Use of ERT2-iCre-ERT2 for conditional transgenesis

We examined the use of ERT2-iCre-ERT2 (Cre2ERT2), a tamoxifen-regulated form of Cre that has been described to have a background activity lower than that of other tamoxifen-regulated Cre constructs, for establishing performant conditional deleter mouse lines. Cre2ERT2 was inserted by homologous recombination into the Rosa26 locus. These mice were mated with R26R Cre-reporter mice. No recombination could be observed in the progenies in the absence of tamoxifen treatment. Tamoxifen treatment at E13-14 led to a high level, albeit variable, recombination in most of the tissues examined: liver, heart, kidney, brain, lung etc. Treatment of adult animals also induced recombination in these tissues, although at a lower level. Northern blot and qPCR studies suggested that these differences are not linked to significant variations of the level of expression of Cre2ERT2. Thus, Cre2ERT2 appears to be a good alternative to existing modulatable Cre systems, displaying a lack of background activity and a high-level inducibility in vivo.     

Highly B lymphocyte‐specific tamoxifen inducible transgene expression of CreERT2 by using the LC‐1 locus BAC vector

The generation of cell type specific inducible Cre transgenic mice is the most challenging and limiting part in the development of spatio‐temporally controlled knockout mouse models. Here we report the generation and characterization of a B lymphocyte‐specific tamoxifen‐inducible Cre transgenic mouse strain, LC‐1‐hCD19‐CreER^T2. We utilized the human CD19 promoter for expression of the tamoxifen‐inducible Cre recombinase (CreER^T2) gene, embedded in genomic sequences previously reported to give minimal position effects after transgenesis. Cre recombinase activity was evaluated by cross‐breeding the LC‐1‐hCD19‐CreER^T2 strain with a strain containing a floxed gene widely expressed in the hematopoietic system. Cre activity was only detected in the presence of tamoxifen and was restricted to B lymphocytes. The efficacy of recombination ranged from 27 to 61% in the hemizygous and homozygous mice, respectively. In conclusion, the LC‐1‐hCD19‐CreER^T2 strain is a powerful tool to study gene function specifically in B lymphocytes at any chosen time point in the lifecycle of the mouse. genesis 47:729–735, 2009. © 2009 Wiley‐Liss, Inc.     

Smad2条件基因剔除载体的构建及LoxP位点有效性鉴定

Smads家族是最新发现的TGF－β信号转导途径中一个重要的新基因家族,SMAD2属于受体激活的SMADs。Smad2在某些肿瘤中发生突变,是一种可能的肿瘤抑制基因。Smad2基因完全剔除小鼠在胚胎期E6．5天死亡,为了研究Smad2在成体各组织器官及肿瘤发生中的可能作用,构建了Smad2条件基因剔除载体,将LoxP置于Smad2基因组序列C末端功能域两侧,并在组成型表达Cre重组酶的大肠杆菌中检测了LoxP位点的功能,该载体的构建为进行Smad2组织特异性基因剔除研究了奠定了基础。     

Efficient recombination in pancreatic islets by a tamoxifen-inducible Cre-recombinase

We generated pdx1(PB)CreERtrade mark transgenic mice in which a pancreatic endocrine-specific enhancer (pdx1(PB)) drives expression of a tamoxifen (TM)-inducible Cre recombinase/estrogen receptor fusion protein. We previously showed that this enhancer directs expression to immature endocrine cells as well as postnatal islets. This transgene provides spatial and temporal control of gene inactivation in pancreatic islets. Three transgenic lines were generated and crossed with R26R mice to assess recombination efficiency. TM-dependent lacZ expression was observed in islets from all three lines. One line was chosen for further study based on its strong islet-specific recombination in embryos and adults. In this line, a dose-dependent increase in recombination efficiency was observed in endocrine cells. Our data suggest that this transgenic line will be a valuable tool to inactivate genes in pancreatic endocrine cells during development or in the adult. The dose-dependent nature of recombination suggests a potential use for this line in the generation of genetic mosaic animals.     

Optimization of spatiotemporal gene inactivation in mouse heart by oral application of tamoxifen citrate

Inducible and tissue-specific gene inactivation in mice has become a powerful tool to bypass embryonic and postnatal lethality of knockout mice. The most frequently used inducible system is based on Cre recombinase fused to either one or two mutated estrogen receptor ligand binding domains, thus rendering Cre function tamoxifen-dependent. To achieve Cre-mediated inactivation of a given gene, 4-OH tamoxifen (4-OHT) dissolved either in alcohol and/or oil is usually administered by repeated intraperitoneal (i.p.) injections. Since this procedure imposes considerable stress on mice, we compared the effect of tamoxifen citrate, mixed into a standard mouse diet at different concentrations, with that of i.p. administration of 4-OHT on Cre-mediated, heart-specific inactivation of thioredoxin reductase 2. Here we show that tamoxifen citrate in the chow was equally effective as 4-OHT given i.p. Oral tamoxifen administration is thus a convenient and cost-saving way for gene induction, and, most importantly, it reduces stress and avoids adverse effects in mice.     

Generation of a conditional allele for the mouse endothelial nitric oxide synthase gene

Mice with endothelial nitric oxide synthase (eNOS) deletions have defined the crucial role of eNOS in vascular development, homeostasis, and pathology. However, cell specific eNOS function has not been determined, although an important role of eNOS has been suggested in multiple cell types. Here, we have generated a floxed eNOS allele in which exons 9–12, encoding the sites essential to eNOS activity, are flanked with loxP sites. Mice homozygous for the floxed allele showed normal eNOS protein levels and no overt phenotype. Conversely, homozygous mice with Cre‐deleted alleles displayed truncated eNOS protein, lack of vascular NO production, and exhibited similar phenotype to eNOS knockout mice, including hypertension, low heart rate, and focal renal scarring. These findings demonstrate that the floxed allele is normal and it can be converted to a non‐functional eNOS allele through Cre recombination. This mouse will allow time‐ and cell‐specific eNOS deletion. genesis 50:685–692, 2012. © 2012 Wiley Periodicals, Inc.     

Generation of multipurpose alleles for the functional analysis of the mouse genome.

A novel generation of retroviral gene-trap vectors has been developed with the ability to induce conditional mutations in most genes expressed in mouse embryonic stem (ES) cells. The vectors rely on directional site-specific recombination systems, which can repair and re-induce the gene-trap mutations when activated in succession. After the gene-trap insertions are passaged into mice, this system enables the induction of temporally and spatially restricted mutations in somatic cells. In addition to their conditional features, the vectors create multipurpose alleles amenable to a wide range of post-insertional modifications. These vectors have been used to assemble the largest library of ES cell lines with conditional mutations in single genes, presently totalling 1724 unique genes. Due to their efficiency, the vectors are part of the core technologies to be used by EUCOMM for establishing a complete collection of conditional null mutations in mice.     

Generation of conditional knockout alleles for PDGF-C

PDGF-C is a newly identified member of the platelet-derived growth factor (PDGF) family, which is involved in multiple cellular functions by signaling through PDGF receptor (PDGFR)-alphaalpha and alphabeta dimers. PDGF-C deficiency is perinatal lethal due to the formation of cleft palate. To further characterize the cellular function of PDGF-C during both embryonic and postnatal development, we have generated two conditional alleles of the Pdgf-c gene in which two loxP sites flank exon 5. Global Cre-mediated excision of the floxed exon 5 in these alleles resulted in a complete loss of PDGF-C expression and caused embryonic defects identical to those previously described for the PDGF-C null embryos. These conditional alleles will therefore be the important genetic tools for dissecting the spatial and temporal roles of PDGF-C during development and in adult tissues. Furthermore, from this work, we have also described a simple approach for creating mouse conditional alleles in an efficient manner.     

配体依赖性Cre重组酶在培养肝细胞中介导条件性基因激活

嵌合性Cre重组酶与肝组织特异性调控区的结合使其在肝细胞上介导的条件性基因激活成为可能。为此 ,首先构建了在小鼠白蛋白基因调控区调控下的Cre ERt表达载体 (Alb Cre ERt) ,然后将其构件分别转染工程化的BRL(大鼠肝细胞 )和BRK(大鼠肾细胞 )细胞株 ,这些细胞携带的floxed βgeo框架位于启动子与人碱性磷酸酶基因 (hAP)之间 ,因而阻碍hAP表达。用 1μmol/L 4 羟基三苯氧胺 (4 hydroxytamoxifen ,4 OHT)处理后 ,经碱性磷酸酶染色 ,部分BRL细胞显示碱性磷酸酶染色阳性 ;用PCR方法证实Cre重组酶介导了floxed βgeo框架的切除。然而 ,在未用 4 OHT处理的BRL细胞未观察到碱性磷酸酶染色阳性细胞 ,在用 4 OHT处理或未处理的BRK细胞同样未观察到碱性磷酸酶染色阳性细胞。这些结果表明已成功构建肝细胞特异表达Alb Cre ERt载体 ,并在表达Cre融合蛋白的BRL细胞证实 4 OHT能够诱导Cre介导的DNA重组 ,从而激活碱性磷酸酶报告基因的表达。该研究将为进一步建立肝细胞特异表达Cre ERt转基因小鼠奠定基础。     

Cre重组酶结构与功能的研究进展

Cre/loxP定位重组系统来源于噬菌体P₁,由Cre重组酶和loxP位点两部分组成。在Cre重组酶的介导下,设定的DNA片段可以被切除,可以发生倒位,亦可造成定点的整合。由于其作用方式高效简单,Cre/loxP定位重组系统已在特定基因的删除、基因功能的鉴定、外源基因的整合、基因捕获及染色体工程等方面得到了有效的利用,在转基因的酵母、植物、昆虫、哺乳动物的体内外DNA重组方面成为一个有力的工具。这里就Cre重组酶的结构、功能及该定位重组系统的应用等方面的研究进行了综述。     

Inducible gene deletion in the entire cardiac conduction system using Hcn4‐CreERT2 BAC transgenic mice

Developmental defects and disruption of molecular pathways of the cardiac conduction system (CCS) can cause life‐threatening cardiac arrhythmias. Despite decades of effort, knowledge about the development and molecular control of the CCS remains primitive. Mouse genetics, complementary to other approaches such as human genetics, has become a key tool for exploring the developmental processes of various organs and associated diseases. Genetic analysis using mouse models will likely provide great insights about the development of the CCS, which can facilitate the development of novel therapeutic strategies to treat arrhythmias. To enable genetic studies of the CCS, CCS‐associated Cre mouse models are essential. However, existing mouse models with Cre activity reported in the CCS have various limitations such as Cre leak, haploinsufficiency, and inadequate specificity of the Cre activity. To circumvent those limitations, we successfully generated Hcn4‐CreERT2 bacterial artificial chromosome (BAC) transgenic mice using BAC recombineering in which Cre activity was specifically detected in the entire CCS after tamoxifen induction. Our Hcn4‐CreERT2 BAC transgenic line will be an invaluable genetic tool with which to dissect the developmental control of CCS and arrhythmias. genesis 52:134–140. © 2013 Wiley Periodicals, Inc.     

Generation of a Mig-6 conditional null allele

Mitogen-inducible gene 6 (Mig-6) is a stress-induced gene that serves as a negative regulator of epidermal growth factor (EGF) signaling and acts as a tumor suppressor. Ablation of Mig-6 results in a significant percentage of embryo lethality as well as abnormalities in multiple tissues. To understand the physiological roles of Mig-6, a conditional null allele, Mig-6(f/f) was generated by introducing LoxP sites that flank exons 2 and 4. The Mig-6(f/f) allele was validated by generating recombined Mig-6(-/-) mice using the Zp3-Cre system. The conditional null allele was confirmed by assaying for Mig-6 gene expression in liver, lung, uterus, and skin. The recombined Mig-6(-/-) mice developed pathological changes, such as degenerative joint diseases and skin hyperplasia similar to the previously reported Mig-6 germline null allele. In addition, these mice also had enlarged uteri with endometrial hyperplasia. In summary, this Mig-6(f/f) mouse is a useful tool for the functional study of the Mig-6 gene in a tissue-specific fashion.     

Induced DNA recombination by Cre recombinase protein transduction

Cre is a DNA recombinase that recognizes 34 base-pair loxP sites of recombination. We have developed a cell-permeable Cre recombinase, TATCre, that is capable of mediating deletion of loxP-flanked targets by simply adding TATCre to cell cultures. Thus, TATCre allows efficient induced DNA recombination without the use of a Cre recombinase transgene or any other genetic material and should prove useful for the genetic manipulation of a wide variety of cell types that have been engineered to possess loxP sites.