Tumors of the retinal pigment epithelium metastasize to inguinal lymph nodes and spleen in tyrosinase-related protein 1/SV40 T antigen transgenic mice

Uveal melanoma modeling in mice and zebrafish

Despite extensive research and refined therapeutic options, the survival for metastasized uveal melanoma (UM) patients has not improved significantly. UM, a malignant tumor originating from melanocytes in the uveal tract, can be asymptomatic and small tumors may be detected only during routine ophthalmic exams; making early detection and treatment difficult. UM is the result of a number of characteristic somatic alterations which are associated with prognosis. Although UM morphology and biology have been extensively studied, there are significant gaps in our understanding of the early stages of UM tumor evolution and effective treatment to prevent metastatic disease remain elusive. A better understanding of the mechanisms that enable UM cells to thrive and successfully metastasize is crucial to improve treatment efficacy and survival rates. For more than forty years, animal models have been used to investigate the biology of UM. This has led to a number of essential mechanisms and pathways involved in UM aetiology. These models have also been used to evaluate the effectiveness of various drugs and treatment protocols. Here, we provide an overview of the molecular mechanisms and pharmacological studies using mouse and zebrafish UM models. Finally, we highlight promising therapeutics and discuss future considerations using UM models such as optimal inoculation sites, use of BAP1mut-cell lines and the rise of zebrafish models.

Retinal Pigment Epithelium Adenoma and Adenocarcinoma: A Review

Adenoma and adenocarcinoma of the retinal pigment epithelium (RPE) are rare intraocular tumours that are often misdiagnosed as posterior uveal melanoma or other simulating lesions. It is important to be able to differentiate these tumours from melanoma for 3 reasons. First, an inability to rule out melanoma often tilts the management towards enucleation. Second, management options like radiotherapy and local resection which work well for melanoma may not be easily applied to these tumours. Third, and most importantly, patients with melanoma need a lifetime follow-up to rule out metastases (metastatic dormancy) whereas RPE tumours hardly metastasize. An abruptly elevated, often deeply pigmented tumour, with a prominent retinal feeding artery and a draining vein causing exudation, should raise a suspicion of RPE tumours. RPE tumours have a remarkable local invasive potential but a low metastatic potential. Most RPE tumours require treatment due to local complications. Small, asymptomatic tumours can be generally observed. Enucleation is still the gold standard of treatment, although local resection has been reported in selected cases with good results. Here, we provide a comprehensive review of the demographic, clinical, and imaging features of true acquired neoplasms of the RPE, namely adenoma and adenocarcinoma, the ways to differentiate them from melanoma, their clinical course and prognosis, and Options for their management.

Transgenic Mouse Models of SV40-Induced Cancer

The SV40 viral oncogene has been used since the 1970s as a reliable and reproducible method to generate transgenic mouse models. This seminal discovery has taught us an immense amount about how tumorigenesis occurs, and its success has led to the evolution of many mouse models of cancer. Despite the development of more modern and targeted approaches for developing genetically engineered mouse models of cancer, SV40-induced mouse models still remain frequently used today. This review discusses a number of cancer types in which SV40 mouse models of cancer have been developed and highlights their relevance and importance to preclinical research.

SV40 TAg mouse models of cancer

The discovery of a number of viruses with the ability to induce tumours in animals and transform human cells has vastly impacted cancer research. Much of what is known about tumorigenesis today regarding tumour drivers and tumour suppressors has been discovered through experiments using viruses. The SV40 virus has proven extremely successful in generating transgenic models of many human cancer types and this review provides an overview of these models and seeks to give evidence as to their relevance in this modern era of personalised medicine and technological advancements.

Carcinogen treatment in mouse selectively expressing activated N-Ras Q61K in melanocytes recapitulates metastatic cutaneous melanoma development

The incidence of melanoma has significantly increased, and a better understanding of its pathogenesis and development of new therapeutic strategies are urgently needed. Here, we describe a murine model of metastatic cutaneous melanoma using C57BL/6 mice expressing a mutated human N-Ras gene under the control of a tyrosinase promoter (TyrRas). These mice were topically exposed to 7,12- dimethylbenzanthracene (DMBA) for brief exposure periods. Cutaneous melanoma developed at the site of exposure on average by 19 weeks of age and in 80% of mice. Importantly, as in humans, melanoma development was associated with subsequent metastasis to tumor-draining lymph nodes. Critically, such metastatic behavior is transplantable, as intradermal inoculation of melanoma cells from TyrRas-DMBA mice into non-transgenic mice led to the growth of melanoma and, again, metastasis to skin-draining lymph nodes. This metastatic melanoma model closely mimics human pathology and should be a useful tool for studying melanoma pathogenesis and developing new therapies.

The TAg-RB murine retinoblastoma cell of origin has immunohistochemical features of differentiated Muller glia with progenitor properties

PURPOSE

Human retinoblastoma arises from an undefined developing retinal cell after inactivation of RB1. This is emulated in a murine retinoblastoma model by inactivation of pRB by retinal-specific expression of simian virus 40 large T-antigen (TAg-RB). Some mutational events after RB1 loss in humans are recapitulated at the expression level in TAg-RB, supporting preclinical evidence that this model is useful for comparative studies between mouse and human. Here, the characteristics of the TAg-RB cell of origin are defined.

METHODS

TAg-RB mice were killed at ages from embryonic day (E)18 to postnatal day (P)35. Tumors were analyzed by immunostaining, DNA copy number PCR, or real-time quantitative RT-PCR for TAg protein, retinal cell type markers, and retinoblastoma-relevant genes.

RESULTS

TAg expression began at P8 in a row of inner nuclear layer cells that increased in number through P21 to P28, when clusters reminiscent of small tumors emerged from cells that escaped a wave of apoptosis. Early TAg-expressing cells coexpressed the developmental marker Chx10 and glial markers CRALBP, clusterin, and carbonic anhydrase II (Car2), but not TuJ1, an early neuronal marker. Emerging tumors retained expression of only Chx10 and carbonic anhydrase II. As with human retinoblastoma, TAg-RB tumors showed decreased Cdh11 DNA copy number and gain of Kif14 and Mycn. It was confirmed that TAg-RB tumors lose expression of tumor suppressor cadherin-11 and overexpress oncogenes Kif14, Dek, and E2f3.

CONCLUSIONS

TAg-RB tumors displayed molecular similarity to human retinoblastoma and origin in a cell with features of differentiated Müller glia with progenitor properties.

Retinal degeneration triggered by inactivation of PTEN in the retinal pigment epithelium

Adhesion between epithelial cells mediates apical-basal polarization, cell proliferation, and survival, and defects in adhesion junctions are associated with abnormalities from degeneration to cancer. We found that the maintenance of specialized adhesions between cells of the retinal pigment epithelium (RPE) requires the phosphatase PTEN. RPE-specific deletion of the mouse pten gene results in RPE cells that fail to maintain basolateral adhesions, undergo an epithelial-to-mesenchymal transition (EMT), and subsequently migrate out of the retina entirely. These events in turn lead to the progressive death of photoreceptors. The C-terminal PSD-95/Dlg/ZO-1 (PDZ)-binding domain of PTEN is essential for the maintenance of RPE cell junctional integrity. Inactivation of PTEN, and loss of its interaction with junctional proteins, are also evident in RPE cells isolated from ccr2(-/-) mice and from mice subjected to oxidative damage, both of which display age-related macular degeneration (AMD). Together, these results highlight an essential role for PTEN in normal RPE cell function and in the response of these cells to oxidative stress.

Predominant formation of heavily pigmented dermal melanocytomas resembling 'animal-type' melanomas in hepatocyte growth factor (C57BL/6 x C3H)F1 mice following neonatal UV irradiation

BACKGROUND

Transgenic mice expressing hepatocyte growth factor (HGF) develop cutaneous melanocytic tumors following neonatal UV exposure. Here, we examined the histologic spectrum of UV-induced melanocytic tumors in HGF mice on a pigmented (C57BL/6 x C3H/HeN)F(1) background.

METHODS

Neonatally irradiated (4000 J/m(2)) mice were monitored for 43 weeks, and 31/34 (91%) animals developed a total of 163 melanocytic tumors.

RESULTS

Of 54 primary tumors analyzed, most (49/54, 91%) demonstrated exclusively dermal collections of epithelioid cells with voluminous densely pigmented cytoplasm. Seven of these also demonstrated a population of spindled cells with mitoses. Several (3/54, 6%) tumors exhibited a junctional component with melanocytes present in the epidermis. Staining with PEP8 confirmed the presence of interfollicular melanocytes at the dermal-epidermal junction in neonatal skin.

CONCLUSIONS

In contrast to HGF animals on an albino (FVB) background, HGF animals on the pigmented (C57BL/6 x C3H/HeN)F(1) background do not develop classic radial growth phase melanoma but rather predominantly develop dermal melanocytomas resembling the 'animal-type' melanoma occasionally seen in humans. These results demonstrate the influence of genetic background on histologic pattern of UV-induced melanomas in mice.

Radiation and inhibition of angiogenesis by canstatin synergize to induce HIF-1alpha-mediated tumor apoptotic switch

Tumor radioresponsiveness depends on endothelial cell death, which leads in turn to tumor hypoxia. Radiation-induced hypoxia was recently shown to trigger tumor radioresistance by activating angiogenesis through hypoxia-inducible factor 1-regulated (HIF-1-regulated) cytokines. We show here that combining targeted radioiodide therapy with angiogenic inhibitors, such as canstatin, enhances direct tumor cell apoptosis, thereby overcoming radio-induced HIF-1-dependent tumor survival pathways in vitro and in vivo. We found that following dual therapy, HIF-1alpha increases the activity of the canstatin-induced alpha(v)beta(5) signaling tumor apoptotic pathway and concomitantly abrogates mitotic checkpoint and tetraploidy triggered by radiation. Apoptosis in conjunction with mitotic catastrophe leads to lethal tumor damage. We discovered that HIF-1 displays a radiosensitizing activity that is highly dependent on treatment modalities by regulating key apoptotic molecular pathways. Our findings therefore support a crucial role for angiogenesis inhibitors in shifting the fate of radiation-induced HIF-1alpha activity from hypoxia-induced tumor radioresistance to hypoxia-induced tumor apoptosis. This study provides a basis for developing new biology-based clinically relevant strategies to improve the efficacy of radiation oncology, using HIF-1 as an ally for cancer therapy.

Effect of Human Skin-Derived Stem Cells on Vessel Architecture, Tumor Growth, and Tumor Invasion in Brain Tumor Animal Models

Glioblastomas represent an important cause of cancer-related mortality with poor survival. Despite many advances, the mean survival time has not significantly improved in the last decades. New experimental approaches have shown tumor regression after the grafting of neural stem cells and human mesenchymal stem cells into experimental intracranial gliomas of adult rodents. However, the cell source seems to be an important limitation for autologous transplantation in glioblastoma. In the present study, we evaluated the tumor targeting and antitumor activity of human skin-derived stem cells (hSDSCs) in human brain tumor models. The hSDSCs exhibit tumor targeting characteristics in vivo when injected into the controlateral hemisphere or into the tail vein of mice. When implanted directly into glioblastomas, hSDSCs distributed themselves extensively throughout the tumor mass, reduced tumor vessel density, and decreased angiogenic sprouts. In addition, transplanted hSDSCs differentiate into pericyte cell and release high amounts of human transforming growth factor-beta1 with low expression of vascular endothelial growth factor, which may contribute to the decreased tumor cell invasion and number of tumor vessels. In long-term experiments, the hSDSCs were also able to significantly inhibit tumor growth and to prolong animal survival. Similar behavior was seen when hSDSCs were implanted into two different tumor models, the chicken embryo experimental glioma model and the transgenic Tyrp1-Tag mice. Taken together, these data validate the use of hSDSCs for targeting human brain tumors. They may represent therapeutically effective cells for the treatment of intracranial tumors after autologous transplantation.

A gene transfer comparative study of HSA-conjugated antiangiogenic factors in a transgenic mouse model of metastatic ocular cancer

Different antiangiogenic and antimetastatic recombinant adenoviruses were tested in a transgenic mouse model of metastatic ocular cancer (TRP1/SV40 Tag transgenic mice), which is a highly aggressive tumor, developed from the pigmented epithelium of the retina. These vectors, encoding amino-terminal fragments of urokinase plasminogen activator (ATF), angiostatin Kringles (K1-3), endostatin (ES) and canstatin (Can) coupled to human serum albumin (HSA) were injected to assess their metastatic and antiangiogenic activities in our model. Compared to AdCO1 control group, AdATF-HSA did not significantly reduce metastatic growth. In contrast, mice treated with AdK1-3-HSA, AdES-HSA and AdCan-HSA displayed significantly smaller metastases (1.19+/-1.19, 0.87+/-1.5, 0.43+/-0.56 vs controls 4.04+/-5.12 mm3). Moreover, a stronger inhibition of metastatic growth was obtained with AdCan-HSA than with AdK1-3-HSA (P=0.04). Median survival was improved by 4 weeks. A close correlation was observed between the effects of these viruses on metastatic growth and their capacity to inhibit tumor angiogenesis. Our study indicates that systemic antiangiogenic factors production by recombinant adenoviruses, particularly Can, might represent an effective way of delaying metastatic growth via inhibition of angiogenesis.

A conserved transcriptional enhancer that specifies Tyrp1 expression to melanocytes

Pigment cells of mammals originate from two different lineages: melanocytes arise from the neural crest, whereas cells of the retinal pigment epithelium (RPE) originate from the optic cup of the developing forebrain. Previous studies have suggested that pigmentation genes are controlled by different regulatory networks in melanocytes and RPE. The promoter of the tyrosinase-related family gene Tyrp1 has been shown to drive detectable transgene expression only to the RPE, even though the gene is also expressed in melanocytes as evident from Tyrp1-mutant mice. This indicates that the regulatory elements responsible for Tyrp1 gene expression in the RPE are not sufficient for expression in melanocytes. We thus searched for a putative melanocyte-specific regulatory sequence and demonstrate that a bacterial artificial chromosome (BAC) containing the Tyrp1 gene and surrounding sequences is able to target transgenic expression to melanocytes and to rescue the Tyrp1b (brown) phenotype. This BAC contains several highly conserved non-coding sequences that might represent novel regulatory elements. We further focused on a sequence located at -15 kb, which we identified as a melanocyte-specific enhancer as shown by cell culture and transgenic mice experiments. In addition, we show that the transcription factor Sox10 can activate this conserved enhancer. The presence of a distal Tyrp1 regulatory element, which specifies melanocyte-specific expression, supports the idea that separate regulatory sequences can mediate differential gene expression in melanocytes and RPE.

The tyrp1-Tag/tyrp1-FGFR1-DN Bigenic Mouse

We describe herein a new transgenic mouse tumor model in which fibroblast growth factor (FGF) receptor activity is selectively inhibited. Tyrp1-Tag mice that develop early vascularized tumors of the retinal pigment epithelium were crossed with tyrp1-FGFR1-DN mice that express dominant-negative FGF receptors in the retinal pigment epithelium to generate bigenic mice. Initial angiogenesis-independent tumor growth progressed equally in tyrp1-Tag and bigenic mice with no significant differences in the number of dividing and apoptotic cells within the tumor. By contrast, at a later stage when tyrp1-Tag tumors rapidly expanded to fill the entire eye posterior chamber and migrate along the optic nerve toward the chiasma, bigenic tumors remained small and were poorly vascularized. Secondary tumors of small size developed in only 20% of bigenic mice by 1 month. Immunohistochemical analysis of secondary tumors from bigenic mice showed a reduction of angiogenesis and an increase in apoptosis in tumor cells. Tumor cells from bigenic mice expressed high levels of truncated FGF receptors and did not induce endothelial tube formation in vitro. All in all, this indicates that the tyrp1-Tag mouse may be a useful model to study selective tumor inhibition and the effect of antitumor therapy that targets a specific growth factor pathway. FGF receptors are required at the onset of tumor invasion and angiogenesis in ocular tumors and are good therapeutic targets in this model. The bigenic mouse may also constitute a useful model to answer more fundamental questions of cancer biology such as the mechanism of tumor escape.

A transgenic mouse model of metastatic carcinoma involving transdifferentiation of a gastric epithelial lineage progenitor to a neuroendocrine phenotype

Human neuroendocrine cancers (NECs) arise in various endoderm-derived epithelia, have diverse morphologic features, exhibit a wide range of growth phenotypes, and generally have obscure cellular origins and ill-defined molecular mediators of initiation and progression. We describe a transgenic mouse model of metastatic gastric cancer initiated by expressing simian virus 40 large tumor antigen (SV40 TAg), under control of regulatory elements from the mouse Atp4b gene, in the progenitors of acid-producing parietal cells. Parietal cells normally do not express endocrine or neural features, and Atp4b-Cre bitransgenic mice with a Cre reporter confirmed that the Atp4b regulatory elements are not active in gastric enteroendocrine cells. GeneChip analyses were performed on laser capture microdissected SV40 TAg-expressing cells in preinvasive foci and invasive tumors. Genes that distinguish invasive from preinvasive cells were then hierarchically clustered with DNA microarray datasets obtained from human lung and gastric cancers. The results, combined with immunohistochemical and electron microscopy studies of Apt4b-SV40 TAg stomachs, revealed that progression to invasion was associated with transdifferentiation of parietal cell progenitors to a neuroendocrine phenotype, and that invasive cells shared molecular features with NECs arising in the human pulmonary epithelium, including transcription factors that normally regulate differentiation of various endocrine lineages and maintain neural progenitors in an undifferentiated state. The 399 mouse genes identified as regulated during acquisition of an invasive phenotype and concomitant neuroendocrine transdifferentiation, plus their human orthologs associated with lung NECs, provide a foundation for molecular classification of NECs arising in other tissues and for genetic tests of the molecular mechanisms underlying NEC pathogenesis.

Systemic administration of a recombinant adenovirus encoding a HSA-Angiostatin kringle 1-3 conjugate inhibits MDA-MB-231 tumor growth and metastasis in a transgenic model of spontaneous eye cancer

We previously reported that intratumoral injection of AdK3, a recombinant adenovirus encoding human angiostatin kringle (K) 1 to 3, inhibits tumor vascularization and tumor growth. To reduce the serum clearance of this factor, we constructed an adenovirus (AdK3-HSA) that carries a chimeric gene encoding a fusion protein between angiostatin K1-3 and human serum albumin (HSA). This conjugate inhibited endothelial cell proliferation as efficiently as K1-3. K3-HSA serum concentrations in immunodeficient mice systemically injected with AdK3-HSA were dramatically higher than in AdK3-injected mice. Furthermore, the growth of MDA-MB-231 tumors grafted into nude mice that had been injected intravenously with AdK3-HSA was inhibited by 79% (versus 17% with AdK3). In TRP-1/SV40 Tag transgenic mice, which spontaneously develop eye tumors with brain metastases, intravenous injections of AdK3-HSA in newborn mice blocked metastatic dissemination efficiently and significantly, and prolonged survival by 3 weeks. After 2 months, only 46% of AdK3-HSA-treated animals developed micrometastases, whereas 94% of the AdCO1-injected group displayed numerous macrometastases. Nevertheless, ocular tumor growth was not modified because of impaired diffusion of the conjugate in the eye compartment. Our results show that HSA genetic coupling is an efficient way to increase the pharmacokinetics of circulating angiogenic inhibitors and thus their antitumoral activity.

Pathways to melanoma development: lessons from the mouse

Because of subtle differences between mouse and human skin, mice have traditionally not been an ideal model to study melanoma development. Understanding of the molecular mechanisms of melanoma predisposition, however, has been greatly improved by modeling various pathway defects in the mouse. This review analyzes the latest developments in mouse models of melanoma, and summarizes what these may indicate about the development of this neoplasm in humans. Mutations of genes involved in human melanoma have been recapitulated with some unexpected results, particularly with respect to the role of the two transcripts (Ink4a and Arf) encoded by the Cdkn2a locus. Both the Ink4a/pRb and Arf/p53 pathways are involved in melanoma development in mice, and possible mechanisms of cross-talk between the two pathways are discussed. We also know from mouse models that Ras/mitogen-activated protein kinase pathway activation is very important in melanoma development, either through direct activation of Ras (e.g., Hras G12V), or via activation of Ras-effector pathways by other oncogenes (e.g., Ret, Hgf/Sf). Ras can cooperate with the Arf/p53 pathway, and probably the Ink4a/Rb pathway, to induce melanoma. These three growth regulation pathways (Ink4a/pRb, Arf/p53, and Ras/mitogen-activated protein kinase) seem to represent three major "axes" of melanoma development in mice. Finally, we summarize experiments using genetically modified mice that have given indications of the intensity and timing of ultraviolet radiation exposure that may be most responsible for melanoma development.

Recent advances in cancer research: mouse models of tumorigenesis

Over the past 20 years, cancer research has gained major insights into the complexity of tumor development, in particular into the molecular mechanisms that underlie the progressive transformation of normal cells into highly malignant derivatives. It is estimated that the transformation of a normal cell to a malignant tumor cell is dependent upon a small number of genetic alterations, estimated to be within the range of four to seven rate-limiting events. Critical events in the evolution of neoplastic disease include the loss of proliferative control, the failure to undergo programmed cell death (apoptosis), the onset of neoangiogenesis, tissue remodeling, invasion of tumor cells into surrounding tissue and, finally, metastatic dissemination of tumor cells to distant organs. In patients, the molecular analysis of these multiple steps is hampered by the unavailability of tumor biopsies from all tumor stages. In contrast, mouse models of tumorigenesis allow the reproducible isolation of all tumor stages, including normal tissue, which are then amenable to pathological, genetic and biochemical analyses and, hence, have been instrumental in investigating cancer-related genes and their role in carcinogenesis. In this review, we discuss mouse tumor models that have contributed substantially to the identification and characterization of novel tumor pathways. In particular, we focus on transgenic and knockout mouse models that closely mimic human cancer and thus can be used as model systems for cancer research.

Absence of fibroblast growth factor 2 does not prevent tumor formation originating from the RPE

We have analysed the importance of fibroblast growth factor 2 (FGF2) in tumor development. In a transgenic mouse model (Tyrp1-Tag) tumors form in the retinal pigment epithelium (RPE), invade surrounding tissues, and metastasize to lymph node and spleen. To address whether RPE tumor formation is dependent on FGF2, we generated FGF2-deficient mice. Such mice appeared healthy and exhibited no impairment of growth or development. Tyrp1-Tag transgenic mice, which are lacking FGF2 (FGF2-/-) developed RPE tumors that metastasize to spleen and lymph nodes. Tumor growth and survival rate are identical to Tyrp1-Tag transgenic littermates expressing FGF2. Cell lines were isolated from RPE tumors of wild-type and FGF2-deficient mice. They grow in culture, are pigmented and form vascularized tumors, when injected subcutaneously into nude mice of either FGF2-/- or FGF2+/+ genetic background. Kinetics of tumor growth was identical and independent of presence of FGF2. Together, these results demonstrate that FGF2 is not essential for tumor formation of the RPE thus suggesting that tumor growth in general may not be dependent on FGF2.

Mutant laboratory mice with abnormalities in pigmentation: annotated tables

Mammalian pigment cell research has recently entered a phase of significantly increased activity due largely to the exploitation of the many mutant mouse stocks that are coming on stream. Numerous transgenic, targeted mutagenesis (so-called 'knockouts'), conditional (so-called 'gene switch') and spontaneous mutant mice develop abnormal coat color phenotypes. The number of mice that exhibit such abnormalities is increasing exponentially as genetic engineering methods become routine. Since defined abnormalities in such mutant mice provide important clues to the as yet often poorly understood functional roles of many gene products, this overview includes a corresponding, annotated table of mutant mice with pigmentation alterations. These range from early developmental defects via a large array of coat color abnormalities to a melanoma metastasis model. This overview should provide helpful pointers to investigators who are looking for mouse models to explore or to compare functional activities of genes of interest and for comparing coat color phenotypes of spontaneous or genetically engineered mouse mutants with novel ones. Secondly, this review includes a table of mouse models of specific human diseases with genetically defined pigmentation abnormalities. In summary, this annotated table should serve as a useful reference for anyone interested in the molecular controls of pigmentation.

Cancer vaccine design: a novel bacterial adjuvant for peptide-specific CTL induction

The recent identification of tumor Ags as potential vaccines has prompted the search for efficient adjuvants and delivery systems, especially in the case of peptide-based vaccination protocols. Here, we investigated the adjuvant potential of the recombinant 40-kDa outer membrane protein of Klebsiella pneumoniae (P40) for specific CTL induction. We studied the CTL response induced in HLA-A*0201/K(b) transgenic mice immunized with peptides derived from two melanoma-associated differentiation Ags, the HLA-A*0201-restricted decapeptide Melan-A(26--35) substituted at position 2 and the K(b)-restricted tyrosinase-related protein 2(181--188) T cell epitope. We found that both peptides are able to generate a specific CTL response when mixed with the protein in the absence of conventional adjuvant. This CTL response is a function of the amount of P40 used for immunization. Moreover, the CTL response generated against the tyrosinase-related protein 2(181-188) peptide in presence of P40 is associated with tumor protection in two different experimental models and is independent of the presence of CD4(+) T lymphocytes. Thus, the recombinant bacterial protein P40 functions as a potent immunological adjuvant for specific CTL induction.

Neural and angiogenic defects in eyes of transgenic mice expressing a dominant-negative FGF receptor in the pigmented cells

Fibroblast growth factors (FGF) are multipotent cytokines with demonstrated mitogenic, neurotrophic and angiogenic properties. There is evidence that they have multiple functions during and after development of the vertebrate eye. Amongst these, the role of FGF receptor mediated signaling in the retinal pigmented epithelium (RPE) is not yet well understood. FGF-2 is produced in RPE cells and may play a role in photoreceptor development and/or survival in vivo. It may also stimulate growth of melanocytes and angiogenesis in the choroid. To address these questions, we have specifically disrupted FGF signaling by generating lines of transgenic mice expressing dominant-negative FGF receptor 1 (FGFR-1) in the pigmented cells. Histological analysis of the eyes were conducted on hemizygous and homozygous mice at different ages. In homozygotes, eye growth is strongly impaired during embryogenesis leading to massive eye degeneration seen in the early post-natal stages. In hemizygotes, the choroid is thinned and the finger-like junctions between RPE cells and photoreceptors are disrupted. Scanning electron microscopy of the choroid vasculature showed that choriocapillary density, diameter and branching are strongly affected. As mice age, they develop progressive retinal degeneration as evidenced by photoreceptor cell loss. Our results are in agreement with the hypothesis that FGF signaling in the RPE participates in photoreceptor survival in vivo. Our model provides evidence that FGF signaling is also involved in choroidal angiogenesis by a process that could relate to induction of terminal branching.

Transgenic mouse models for tumors of melanocytes and retinal pigment epithelium

Cutaneous and ocular melanomas are due to malignant transformation of neural crest-derived melanocytes. The rising incidence of this tumor in humans has stimulated experiments to devise suitable mouse models. In the past years, transgenic mouse lines have been generated using different oncogenes - Ha-ras, SV40 T antigen (Tag), ret - which develop benign lesions of melanocytes, melanoma, and/or eye tumors. Pigment cell tumors in humans, although rather rare, can also develop from the retinal pigment epithelium (RPE), a cell layer of neuroectodermal origin. We, therefore, established transgenic models for this ocular tumor. Regulated by the promoter of tyrosinase-related protein-1 (TRP-1), two oncogenes, ret and SV40 Tag, were targeted to the developing RPE in transgenic mice. The TRP-1/ret transgenic mice displayed microphthalmia and benign tumors of the RPE. Expression of SV40 T antigen (TRP-1/Tag) led to malignant tumors, which were invasive and metastasized to inguinal lymph node and spleen.

Ectopic expression of RET results in microphthalmia and tumors in the retinal pigment epithelium

The retinal pigment epithelium (RPE) is essential for eye development by interacting with the overlaying neuroepithelium. Regulatory sequences of the gene encoding for tyrosinase-related protein 1 (TRP-1), linked to the lacZ reporter gene, lead to strong and specific beta-galactosidase expression in the RPE. We asked how the oncogene ret would affect this epithelial cell type during mouse development. We used the TRP-1 promoter to express ret in the developing RPE, and obtained transgenic mouse lines, which showed mild to severe microphthalmia. During development, the RPE changed to a stratified epithelium with reduced or absent pigmentation from E10.5 onward. In addition, proliferation of RPE cells and tumor formation were observed from E12.5 onward. These early events prevent closure of choroid fissure and lead to microphthalmia and secondary malformations after birth. We conclude that ret transgene expression in the RPE prevents normal differentiation of this epithelial layer and induces proliferation and tumor formation. The appearance of the microphthalmic phenotype underlines the requirement of a normally developed RPE for eye development.