Wrinkle-free (wrfr) is a previously uncharacterized, spontaneous, autosomal recessive mouse mutation resulting in very tight, thick skin. wrfr mutant mice exhibit severe breathing difficulties secondary to their tight skin and die shortly after birth. This phenotype is strikingly similar to a very rare human genetic disorder, restrictive dermopathy. wrfr mutant mice display a defective skin barrier, which is normally imparted by the cornified envelope, a composite of protein and lipid that prevents loss of water from within and entry of potentially harmful substances from without. In addition, hair growth from grafted wrfr skin is impaired. Positional cloning of the wrfr mutation revealed a retrotransposon insertion into a coding exon of Slc27a4, the gene encoding fatty acid transport protein (FATP)4. FATP4 is the primary intestinal FATP and is thought to play a major role in dietary fatty acid uptake; it therefore is viewed as a target to prevent or reverse obesity. However, its function in vivo had not been determined. Our results demonstrate an unexpected yet critical role for FATP4 in skin and hair development and suggest Slc27a4 to be a candidate gene for restrictive dermopathy.T he skin of mammals is composed of a dermis and an epidermis separated by a basement membrane. The epidermis is stratified, consisting of basal keratinocyte, spinous͞ prickle, granular, and squamous͞cornified layers. Keratinocytes move upward from the basement membrane and progress through a scheduled program of differentiation, with cell death marking their final differentiation step. During this differentiation program, keratinocytes flatten and accumulate lipids that are discharged into the intercellular space (1). In the stratum corneum the lipids are crosslinked with a number of proteins including loricrin and involucrin to form the cornified envelope (2). The insoluble cornified envelope is a composite of protein and lipid that serves as a barrier to loss of water from within and to entry of potentially harmful substances from without. Without such a barrier, life on land could not exist (3).We discovered a spontaneous, autosomal recessive mutation in our mouse colony causing extremely tight, thick skin. We named the mutation wrinkle-free (wrfr). The wrfr phenotype is similar to a rare human disease called restrictive dermopathy (4, 5). Newborn wrfr Ϫ͞Ϫ mice have difficulty breathing because of the tight skin, do not suckle, exhibit a defective skin barrier, and die several hours after birth. There are also defects in hair follicle morphogenesis and hair growth. Because of the presumed fundamental importance of the mutated gene to skin development and its potential relevance to human disease, we sought to identify the affected gene. Here we present a characterization of the wrfr phenotype and the positional cloning of the wrfr mutation.
Materials and MethodsMicrosatellite Marker Analysis. Genomic DNA was prepared from tissues by standard proteinase K digestion, phenol͞chloroform extraction, and ethanol precipitation (6) or by ...