Cyclic Alopecia in Msx2 Mutants: Defects in Hair Cycling and Hair Shaft Differentiation

Msx2-deficient mice demonstrated progressive hair loss beginning at P14, characterized by cycles of wavelike regrowth and loss. The deficiency led to a shortened anagen phase and prolonged catagen and telogen phases, with structurally abnormal hair shafts. Molecular analysis indicated involvement of a Bmp4/Bmp2/Msx2/Foxn1 acidic hair keratin pathway. The abnormal hairs were easily dislodged during catagen, suggesting a premature exogen phase. The study revealed that distinct skin domains on the same mouse cycled asynchronously, although hairs within each domain cycled in synchronized waves. These findings explained the cyclic alopecia phenotype observed in the Msx2 mutants.