beta 1 integrins are ubiquitously expressed receptors that mediate cell-cell and cell-extracellular matrix interactions. To analyze the function of beta1 integrin in skin we generated mice with a keratinocyte-restricted deletion of the beta 1 integrin gene using the cre-loxP system. Mutant mice developed severe hair loss due to a reduced proliferation of hair matrix cells and severe hair follicle abnormalities. Eventually, the malformed hair follicles were removed by infiltrating macrophages. The epidermis of the back skin became hyperthickened, the basal keratinocytes showed reduced expression of alpha 6 beta 4 integrin, and the number of hemidesmosomes decreased. Basement membrane components were atypically deposited and, at least in the case of laminin-5, improperly processed, leading to disruption of the basement membrane and blister formation at the dermal-epidermal junction. In contrast, the integrity of the basement membrane surrounding the beta 1-deficient hair follicle was not affected. Finally, the dermis became fibrotic. These results demonstrate an important role of beta 1 integrins in hair follicle morphogenesis, in the processing of basement membrane components, in the maintenance of some, but not all basement membranes, in keratinocyte differentiation and proliferation, and in the formation and/or maintenance of hemidesmosomes.

Telomerase transgenics are an important tool to assess the role of telomerase in cancer, as well as to evaluate the potential use of telomerase for gene therapy of age-associated diseases. Here, we have targeted the expression of the catalytic component of mouse telomerase, mTERT, to basal keratinocytes using the bovine keratin 5 promoter. These telomerase-transgenic mice are viable and show histologically normal stratified epithelia with high levels of telomerase activity and normal telomere length. Interestingly, the epidermis of these mice is highly responsive to the mitogenic effects of phorbol esters, and it is more susceptible than that of wild-type littermates to the development skin tumors upon chemical carcinogenesis. The epidermis of telomerase-transgenic mice also shows an increased wound-healing rate compared with wild-type littermates. These results suggest that, contrary to the general assumption, telomerase actively promotes proliferation in cells that have sufficiently long telomeres and unravel potential risks of gene therapy for age-associated diseases based on telomerase upregulation.

We describe here a mouse line bearing a bovine keratin K5Cre recombinase transgene. These mice showed a dual pattern of Cre-mediated recombination, depending on the parent transmitting the transgene. In paternal transmission, recombination occurred specifically in the skin and stratified epithelia-as expected according to the expression of endogenous keratin K5. However, constitutive recombination between loxP sites transmitted by the sperm took place when the mother possessed the K5Cre transgene, even when the transgene was absent in the progeny. Cre expression in late-stage oocytes, with the Cre protein persisting into the developing embryo, leads to the constitutive recombination observed. Thus, this transgenic line allows for both tissue-specific and generalized recombination, depending on the breeding scheme.

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Odontogenic tumours are a heterogeneous group of lesions that develop in the oral cavity region and are characterized by the formation of tumoural structures that differentiate as teeth. Due to the diversity of their histopathological characteristics and clinical behaviour, the classification of these tumours is still under debate. Alterations in morphogenesis pathways such as the Hedgehog, MAPK and WNT/β-catenin pathways are implicated in the formation of odontogenic lesions, but the molecular bases of many of these lesions are still unknown. In this study, we used genetically modified mice to study the role of IKKβ (a fundamental regulator of NF-κB activity and many other proteins) in oral epithelial cells and odontogenic tissues. Transgenic mice overexpressing IKKβ in oral epithelial cells show a significant increase in immune cells in both the oral epithelia and oral submucosa. They also show changes in the expression of several proteins and miRNAs that are important for cancer development. Interestingly, we found that overactivity of IKKβ in oral epithelia and odontogenic tissues, in conjunction with the loss of tumour suppressor proteins (p53, or p16 and p19), leads to the appearance of odontogenic tumours that can be classified as ameloblastic odontomas, sometimes accompanied by foci of secondary ameloblastic carcinomas. These tumours show NF-κB activation and increased β-catenin activity. These findings may help to elucidate the molecular determinants of odontogenic tumourigenesis and the role of IKKβ in the homoeostasis and tumoural transformation of oral and odontogenic epithelia.

Transgenic mice expressing human insulin-like growth factor 1 (IGF-1) in basal epithelial cells of prostate have been characterized. Transgene expression led to activation of the IGF-1 receptor and spontaneous tumorigenesis in prostate epithelium. Hyperplasia was evident in these mice by 2-3 months of age. Atypical hyperplasias and prostatic intraepithelial neoplasia were evident by 6 -7 months of age. Well differentiated adenocarcinomas appeared in mice 6 months or older. Less differentiated tumors, diagnosed as small cell carcinomas, were also observed in two of the older mice. Both lobes of the mouse prostate gland (dorsolateral and ventral) presented preneoplastic and neoplastic changes. The incidence of tumors in mice >6 months of age (38 mice total) was 50%. The development of neoplasia in these transgenic mice appeared to follow a stepwise progression through early preneoplastic changes that ultimately culminated in frank neoplasia. These mice offer an animal model for prostate cancer that will allow study of the stepwise development of this disease and the mechanism(s) whereby IGF-1 mediates this process. P rostate cancer is the most commonly diagnosed cancer in men in the United States (1). Progress in prostate disease research has been impaired by the lack of adequate animal models that reproduce the human disease. There are several established rat models of prostate cancer that are either hormonally and͞or chemically induced, such as the Lobund Wistar or Nobel rat models (2-5). In these models, the time frame to adenocarcinoma is 12-24 months. Spontaneous adenocarcinomas develop in the Dunning model (R-3327 system), which is carried as both cell lines and transplantable tumors in syngeneic Copenhagen rats (4). All of these model systems have certain limitations that have hampered their utility. Recently, several laboratories have created transgenic models in which prostate adenocarcinomas develop with high frequency (6-10). All of these models are based on expression of SV40-T antigen in prostate epithelium. Thus, a potential limitation of these models is the use of a transgene not directly involved in human prostate cancer. In some of these models, tumors develop rapidly (in some cases by 10-12 weeks), are poorly differentiated or undifferentiated, and progress rapidly to metastatic disease (6-8, 10).Recently, Chan et al. (11) reported a strong positive association between serum insulin-like growth factor 1 (IGF-1) levels and prostate cancer risk. The importance of IGF-1 receptor (IGF-1r) signaling in neoplastic transformation is clearly evident from a variety of studies (reviewed in refs. 12-16). Several transgenic models have been developed to explore the role of IGF-1r signaling in cellular growth and neoplasia (17)(18)(19)(20). However, with the exception of transgenic mice in which IGF-2 expression was driven by the major urinary protein promoter (MUP), none developed spontaneous tumors in any tissue. The MUP͞IGF-2 transgenic mice developed a variety of tumors, primarily hepatocellular carcinoma...

The transcription factor Myc (c-Myc) plays an important role in cell growth and cell death, yet its physiological function remains unclear. Ectopic activation of Myc has been recently suggested to regulate cell mass, and Drosophila dmyc controls cellular growth and size independently of cell division. By contrast, it has been proposed that in mammals Myc controls cell division and cell number. To gain insights into this debate we have specifically knocked out Myc in epidermis. Myc epidermal knockout mice are viable and their keratinocytes continue to cycle, but they display severe skin defects. The skin is tight and fragile, tears off in areas of mechanical friction and displays impaired wound healing. Steady-state epidermis is thinner, with loss of the proliferative compartment and premature differentiation. Remarkably, keratinocyte cell size, growth and endoreplication are reduced, and stem cell amplification is compromised. The results provide new and direct evidence for a role for endogenous Myc in cellular growth that is required for hyperproliferative cycles and tissue homeostasis.

The inhibition of cell proliferation and Akt and PKC activities was also observed although to a minor extent in low hK10-expressing mice. These animals displayed no overt epidermal phenotype nor overexpression of K10. In these non-phenotypic mice, ectopic K10 expression also resulted in decreased skin tumorigenesis. Collectively, these data demonstrate that keratin K10 in vivo functions include the control of epithelial proliferation in skin epidermis.Keratins are the main components of the intermediate filament cytoskeleton in epithelial cells. They are a large family of proteins that includes ϳ30 different polypeptides expressed in a cell type-and differentiation-specific manner. Their functions have long been presumed to be predominantly structural. This role was clarified when human epithelial fragility syndromes became attributable to mutations within epidermal keratin genes (for reviews see Refs. 1-4). However, this shared function does not provide a clear explanation of the great diversity of these proteins, which suggests that they may have additional specific functions.Changes in keratin expression pattern are particularly important in the epidermis. Keratins K5 and K14 are expressed in the mitotically active basal cells. As these cells enter the terminal differentiation program, becoming postmitotic and suprabasal, keratins K5 and K14 are substituted by keratins K1 and K10 (5). Under the influence of hyperproliferative stimuli, for example during wound healing and in certain disorders including cancer, epidermal expression of K1 and K10 is drastically reduced. Keratins K6 and K16, normally absent from interfollicular epidermis, are, however, induced (6). As a whole, these changes suggest that each keratin pair provides specific functional requirements to epidermal keratinocytes. This is also highlighted by recent findings in which K16 was expressed ectopically (7) to rescue the epidermal fragility promoted by inactivation of the keratin K14 gene (8). These rescued animals show neither epidermal fragility nor neonatal mortality, but they exhibit strong phenotypic alterations such as alopecia, chronic epidermal ulcers, and alterations in other stratified epithelia (7). This demonstrates that these two proteins are not functionally equivalent.In search of specific keratin functions, we have shown that the forced expression of particular keratin polypeptides may influence proliferation in cultured cells. It has been specifically demonstrated that the ectopic expression of keratin K10 inhibits cell proliferation (9). The modulation of cell growth exerted by keratin K10 is linked to the retinoblastoma (pRb) protein and the molecular machinery controlling cell cycle progression during G 1 , in particular cyclin D1 expression (9). This activity appears to involve the sequestration of Akt/PKB and atypical PKC to the keratin cytoskeleton, mediated by keratin K10 through its amino terminus (10). Therefore, the presence of K10 leads to impaired phosphoinositide 3-kinase (PI3K) 1 signaling. Most of this information...