Maternal and paternal genes don’t always have the same effect on offspring.

Paternal and maternal genes play a complicated balancing act in neurons.

The genes you inherited from your mom and those passed along from your dad don’t have equal footing when it comes to how they influence your biology. Research from a team of HHMI-supported scientists suggests that, throughout an individual’s lifetime, the effect of maternal and paternal genes ebbs and flows in an intricate way.

The interdisciplinary team of scientists—led by HHMI investigator Catherine Dulac of Harvard University, and funded by an HHMI Collaborative Innovation Award—set out to find genes in the mouse brain that had only one activated copy. While mammals have two copies of almost all genes, chemical marks on one of the copies can result in only one being activated.

To find out the frequency of this phenomenon, called imprinting, the researchers bred two genetically distinct species of mice, making it easy to distinguish maternal and paternal genes in the offspring. Then they sampled various sections of the brains of 15-day-old embryos and adults. By sequencing RNA gene products, the scientists could determine whether both copies of that gene were making RNA or whether one copy was muted.

They discovered a whopping 1,308 imprinted genes. What’s more, different genes were imprinted in different regions of the brain, and the patterns of imprinting varied between female and male offspring as well as between embryos and adult mice. About 60 percent of imprinted genes in the mouse embryo brains had the maternal copy turned on and the paternal version stifled. In adult mouse brains, however, about 70 percent of the imprinted genes favored the paternal copy. Almost 350 genes were imprinted in only males or only females. The results appear in two papers published August 6, 2010, in Science.

“It’s exciting because it suggests that the maternal and paternal genomes are not providing the same information in the brains of mammals,” says Dulac. “And it affects many, many genes.”

Her team plans to look into whether the imprinting patterns are linked to any diseases. One of the genes that was imprinted only in female mice has been linked to multiple sclerosis, which predominantly affects women. Further research could reveal whether these facts are connected.

Illustration: Catherine Dulac and Chris Gregg