Angora is an autosomal recessive mouse mutation caused by a deletion of approximately 2 kilobases in the fibroblast growth factor 5 (Fgf5) gene. Phenotypically, homozygous angora (Fgf5go/Fgf5go) mice have excessively long truncal hair and can be differentiated from heterozygous (+/Fgf5go) and wild-type (+/+) littermates by 21 days of age. Abnormal hair length is due to a prolongation of the anagen phase of the hair cycle of approximately 3 days. In addition, widely scattered hair follicles produce structurally defective hair shafts that twist within the follicle, presumably causing secondary hyperplasia of the outer root sheath and epidermis adjacent to the follicle. These follicular abnormalities were accentuated by immunohistochemical detection of mouse specific keratin 6, a nonspecific marker of epidermal hyperplasia. These abnormalities could be identified from birth throughout life in angora mice genotyped by polymerase chain reaction techniques. Moreover, the long truncal hair phenotype was maintained in skin grafted onto C.B-17/Sz-scid/scid mice that had normal pelage hairs and hair cycles, suggesting that circulating or diffusible humoral factors regulating the mouse hair cycle are not involved in this mutation. The angora mutation provides another useful mouse model for studying the hair cycle and its modulation.
A new autosomal recessive mutation of the house mouse developed generalized alopecia associated with breakage of abnormal hair shafts. This mutation, named 'lanceolate hair' (symbol: lah), arose in a mutagenesis experiment using ethylnitrosourea. Hair shafts were short with a focal degeneration at the breakpoint characterized by a pronounced enlargement at the apex, resembling a lance head. Plucked hair fibers were 2.0 to 3.5 mm in length with a normal base, suggesting that there was a synchronized developmental defect. Histologic examination of anagen follicles revealed abnormal cornification of the matrix region with degeneration resulting in the focal hair shaft deformity. Catagen follicles showed pronounced follicular dystrophy but telogen follicles were almost normal. There was a marked, persistent thickening of the epidermis associated with a non-scarring, relatively non-inflammatory ichthyosiform dermatitis. These features are found in the Netherton's syndrome of the human, for which this mouse mutation may represent a model. The lah mutation has been localized to the centromeric end of mouse Chromosome 18.
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