The asebia hairless mutation arose as a spontaneous mutation in the stearoyl-Coenzyme A desaturase 1 gene in the BALB/cCrglGa strain. Homozygotes may be recognized at 7 days of age by retarded growth of the coat. Alopecia increases, and at adulthood the hair is very sparse. Homozygotes are viable and fertile, but fertility of females is somewhat reduced. Hyperplasia of the cellular layers of the skin is apparent at birth and increases markedly with age. Fibroblasts in the dermis are morphologically abnormal, and collagen and elastin show alterations. Hair follicles are initially normal, but soon become abnormal, with cells of the inner root sheath plugging the hair canal and adhering to the emerging hair. Sebaceous glands are present but differentiate abnormally, with abnormal smooth endoplasmic reticulum and mitochondria, and few lipid droplets. Meibomian glands are also defective. Results of reciprocal transplantation of skin between normal and mutant mice suggest that some diffusible substance synthesized by normal skin can stimulate hair growth and alleviate the hyperkeratosis characteristic of the mutant skin. The skin is deficient in esterified sterols and waxes, but rich in free sterols. Homozygotes for targeted and spontaneous mutations exhibit alopecia, scaly skin, sebaceous gland hypoplasia, impaired ocular lubrication and synthesis and storage of triglycerides, higher lipid oxidation, reduced growth, and lower fertility in females.
A spontaneous, autosomal, recessive mouse mutation exhibiting mild scaly skin, progressive scarring alopecia, slightly runted growth, and photophobia arose at The Jackson Laboratory in 1993 in the inbred mouse strain DBA/1LacJ. Because this mutant mouse showed genetic, anatomical, and laboratory similarities to the asebia mutation, crosses were done between the new mutant and mice carrying the asebia-J allele. Because the F1 offspring were affected, indicating the two mutants were allelic, the new mutation was named asebia-2J. Careful histological analysis of skin development of mice homozygous and heterozygous for either asebia-J or asebia-2J revealed that both types of mutant mice are very similar regardless of their background. Notable histopathological features of mice homozygous for either allele included extreme sebaceous gland hypoplasia, abnormally long anagen follicles, retained inner root sheath, hair fiber perforation of the bulb region as anagen progressed to catagen, foreign body reaction to hair fibers in the dermis, and progressive follicular replacement by scarring. A new pathogenetic hypothesis based on the importance of the sebaceous gland in hair fiber sheath dissociation was suggested by Sundberg et al. (2000): in the absence of a functional sebaceous gland the hair follicle is destroyed. The cutaneous lesion of this mutant mouse underscores the importance of the sebaceous gland to follicular biology and presents an animal model for studying the human scarring alopecias(now called cicatrical alopecias), which characteristically begin with sebaceous gland ablation.
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