Transylvanian naked neck chickens have been bred for more than 200 years, yet the biological basis of their feather-free necks is a mystery. Now, an international team of scientists has linked the trait to high levels of a protein involved in skin development.

The trait helps chickens cool off, and naked necked-chickens tend to produce more eggs and yeild more meat in hot climates than other birds, says Denis Headon, of the Roslin Institute at the University of Edinburgh, UK.

His team found that the genomes of naked necks contain an extra chunk of DNA on their third chromosomes that boosts levels of a protein called BMP12. The protein is part of a family known to block feather formation. Adding extra BMP12 to cultured patches of neck skin from normal chickens prevented feather formation. Yet this treatment had little effect on skin cultures from other parts of the body. The work is published today in PLoS Biology.

To explain why BMP12 only blocks neck feathers from growing, Headon’s team looked for genes more active in the developing skin from neck than other parts of the body. Genes involved in making a signalling molecule important in development called retinoic acid proved more active in neck skin from chicken embryos than elsewhere.

Meanwhile, treating chicken skin cultures with retinoic acid prevented feather formation, no matter the location of the skin. Retinoic acid and BMP12 added together had an even stronger effect, Headon’s team found. The signalling molecules, he says, makes neck skin more sensitive to the extra BMP12 produce by naked necks. “There’s this map underlying the skin in the neck which primes the region to lose its feathers.”

Image courtesy of The Roslin Institute, University of Edinburgh