Abnormal hair development and apparent follicular transformation to mammary gland in the absence of Hedgehog signaling

One single molecule determines how stem cells in the hair follicle develop.

A study at the Sahlgrenska Academy at Göteborg University in Sweden has shown that cells that should give rise to hair can instead give rise to mammary gland cells in mice who lack this molecule.

The study will be published Monday January 14 in the prestigious medical journal Developmental Cell.

This molecule is part of a complex signalling system known as the "Hedgehog pathway". This signalling system controls the development of many different organs.

"If we can find out more about how the signalling system regulates the behaviour of stem cells, we may be able to develop new treatments for not only hair loss but also for cancer", says Amel Gritli-Linde, associate professor in oral biochemistry at the Sahlgrenska Academy.

The signalling system consists of chain reactions in which several proteins together control the behaviour of cells.

The study has shown that the Hedgehog system is responsible for stem cells in skin being given the signal that allows them to develop into a certain type of cell. The molecule that has been studied is called "Smoothened", and it forms a link in the chain of information.

If Smoothened is missing, the information never reaches the nucleus of the cell. The study used transgenic mice that lacked the molecule in parts of their skin. "The stem cells at the hair follicles normally lie in special small niches in the tissue, but the transgenic mice lack these protective niches.

The stem cells that should have become hair develop instead into cells from the mammary gland", says Amel Gritli-Linde. Previous work has shown that intensive Hedgehog signalling can lead to cancer. The new study shows that raised signalling activity can also prevent the formation of mammary glands. It is Hedgehog signalling that determines whether hair or breast tissue is formed.

It's not unusual that researchers in odontology study skin and hair follicles. The hair that is formed in the follicles develops in a way that is similar to the way that teeth develop in tooth buds.

"We gain a lot of information as dentists, studying the mechanisms of hair development. It's not impossible that we will be able to get hair stem cells to form new teeth. Millions of people all over the world may be able to obtain new teeth," says Amel Gritli-Linde.

The study has been carried out in collaboration with researchers in the USA and Great Britain.