mice and humans is similar, these combined findings may indicate a relationship between genetic inheritance and nurturing behavior in humans.

There are, however, no future studies planned to explore this notion-for the time being, the researchers plan to seek out more imprinted genes on chromosome 19 as well as the remainder of the human genome.