The matted mutation arose spontaneously in 1952 in the CBA/Gr strain at the University College of London. Mutant mice were imported to The Jackson Laboratory in 1957 and a congenic C57BL/6J strain created. Flaky tail arose spontaneously in 1958 at The Jackson Laboratory in progeny of crosses between heterogeneous stocks. Both mutations map closely on mouse Chr. 3 within the epidermal differentiation gene cluster. They are maintained as a compound mutant as they are tightly linked and their phenotypes do not appear to overlap. The flaky tail mice develop scaling on their tails and feet as early as 2-4 days of age. By 5-14 days of age the tail develops prominent scaling and circumferential constrictions. Autoamputation at these constriction sites can occur resulting in short tails. Lesions begin to resolve at 3-4 weeks of age and are no longer apparent by 5 weeks of age. Mice usually go through puberty around 6 weeks of age so with the exception of the short tails, it can be almost impossible to differentiate wildtype from mutant mice. To circumvent this problem, the matted mutation is maintained on this stock. Matted mutant mice can be identified between 2-4 weeks of age because their truncal hairs stand up and stick together.
Initially, the flaky tail mutant mouse was considered to be a potential model for Vohlwinkle’s Syndrome in humans that was originally thought to be due to a mutation in the loricrin gene. Although the connection was made, the human cases were subsequently classified as pseudVolwinkle’s syndrome. While flaky tail had features resembling this human disease, no mutations in loricrin were found. Subsequently, and adjacent gene, profilaggrin, was considered since flaky tail mutant mice have a marked reduction in the thickness of the stratum granulosum where this protein is found. Immunofluorescence and protein studies revealed marked downregulation of profilaggrin compared to wildtype controls. While the specific profilaggrin repeat has yet to be defined that is abnormal in this gene, similar molecular and clinical features also involving profilaggrin are found in the ichthiosis vulgaris with an agranular layer in human patients.
The matted mutation is currently being cloned. Morphologic studies have been limited but indicate there are defects in the hair follicle matrix and root sheaths. Hair fibers are extremely fragile and lack cuticles. Studies are in progress to define the specific anatomical abnormalities.
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