The hair follicular cycle of the cryptothrix mouse and the characteristics of its abnormal hair.
The hair follicular changes of the cryptothrix mutant mouse (crh mouse) were examined sequentially from birth to 365 days of age and the characteristics of the abnormal hair were observed. The homozygous crh mouse had no hair coat on the skin surface during the period of observation, but a small number of fuzzy soft hairs in the black pigmented skin of the anagen phase was seen. Cyclic folliculogenesis, however, was observed histologically in the dermis. The first anagen phase developed at 3 to 4 days of age and lasted until about 15 days of age. The hair follicles then entered the telogen phase, which lasted until about 18 to 32 days of age. Thereafter, the follicular cycles were repeated three times about every 20 days until 90 days of age. This pattern coincided well with the normal hair cyclic pattern reported for the mouse and rat. After 100 days of age, however, alternating anagen and telogen phases formed a striped pattern in the skin, with black bands. These black bands became progressively thinner and shifted anteriorly, showing a wavy pattern. The abnormal hair of the homozygous crh mouse showed separation of the hair medulla due to incomplete trichilemmal keratinization in the internal root sheath. The tips of the hair shafts were folded and collapsed under the epidermis and did not erupt on the skin surface. The hair follicles, however, did not differ from those of heterozygous crh mice. Because the homozygous crh mouse failed to form a complete hair shaft, cyclic folliculogenesis of the epidermis could be easily observed macroscopically without depilation. The homozygous crh mouse may prove useful in evaluating new drugs for hair follicular growth.
Division of Pathology, Institute of Gerontology, Nippon Medical School, Kawasaki-city, Kanagawa.
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D000818:Animals; D002453:Cell Cycle; D005260:Female; D005614:Freeze Fracturing; D006197:Hair / Q000254:growth & development* / Q000648:ultrastructure; D006579:Heterozygote; D006720:Homozygote; D008297:Male; D051379:Mice; D008812:Mice, Hairless; D008855:Microscopy, Electron, Scanning; D012880:Skin Pigmentation; D013997:Time Factors