Histopathological Analysis on Keratin2-6 G Expression in Hair Mutant Mouse Hague

Mouse hair mutants are useful animal models to study molecular mechanism of hair development and human hair disease. A spontaneous mouse hair mutation, Hague (Japanese word for bald) on Chromosome 15 was recovered in C3H/HeN mice colony. In this mutant colony, the semidominant allele is unstable and easily turn to be recessive one. The purpose of this study is to clarify histopathological characteristics of the mutant hair follicle and to examine the expression of a novel type II cytokeratin, keratin2-6g in the mutant and control mice. We compared immunohistologically and by in situ hybridization the dorsal skin hair follicles of wild type (+/+), semidominant heterozygotes (Hag/+), semidominant homozygotes (Hag/Hag) and recessive homozygotes (hag/hag) . The results indicated that the morphology of hair follicles and hair shafts of each genotype clearly differed to each other. In Hag/Hag mice the inner root sheath (IRS) cells were degenerated and disrupted by large vacuolation. In Hag/+ mice vacuolation also detected in the IRS. But the number of vacuoles were less than those detected in Hag/Hag mice. In hag/hag mice vacuolation was not observed, but instead, tricohyaline granules in the IRS cells were found larger than those of wild type mice. In situ hybridization and immunohistochemistry revealed that the expression of keratin2-6g gene was only small amount and the keratin protein was not detectable in the mutant. These results indicated that keratin2-6g in the IRS was essential for hair follicle development, and Hag and hag alleles had different affects on the IRS cells.