Phenotypic consequences of lung-specific inducible expression of FGF-3

Low frequency nanobubble-enhanced ultrasound mechanotherapy for noninvasive cancer surgery

Scaling down the size of microbubble contrast agents to the nanometer level holds the promise for noninvasive cancer therapy. However, the small size of nanobubbles limits the obtained bioeffects as a result of ultrasound cavitation, when operating near the nanobubble resonance frequency. Here we show that coupled with low energy insonation at a frequency of 80 kHz, well below the resonance frequency of these agents, nanobubbles serve as noninvasive therapeutic warheads that trigger potent mechanical effects in tumors following a systemic injection. We demonstrate these capabilities in tissue mimicking phantoms, where a comparison of the acoustic response of micro- and nano-bubbles after insonation at a frequency of 250 or 80 kHz revealed that higher pressures were needed to implode the nanobubbles compared to microbubbles. Complete nanobubble destruction was achieved at a mechanical index of 2.6 for the 250 kHz insonation vs. 1.2 for the 80 kHz frequency. Thus, the 80 kHz insonation complies with safety regulations that recommend operation below a mechanical index of 1.9. In vitro in breast cancer tumor cells, the cell viability was reduced to 17.3 ± 1.7% of live cells. In vivo, in a breast cancer tumor mouse model, nanobubble tumor distribution and accumulation were evaluated by high frequency ultrasound imaging. Finally, nanobubble-mediated low frequency insonation of breast cancer tumors resulted in effective mechanical tumor ablation and tumor tissue fractionation. This approach provides a unique theranostic platform for safe, noninvasive and low energy tumor mechanotherapy.

Steroid-induced fibroblast growth factors drive an epithelial-mesenchymal inflammatory axis in severe asthma

Asthma and inflammatory airway diseases restrict airflow in the lung, compromising gas exchange and lung function. Inhaled corticosteroids (ICSs) can reduce inflammation, control symptoms, and improve lung function; however, a growing number of patients with severe asthma do not benefit from ICS. Using bronchial airway epithelial brushings from patients with severe asthma or primary human cells, we delineated a corticosteroid-driven fibroblast growth factor (FGF)-dependent inflammatory axis, with FGF-responsive fibroblasts promoting downstream granulocyte colony-stimulating factor (G-CSF) production, hyaluronan secretion, and neutrophilic inflammation. Allergen challenge studies in mice demonstrate that the ICS, fluticasone propionate, inhibited type 2-driven eosinophilia but induced a concomitant increase in FGFs, G-CSF, hyaluronan, and neutrophil infiltration. We developed a model of steroid-induced neutrophilic inflammation mediated, in part, by induction of an FGF-dependent epithelial-mesenchymal axis, which may explain why some individuals do not benefit from ICS. In further proof-of-concept experiments, we found that combination therapy with pan-FGF receptor inhibitors and corticosteroids prevented both eosinophilic and steroid-induced neutrophilic inflammation. Together, these results establish FGFs as therapeutic targets for severe asthma patients who do not benefit from ICS.

Kinase domain activation of FGFR2 yields high-grade lung adenocarcinoma sensitive to a Pan-FGFR inhibitor in a mouse model of NSCLC

Somatic mutations in FGFR2 are present in 4% to 5% of patients diagnosed with non-small cell lung cancer (NSCLC). Amplification and mutations in FGFR genes have been identified in patients with NSCLCs, and clinical trials are testing the efficacy of anti-FGFR therapies. FGFR2 and other FGFR kinase family gene alterations have been found in both lung squamous cell carcinoma and lung adenocarcinoma, although mouse models of FGFR-driven lung cancers have not been reported. Here, we generated a genetically engineered mouse model (GEMM) of NSCLC driven by a kinase domain mutation in FGFR2. Combined with p53 ablation, primary grade 3/4 adenocarcinoma was induced in the lung epithelial compartment exhibiting locally invasive and pleiotropic tendencies largely made up of multinucleated cells. Tumors were acutely sensitive to pan-FGFR inhibition. This is the first FGFR2-driven lung cancer GEMM, which can be applied across different cancer indications in a preclinical setting.

Association of a FGFR-4 gene polymorphism with bronchopulmonary dysplasia and neonatal respiratory distress

Background. Bronchopulmonary dysplasia (BPD) is the most common chronic lung disease of premature birth, characterized by impaired alveolar development and inflammation. Pathomechanisms contributing to BPD are poorly understood. However, it is assumed that genetic factors predispose to BPD and other pulmonary diseases of preterm neonates, such as neonatal respiratory distress syndrome (RDS). For association studies, genes upregulated during alveolarization are major candidates for genetic analysis, for example, matrix metalloproteinases (MMPs) and fibroblast growth factors (FGFs) and their receptors (FGFR). Objective. Determining genetic risk variants in a Caucasian population of premature neonates with BPD and RDS. Methods. We genotyped 27 polymorphisms within 14 candidate genes via restriction fragment length polymorphism (RFLP): MMP-1, -2, -9, and -12, -16, FGF receptors 2 and 4, FGF-2, -3, -4, -7, and -18, Signal-Regulatory Protein α (SIRPA) and Thyroid Transcription Factor-1 (TTF-1). Results. Five single nucleotide polymorphisms (SNPs) in MMP-9, MMP-12, FGFR-4, FGF-3, and FGF-7 are associated (P < 0.05) with RDS, defined as surfactant application within the first 24 hours after birth. One of them, in FGFR-4 (rs1966265), is associated with both RDS (P = 0.003) and BPD (P = 0.023). Conclusion. rs1966265 in FGF receptor 4 is a possible genetic key variant in alveolar diseases of preterm newborns.

Rapid induction of lung adenocarcinoma by fibroblast growth factor 9 signaling through FGF receptor 3

Fibroblast growth factors (FGF) are expressed in many non-small cell lung carcinoma (NSCLC) primary tumors and derived cell lines, and mutations in FGF receptor 3 (FGFR3) have been identified in human lung adenocarcinoma. FGF9 has been implicated in the pathogenesis of NSCLC by synergizing with EGFR pathways or by providing an escape pathway mediating resistance to EGFR inhibition. To model pathogenic mechanisms mediated by FGF signals, we have established a mouse model in which FGF9 expression can be induced in adult lung epithelium. Here, we show that induced expression of FGF9 in adult lung leads to the rapid proliferation of distal airway epithelial cells that express the stem cell marker, Sca-1, and the proximal and distal epithelial markers, Sftpc and CC10, the rapid formation of Sftpc-positive adenocarcinomas, and eventual metastasis in some mice. Furthermore, we have identified FGFR3 as the obligate receptor mediating the FGF9 oncogenic signal. These results identify an FGF9-FGFR3 signal as a primary oncogenic pathway for lung adenocarcinoma and suggest that this pathway could be exploited for customized therapeutic applications for both primary tumors and those that have acquired resistance to inhibition of other signaling pathways.

Progressive myopathy in an inducible mouse model of oculopharyngeal muscular dystrophy

The genetic basis of oculopharyngeal muscular dystrophy (OPMD) is a short expansion of a polyalanine tract (normal allele: 10 alanines, mutant allele: 11-17 alanines) in the nuclear polyadenylate binding protein PABPN1 which is essential for controlling poly(A) tail length in messenger RNA. Mutant PABPN1 forms nuclear inclusions in OPMD muscle. To investigate the pathogenic role of mutant PABPN1 in vivo, we generated a ligand-inducible transgenic mouse model by using the mifepristone-inducible gene expression system. Induction of ubiquitous expression of mutant PABPN1 resulted in skeletal and cardiac myopathy. Histological changes of degenerative myopathy were preceded by nuclear inclusions of insoluble PABPN1. Downregulation of mutant PABPN1 expression attenuated the myopathy and reduced the nuclear burden of insoluble PABPN1. These results support association between mutant PABPN1 accumulation and degenerative myopathy in mice. Resolution of myopathy in mice suggests that the disease process in OPMD patients may be treatable.

Blocking the glucocorticoid receptor with RU-486 does not prevent glucocorticoid control of autoimmune mouse hearing loss

BACKGROUND/AIMS

Glucocorticoids effectively manage autoimmune hearing loss, although the cochlear mechanisms involved are unknown. Previous studies of steroid-responsive hearing loss in autoimmune (lupus) mice showed glucocorticoids and mineralocorticoids were equally effective, suggesting the ion homeostasis functions of glucocorticoids may be as relevant as immunosuppression for control of autoimmune-induced inner ear disease. Therefore, to better characterize the role of the glucocorticoid receptor in autoimmune hearing loss therapy, its function was blocked with the antagonist RU-486 (mifepristone) during glucocorticoid (prednisolone) treatments.

METHODS

Following baseline auditory brainstem response (ABR) thresholds, MRL/MpJ-Fas(lpr) autoimmune mice were implanted with pellets providing combinations of 1.25 mg/kg of RU-486, 4 mg/kg of prednisolone, or their respective placebos. After 1 month, animals were retested with ABR and blood was collected for immune complex analyses.

RESULTS

Mice receiving no prednisolone (placebo + placebo and placebo + RU-486) showed continued declines in hearing. On the other hand, mice receiving prednisolone (prednisolone + placebo and prednisolone + RU-486) had significantly better hearing (p < 0.05) than the non-prednisolone groups. Immune complexes were significantly elevated in the placebo + RU-486 group, suggesting RU-486 effectively blocked glucocorticoid receptor-mediated immune suppression. These results showed that blockage of the glucocorticoid receptor with RU-486 did not prevent prednisolone's effects in the ear, suggesting its ion homeostasis actions via the mineralocorticoid receptor were more relevant in hearing control.

CONCLUSION

The mineralocorticoid receptor-mediated actions of glucocorticoids are potentially relevant in steroid-responsive hearing disorders, implying disrupted cochlear ion transport functions may underlie the vascular problems proposed in some forms of immune-mediated hearing loss.

Mifepristone-inducible LexPR system to drive and control gene expression in transgenic zebrafish

Effective transgenesis methods have been successfully employed in many organisms including zebrafish. However, accurate spatiotemporal control of transgene expression is still difficult to achieve. Here we describe a system for chemical-inducible gene expression and demonstrate its feasibility for generating transgenic driver lines in zebrafish. The key element of this system is a hybrid transcription factor engineered by fusion of the DNA-binding domain of the bacterial LexA repressor, a truncated ligand-binding domain of the human progesterone receptor, and the activation domain of the human NF-kappaB/p65 protein. This hybrid transcription factor (LexPR transactivator) binds to the synthetic steroid, mifepristone (RU-486), and functions in a ligand-dependent manner to induce expression of the gene(s) placed under the control of a synthetic operator-promoter sequence that harbors LexA binding sites. Transgene expression is strictly controlled and can be induced at any stage of the life cycle through administration of mifepristone in the water. To demonstrate the utility of this system, we generated stable transgenic lines which allow inducible tissue-specific expression of activated K-ras(V12). Combined with the Ac/Ds-mediated transgenesis, the LexPR expression system has many potential applications in the fields of genetics and biotechnology.

Duration-dependent cytoprotective versus inflammatory effects of lung epithelial fibroblast growth factor-7 expression

Fibroblast growth factor-7 (FGF7) is a lung epithelial cell mitogen that is cytoprotective during injury. Transgenic mice that conditionally expressed FGF7 were used to dissect the mechanisms of FGF7 protection during lung injury. FGF7 improved survival when induced 3 days prior to acute lung injury. In contrast, FGF7 caused pulmonary inflammation and lung injury after 7 days or longer. Gene expression analysis of mouse lung mRNA identified mRNAs that contribute to the protective effects of FGF7. FGF7 improved survival during acute lung injury in adult mouse lung after short-term expression, but paradoxically induced inflammation and injury after persistent expression.

Mutational analysis of EGFR and related signaling pathway genes in lung adenocarcinomas identifies a novel somatic kinase domain mutation in FGFR4

Background

Fifty percent of lung adenocarcinomas harbor somatic mutations in six genes that encode proteins in the EGFR signaling pathway, i.e., EGFR, HER2/ERBB2, HER4/ERBB4, PIK3CA, BRAF, and KRAS. We performed mutational profiling of a large cohort of lung adenocarcinomas to uncover other potential somatic mutations in genes of this signaling pathway that could contribute to lung tumorigenesis.

Methodology/Principal Findings

We analyzed genomic DNA from a total of 261 resected, clinically annotated non-small cell lung cancer (NSCLC) specimens. The coding sequences of 39 genes were screened for somatic mutations via high-throughput dideoxynucleotide sequencing of PCR-amplified gene products. Mutations were considered to be somatic only if they were found in an independent tumor-derived PCR product but not in matched normal tissue. Sequencing of 9MB of tumor sequence identified 239 putative genetic variants. We further examined 22 variants found in RAS family genes and 135 variants localized to exons encoding the kinase domain of respective proteins. We identified a total of 37 non-synonymous somatic mutations; 36 were found collectively in EGFR, KRAS, BRAF, and PIK3CA. One somatic mutation was a previously unreported mutation in the kinase domain (exon 16) of FGFR4 (Glu681Lys), identified in 1 of 158 tumors. The FGFR4 mutation is analogous to a reported tumor-specific somatic mutation in ERBB2 and is located in the same exon as a previously reported kinase domain mutation in FGFR4 (Pro712Thr) in a lung adenocarcinoma cell line.

Conclusions/Significance

This study is one of the first comprehensive mutational analyses of major genes in a specific signaling pathway in a sizeable cohort of lung adenocarcinomas. Our results suggest the majority of gain-of-function mutations within kinase genes in the EGFR signaling pathway have already been identified. Our findings also implicate FGFR4 in the pathogenesis of a subset of lung adenocarcinomas.

Mouse models for human lung cancer

In recent years several new mouse models for lung cancer have been described. These include models for both non-small-cell lung cancer (NSCLC) and small-cell lung cancer (SCLC). Tumorigenesis in these conditional mouse tumor models can be initiated in adult mice through Cre-recombinase-induced activation of oncogenic mutations in a subset of the cells. They present a marked improvement over mouse models that depend on carcinogen induction of tumors. These models permit us to study the consecutive steps involved in initiation and progression and allow us to address questions like the cell of origin, and the role of cancer stem cells in the maintenance of these tumors. They now need to be validated as suitable preclinical models for intervention studies in which questions with respect to therapy response and resistance can be addressed.

Genetically engineered mouse models for lung cancer

The lung is a complex organ consisting of numerous cell types that function to ensure sufficient gas exchange to oxygenate the blood. In order to accomplish this function, the lung must be exposed to the external environment and at the same time maintain a homeostatic balance between its function in gas exchange and the maintenance of inflammatory balance. During the past two decades, as molecular methodologies have evolved with the sequencing of entire genomes, the use of in vivo models to elucidate the molecular mechanisms involved in pulmonary physiology and disease have increased. The mouse has emerged as a potent model to investigate pulmonary physiology due to the explosion in molecular methods that now allow for the developmental and tissue-specific regulation of gene transcription. Initial efforts to manipulate gene expression in the mouse genome resulted in the generation of transgenic mice characterized by the constitutive expression of a specific gene and knockout mice characterized by the ablation of a specific gene. The utility of these original mouse models was limited, in many cases, by phenotypes resulting in embryonic or neonatal lethality that prevented analysis of the impact of the genetic manipulation on pulmonary biology. Second-generation transgenic mouse models employ multiple strategies that can either activate or silence gene expression thereby providing extensive temporal and spatial control of the experimental parameters of gene expression. These highly regulated mouse models are intended to serve as a foundation for further investigation of the molecular basis of human disease such as tumorigenesis. This review describes the principles, progress, and application of systems that are currently employed in the conditional regulation of gene expression in the investigation of lung cancer.

Classification of Proliferative Pulmonary Lesions of the Mouse

Rapid advances in generating new mouse genetic models for lung neoplasia provide a continuous challenge for pathologists and investigators. Frequently, phenotypes of new models either have no precedents or are arbitrarily attributed according to incongruent human and mouse classifications. Thus, comparative characterization and validation of novel models can be difficult. To address these issues, a series of discussions was initiated by a panel of human, veterinary, and experimental pathologists during the Mouse Models of Human Cancers Consortium (NIH/National Cancer Institute) workshop on mouse models of lung cancer held in Boston on June 20-22, 2001. The panel performed a comparative evaluation of 78 cases of mouse and human lung proliferative lesions, and recommended development of a new practical classification scheme that would (a) allow easier comparison between human and mouse lung neoplasms, (b) accommodate newly emerging mouse neoplasms, and (c) address the interpretation of benign and preinvasive lesions of the mouse lung. Subsequent discussions with additional experts in pulmonary pathology resulted in the current proposal of a new classification. It is anticipated that this classification, as well as the complementary digital atlas of virtual histological slides, will help investigators and pathologists in their characterization of new mouse models, as well as stimulate further research aimed at a better understanding of proliferative lesions of the lung.

p63 is the molecular switch for initiation of an epithelial stratification program

Development of stratified epithelia, such as the epidermis, requires p63 expression. The p63 gene encodes isoforms that contain (TA) or lack (DeltaN) a transactivation domain. We demonstrate that TAp63 isoforms are the first to be expressed during embryogenesis and are required for initiation of epithelial stratification. In addition, TAp63 isoforms inhibit terminal differentiation, suggesting that TAp63 isoforms must be counterbalanced by DeltaNp63 isoforms to allow cells to respond to signals required for maturation of embryonic epidermis. Our data demonstrate that p63 plays a dual role: initiating epithelial stratification during development and maintaining proliferative potential of basal keratinocytes in mature epidermis.

FGF signaling is required for pulmonary homeostasis following hyperoxia

To assess the role of fibroblast growth factor (FGF) signaling in pulmonary function in the postnatal period, we generated transgenic mice in which a soluble FGF receptor (FGFR-HFc) was conditionally expressed in respiratory epithelial cells of the mouse lung, thereby inhibiting FGF activity. Although FGFR-HFc did not alter postnatal lung morphogenesis, male FGFR-HFc transgenic mice were more susceptible to hyperoxia and failed to recover when ambient oxygen concentrations were normalized. Inflammation, alveolar-capillary leak, and mortality were increased following exposure to 95% Fi(O(2)). Expression of surfactant protein (SP)-A and SP-B were significantly decreased in association with decreased immunostaining for thyroid transcription factor-1. FGF signaling is required for maintenance of surfactant homeostasis and lung function during hyperoxia in vivo, mediated, at least in part, by its role in the maintenance of SP-B expression.

SP-B deficiency causes respiratory failure in adult mice

Targeted deletion of the surfactant protein (SP)-B locus in mice causes lethal neonatal respiratory distress. To assess the importance of SP-B for postnatal lung function, compound transgenic mice were generated in which the mouse SP-B cDNA was conditionally expressed under control of exogenous doxycycline in SP-B-/- mice. Doxycycline-regulated expression of SP-B fully corrected lung function in compound SP-B-/- mice and protected mice from respiratory failure at birth. Withdrawal of doxycycline from adult compound SP-B-/- mice resulted in decreased alveolar content of SP-B, causing respiratory failure when SP-B concentration was reduced to <25% of normal levels. Decreased SP-B was associated with low alveolar content of phosphatidylglycerol, accumulation of misprocessed SP-C proprotein in the air spaces, increased protein content in bronchoalveolar lavage fluid, and altered surfactant activity in vitro. Consistent with surfactant dysfunction, hysteresis, maximal tidal volumes, and end expiratory volumes were decreased. Reduction of alveolar SP-B content causes surfactant dysfunction and respiratory failure, indicating that SP-B is required for postnatal lung function.

"Blue heart": characterization of a mifepristone-dependent system for conditional gene expression in genetically modified animals

A detailed characterization of a cardiac muscle-specific, ligand-regulated gene expression system was performed in transgenic mice using the inducing ligand mifepristone (MFP). Several lines of double transgenic mice were created that expressed a bacterial lacZ reporter gene in the heart, under the control of a MFP-activated transcription factor constitutively expressed in cardiac muscle. The transgenic mice, which were administered MFP at a dose of 1 micromol/l in the drinking water, responded to the ligand within 24 h. Induction of beta-galactosidase enzyme activity in the heart continued for up to 21 days and resulted in an average 17-fold increase in enzyme activity. The highest individual animal response measured was a 94-fold increase in enzyme activity. The EC(50) for MFP induction of beta-galactosidase activity in the heart was 0.7 micromol/l when MFP was administered in the drinking water. Pharmacokinetic analysis of MFP dosing in wild-type FVB/N mice showed that absorption was very rapid (T(max) 1-10 min), bioavailability was modest ( approximately 10%) and the t(1/2) of MFP in mouse plasma was determined to be approximately 5 h. Thus, the system functions effectively in transgenic mouse heart where induction of gene expression is sensitive and can be accomplished by a simple and broadly applicable drinking water protocol.

Antiprogestin-controllable transgene regulation in vivo

Gene control systems that provide temporal and spatial regulation of transgene expression in response to orally delivered drugs are needed for advances in functional genomics, models of human disease and gene therapy. A regulation system based on the altered binding and activation properties of a truncated ligand-binding domain derived from the progesterone receptor has been shown to be effective in providing tissue-specific, antiprogestin-controllable gene expression in transgenic mice, transgenic fruit flies and animals that have been administered viral-based or plasmid-based gene therapy vectors.

Identification of Indian hedgehog as a progesterone-responsive gene in the murine uterus

Progesterone (P4) plays a central role in normal uterine function, from embryo implantation in endometrium to establishment and maintenance of uterine quiescence during pregnancy in the myometrium. Considering its diverse physiological effects on female reproductive function, rather little is known about downstream events of P4 action. Recent progress in differential screening technologies facilitated identification of such inducible genes. We used uteri of wild-type and progesterone receptor null mutant mice as a starting material and screened for differentially expressed genes by medium-density cDNA expression array. Here, we report that the expression of the morphogen, Indian hedgehog (Ihh), is rapidly stimulated by P4 in the mouse uterus. The level of Ihh mRNA is induced within 3 h, after a single administration of P4 to ovariectomized mice. The induced Ihh mRNA and protein were localized to the luminal and glandular epithelial compartment of the endometrium. During pseudopregnancy, the Ihh mRNA level was transiently increased in the preimplantation period and d 3 and d 4 post coitum and then decreased rapidly at d 5 post coitum. Furthermore, the expression profile of patched-1, hedgehog interacting protein-1, and chicken ovalbumin upstream promoter-transcription factor II, genes known to be in the hedgehog signaling pathway in other tissues, followed the expression pattern of Ihh during the periimplantation period. Our results suggested that Ihh is regulated by P4, and the Ihh signaling axis may play a role in the preparation of the uterus for implantation during the periimplantation period.

Inducible control of tissue-specific transgene expression in Xenopus tropicalis transgenic lines

Analysis of gene function in vertebrates is facilitated by gain-of-function studies, such as injection of synthetic mRNA in amphibian embryos. This approach is hampered by lack of spatial and temporal control of expression of the introduced gene product. An additional level of control is obtained by nuclear-transfer-mediated transgenesis, but functional analyses are complicated by variability and background abnormalities in primary transgenic embryos. The GAL4/UAS system permits establishment of stable lines and elimination of nuclear-transfer-associated abnormalities, through generation of separate UAS-'effector' and GAL4 'transactivator' transgenic lines. When the GAL4 DNA-binding domain is combined with a steroid hormone ligand-binding domain, this system allows full temporal regulation of transgene expression by introduction of an exogenous steroid analogue, the progesterone antagonist RU486. We show here that by crossing stable Xenopus tropicalis transgenic lines, one bearing a UAS-enhanced cyan fluorescent protein (ECFP) reporter construct, and the other with a GAL4-progesterone receptor fusion driven by a retina-specific promoter, reporter expression in the resulting embryos can be induced with RU486 in a tissue-specific manner. These results suggest that the inducible binary system, in which the target gene expression can be controlled in a stage- and tissue-specific pattern, should be readily applicable for gene function studies at all stages of development.

Inducible expression of FGF-3 in mouse mammary gland

Fibroblast growth factor-3 (FGF-3) is a crucial developmental regulator. Aberrant activation of this gene by mouse mammary tumor virus insertion results in pregnancy-responsive mammary tumorigenesis. To characterize better FGF-3 function in postnatal mammary gland development and cancer initiation/progression, we used a mifepristone (RU486)-inducible regulatory system to express conditionally FGF-3 in the mammary epithelium of transgenic mice. Ectopic overexpression of FGF-3 in pubescent mammary glands elicited severe perturbations in early mammary gland development leading to mammary hyperplasia. Ductal elongation was retarded, multiple cysts persisted in the virgin ducts, and ductal epithelium was expanded and multilayered. The altered ductal architecture and the persistence of hyperplastic multilayered epithelium reflect a defect in growth regulation, which resulted from an imbalance between mitogenic and apoptotic signals. By altering the duration of RU486 treatment, we showed that the persistence of mitogenic signal elicited by FGF-3 is crucial for the initiation, progression, and maintenance of the hyperplastic characteristic of the mammary epithelium. The manifestations elicited by FGF-3 could be reversed by RU486 withdrawal. In addition, synergism between the stimulus from estrogen and FGF-3 mitogenic pathways was evident and likely contributes to the pregnancy-dependent tumorigenesis of FGF-3. Taken together, the mifepristone-inducible regulatory system provides a powerful means for understanding the diverse roles of FGF-3 and its interactions with hormones in mammary gland tumorigenesis.

Fibroblast growth factor 18 influences proximal programming during lung morphogenesis

The structure and functions of the airways of the lung change dramatically along their lengths. Large-diameter conducting airways are supported by cartilaginous rings and smooth muscle tissue and are lined by ciliated and secretory epithelial cells that are involved in mucociliary clearance. Smaller peripheral airways formed during branching morphogenesis are lined by cuboidal and squamous cells that facilitate gas exchange to a network of fine capillaries. The factors that mediate formation of these changing cell types and structures along the length of the airways are unknown. We report here that conditional expression of fibroblast growth factor (FGF)-18 in epithelial cells of the developing lung caused the airway to adopt structural features of proximal airways. Peripheral lung tubules were markedly diminished in numbers, whereas the size and extent of conducting airways were increased. Abnormal smooth muscle and cartilage were found in the walls of expanded distal airways, which were accompanied by atypically large pulmonary blood vessels. Expression of proteins normally expressed in peripheral lung tubules, including SP-B and pro-SP-C, was inhibited. FGF-18 mRNA was detected in normal mouse lung in stromal cells surrounding proximal airway cartilage and in peripheral lung mesenchyme. Effects were unique to FGF-18 because expression of other members of the FGF family had different consequences. These data show that FGF-18 is capable of enhancing proximal and inhibiting peripheral programs during lung morphogenesis.

The mifepristone-inducible gene regulatory system in mouse models of disease and gene therapy

The mifepristone (Mfp)-inducible gene regulatory system is designed to allow control of the spatiotemporal expression of transgenes in vivo in a ligand-dependent manner. This regulatory system is composed of two components: (1) a chimeric transactivator protein that activates transgene transcription only in the presence of the progesterone antagonist Mfp, and (2) a target transgene placed in the context of a promoter which is responsive only to the Mfp-bound chimeric transactivator. Incorporation of the components of the Mfp-inducible gene regulatory system into transgenic mice has resulted in the establishment of several novel, Mfp-dependent models of disease. Similarly, adaptation of the Mfp-inducible system for use in gene knockout models has resulted in the development of new gene ablation technology which is both tissue-specific and Mfp-dependent. Additionally, the Mfp-inducible gene regulatory system has been used in animal experiments involving somatic gene therapy, where it has shown considerable promise in the regulation of both reporter and therapeutic gene expression. This review focuses on recent application of the Mfp-inducible system to transgenic models, gene knockout models, and somatic gene therapy experiments. In so doing, it demonstrates the considerable promise that future use of this system holds for better understanding and treatment of human disease.

Ectopic expression of FGF-3 results in abnormal prostate and Wolffian duct development

To evaluate the effects of FGF-3 expression in the prostate and male reproductive tract, we employed a bitransgenic system to target FGF-3 to these organs. We present a first study that ectopic FGF-3 expression resulted in exuberant hyperplasia of all bigenic prostatic lobes typified by epithelial stratification, cribiform structures and papillary tufts. These cells displayed increased nuclear-to-cytoplasmic ratios and bromodeoxyuridine (BrdU) proliferative index but retained relatively uniform nuclear androgen receptor (AR) and the tumor suppressor C-CAM1 staining. Furthermore, the dysmorphogenic prostatic cells also resembled PIN (prostatic intraepithelial neoplasia)-like lesions but did not appear to have invaded the basal lamina. In addition to these phenotypes, profound disorders of the bigenic Wolffian duct derivatives were observed. The bigenic ampullary glands and vas deferens were extremely cystic, hypertrophic and hyperplastic; the enlarged epididymi showed a reduction of spermatozoa and the seminal vesicles exhibited a dramatic reduction of seminal secretions. Because of these severe abnormalities, these infertile males presented with diaphragmatic hernias, hemoperitoneum and many secondary abnormalities at sacrifice. Taken together, we show that ectopic FGF-3 expression severely perturbs normal prostate development and our system should be useful for the analyses of early changes in prostatic hyperplasia.

Effects of mouse strain, position of integration and tetracycline analogue on the tetracycline conditional system in transgenic mice

The tetracycline conditional system is a very powerful method for achieving control of gene expression in transgenic mice, allowing one to turn expression both off and on in the same animal. We have used it to make a tissue-specific transgenic mouse model of Charcot-Marie-Tooth disease type 1A. This disease is most commonly caused by overexpression of peripheral myelin protein 22 (PMP22) in Schwann cells of the peripheral nervous system. Here we describe the effects of position of integration of the transgene, tetracycline analogue and mouse strain in this model. The small transgenes used to express tTA, the LacZ reporter and the pmp22 cDNA were all very dependent on the position of integration with few of the transgenic lines working successfully. In contrast, the single transgenic made with the 560 kb yeast artificial chromosome construct containing the tTA open reading frame worked well. Tetracycline was found to be cleared from mice relatively fast in comparison with doxycycline and is thus useful if one wants to switch on gene expression after extended periods of administration. Finally, the initial litters were on a mixed genetic background and the level of LacZ or pmp22 expression was very variable between mice. We found that expression became uniform between mice, and occurred in a higher proportion of cells, when the transgenes were crossed onto the CBA/Ca background in comparison with the C57BL/6J background.

Induction and apoptotic regression of lung adenocarcinomas by regulation of a K-Ras transgene in the presence and absence of tumor suppressor genes

To investigate the role of an activated K-Ras gene in the initiation and maintenance of lung adenocarcinomas, we developed transgenic mice that express murine K-Ras4b(G12D) under the control of doxycycline in type II pneumocytes. Focal proliferative lesions of alveolar type II pneumocytes were observed as early as seven days after induction with doxycycline; after two months of induction, the lungs contained adenomas and adenocarcinomas, with focal invasion of the pleura at later stages. Removal of doxycycline caused a rapid fall in levels of mutant K-Ras RNA and concomitant apoptotic regression of both the early proliferative lesions and the tumors. Tumor burden was dramatically decreased by three days after withdrawal, and tumors were undetectable after one month. When similar experiments were performed with animals deficient in either the p53 gene or the Ink4A/Arf locus, tumors arose more quickly (within one month of exposure to doxycycline) and displayed more obvious histological features of malignancy; nevertheless, these tumors also regressed rapidly when the inducer was removed, implying that continued production of mutant K-Ras is necessary to maintain the viability of tumor cells in the absence as well as the presence of tumor suppressor genes. We also show that the appearance and regression of these pulmonary tumors can be readily monitored in anesthetized transgenic animals by magnetic resonance imaging.

Targeted gene regulation and gene ablation

Investigations of the mechanisms involved in appropriate, developmentally regulated tissue-specific gene transcription have laid the foundations for transgenic and gene-therapy technologies directing specific induction or ablation of genes of interest in a tissue-restricted manner. This technology has further evolved to allow for temporal control of gene expression and ablation. Genes can now be switched on and off or be ablated by administering exogenous compounds. These technologies are based on the development of ligand-inducible transcription factors or recombinases that regulate gene expression or ablation by the administration of specific ligands and should lead to animal models that are better suited for investigating the molecular basis of human disease. This review describes the evolution, components and applications of systems that are currently being employed in transgenic and mutant-mouse technology for the conditional regulation of gene expression and ablation.