involucrin and Eye-Abnormalities

Nude mice are characterized by the absence of visible hair, epidermal defects, and the failure to develop a thymus. This phenotype results from loss-of-function mutations in Whn (Hfh11), a winged-helix transcription factor. In murine epidermis and hair follicles, endogenous whn expression is induced as epithelial cells initiate terminal differentiation. Using the promoter for the differentiation marker involucrin, transgenic mice that ectopically express whn in stratified squamous epithelia, hair follicles, and the transitional epithelium of the urinary tract were generated. Transgenic epidermis and hair follicles displayed impaired terminal differentiation and a subset of hair defects, such as delayed growth, a waved coat, and curly whiskers, correlated with decreased transforming growth factor (TGF)-alpha expression. The exogenous Whn protein also stimulated epithelial cell multiplication. In the epidermis, basal keratinocytes exhibited hyperproliferation, though transgene expression was restricted to suprabasal, postmitotic cells. Hair follicles failed to enter telogen (a resting period) and remained continuously in an abnormal anagen (the growth phase of the hair cycle). Ureter epithelium developed severe hyperplasia, leading to the obstruction of urine outflow and death from hydronephrosis. Though an immune infiltrate was present occasionally in transgenic skin, the infiltrate was not the primary cause of the epithelial hyperproliferation, as the immune reaction was not observed in all affected transgenics, and the transgene induced identical skin and urinary tract abnormalities in immunodeficient Rag1-null mice. Given the effects of the transgene on cell proliferation and TGFalpha expression, the results suggest that Whn modulates growth factor production by differentiating epithelial cells, thereby regulating the balance between proliferative and postmitotic populations in self-renewing epithelia.

Topics: Animals; Calcium; Cell Culture Techniques; Cell Differentiation; Cell Division; DNA-Binding Proteins; Dose-Response Relationship, Drug; Epithelium; Eye Abnormalities; Forkhead Transcription Factors; Humans; Keratinocytes; Mice; Mice, Nude; Mice, Transgenic; Phenotype; Protein Precursors; Skin; Skin Abnormalities; Skin Transplantation; Time Factors; Transcription Factors; Transforming Growth Factor alpha; Urogenital System; Vibrissae

Eyelid fusion normally occurs between E15.5 and E16.5 of mouse embryonic development and results from the migration of a population of periderm-derived epithelial cells over the corneal surface. Cell migration is known to depend on extracellular matrix receptors of the integrin family and to be regulated by growth factors. We were therefore interested that a failure of eyelid fusion has been reported in mice that are homozygous null for the transforming growth factor alpha (TGF-alpha) gene and in mice (invalpha5beta1) in which a transgenic alpha5beta1 integrin under the control of the involucrin promoter is misexpressed in differentiating keratinocytes. We examined expression of the alpha2beta1, alpha3beta1, alpha5beta1 and alpha6beta4 integrins during eyelid fusion in wild-type embryos and found selective upregulation of the alpha5beta1 integrin and its ligand, fibronectin, in the migrating eyelid tip cells. In TGF-alpha null embryos, the failure of eyelid fusion was correlated with a failure to upregulate the alpha5beta1 integrin and fibronectin in the tip cells. Using beta-galactosidase as a reporter gene in transgenic mice, we observed specific activity of the involucrin promoter in the eyelid tip cells. In invalpha5beta1 mice the transgenic human integrin was overexpressed not only in the tip cells but throughout the eyelid epidermis. In contrast, the endogenous, murine, alpha5beta1 integrin was only weakly expressed in the tip cells. We speculate that selective and coordinated expression of the alpha5beta1 integrin and fibronectin in eyelid tip cells is required for eyelid fusion and may be under the control of growth factors that include TGF-alpha.

Topics: Animals; Antigens, Surface; Cell Movement; Epidermis; Eye Abnormalities; Eyelids; Female; Humans; Integrin alpha3beta1; Integrin alpha6beta4; Integrins; Male; Mice; Mice, Inbred C57BL; Mice, Knockout; Morphogenesis; Promoter Regions, Genetic; Protein Precursors; Receptors, Collagen; Receptors, Fibronectin; Recombinant Fusion Proteins; Transforming Growth Factor alpha