Women’s breasts ‘eat’ themselves after breastfeeding

*Discovery may shed light on causes of cancer

Scientists have identified the molecular switch that causes women’s breasts to stop producing milk when they stop breastfeeding.

The study was published in the journal Developmental Cell.

Once lactation is complete, cells in the breasts devour dead cells that are left over from the breastfeeding process.

Scientists had previously been baffled about how breasts could rapidly transform from milk-making machines back to their natural state in a matter of days.

Researchers set out to investigate whether a protein called Rac1, which is known to be a vital element of milk production, is responsible for the post-breastfeeding transformation.

They deleted the gene from female mice and found that their first litter survived, but were undersized.

It was suggested that this could be a result of lower fat and protein levels in the milk.

However, subsequent litters of the mice did not survive. Without Rac1, the rodents’ breasts were flooded with milk and dead cells, causing continuous swelling, which is thought to have inhibited the mice’s ability to regenerate cell tissue and produce milk.

The study shows for the first time that Rac1 is essential for clearing out dead cells and milk when lactation is over. It is hoped that the new research could provide vital insights into the development of breast cancer.

“Women’s breasts comprise a network of ducts, covered by a layer of fatty tissue,” explains Linda Geddes, writing for New Scientist.

“During pregnancy, hormonal signals cause epithelial cells lining the ducts to proliferate and form ball-like structures called alveoli, which is where milk is made when the baby is born. However, once women stop breastfeeding, these structures self-destruct – a process that involves massive cellular suicide, and the removal of the debris.”