‘Battle of the sexes’ begins in the womb – study

Genes from both parents compete for nutrients as the fetus grows, new research shows

Scientists have found that the proverbial ‘battle of the sexes’ begins before birth, with “greedy” genes inherited from the father competing with those from the mother over how much nutrition a fetus should receive.

In a new study, published on Monday in the Development Cell journal, researchers found that a “tug of war” takes place between genes from either parent in the womb once the fetus communicates its need for more nutrients by sending out a hormonal signal known as IGF2.

The study investigated why some babies struggle to grow properly in the womb. Between 10-15% of babies grow poorly in the womb, often showing reduced growth of blood vessels in the placenta. The researchers used genetically engineered mice – which are biologically similar to humans.

The team found that the paternal genes respond to the IGF2 signal by expanding blood vessels in the placenta to increase nutrient supply. Meanwhile, genes from the mother try to restrict this expansion.

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Too much IGF2 leads to excessive growth, while too little (caused by a dominance of the maternal gene) is linked to too little growth – but both extremes are associated with health complications.

“One theory about imprinted genes is that paternally-expressed genes are greedy and selfish. They want to extract the most resources as possible from the mother. But maternally-expressed genes act as countermeasures to balance these demands,” the study’s lead author, Miguel Constancia, said.

The father’s gene drives the fetus’s demands for larger blood vessels and more nutrients, while the mother’s gene in the placenta tries to control how much nourishment she provides. There’s a tug-of-war taking place, a battle of the sexes at the level of the genome.

However, the researchers say this competition is actually a good thing since the genes are balancing each other out and making sure the fetus receives the correct nutritional intake.

The team said their findings will help improve understanding of how the fetus, placenta and mother communicate with each other during pregnancy. This could lead to new ways of measuring the levels of IGF2 in the fetus and open up avenues to use medication to normalize these levels.