调控型表达丙型肝炎病毒NS3／4A蛋白酶转基因小鼠的建立

目的建立调控因素存在下表达丙型肝炎病毒（HCV）NS3/4A丝氨酸蛋白酶的转基因小鼠。方法采用分子克隆技术构建可受Tet-On调控系统和Cre-LoxP基因敲除系统双重调控表达HCV NS3/4A丝氨酸蛋白酶的真核表达质粒PBI-Ⅲ/LoxP-Luc-PolyA-LoxP-NS3/4A。该重组质粒线性化后,经显微注射制备转基因小鼠。首建鼠及经PCR检测阳性的子代鼠与C57BL/6小鼠交配传代。选择部分F2鼠与已经稳定建系的转基因小鼠Lap杂交,利用在体生物发光成像系统（BLI）检测肝脏稳定表达荧光素酶（Luc）报告基因的经盐酸强力霉素（Dox）诱导的双转基因子代鼠,并选择性针对稳定表达系传代扩群。结果酶切鉴定和测序分析显示重组载体构建成功。经PCR检测得到6只转基因首建鼠,其中3只可繁殖传代并持续检测到阳性子代鼠。BLI结果显示,由其中1只首建鼠传代而来的不同F2鼠与Lap鼠杂交得到的部分双转基因鼠肝脏部位发光信号强烈,表明这些小鼠肝细胞内报告基因Luc特异高效表达。结论建立了转基因小鼠NS3/4A,并筛选到调控因素存在时转入外源基因特异稳定表达的转基因小鼠,为进一步建立严格调控型表达NS3/4A蛋白酶的小鼠模型奠定基础。     

肝细胞特异性表达Cre重组酶转基因小鼠的建立

目的 构建在小鼠肝细胞中特异表达Cre重组酶的转基因小鼠。方法 利用聚合酶链反应(PCR)获得小鼠肝细胞特异性启动子——白蛋白启动子，指导Cre重组酶在肝细胞中特异表达。通过受精卵显微注射的方法，将转基因载体导入小鼠受精卯中，获得转基因小鼠。利用逆转录聚合酶链反应(RT～PCR)检测转基因小鼠中Cre重组酶转录的组织特异性，并将转基因小鼠与Smad4条件基因打靶小鼠进行杂交，利用PCR和Southern Blot进一步检测Cre重组酶在小鼠体内表达的组织特异性及其介导lox P位点之间发生重组的活性。结果 获得了白蛋白启动子，构建了转基因载体pAlb-Cre。将转基因载体进行显微注射，共注射了837枚小鼠受精卵。PCR检测显示53只子代小鼠中有7只整合了Cre重组酶基因，Southern杂交结果证实共获得6只基因组上整合Cre重组酶基因的首建者小鼠。RT—PCR结果表明其中3只阳性小鼠的子代鼠在肝脏和睾丸中正确转录了外源基因。将在肝脏和睾丸中正确转录了外源基因的两只阳性鼠与Smad4条件基因打靶的小鼠杂交，通过PCR检测发现Cre转基因与Smad4条件基因打靶双阳性的子代鼠在肝脏中特异表达Cre重组酶，并能介导基因组中loxP序列间的基因重组，此结果通过Southern杂交得到了进一步证实。结论 成功构建了在小鼠肝细胞中特异表达Cre重组酶的转基因小鼠，为利用条件基因打靶技术研究基因在肝脏发育及相关疾病中的功能及机制奠定了基础。     

肝癌相关基因DLK1转基因小鼠的构建与鉴定

目的 构建并鉴定肝脏特异性表达的DLKl转基因小鼠.方法 通过基因重组方法,将小鼠DLK1 cDNA片段置于小鼠白蛋白基因增强子和启动子序列下游,构建肝脏特异性表达的DLKl重组质粒,酶切重组质粒得到转基因片段,转基因在体外进行表达鉴定后,显微注射获得DLK1转基因首建小鼠,对首建小鼠进行传代,利用F1代小鼠进行DLK1转基因表达的鉴定.结果 逆转录(RT)-PCR和细胞免疫荧光显示,转基因DLK1片段可在小鼠肝癌细胞系Hep1-6中表达.RT-PCR和免疫组化结果显示,DLK1在F1代成年转基因小鼠肝脏中特异性表达.结论 成功构建了肝脏特异性表达的DLK1转基因小鼠.     

丙型肝炎病毒cDNA与荧光素酶融合基因可调控逆转录病毒载体的构建

目的 构建丙型肝炎病毒(HCV)cDNA与荧光素酶(Luc)融合基因可调控逆转录病毒载体,以建立容易检测的HCV体外细胞模型。方法 利用基因重组技术,将HCV5’非编码区(5’NCR)和/或核心(C)区基因克隆于pGEM-Luc-DNA载体,使其与Luc基因相融合,然后再将融合基因插入可调控逆转录病毒载体(PBPSTR1)。结果pCEM-HCVl和pBPSTRl-HCV经酶切鉴定,HCV5’NCR和/或C区cDNA已与Luc基因融合,并被克隆于pBPSTRl。结论 通过体外分子克隆技术可使HCV基因cDNA带上Luc报告基因,并可克隆于逆转录病毒载体,为建立易检测的HCV细胞模型和进一步抗病毒基因治疗以及药物的筛选奠定了基础。     

盐酸多西环素对重组质粒pBI-EGFP-hHO-1表达的调控

目的 构建Tet-off调控的血色素氧化酶-1(HO-1)真核表达载体pBI-EGFP-hHO-1,并确定盐酸多西环素对其表达的调控剂量.方法 利用分子生物学技术,将hHO-1基因与质粒pBI-EGFP连接构成重组质粒.NheI和MluI双酶切鉴定后采用RT-PCR技术及免疫细胞化学的方法检测其在人肝癌细胞SMMC-7721中的表达情况.利用RT-PCR技术检测Tet-off和pBI-EGFP-hHO-1双转染后不同浓度盐酸多西环素对hHO-1基因mRNA表达量的影响,确定该四环素调控系统的盐酸多西环素诱导量.结果 用NheI和MluI双酶切证明hHO-1成功克隆入应答质粒pBI-EGFP；RT-PCR、免疫细胞化学检测结果表明重组质粒在SMMC-7721细胞中表达；经RT-PCR检测显示当盐酸多西环素浓度≥2000 ng/ml时,HO-1基因mRNA表达降低,与未转染组接近.结论 成功构建了由Tet-off调控的真核表达载体pBI-EGFP-hHO-1,并确定盐酸多西环素对其调控剂量为2 000 ng/ml.     

ICOS信号对感染日本血吸虫小鼠CD154/CD40表达的影响

目的探讨可诱导共刺激分子(Inducible costimulator,ICOS)信号对感染日本血吸虫小鼠的CD154/CD40表达及免疫病理的影响。方法建立ICOS转基因(ICOS transgenic,ICOS-Tg)小鼠及野生型FVB/NJ小鼠日本血吸虫病模型,应用流式细胞术、免疫组化技术分别检测感染前后的小鼠脾淋巴细胞与肝脏虫卵肉芽肿周围炎性浸润细胞CD154、CD40表达水平。应用HE染色法观察小鼠肝脏虫卵肉芽肿病变动态变化。结果与野生型FVB/NJ小鼠相比,ICOS-Tg小鼠脾淋巴细胞CD154、CD40表达水平升高,在感染后12、16周差异有统计学意义(P均0.05);ICOS-Tg小鼠肝脏虫卵肉芽肿炎性浸润细胞CD154、CD40表达亦显著升高,在感染后7、12、16、20周差异有统计学意义(P均0.05)。且ICOS-Tg小鼠肝脏虫卵肉芽肿体积显著大于野生型小鼠(P0.01或0.05)。结论在日本血吸虫感染中,ICOS信号对CD154/CD40表达具有一定的调控作用,在免疫病理中起重要调控作用。     

COS信号对感染日本血吸虫小鼠CD154/CD40 表达的影响

目的 目的 探讨可诱导共刺激分子 （Inducible costimulator, ICOS） 信号对感染日本血吸虫小鼠的CD154/CD40表达及免疫病理的影响。方法 方法 建立ICOS转基因 （ICOS transgenic,ICOS?Tg） 小鼠及野生型FVB/NJ小鼠日本血吸虫病模型, 应用流式细胞术、 免疫组化技术分别检测感染前后的小鼠脾淋巴细胞与肝脏虫卵肉芽肿周围炎性浸润细胞CD154、 CD40 表达水平。应用HE染色法观察小鼠肝脏虫卵肉芽肿病变动态变化。结果 结果 与野生型FVB/NJ小鼠相比, ICOS?Tg小鼠脾淋巴细胞CD154、 CD40表达水平升高, 在感染后12、 16周差异有统计学意义 （P均 < 0.05）; ICOS?Tg小鼠肝脏虫卵肉芽肿炎性浸润细胞CD154、 CD40表达亦显著升高, 在感染后7、 12、 16、 20周差异有统计学意义 （P均 < 0.05）。且ICOS?Tg小鼠肝脏虫卵肉芽肿体积显著大于野生型小鼠 （P < 0.01或0.05）。结论 结论 在日本血吸虫感染中, ICOS信号对CD154/CD40表达具有一定的调控作用, 在免疫病理中起重要调控作用。     

胰岛素抵抗的HCV转基因鼠模型的建立

目的 建立胰岛素抵抗的丙型肝炎病毒(HCV)转基因鼠模型.方法 利用携带HCV Core稳定型表达载体,应用基因重组技术和显微注射技术,制备HCV转基因小鼠,用糖耐量试验和胰岛素耐量试验鉴定HCV转基因鼠出现胰岛素抵抗.结果 RT-PCR和Western blot结果表明成功构建了携带HCV Core转基因小鼠模型.1月龄转基因小鼠胰岛素水平明显高于正常鼠,胰岛素耐量试验异常,出现胰岛索抵抗.6月龄转基因小鼠出现肝脂肪变性.结论 成功制备胰岛素抵抗的HCV转基因鼠模型,为研究HCV核心蛋白所致胰岛素抵抗发病机制奠定了基础.     

丙型肝炎病毒5''非翻译区DNA序列在HepG2细胞中的启动子活性

目的研究丙型肝炎病毒(HCV)基因组5'非翻译区(5'UTR)DNA序列在HepG2细胞中的启动子活性,以了解HCV的复制调控机制.方法分别构建HCV基因组5'UTR DNA正反向序列驱动虫荧光素酶基因表达的质粒5'UTR- Luc(+)/(-)和5'UTR DNA序列驱动绿色荧光蛋白基因表达的质粒5'UTR -EGFP(+)/(-),分别转染HepG2细胞,用双荧光素酶检测系统检测虫荧光素酶的表达水平,逆转录聚合酶链反应检测虫荧光素酶基因m R N A水平,荧光显微镜观察绿色荧光蛋白基因的表达水平,并与相应对照作比较,来证实H CV基因组5'UTR DNA序列的启动子活性.结果 5'UTR- LUc(+)有明显的虫荧光素酶表达,但比pGL3 control表达水平低(Luc/R为0.690 ± 0.086,Luc/RL为4.210±0.340),而5'UTR-Luc(-)和pGL3 enhancer无明显虫荧光素酶表达(Luc/RL分别为0.095±0.008和0.044±0.00 5);逆转录聚合酶链反应结果与之相符,5'UTR- Luc(+)检测到虫荧光素酶基因mRNA,而5'UTRLuc(-)则未检测到.5'UTR- EGFP(+)观察到较强绿色荧光,而5'UTR -EGFP(-)无荧光表达.结论 HCV基因组5'UTR DNA序列具有明显的启动子活性,能启动下游基因的表达,在HCV基因组复制过程中有重要作用.     

丙型肝炎病毒结构基因转基因小鼠模型的建立

目的建立丙型肝炎病毒(HCV)转基因小鼠模型，探讨丙型肝炎发病机制，研究HCV结构蛋白编码基因的功能与致病作用。方法采用长片段聚合酶链反应技术扩增HCV结构基因，构建稳定表达与诱导表达两种真核细胞表达重组体，经体外细胞转染后，将具有表达功能的线性化表达元件采用显微注射法，直接导入1736枚小鼠受精卵，先后移入69只假孕母鼠输卵管。结果妊娠受体25只，产仔105只，成活57只。注射卵成仔率仅3．28％。经聚合酶链反应扩增、测序、酶切及Southern杂交鉴定，获阳性首建鼠26只，注射卵首建鼠成功率仅1．50％。其中稳定表达型10只，诱导表达型16只。经与正常鼠交配，获F1阳性杂合鼠分别38只、20只。一个纯合子品系。结论研究建立了稳定表达与诱导表达两类HCV结构基因转基因小鼠，为进一步研究HCV致病机制，HCV基因功能奠定了基础。     

A novel technique for temporally regulated cell type-specific Cre expression and recombination in the pituitary gonadotroph

Inducing tissue-specific genetic alterations under temporal control allows for the analysis of gene function in particular cell types at specified points in time. We have generated a system for tetracycline-controlled expression of Cre recombinase in mice using the unique CreTeR vector. The gonadotroph-specific bovine alpha-subunit (Balpha) promoter fragment was subcloned into the CreTeR vector, creating a technique for highly regulated expression of Cre recombinase exclusively in pituitary gonadotrophs. Control of Cre recombinase in the CreTeR vector was demonstrated in LbetaT2 pituitary cell lines, where Cre protein was detected in cells treated with doxycycline, but not in untreated cells. In transgenic mice, Cre was expressed in pituitary gonadotrophs of mice treated with doxycycline, but not in non-pituitary tissues or in transgenic mice not treated with doxycycline. We demonstrated Cre expression in the gonadotroph by immunostaining showing co-localization of Cre recombinase with the beta-subunit of LH (LH-beta). Furthermore, by crossing Balpha/CreTeR with R26R mice, we were able to demonstrate functional recombination within pituitary gonadotrophs, detected by lacZ expression. The Balpha/CreTeR mice described here can be used to study the function of virtually any gene in the gonadotroph; in particular, this will be useful in studying genes, which may have distinct roles in development and in the adult.     

Site-specific recombination of a transgene in fertilized eggs by transient expression of Cre recombinase.

An efficient method of transgene modulation in fertilized eggs has been developed that uses the Cre/loxP recombination system. Twelve transgenic mouse lines carrying a chicken beta-actin promoter-loxP-chloramphenicol acetyltransferase (CAT) gene-loxP-beta-galactosidase gene construct were produced. After selection of the line showing the highest expression of the CAT gene in a variety of tissues, eggs of this line were injected in the male or female pronucleus with a Cre expression vector placed under the control of the chicken beta-actin promoter and kept in a circular form to avoid genomic integration. This resulted in a transient expression of Cre in the eggs, leading to recombination of the transgene as detected by galactosidase expression and DNA analysis. Recombination was completed before the morula stage with both types of pronuclear injections and occurred with a very high frequency; no mosaicism, no incomplete recombination, and no integration of the Cre sequence were observed in 18 mice born with this modified transgene. The beta-galactosidase gene was expressed in various tissues at levels comparable to those found for the CAT gene in the founder line. This Cre transient expression system should be useful for breeding transgenic lines in which transgene expression leads to sterility or lethality--in particular, for selecting transgenic lines with high expression of a potentially lethal transgene whose full activity is difficult to explore in a conventional transgenic system because of the risk of selecting for transgenic lines carrying only poorly expressed transgenes.     

Inducible gene targeting in postnatal myocardium by cardiac-specific expression of a hormone-activated Cre fusion protein

Cardiac-restricted expression of Cre recombinase can provoke lineage-specific gene excision in the myocardium. However, confounding early lethality may still preclude using loss-of-function models to study the postnatal heart. Here, we have tested whether inducible, heart-specific recombination can be triggered after birth by transgenic expression of a Cre fusion protein that incorporates a mutated progesterone receptor ligand binding domain (PR1) that is activated by the synthetic antiprogestin, RU486, but not by endogenous steroid hormones. CrePR1 driven by the alpha-myosin heavy chain (alphaMHC) promoter was expressed specifically in heart. Translocation of CrePR1 from cytoplasm to nuclei in ventricular myocytes was induced by RU486. To establish whether this approach can mediate cardiac-specific, drug-dependent excision between loxP sites in vivo, we mated alphaMHC-CrePR1 mice with a ubiquitously expressed (ROSA26) Cre reporter line. Offspring harboring alphaMHC-CrePR1 and/or the floxed allele were injected with RU486 versus vehicle, and the prevalence of beta-galactosidase (beta-gal)-positive cells was determined, indicative of Cre-mediated excision. Little or no baseline recombination was seen 1 week after birth. Cardiac-restricted, RU486-inducible recombination was demonstrated in bigenic mice at age 3 and 6 weeks, using each of 3 independent CrePR1 lines. Recombination in the absence of ligand paralleled the levels of CrePR1 protein expression and was more evident at 6 weeks. Thus, conditional, posttranslational activation of a Cre fusion protein can bypass potential embryonic and perinatal effects on the heart and permits inducible recombination in cardiac muscle. High levels of the chimeric Cre protein, in particular, were associated with progressive recombination in the absence of drug.     

Illegitimate Cre-dependent chromosome rearrangements in transgenic mouse spermatids

The bacteriophage P1 Cre/loxP system has become a powerful tool for in vivo manipulation of the genomes of transgenic mice. Although in vitro studies have shown that Cre can catalyze recombination between cryptic "pseudo-loxP" sites in mammalian genomes, to date there have been no reports of loxP-site infidelity in transgenic animals. We produced lines of transgenic mice that use the mouse Protamine 1 (Prm1) gene promoter to express Cre recombinase in postmeiotic spermatids. All male founders and all Cre-bearing male descendents of female founders were sterile; females were unaffected. Sperm counts, sperm motility, and sperm morphology were normal, as was the mating behavior of the transgenic males and the production of two-celled embryos after mating. Mice that expressed similar levels of a derivative transgene that carries an inactive Cre exhibited normal male fertility. Analyses of embryos from matings between sterile Cre-expressing males and wild-type females indicated that Cre-catalyzed chromosome rearrangements in the spermatids that lead to abortive pregnancies with 100% penetrance. Similar Cre-mediated, but loxP-independent, genomic alterations may also occur in somatic tissues that express Cre, but, because of the greater difficulty of assessing deleterious effects of somatic mutations, these may go undetected. This study indicates that, following the use of the Cre/loxP site-specific recombination systems in vivo, it is prudent to eliminate or inactivate the Cre recombinase gene as rapidly as possible.     

Reporter expression, induced by a growth hormone promoter-driven Cre recombinase (rGHp-Cre) transgene, questions the developmental relationship between somatotropes and lactotropes in the adult mouse pituitary gland

This report describes the development and validation of the rGHp-Cre transgenic mouse that allows for selective Cre-mediated recombination of loxP-modified alleles in the GH-producing cells of the anterior pituitary. Initial screening of the rGHp-Cre parental line showed Cre mRNA was specifically expressed in the anterior pituitary gland of adult Cre+/- mice and cephalic extracts of e17 Cre+/- fetuses. Heterozygote rGHp-Cre transgenic mice were crossbred with Z/AP reporter mice to generate Cre+/-,Z/AP+/- offspring. In this model system, the GH promoter-driven, Cre-mediated recombination of the Z/AP reporter leads to human placental alkaline phosphatase (hPLAP) expression that serves to mark cells that currently produce GH, in addition to cells that would have differentiated from GH cells but currently do not express the GH gene. Double immunocytochemistry of adult male and female Cre+/-,Z/AP+/- pituitary cells revealed the majority (approximately 99%) of GH-producing cells of the anterior pituitary also expressed hPLAP, whereas ACTH-, TSH-, and LH-producing cells were negative for hPLAP, confirming previous reports that corticotropes, thyrotropes, and gonadotropes develop independently of the somatotrope lineage. A small subset (approximately 10%) of the prolactin-producing cells was positive for hPLAP, consistent with previous reports showing lactotropes can arise from somatotropes during pituitary development. However, the fact that 90% of prolactin-producing cells were negative for hPLAP suggests that the majority of lactotropes in the adult mouse pituitary gland develop independently of the somatotrope lineage. In addition to developmental studies, the rGHp-Cre transgenic mouse will provide a versatile tool to study the role of a variety of genes in somatotrope function and neoplastic transformation.     

A tamoxifen-inducible chimeric Cre recombinase specifically effective in the fetal and adult mouse liver

The spatiotemporal control of somatic mutagenesis in mice is considered a promising step to determine the function of a given gene product in a defined population of cells at any given time during animal life and also to generate better mouse models of human diseases. To introduce defined mutations in a temporally controlled manner in the liver, we established transgenic mice expressing a tamoxifen-inducible Cre recombinase under the control of the transthyretin promoter (TTR-Cre ind). The recombinase activity was examined on 2 different floxed alleles by crossing TTR-Cre ind mice with either the reporter strain ROSA 26 or with homozygous mice carrying floxed catalytic alpha2 subunit of the adenosine monophosphate (AMP)-activated protein kinase gene. By placing 2 mutated hormone-binding domains of murine estrogen receptor (Mer) at both termini of the Cre, we show that the fusion protein is active only on administration of the synthetic estrogen antagonist 4-hydroxytamoxifen (4-OHT) without any background in the absence of the inducing agent. The recombination is specific of the fetal and adult liver, and we show that the efficiency of recombination reached 80% to 100% after treatment with 4-OHT. In conclusion, TTR-Cre ind transgenic mice represent a valuable tool for temporally controlling the desired gene modifications in vivo in the fetal and adult liver. This would certainly help to understand the physiologic functions of genes in the liver, to create various mouse models mimicking human diseases, and to contribute to liver cancer-specific suicide gene therapy studies.     

Improved reporter strain for monitoring Cre recombinase-mediated DNA excisions in mice

Effective use of conditional Cre recombinase-loxP gene modification requires Cre-expressing mouse strains with defined patterns of expression. To assess the in vivo functionality of Cre-expressing mice, we have engineered an improved reporter strain for monitoring Cre-mediated excisions. The beta-galactosidase-neomycin phosphotransferase fusion gene (betageo)-trapped ROSA26 locus was modified by gene targeting such that betageo is expressed only after Cre-mediated excision of loxP-flanked DNA sequences. betageo from the excised ROSA26 allele is expressed ubiquitously in embryos and adult mice. By mating the reporter strain with Cre-expressing transgenic mice, we have shown that the loxP-flanked ROSA26 allele is accessible to Cre during early embryogenesis, as well as in a specific hematopoietic lineage (T lymphocytes). This improved reporter strain should facilitate monitoring in vivo Cre-mediated excision events in a variety of experimental contexts.     

Notch inhibits osteoblast differentiation and causes osteopenia

Notch receptors are determinants of cell fate decisions. To define the role of Notch in the adult skeleton, we created transgenic mice overexpressing the Notch intracellular domain (NICD) under the control of the type I collagen promoter. First-generation transgenics were small and osteopenic. Bone histomorphometry revealed that NICD caused a decrease in bone volume, secondary to a reduction in trabecular number; osteoblast and osteoclast number were decreased. Low fertility of founder mice and lethality of young pups did not allow the complete establishment of transgenic lines. To characterize the effect of Notch overexpression in vitro, NICD was induced in osteoblasts and stromal cells from Rosa(notch) mice, in which a STOP cassette flanked by lox(P) sites is upstream of NICD, by transduction with an adenoviral vector expressing Cre recombinase (Cre) under the control of the cytomegalovirus (CMV) promoter (Ad-CMV-Cre). NICD impaired osteoblastogenesis and inhibited Wnt/beta-catenin signaling. To determine the effects of notch1 deletion in vivo, mice in which notch1 was flanked by lox(P) sequences (notch1(loxP/loxP)) were mated with mice expressing Cre recombinase under the control of the osteocalcin promoter. Conditional null notch1 mice had no obvious skeletal phenotype, possibly because of rescue by notch2; however, 1-month-old females exhibited a modest increase in osteoclast surface and eroded surface. Osteoblasts from notch1(loxP/loxP) mice, transduced with Ad-CMV-Cre and transfected with Notch2 small interfering RNA, displayed increased alkaline phosphatase activity. In conclusion, Notch signaling in osteoblasts causes osteopenia and impairs osteo-blastogenesis by inhibiting the Wnt/beta-catenin pathway.     

A transgenic mouse line with specific Cre recombinase expression in the adrenal cortex

The Cre-loxP system combined with gene targeting strategies has proven to be very useful for gene inactivation in specific tissues and/or cell types. To achieve adrenal cortex specific recombination in vivo, we used a 0.5-kb fragment of the 5′-flanking region of the akr1b7 gene to drive Cre expression in adrenocortical cells. The resulting 0.5 akr1b7-Cre mice express Cre in all steroidogenic zones of the adrenal cortex but not in the gonads. Although recombination of the ROSA26R reporter locus was not observed in all cortical cells, we provide evidence that Cre is expressed in all the cells of the cortex in adult mice. In addition, Cre activity was found in collecting ducts and maturing glomeruli of the kidney. This line is the first to show specific Cre expression in the adrenal cortex in the absence of Cre expression in the gonads. This transgene thus provides a valuable tool for specific gene recombination in the adrenal cortex and kidney.     

Cre/lox-regulated transgenic zebrafish model with conditional myc-induced T cell acute lymphoblastic leukemia

We have created a stable transgenic rag2-EGFP-mMyc zebrafish line that develops GFP-labeled T cell acute lymphoblastic leukemia (T-ALL), allowing visualization of the onset and spread of this disease. Here, we show that leukemias from this transgenic line are highly penetrant and render animals moribund by 80.7 +/- 17.6 days of life (+/-1 SD, range = 50-158 days). These T cell leukemias are clonally aneuploid, can be transplanted into irradiated recipient fish, and express the zebrafish orthologues of the human T-ALL oncogenes tal1/scl and lmo2, thus providing an animal model for the most prevalent molecular subgroup of human T-ALL. Because T-ALL develops very rapidly in rag2-EGFP-mMyc transgenic fish (in which "mMyc" represents mouse c-Myc), this line can only be maintained by in vitro fertilization. Thus, we have created a conditional transgene in which the EGFP-mMyc oncogene is preceded by a loxed dsRED2 gene and have generated stable rag2-loxP-dsRED2-loxP-EGFP-mMyc transgenic zebrafish lines, which have red fluorescent thymocytes and do not develop leukemia. Transgenic progeny from one of these lines can be induced to develop T-ALL by injecting Cre RNA into one-cell-stage embryos, demonstrating the utility of the Cre/lox system in the zebrafish and providing an essential step in preparing this model for chemical and genetic screens designed to identify modifiers of Myc-induced T-ALL.