BBC Science Reporter Pallab Ghosh: Women may see it as sexy, but bald men often find it embarrassing

Researchers at the Howard Hughes Institute at the University of Chicago have managed to get hair follicles to form in the mature skin cells of mice.

This is remarkable because follicle formation is a once-in-a-lifetime event that ordinarily happens only during early the earliest stages of human development.

Once hair follicles are gone, they are not replaced.

Normal hair: A non genetically-engineered mouse

This latest research, published in the journal Cell, suggests a molecule called beta-catenin may be the key messenger that tells embryonic cells - cells that have yet to develop in specific directions - to become hair follicles.

If this is correct, the scientists may be able to use this knowledge to develop treatments that will promote the re-growth of hair in bald men.

"Beta-catenin can cause adult epithelial cells to revert to an embryonic-like state where they have the ability to choose to become a hair follicle," said Professor Elaine Fuchs, the lead author on the paper.

"This is exciting because current treatments for baldness only work if there are living follicles left, or if the patient undergoes hair transplant surgery.

"Our research shows that new follicles can be created from adult skin cells if certain molecular players are induced to act."

Dual role

The Chicago team have shown that beta-catenin performs two very different functions.

In adult cells, it helps to bind neighbouring cells together so that they can "talk" to each other.

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However, during embryogenesis - the crucial early stages after fertilisation - beta-catenin appears to have another role: it reacts with a molecule called LEF-1, which is expressed only in cells that will eventually become hair follicles.

Together, these two molecules bind to the DNA in a cell and tell it to become a hair follicle.

The mice, which were genetically engineered to have plenty of beta-catenin in their cells, were said to be "exceptionally hairy".

However, this led to problems with benign follicle tumours forming on the mice.

Further research

"This is a case of too much of a good thing leading to a bad thing," said Professor Fuchs. She cautioned that much further work was required before hair growth could be induced without the danger of unwanted side-effects.

A cure for baldness is still many years away

"If we can find a way to transiently express beta-catenin in these skin cells, just until new follicles are established, and then turn it off, we may be able to prevent tumour formation and still allow hair follicles to form."

Scientists have been able to grow hair follicles in the laboratory for about a decade.

The difficulty has been finding the right chemical messengers that might trigger the re-growth of hair in men suffering from male pattern baldness - the main cause of hair loss.

But the knowledge gained by such experiments may also help us to prevent the excessive and unwanted growth of hair experienced by some women.

It could also be used to engineer sheep with thicker wool.

Pictures: Linda Degenstein and Chuck Wellek