Gene transactivation mediated by the TAT gene of human immunodeficiency virus in transgenic mice

Use of the transgenic mouse in models of AIDS cardiomyopathy

Heart disease in AIDS, particularly cardiomyopathy (CM), is an increasingly recognized clinical problem with as yet undefined pathogenetic mechanisms. Among the potential etiologies of AIDS CM are HIV-1 infection of cardiac myocytes and subsequent cardiac dysfunction, opportunistic infection, inflammatory reactions, cytokine effects, and cardiotoxicity of prescribed or illicit drugs. It seems probable that multiple factors may impact on the development of CM in AIDS. Transgenic mice (TG) are useful biological tools to explore mechanisms of cardiac function and disease. In AIDS models, TG offer novel ways to elucidate mechanisms of AIDS CM through combined in vivo and in vitro studies. With targeted and non-targeted TG, structural and functional effects of specific HIV-1 gene products on heart tissue may be addressed. The impact of environmental agents including therapeutics or cardiotoxins may also be defined. To address the complexity of AIDS CM using TG, an experimental approach has been employed in our laboratories to model the clinical condition. We utilize AIDS TG with generalized expression of HIV-1 gene products in CM models with combined antiretroviral regimens to define the cardiovascular effects of AIDS and its therapy on the structure and function of the murine heart. We are developing a series of cardiac specific TG bearing selected HIV-1 genes. These TG target the selected HIV-1 genes expressed in cardiac ventricular myocytes. Tissue-specific targeting of this type enables us to define structural and functional effects of specific HIV-1 gene products on the cardiac myocyte.

Of mice and models: improved animal models for biomedical research

The ability to engineer the mouse genome has profoundly transformed biomedical research. During the last decade, conventional transgenic and gene knockout technologies have become invaluable experimental tools for modeling genetic disorders, assigning functions to genes, evaluating drugs and toxins, and by and large helping to answer fundamental questions in basic and applied research. In addition, the growing demand for more sophisticated murine models has also become increasingly evident. Good state-of-principle knowledge about the enormous potential of second-generation conditional mouse technology will be beneficial for any researcher interested in using these experimental tools. In this review we will focus on practice, pivotal principles, and progress in the rapidly expanding area of conditional mouse technology. The review will also present an internet compilation of available tetracycline-inducible mouse models as tools for biomedical research (http://www.zmg.uni-mainz.de/tetmouse/).

Conditional control of gene expression in the mouse

One of the most powerful tools that the molecular biology revolution has given us is the ability to turn genes on and off at our discretion. In the mouse, this has been accomplished by using binary systems in which gene expression is dependent on the interaction of two components, resulting in either transcriptional transactivation or DNA recombination. During recent years, these systems have been used to analyse complex and multi-staged biological processes, such as embryogenesis and cancer, with unprecedented precision. Here, I review these systems and discuss certain studies that exemplify the advantages and limitations of each system.

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.

A novel RU486 inducible system for the activation and repression of genes

We have developed an inducible system that consists of a transactivator and a target gene. The transactivator encodes a chimeric regulator that is responsive to RU486 (mifepristone, a progesterone receptor antagonist) but not to progestins and other hormones or endogenous ligands for activation. The target gene can be any gene under the control of Gal4 DNA binding sites. When the regulator is activated by RU486, it induces target gene expression by binding to the Gal4 recognition sequences upstream of the target. To verify this concept, we have successfully demonstrated the functionality of this system in tissue culture and in transgenic mice. Furthermore, for applications that require higher levels of a target gene, we also have generated regulators that can induce greater target gene expression. In addition, we also have constructed a modified regulator which can repress gene expression. The versatility of our system should prove useful for many applications in biology and gene therapy.

Myopathy and spontaneous Pasteurella pneumotropica-induced abscess formation in an HIV-1 transgenic mouse model

In an effort to augment human immunodeficiency virus type 1 (HIV-1) gene expression in transgenic mice, an infectious proviral DNA clone was modified by deleting the two NF kappa B binding sites and some adjacent upstream LTR sequences and replacing them with the core enhancer of Moloney murine leukemia virus (MLV). Two independent lines of MLV/HIV transgenic mice were established that expressed HIV-1-specific RNA in lymphoid tissue, striated skeletal muscle, and the eye lens. Heterozygous animals from each transgenic line spontaneously developed an inflammatory disease of the eye associated with the production of copious amounts of purulent lacrimal secretions beginning at 2 weeks of age. Periorbital abscess formation became grossly apparent by 2 months of age and Pasteurella pneumotropica was cultured from the harderian glands and conjunctival surfaces of many of the MLV/HIV animals but not their nontransgenic, cohabiting littermates. This gram-negative commensal bacterium has been previously associated with a similar disease phenotype in immunocompromised (e.g., nude mice) rodent colonies. MLV/HIV mice developed normally until 15 weeks of age, when weight loss and wasting occurred, culminating in premature death (as earlier as 6 months of age). The cachexia was associated with an initially focal and subsequently progressive myopathy, coinciding with age-related increases of HIV gene expression in muscle.

HIV type 1 Nef perturbs eye lens development in transgenic mice

HIV transgenic mice often display lens cataracts as a consequence of viral-specific expression of HIV gene products in the developing lens. Cataractous mouse lines encoding either HIV-1 proviral DNA, HIV delta Gag/Pol] proviral DNA, or the HIV-1 nef gene alone were examined to ascertain the effect of Nef on murine lens development. Ocular disease was characterized by a progressive architectural disorganization within the lens fiber cell compartment developing in 100% of HIV-positive mice in five reported transgenic lines. Late embryonic stage transgenic lenses featured a mild microphthalmia, pyknotic nuclei within the lens fiber department, ballooning lens fiber cells, and elongated lens epithelial cells. Increased DNA fragmentation was evident in transgenic embryonic lenses, suggesting that cell death occurred by apoptosis. As studied in HIV delta Gag/Pol] transgenic mice, HIV transcription was developmentally linked to alpha A- and alpha B-crystallin gene expression, preceded disease development (in E14.5-E16.5 embryos), and persisted for weeks after birth. HIV-1 Nef was the predominant HIV gene product detected in the lens fiber cells of this line and was expressed almost to the exclusion of other HIV gene products. Nef was implicated as a major determinant of disease because (1) cataracts developed in mice transgenic for Nef alone and (2) the expression of other HIV gene products in wild-type HIV provirus transgenic mice occurred without a concomitant change in lens pathology.

Transgenic models of human immunodeficiency virus type-1

Transgenic models have provided significant insights into HIV-1 pathogenesis, particularly with regards to Kaposi's sarcoma. HIV-associated nephropathy, the tissue-restricted expression of CNS strains of HIV-1, and the function of Nef in vivo. Both multigenic and single gene constructs have contributed to our understanding of HIV-1-induced diseases. While failing to provide models suitable for vaccine development, these transgenic models have provided great insight into HIV pathogenesis and may yet provide a means for the development and testing of molecular based therapies for AIDS.

Spatial and temporal regulation of a lacZ reporter transgene in a binary transgenic mouse system

The transgenic mouse system is a powerful tool for the study of gene function. However, when the analysis involves genes that are critical for the normal developmental process, the usefulness of transgenic mouse systems is limited (for review see Hanahan, 1989; Westphal and Gruss, 1989; Byrne et al., 1991). This is due to potential transgene interference with development in case of ectopic or high level expression. As a result, establishing permanent transgenic mouse lines expressing these types of genes has proven difficult. To circumvent these difficulties, a binary transgenic mouse system has been established, termed the Multiplex System (Byrne and Ruddle, 1989). This is a two-tiered gene activation system in which expression of the gene of interest occurs only in offspring carrying transgenes encoding both components: transactivator and transresponder. Transactivator lines contain the gene encoding the VP16 protein of herpes simplex virus. Transresponder lines harbour the gene of interest linked to the IE promoter which includes recognition sequences for the VP16 transactivator. Previously, the inducibility of a chloramphenicol acetyltransferase reporter gene in newborn offspring that carried both a transactivator and transresponder transgene (Byrne and Ruddle, 1989) has been shown. Moreover, it has been demonstrated that expression of the VP16 protein was not detrimental to development and that transactivation appeared to be tissue specific. Here, the potential of the system for the expression of transgenes in early mouse embryogenesis was examined, using the Escherichia coli beta-galactosidase gene as a reporter in the transresponder mouse strain. To direct expression of VP16, the murine Hoxc-8 promoter, which is known to be active during early development, was used. Embryos from crosses of transactivators to transresponders were isolated at different stages of development and stained for beta-galactosidase activity. Transactivation, as demonstrated by strong beta-galactosidase staining, could be detected as early as eight days of development. At all stages examined, the pattern of lacZ transresponder gene expression accurately reflected the activity of the Hoxc-8 promoter controlling VP16 expression. It is demonstrated that the Multiplex System can be used to express transresponder transgenes in a spatially and temporally defined manner in multiple cell types early during mouse embryogenesis.

Retrovirus-mediated transfer and long-term expression of HIV type 1 tat gene in murine hematopoietic tissues

Replication of the human immunodeficiency virus (HIV) is regulated tightly by the tat and rev genes. The tat gene of HIV is a potent trans-activator of virus gene expression. trans-Activation is mediated through the tat-responsive element (TAR). Tat also has been shown to affect transcription of cellular genes and to trans-activate other viral promoters. In transgenic animals, tat expression in skin was implicated in the development of lesions resembling Kaposi's sarcoma (KS). More recently, evidence has been presented that suggests that Tat might play a role in the maintenance of KS cells. To study the possible role(s) of Tat in pathogenesis and disease progression, we have developed a retroviral vector for the transfer of tat into murine bone marrow cells. We used this transduced bone marrow to repopulate recipient animals, which expressed the tat gene in peripheral blood 6 months after transplantation as determined by PCR amplification of first-strand cDNA. Analysis of the hematopoietic tissues of mice 6 months posttransplantation indicated persistence of the tat gene and its expression in thymus, lymph nodes, spleen, bone marrow, and peripheral blood. Although tat expression was sustained in all hematopoietic tissues, no gross abnormalities were observed. The presence of tat in all hematopoietic tissues strongly suggests transduction of stem or multipotential progenitor cells.

Hepatitis B virus X gene product acts as a transactivator in vivo

It has previously been shown that the hepatitis B virus X gene product, pX, transactivates homologous and heterologous transcriptional regulatory sequences of viruses and various cellular genes in vitro. However, there is no evidence about the reproducibility and the relevance of this phenomenon in vivo. In this study we crossbred transgenic mice expressing the X gene under the control of the human antithrombin III (ATIII) gene regulatory sequences with transgenics carrying either the chloramphenicol acetyl-transferase or the LacZ bacterial reporter genes driven by the HIV1-LTR, which is known to be activated in trans by pX. Expression of pX in the liver stimulates the HIV1-LTR driven expression of both chloramphenicol acetyl-transferase and beta-galactosidase reporter genes in double transgenic mice. No detectable increase in chloramphenicol acetyl-transferase expression was observed in tissues, such as the spleen, brain and heart, that do not express pX. Our results confirm the transactivating properties of pX in vivo for the first time and support the hypothesis that pX might indeed modify gene expression in HBV-infected hepatocytes and influence viral pathogenesis.

Targeted gene expression as a means of altering cell fates and generating dominant phenotypes

We have designed a system for targeted gene expression that allows the selective activation of any cloned gene in a wide variety of tissue- and cell-specific patterns. The gene encoding the yeast transcriptional activator GAL4 is inserted randomly into the Drosophila genome to drive GAL4 expression from one of a diverse array of genomic enhancers. It is then possible to introduce a gene containing GAL4 binding sites within its promoter, to activate it in those cells where GAL4 is expressed, and to observe the effect of this directed misexpression on development. We have used GAL4-directed transcription to expand the domain of embryonic expression of the homeobox protein even-skipped. We show that even-skipped represses wingless and transforms cells that would normally secrete naked cuticle into denticle secreting cells. The GAL4 system can thus be used to study regulatory interactions during embryonic development. In adults, targeted expression can be used to generate dominant phenotypes for use in genetic screens. We have directed expression of an activated form of the Dras2 protein, resulting in dominant eye and wing defects that can be used in screens to identify other members of the Dras2 signal transduction pathway.

Animal models for anti-AIDS therapy

Primate and non-primate species have been used to study the pathobiology of the simian immunodeficiency virus (SIV) and of the human immunodeficiency virus type 1 (HIV-1), respectively, and to develop new therapeutic regimes. Transgenic mice which express either the entire HIV-1 provirus or subgenomic fragments have been used to analyze viral gene products in vivo and may serve as models for the development of agents targeted to select viral functions. Chimeric mice which were created by transplanting human hematolymphoid cells into mice suffering from congenital severe combined immunodeficiency (scid/scid or so called SCID mice), can be infected with HIV-1 and allow one to study the entire HIV-1 replicative cycle. Type C murine leukemia virus models have been used to develop new prophylactic and therapeutic strategies but their use is restricted to the evaluation of select antiviral drug inhibition, targeted to retroviral genes common to both Lentivirinae and Oncovirinae. The role of various animal model systems in the development of anti-HIV-1 and anti-AIDS therapies is summarized.

Targeted oncogene activation by site-specific recombination in transgenic mice

An efficient and accurate method for controlled in vivo transgene modulation by site-directed recombination is described. Seven transgenic mouse founder lines were produced carrying the murine lens-specific alpha A-crystallin promoter and the simian virus 40 large tumor-antigen gene sequence, separated by a 1.3-kilobase-pair Stop sequence that contains elements preventing expression of the large tumor-antigen gene and Cre recombinase recognition sites. Progeny from two of these lines were mated with transgenic mice expressing the Cre recombinase under control of either the murine alpha A-crystallin promoter or the human cytomegalovirus promoter. All double-transgenic offspring developed lens tumors. Subsequent analysis confirmed that tumor formation resulted from large tumor-antigen activation via site-specific, Cre-mediated deletion of Stop sequences.

Efficient production of human immunodeficiency virus proteins in transgenic mice

Transgenic mice containing the complete human immunodeficiency virus (HIV) coding sequences fused to the mouse mammary tumor virus long terminal repeat were generated. They were found to produce high levels of authentic gag and env HIV proteins in several tissues known to support mouse mammary tumor virus-driven transcription. HIV proteins were also detected in serum and in body fluids (milk and epididymal secretions) known to be natural sites of retrovirus, and specifically of HIV, production. These results indicate that primary mouse cells from different tissues have the capacity to produce HIV proteins. These mice represent a novel animal model for HIV infection.

Development of antiviral treatment strategies in murine models

Murine models with type C murine leukemia viruses have been used to develop major new prophylactic and therapeutic strategies in vaccination, drug therapy of acute virus exposure and chronic viremia, combination therapy, prevention of maternal transmission, and therapy targeted to the central nervous system. Transgenic mice expressing either the whole human immunodeficiency virus type 1 (HIV-1) provirus or subgenomic sequences allow the in vivo analysis of selected HIV-1 functions. The full replicative cycle of HIV-1 can be studied in human/mouse chimerae which were created by transplanting human hematolymphoid cells into SCID mice. The chimeric SCID mouse models have been used successfully to evaluate anti-HIV-1 drugs. The role of the various murine retrovirus systems in the development of anti-HIV-1 and anti-AIDS therapies is summarized.

UV activation of human immunodeficiency virus gene expression in transgenic mice

Human immunodeficiency virus (HIV) infection is associated with a clinical latency of as long as 10 years before the development of disease. One explanation for this delay is the requirement of cofactors such as other DNA or RNA viruses, cytokines critical for immune modulation, or environmental UV light. At least in tissue culture studies, these agents are capable of inducing HIV gene expression in cell lines which either harbor the entire viral genome or contain a reporter gene under the control of the viral long terminal repeat regulatory region. The role of these cofactors in terminating clinical latency and inducing disease has been difficult to ascertain because of the lack of an appropriate animal model. We now report that UV light can markedly induce HIV gene expression in transgenic mice carrying both the cis-acting (long terminal repeat) and trans-acting (the tat gene) elements which are essential for viral transactivation and replication in infected cells. Our finding may explain the clinical observations that cutaneous lesions in HIV-infected individuals are often seen in the sunlight exposed areas of the skin, including the face and neck.

Ultraviolet radiation increases HIV-long terminal repeat-directed expression in transgenic mice

Previously described FVB/N mice harboring a human immunodeficiency virus (HIV) long terminal repeat (LTR)/chloramphenicol acetyl transferase (CAT) transgene were treated with varying amounts of 254 nm UV-C radiation or 312 nm UV-B radiation. At optimal exposure periods, a 20-fold increase in HIV-LTR-directed expression was observed in ear specimens collected 24 h following UV-C exposure; a fourfold increase in expression was induced by UV-B exposure. Investigation of the kinetics of UV-C induction in vivo revealed that LTR-directed gene expression began to increase 2 hours after exposure and reached a maximum on Day 3 following exposure (greater than 30-fold induction). In experiments examining the kinetics of UV-B activation, the maximum level of CAT activity in the ears of irradiated transgenic animals was fivefold above levels in unirradiated transgenic controls (Day 5). Furthermore, CAT activity was not induced in fur-bearing skin following UV exposure; however, a fourfold increase in HIV-LTR-directed expression could be elicited when hair was removed by shaving prior to UV-B treatment.

Binary system for regulating transgene expression in mice: targeting int-2 gene expression with yeast GAL4/UAS control elements

We have developed a binary transgenic system that activates an otherwise silent transgene in the progeny of a simple genetic cross. The system consists of two types of transgenic mouse strains, targets and transactivators. A target strain bears a transgene controlled by yeast regulatory sequences (UAS) that respond only to the yeast transcriptional activator GAL4. A transactivator strain expresses an active GAL4 gene that can be driven by any selected promoter. The current paradigm uses the murine growth factor int-2 cDNA as the target gene and the GAL4 gene driven by the mouse mammary tumor virus long terminal repeat as the transactivator. Both target and transactivator strains are phenotypically normal. By contrast, the bigenic offspring of these two strains express high levels of the target int-2 gene in each organ expressing the GAL4 transactivator. They also display a characteristic dominant int-2 phenotype that consists of epithelial hyperplasia in mammary and salivary glands, as well as prostatic and epididymal hypertrophy, which results in male sterility.

Regulation of the mouse alpha A-crystallin gene: isolation of a cDNA encoding a protein that binds to a cis sequence motif shared with the major histocompatibility complex class I gene and other genes

We have shown by site-directed mutagenesis that the sequence between positions -69 and -40 of the mouse alpha A-crystallin gene is crucial for tissue-specific gene expression in a transfected mouse lens epithelial cell line transformed with the early region of simian virus 40. Gel retardation experiments with synthetic oligodeoxynucleotides revealed a mouse lens nuclear protein which bound specifically to the palindromic sequence 5'-GGGAAATCCC-3' at positions -66 to -57 in the alpha A-crystallin promoter. By screening a bacteriophage lambda gt11 expression library of the transformed lens cells, we isolated a 2.5-kilobase-pair cDNA encoding a fusion protein which bound to this sequence and to the regulatory element of the major histocompatibility complex (MHC) class I gene. This cDNA hybridized to a 10-kilobase-pair polyadenylated RNA present in many different tissues, including lens. It encoded a protein, tentatively called alpha A-CRYBP1, containing at least two zinc fingers. alpha A-CRYBP1 is either homologous or very similar to the human nuclear proteins MBP-1 (Baldwin et al., Mol. Cell. Biol. 10:1406-1414, 1990), PRDII-BFI (Fan and Maniatis, Genes Dev. 4:29-42, 1990), and HIV-EP1 (Maekawa et al., J. Biol. Chem. 264:14591-14593, 1989), which bind to regulatory elements of the MHC class I, beta interferon, and human immunodeficiency virus genes, respectively. Our results suggest that the lens-specific alpha A-crystallin, MHC class I, beta interferon and other genes have a similar cis-acting DNA regulatory motif that shares alpha A-CRYBPI, MBP-1, PRDII-BF1, HIV-EP1, or other closely related proteins as trans-acting factors.

Regulation of the mouse alpha A-crystallin gene: isolation of a cDNA encoding a protein that binds to a cis sequence motif shared with the major histocompatibility complex class I gene and other genes

We have shown by site-directed mutagenesis that the sequence between positions -69 and -40 of the mouse alpha A-crystallin gene is crucial for tissue-specific gene expression in a transfected mouse lens epithelial cell line transformed with the early region of simian virus 40. Gel retardation experiments with synthetic oligodeoxynucleotides revealed a mouse lens nuclear protein which bound specifically to the palindromic sequence 5'-GGGAAATCCC-3' at positions -66 to -57 in the alpha A-crystallin promoter. By screening a bacteriophage lambda gt11 expression library of the transformed lens cells, we isolated a 2.5-kilobase-pair cDNA encoding a fusion protein which bound to this sequence and to the regulatory element of the major histocompatibility complex (MHC) class I gene. This cDNA hybridized to a 10-kilobase-pair polyadenylated RNA present in many different tissues, including lens. It encoded a protein, tentatively called alpha A-CRYBP1, containing at least two zinc fingers. alpha A-CRYBP1 is either homologous or very similar to the human nuclear proteins MBP-1 (Baldwin et al., Mol. Cell. Biol. 10:1406-1414, 1990), PRDII-BFI (Fan and Maniatis, Genes Dev. 4:29-42, 1990), and HIV-EP1 (Maekawa et al., J. Biol. Chem. 264:14591-14593, 1989), which bind to regulatory elements of the MHC class I, beta interferon, and human immunodeficiency virus genes, respectively. Our results suggest that the lens-specific alpha A-crystallin, MHC class I, beta interferon and other genes have a similar cis-acting DNA regulatory motif that shares alpha A-CRYBPI, MBP-1, PRDII-BF1, HIV-EP1, or other closely related proteins as trans-acting factors.

Human and murine urokinase cDNAs linked to the murine alpha A-crystallin promoter exhibit lens and non-lens expression in transgenic mice

cDNAs encoding either the human or the murine urokinase-type plasminogen activator (uPA) were fused downstream from the promoter-enhancer element of the murine gene encoding alpha A-crystallin, a protein found exclusively in the ocular lens. The DNAs were microinjected into fertilized mouse eggs as linear fragments free of bacterial sequences, and for each construct one line of transgenic mice was generated. In both lines transgenic uPA activity was detected in the ocular lens, in agreement with previous results reported on transgenic mice bearing genes fused to the same regulatory region. Unexpectedly however relatively high levels of this activity were found also in the retina, and furthermore, human uPA activity was found also in different parts of the brain and in the bone marrow, and to a lesser extent in the spleen, thymus and optic nerve. Transgenic uPA transcript was found in the lens, retina, brain and thymus of mice carrying the murine cDNA. Such a pattern of expression was different from that exhibited by the endogenous murine uPA gene and, excluding the lens, it appeared to be conferred by the cDNAs. The putative regulation by uPA cDNAs is suggested to be mediated through an internal enhancer-like element functioning in combination with the alpha A-crystallin promoter in a fashion independent of the specific nature of the promoter.

Expression from the HIV-LTR is stimulated by glucocorticoids and pregnancy

Gene regulation in several retroviral systems is subject to steroid hormone control. Clinical studies have shown that the human immunodeficiency virus (HIV) core protein p24 is more readily detectable in infected women during pregnancy. Here we show that expression of the HIV long terminal repeat (LTR) is induced by glucocorticoids in tissue culture cells and by pregnancy in placental and uterine tissue of transgenic mice. We suggest that hormonal stimulation could influence proviral activation and that placental expression of the HIV-LTR could contribute to the high perinatal transmission rate of HIV.

Phorbol ester-mediated induction of HIV-1 from a chronically infected promonocyte clone: blockade by protein kinase inhibitors and relationship to tat-directed trans-activation

Potent inhibitors of protein kinases C and A, including 1-(5 isoquinolinyl sulfonyl) 2-methyl piperazine (H7), staurosporine, and 2-aminopurine, depressed phorbol ester-induced HIV-1 virion production and HIV-specific transcripts by greater than 90% in chronically infected promonocytic cells. Suppression was dose-dependent and occurred at concentration that had little effect on cell growth. These effects appeared to be specific to activation of the PKC-diacylglycerol system. They did not alter IUdr-mediated induction of HIV. In addition, PMA enhancement of an HIV-LTR driven reporter gene was not blocked by H7 in the presence or absence of exogenous tat, at concentrations capable of inhibiting upregulation of virus at the cellular level. Insight into the biochemical mechanisms of these processes is critical to understanding interactions of HIV with the immune system, and may eventually uncover new therapeutic strategies.

Multiplex gene regulation: a two-tiered approach to transgene regulation in transgenic mice

Transgenic mice have been used to study gene function and regulation by introducing inducible or tissue-specific transgenes. This approach is generally limited to studying gene function in adult mice since ectopic expression of many interesting genes is disease causing or may be lethal to the developing embryo. To extend the utility of the transgenic mouse system to the early stages of embryogenesis, we have developed a two-tiered method of gene regulation to control transgene expression. Our multiplex gene regulatory system (MGR) allows the establishment of transgenic lines that harbor inducible potentially lethal transgenes. These inducible transgenes are activated only when mated to a second transgenic animal. Induction in the MGR system provides a high degree of temporal and spatial control over transgene expression and should be suitable for engineering "gain of function mutations" for many developmental genes.

The HIV tat gene induces dermal lesions resembling Kaposi's sarcoma in transgenic mice

When the human immunodeficiency virus transactivating gene under the control of the viral regulatory region is introduced into the germline of mice, skin lesions are induced that resemble Kaposi's sarcoma seen in AIDS. Our findings indicate that HIV could play a direct part in causing cancer.