The gene that controls hair and bristle development in Drosophila melanogaster also underlies hair patterning in mammals, a new study shows.

Members of the large frizzled (fz) family of genes, first identified in D. melanogaster as being required for correct orientation (tissue polarity) of cuticular hairs and bristles, are known to act as Wnt receptors and have been found in all animals studied so far, including mammals. Given that mammals and D. melanogaster have a similar tissue-polarity system, it was surprising that no mammalian Fz gene had been shown to be involved in this pathway.

Nini Guo and colleagues have filled this gap. As part of their continuing effort to characterize mammalian Fz genes, they knocked out Fz6 in mouse embryonic stem cells through gene targeting, and subsequently generated heterozygous and homozygous knockout mice.

The reporter gene that they placed under the control of the Fz6 promoter in these mice indicated that the gene is expressed in the skin and hair follicles: a promising sign that they might have found a mammalian Fz gene involved in tissue polarity. The phenotype of the Fz6−/− mice was even more promising: these mice had distinctive and abnormal hair patterns on the feet, torso and head. These patterns were strikingly similar to those seen in D. melanogaster tissue-polarity mutants: the hairs were misorientated but locally ordered, with neighbouring hairs tending to point in the same direction.

By creating chimeric Fz6−/−:Fz6+/+ mice, the authors went on to show a clear correlation between expression of the Fz reporter gene and the location and severity of the hair-patterning defects. So, it would seem that the local effects of the absence of Fz6 on hair development causes the unusual macroscopic hair patterns seen in Fz6−/−mice.

Now that we have identified a role for Fz6 in mammalian tissue polarity, it is not a big jump to speculate that variation in this gene, or others in the same pathway, might underlie differences in hair patterns within and among mammal species. But is this finding of interest to anybody but Frizzled fans and hairdressers? Recent indications that that same pathway might have a role in patterning left–right asymmetry in the brain suggest that neurogeneticists could also be interested in mutants that have problems with their hairing.