SYDNEY: Hair patterns are more complex than previously thought, according to U.S. scientists who have uncovered the two part mechanism that controls them.
"We have found that hair follicles are oriented in a two-step process," said Jeremy Nathans of the Johns Hopkins University School of Medicine in Maryland, USA, who led the research team. "The precise arrangement of hairs … implies a sophisticated guidance system."
The two-step process involves a gene called 'Frizzled6' which is active in the skin and hair follicles of all mammals (including humans), as well as in fish scales and bird feathers. Scientists believe that the gene works the same way in all of these animals.
Frizzled6 was discovered in 2004, when the same researchers noticed that mice lacking the gene developed bizarre hair patterns: unusual whorls, waves and tufts of fur that grew randomly over their bodies. Until now, however, it remained unclear whether the Frizzled6 gene was the only factor controlling the arrangement of hairs.
The research team thinks that Frizzled6 only controls part of the hair orientation process. "A global orienting system acts early in development and is Frizzled6-dependant, and a local self-organising system … acts later and is Frizzled6 independent," the researchers reported today in the U.S. journal Proceedings of the National Academy of Sciences.
In the study, the researchers 'knocked out' - or removed - the Frizzled6 gene from the genome of a group of mice. They then examined specific areas of skin and hair as the mice developed.
Hair follicles are created by the surface of the skin folding inwards. In hair development, the root forms first and then elongates as new material enters the shaft.
In mice without the Frizzled6 gene, the hair roots initially pointed in random directions. But as the mice developed, the hairs began to align with each other, leading the researchers to conclude that there are two stages to the orientation of hair.
To determine whether grooming also plays a role in the development of hair patterns, the researchers then shaved the mice every day. They found that grooming (or shaving) had no effect on the pattern of hair development.
According to the researchers, an orienting signal must be locally produced in each area of the mouse body. This signal would generate mature hair patterns by minimising differences in orientation between neighbouring follicles.
The researchers tried to estimate the area over which the local hair orienting system operates by creating a 'chimera' - a single mouse that originated from two different embryos fused together. Each cell in the mouse chimera possessed one of two distinct genomes: one which had the Frizzled6 gene, and one which did not.
Where zones of the two types of hair met on the mouse, hair follicles without the Frizzled6 gene began growing in the same direction as hair with the Frizzled6 gene. This would occur for hair growing two to three follicles away from the tissue containing Frizzled6, which may represent the range of the orienting signal.
Using this information, the researchers developed a mathematical model representing hair growth. They anticipate that this could be applied to many other complex systems, such as the development of fingerprints, fish schooling and locust migration.
According to Nathans, "at a mathematical level the model is very general and applies to any system that self-organises ... based on local consensus interactions."
