Small interfering RNA and gene silencing in transgenic mice and rats

Molecular Characterization and Expression Profiling of Three Transformer-2 Splice Isoforms in the Redclaw Crayfish, Cherax quadricarinatus

Sex determination/sex differentiation is determined by genetics, environmental factors, or the interactions of the two. The Transformer-2 (Tra-2) gene plays an important role in the sex determination cascade signal pathway in insects. In this study, the Tra-2 gene was isolated and characterized from the cDNA library of gonad tissues in the redclaw crayfish, Cherax quadricarinatus. Three splice variants were identified, designated as CqTra-2A, CqTra-2B, and CqTra-2C, and sequence analysis showed that they had a highly conserved RRM domain. Phylogenetic analysis was performed by the NJ method, and the results revealed that the Tra-2 protein of the redclaw crayfish was very closely related to those of Macrobrachium rosenbergii, Fenneropenaeus chinensis, and Macrobrachium nipponense. Real-time PCR analysis showed that the three isoforms were predominantly expressed in the ovary and gradually increased with embryonic development. Additionally, the expression pattern of CqTra-2 at different developmental stages was analyzed by qPCR and revealed that the phase of having a body length of 3 cm may be the key period for the sex differentiation of C. quadricarinatus. RNAi-targeting gene silencing further confirmed the function of CqTra-2 in sexual differentiation in redclaw crayfish. Our experimental data will contribute to understanding the mechanism of sex determination in crustaceans.

Molecular Characterization and Functional Study of Insulin-Like Androgenic Gland Hormone Gene in the Red Swamp Crayfish, Procambarus clarkii

The androgenic gland (AG) is a male-specific endocrine organ that controls the primary and secondary sexual characteristics in male crustaceans. More evidence indicates that the insulin-like androgenic gland hormone gene (IAG) is the key male sexual differentiation factor, particularly the application of RNA interference (RNAi) technology on IAG. In this study, the full-length cDNA of IAG (termed PcIAG) was isolated from the red swamp crayfish, Procambarusclarkii. Tissue distribution analysis showed that in addition to its expression in the AG of male P. clarkii, PcIAG was widely expressed in female tissues and other male tissues. The PcIAG protein was detected in the reproductive and nervous systems of adult male P. clarkii. Additionally, RNAi results showed that the PcIAG expression could be silenced efficiently, and the male sperm maturation and release possibly present a transient adverse interference at lower doses (0.1 μg/g and 1 μg/g) of PcIAG–dsRNA (PcIAG double-stranded RNA). Dramatically, the expression level of PcIAG increased sharply shortly after the injection of higher doses (5 μg/g and 10 μg/g) of PcIAG–dsRNA, which might accelerate the maturation and release of sperm. Moreover, the expression of PcSxl (P. clarkii Sex-lethal) was detected by Quantitative Real-Time PCR (qPCR) after the injection of PcIAG–dsRNA to explore whether the PcIAG gene regulates the PcSxl gene, and we found that the PcIAG did not directly regulate PcSxl in P. clarkii. The study could help accelerate the progress of PcIAG functional research and provide a useful reference for the single-sex selective breeding of P. clarkii.

Targeted Manipulation of Brain Serotonin: RNAi-Mediated Knockdown of Tryptophan Hydroxylase 2 in Rats

Tryptophan hydroxylase (TPH) is the rate-limiting enzyme in the biosynthesis of the biogenic monoamine serotonin (5-hydroxytryptamine, 5-HT). Two existing TPH isoforms are responsible for the generation of two distinct serotonergic systems in vertebrates. TPH1, predominantly expressed in the gastrointestinal tract and pineal gland, mediates 5-HT biosynthesis in non-neuronal tissues, while TPH2, mainly found in the raphe nuclei of the brain stem, is accountable for the production of 5-HT in the brain. Neuronal 5-HT is a key regulator of mood and behavior and its deficiency has been implicated in a variety of neuropsychiatric disorders, e.g., depression and anxiety. To gain further insights into the complexity of central 5-HT modulations of physiological and pathophysiological processes, a new transgenic rat model, allowing an inducible gene knockdown of Tph2, was established based on doxycycline-inducible shRNA-expression. Biochemical phenotyping revealed a functional knockdown of Tph2 mRNA expression following oral doxycycline administration, with subsequent reductions in the corresponding levels of TPH2 enzyme expression and activity. Transgenic rats showed also significantly decreased tissue levels of 5-HT and its degradation product 5-Hydroxyindoleacetic acid (5-HIAA) in the raphe nuclei, hippocampus, hypothalamus, and cortex, while peripheral 5-HT concentrations in the blood remained unchanged. In summary, this novel transgenic rat model allows inducible manipulation of 5-HT biosynthesis specifically in the brain and may help to elucidate the role of 5-HT in the pathophysiology of affective disorders.

From Classical Toxicology to Tox21: Some Critical Conceptual and Technological Advances in the Molecular Understanding of the Toxic Response Beginning From the Last Quarter of the 20th Century

Toxicology has made steady advances over the last 60+ years in understanding the mechanisms of toxicity at an increasingly finer level of cellular organization. Traditionally, toxicological studies have used animal models. However, the general adoption of the principles of 3R (Replace, Reduce, Refine) provided the impetus for the development of in vitro models in toxicity testing. The present commentary is an attempt to briefly discuss the transformation in toxicology that began around 1980. Many genes important in cellular protection and metabolism of toxicants were cloned and characterized in the 80s, and gene expression studies became feasible, too. The development of transgenic and knockout mice provided valuable animal models to investigate the role of specific genes in producing toxic effects of chemicals or protecting the organism from the toxic effects of chemicals. Further developments in toxicology came from the incorporation of the tools of "omics" (genomics, proteomics, metabolomics, interactomics), epigenetics, systems biology, computational biology, and in vitro biology. Collectively, the advances in toxicology made during the last 30-40 years are expected to provide more innovative and efficient approaches to risk assessment. A goal of experimental toxicology going forward is to reduce animal use and yet be able to conduct appropriate risk assessments and make sound regulatory decisions using alternative methods of toxicity testing. In that respect, Tox21 has provided a big picture framework for the future. Currently, regulatory decisions involving drugs, biologics, food additives, and similar compounds still utilize data from animal testing and human clinical trials. In contrast, the prioritization of environmental chemicals for further study can be made using in vitro screening and computational tools.

Efficient Gene Suppression in Dorsal Root Ganglia and Spinal Cord Using Adeno-Associated Virus Vectors Encoding Short-Hairpin RNA

RNA interference is a powerful tool used to induce loss-of-function phenotypes through post-transcriptional gene silencing. Small interfering RNA (siRNA) molecules have been used to target the central nervous system (CNS) and are expected to have clinical utility against refractory neurodegenerative diseases. However, siRNA is characterized by low transduction efficiency, insufficient inhibition of gene expression, and short duration of therapeutic effects, and is thus not ideal for treatment of neural tissues and diseases. To address these problems, viral delivery of short-hairpin RNA (shRNA) expression cassettes that support more efficient and long-lasting transduction into target tissues is expected to be a promising delivery tool. Various types of gene therapy vectors have been developed, such as adenovirus, adeno-associated virus (AAV), herpes simplex virus and lentivirus; however, AAV is particularly advantageous because of its relative lack of immunogenicity and lack of chromosomal integration. In human clinical trials, recombinant AAV vectors are relatively safe and well-tolerated. In particular, serotype 9 of AAV (AAV9) vectors show the highest tropism for neural tissue and can cross the blood-brain barrier, and we have shown that intrathecal delivery of AAV9 yields relatively high gene transduction into dorsal root ganglia or spinal cord. This chapter describes how to successfully use AAV vectors encoding shRNA in vivo, particularly for RNA interference in the central and peripheral nervous system.

Assessment of Artificial MiRNA Architectures for Higher Knockdown Efficiencies without the Undesired Effects in Mice

RNAi-based strategies have been used for hypomorphic analyses. However, there are technical challenges to achieve robust, reproducible knockdown effect. Here we examined the artificial microRNA (amiRNA) architectures that could provide higher knockdown efficiencies. Using transient and stable transfection assays in cells, we found that simple amiRNA-expression cassettes, that did not contain a marker gene (−MG), displayed higher amiRNA expression and more efficient knockdown than those that contained a marker gene (+MG). Further, we tested this phenomenon in vivo, by analyzing amiRNA-expressing mice that were produced by the pronuclear injection-based targeted transgenesis (PITT) method. While we observed significant silencing of the target gene (eGFP) in +MG hemizygous mice, obtaining −MG amiRNA expression mice, even hemizygotes, was difficult and the animals died perinatally. We obtained only mosaic mice having both “−MG amiRNA” cells and “amiRNA low-expression” cells but they exhibited growth retardation and cataracts, and they could not transmit the –MG amiRNA allele to the next generation. Furthermore, +MG amiRNA homozygotes could not be obtained. These results suggested that excessive amiRNAs transcribed by −MG expression cassettes cause deleterious effects in mice, and the amiRNA expression level in hemizygous +MG amiRNA mice is near the upper limit, where mice can develop normally. In conclusion, the PITT-(+MG amiRNA) system demonstrated here can generate knockdown mouse models that reliably express highest and tolerable levels of amiRNAs.

CRISPR/Cas9-based generation of knockdown mice by intronic insertion of artificial microRNA using longer single-stranded DNA

Knockdown mouse models, where gene dosages can be modulated, provide valuable insights into gene function. Typically, such models are generated by embryonic stem (ES) cell-based targeted insertion, or pronuclear injection, of the knockdown expression cassette. However, these methods are associated with laborious and time-consuming steps, such as the generation of large constructs with elements needed for expression of a functional RNAi-cassette, ES-cell handling, or screening for mice with the desired knockdown effect. Here, we demonstrate that reliable knockdown models can be generated by targeted insertion of artificial microRNA (amiRNA) sequences into a specific locus in the genome [such as intronic regions of endogenous eukaryotic translation elongation factor 2 (eEF-2) gene] using the Clustered Regularly Interspaced Short Palindromic Repeats/Crispr associated 9 (CRISPR/Cas9) system. We used in vitro synthesized single-stranded DNAs (about 0.5-kb long) that code for amiRNA sequences as repair templates in CRISPR/Cas9 mutagenesis. Using this approach we demonstrate that amiRNA cassettes against exogenous (eGFP) or endogenous [orthodenticle homeobox 2 (Otx2)] genes can be efficiently targeted to a predetermined locus in the genome and result in knockdown of gene expression. We also provide a strategy to establish conditional knockdown models with this method.

Multiple renal cyst development but not situs abnormalities in transgenic RNAi mice against Inv::GFP rescue gene

In this study we generated RNA interference (RNAi)-mediated gene knockdown transgenic mice (transgenic RNAi mice) against the functional Inv gene. Inv mutant mice show consistently reversed internal organs (situs inversus), multiple renal cysts and neonatal lethality. The Inv::GFP-rescue mice, which introduced the Inv::GFP fusion gene, can rescue inv mutant mice phenotypes. This indicates that the Inv::GFP gene is functional in vivo. To analyze the physiological functions of the Inv gene, and to demonstrate the availability of transgenic RNAi mice, we introduced a short hairpin RNA expression vector against GFP mRNA into Inv::GFP-rescue mice and analyzed the gene silencing effects and Inv functions by examining phenotypes. Transgenic RNAi mice with the Inv::GFP-rescue gene (Inv-KD mice) down-regulated Inv::GFP fusion protein and showed hypomorphic phenotypes of inv mutant mice, such as renal cyst development, but not situs abnormalities or postnatal lethality. This indicates that shRNAi-mediated gene silencing systems that target the tag sequence of the fusion gene work properly in vivo, and suggests that a relatively high level of Inv protein is required for kidney development in contrast to left/right axis determination. Inv::GFP protein was significantly down-regulated in the germ cells of Inv-KD mice testis compared with somatic cells, suggesting the existence of a testicular germ cell-specific enhanced RNAi system that regulates germ cell development. The Inv-KD mouse is useful for studying Inv gene functions in adult tissue that are unable to be analyzed in inv mutant mice showing postnatal lethality. In addition, the shRNA-based gene silencing system against the tag sequence of the fusion gene can be utilized as a new technique to regulate gene expression in either in vitro or in vivo experiments.

An RNAi-based approach to down-regulate a gene family in vivo

Genetic redundancy poses a major problem to the analysis of gene function. RNA interference allows the down-regulation of several genes simultaneously, offering the possibility to overcome genetic redundancy, something not easily achieved with traditional genetic approaches. Previously we have used a polycistronic miR155-based framework to knockdown expression of three genes of the early B cell factor family in cultured cells. Here we develop the system further by generating transgenic mice expressing the RNAi construct in vivo in an inducible manner. Expression of the transgene from the strong CAG promoter is compatible with a normal function of the basal miRNA/RNAi machinery, and the miR155 framework readily allows inducible expression from the Rosa26 locus as shown by Gfp. However, expression of the transgene in hematopoietic cells does not lead to changes in B cell development and neuronal expression does not affect cerebellar architecture as predicted from genetic deletion studies. Protein as well as mRNA levels generated from Ebf genes in hetero- and homozygous animals are comparable to wild-type levels. A likely explanation for the discrepancy in the effectiveness of the RNAi construct between cultured cells and transgenic animals lies in the efficiency of the sequences used, possibly together with the complexity of the transgene. Since new approaches allow to overcome efficiency problems of RNAi sequences, the data lay the foundation for future work on the simultaneous knockdown of several genes in vivo.

Accelerating cancer modeling with RNAi and nongermline genetically engineered mouse models

For more than two decades, genetically engineered mouse models have been key to our mechanistic understanding of tumorigenesis and cancer progression. Recently, the massive quantity of data emerging from cancer genomics studies has demanded a corresponding increase in the efficiency and throughput of in vivo models for functional testing of putative cancer genes. Already a mainstay of cancer research, recent innovations in RNA interference (RNAi) technology have extended its utility for studying gene function and genetic interactions, enabling tissue-specific, inducible and reversible gene silencing in vivo. Concurrent advances in embryonic stem cell (ESC) culture and genome engineering have accelerated several steps of genetically engineered mouse model production and have facilitated the incorporation of RNAi technology into these models. Here, we review the current state of these technologies and examine how their integration has the potential to dramatically enhance the throughput and capabilities of animal models for cancer.

Transgenically mediated shRNAs targeting conserved regions of foot-and-mouth disease virus provide heritable resistance in porcine cell lines and suckling mice

Foot-and-mouth disease virus (FMDV) is responsible for substantial economic losses in livestock breeding each year, and the development of new strategies is needed to overcome the limitations of existing vaccines and antiviral drugs. In this study, we evaluated the antiviral potential of transgenic porcine cells and suckling mice that simultaneously expressed two short-hairpin RNAs (shRNAs) targeting the conserved regions of the viral polymerase protein 3D and the non-structural protein 2B. First, two recombinant shRNA-expressing plasmids, PB-EN3D2B and PB-N3D2B, were constructed and the efficiency of the constructs for suppressing an artificial target was demonstrated in BHK-21 cells. We then integrated PB-EN3D2B into the genome of the porcine cell line IBRS-2 using the piggyBac transposon system, and stable monoclonal transgenic cell lines (MTCL) were selected. Of the 6 MTCL that were used in the antiviral assay, 3 exhibited significant resistance with suppressing ratios of more than 94% at 48 hours post-challenge (hpc) to both serotype O and serotype Asia 1 FMDV. MTCL IB-3D2B-6 displayed the strongest antiviral activity, which resulted in 100% inhibition of FMDV replication until 72 hpc. Moreover, the shRNA-expressing fragment of PB-N3D2B was integrated into the mouse genome by DNA microinjection to produce transgenic mice. When challenged with serotype O FMDV, the offspring of the transgenic mouse lines N3D2B-18 and N3D2B-81 exhibited higher survival rates of 19% to 27% relative to their non-transgenic littermates. The results suggest that these heritable shRNAs were able to suppress FMDV replication in the transgenic cell lines and suckling mice.

miR-200b and miR-429 function in mouse ovulation and are essential for female fertility

Ovulation in the mouse and other mammals is controlled by hormones secreted by the hypothalamo-pituitary-ovarian axis. We describe anovulation and infertility in female mice lacking the microRNAs miR-200b and miR-429. Both miRNAs are strongly expressed in the pituitary gland, where they suppress expression of the transcriptional repressor ZEB1. Eliminating these miRNAs, in turn, inhibits luteinizing hormone (LH) synthesis by repressing transcription of its β-subunit gene, which leads to lowered serum LH concentration, an impaired LH surge, and failure to ovulate. Our results reveal roles for miR-200b and miR-429, and their target the Zeb1 gene, in the regulation of mammalian reproduction. Thus, the hypothalamo-pituitary-ovarian axis was shown to require miR-200b and miR-429 to support ovulation.

Recent advances in the development of new transgenic animal technology

Transgenic animal technology is one of the fastest growing biotechnology areas. It is used to integrate exogenous genes into the animal genome by genetic engineering technology so that these genes can be inherited and expressed by offspring. The transgenic efficiency and precise control of gene expression are the key limiting factors in the production of transgenic animals. A variety of transgenic technologies are available. Each has its own advantages and disadvantages and needs further study because of unresolved technical and safety issues. Further studies will allow transgenic technology to explore gene function, animal genetic improvement, bioreactors, animal disease models, and organ transplantation. This article reviews the recently developed animal transgenic technologies, including the germ line stem cell-mediated method to improve efficiency, gene targeting to improve accuracy, RNA interference-mediated gene silencing technology, zinc-finger nuclease gene targeting technology and induced pluripotent stem cell technology. These new transgenic techniques can provide a better platform to develop transgenic animals for breeding new animal varieties and promote the development of medical sciences, livestock production, and other fields.

Target validation in mice by constitutive and conditional RNAi

Gene silencing by RNA interference (RNAi) has become a standard method for the characterization of gene function in mammalian cells. Short hairpin (sh) RNAs expressed from stably integrated vectors mediate gene knockdown both in cultured cells and in mice, presenting a fast alternative to gene knockout approaches. We describe three strategies to control gene silencing in mice that can be applied to any transcript of interest. This shRNA based approach enables either i) constitutive body-wide knockdown, ii) cell type-specific knockdown controlled by Cre recombinase, or iii) inducible body-wide knockdown controlled by doxycycline. For reliable expression the shRNA vector of interest is inserted into a Rosa26 docking site of ES cells by a site-specific recombinase. These ES cells can then be used to generate shRNA transgenic mice. This technology enables the production of adult knockdown mice within 11 months for an expedite in vivo validation of drug targets.

Transgenic sheep generated by lentiviral vectors: safety and integration analysis of surrogates and their offspring

The safety of HIV-1 based vectors was evaluated during the production of transgenic sheep. Vectors were introduced into the perivitelline space of in vivo derived one-cell sheep embryos by microinjection then transferred into the oviducts of recipient females. At 60-70 days of gestation, a portion of the recipients were euthanized and tissues collected from both surrogates and fetuses. Other ewes were allowed to carry lambs to term. Inadvertent transfer of vector from offspring to surrogates was evaluated in 330 blood and tissue samples collected from 57 ewes that served as embryo recipients. Excluding uterine contents, none of the samples tested positive for vector, indicating that that the vector did not cross the fetal maternal interface and infect surrogate ewes. Evaluating ewes, fetuses and lambs for replication competent lentivirus (RCL); 84 serum samples analyzed for HIV-1 capsid by ELISA and over 600 blood and tissue samples analyzed by quantitative PCR for the VSV-G envelopes revealed no evidence of RCL. Results of these experiments provide further evidence as to the safety of HIV-1 based vectors in animal and human applications.

RNA interference with special reference to combating viruses of crustacea

RNA interference has evolved from being a nuisance biological phenomenon to a valuable research tool to determine gene function and as a therapeutic agent. Since pioneering observations regarding RNA interference were first reported in the 1990s from the nematode worm, plants and Drosophila, the RNAi phenomenon has since been reported in all eukaryotic organisms investigated from protozoans, plants, arthropods, fish and mammals. The design of RNAi therapeutics has progressed rapidly to designing dsRNA that can specifically and effectively silence disease related genes. Such technology has demonstrated the effective use of short interfering as therapeutics. In the absence of a B cell lineage in arthropods, and hence no long term vaccination strategy being available, the introduction of using RNA interference in crustacea may serve as an effective control and preventative measure for viral diseases for application in aquaculture.

AAV-based RNAi silencing of NADPH oxidase gp91(phox) attenuates cold-induced cardiovascular dysfunction

Clinical observations and epidemiological surveys indicated that the prevalence of hypertension and heart diseases is increased in cold regions or during winter. Cold exposure increased NADPH oxidase gp91(phox) protein expression in heart, kidneys, and aorta in rats. The aim of this study was to investigate if RNA interference (RNAi) silencing of gp91(phox) would attenuate cold-induced hypertension and cardiovascular and renal damage. The recombinant adeno-associated virus serotype 2 (AAV-2) vector carrying gp91(phox)-shRNA (gp91-shRNA) was constructed for inhibiting gp91(phox) protein expression in cold-exposed rats. Blood pressure (BP) was monitored using a telemetry system. BP was increased in the Control-shRNA and PBS groups within 1 week of exposure to moderate cold (5°C) and reached a plateau after 7 weeks. The cold-induced increase in BP was attenuated significantly by intravenous delivery of gp91-shRNA (1.25×10(10) particles/rat, 0.5 mL). One single dose of gp91-shRNA controlled hypertension for up to 10 weeks. In addition, gp91-shRNA reversed cold-induced vascular dysfunction. gp91-shRNA abolished the cold-induced up-regulation of gp91(phox) protein expression in heart, kidneys, and aorta, confirming effective silencing of gp91(phox). The cold-induced increases in NADPH oxidase activity and superoxide production were eliminated by silencing of gp91(phox), suggesting that the cold-induced up-regulation of NADPH oxidase activity may be attributed to the increased gp91(phox) protein expression. RNAi silencing of gp91(phox) abolished cold-induced cardiac and renal hypertrophy and attenuated aortic, coronary, and renal remodeling. The up-regulation of gp91(phox) may play a critical role in cold-induced cardiovascular dysfunction and organ damage. AAV delivery of gp91-shRNA may be a new and effective therapeutic approach for cold-related cardiovascular disorders.

Rat placentation: an experimental model for investigating the hemochorial maternal-fetal interface

The rat possesses hemochorial placentation with deep intrauterine trophoblast cell invasion and trophoblast-directed uterine spiral artery remodeling; features shared with human placentation. Recognition of these similarities spurred the establishment of in vitro and in vivo research methods using the rat as an animal model to address mechanistic questions regarding development of the hemochorial placenta. The purpose of this review is to provide the requisite background to help move the rat to the forefront in placentation research.

Lentiviral transgenic microRNA-based shRNA suppressed mouse cytochromosome P450 3A (CYP3A) expression in a dose-dependent and inheritable manner

Cytochomosome P450 enzymes (CYP) are heme-containing monooxygenases responsible for oxidative metabolism of many exogenous and endogenous compounds including drugs. The species difference of CYP limits the extent to which data obtained from animals can be translated to humans in pharmacodynamics or pharmacokinetics studies. Transgenic expression of human CYP in animals lacking or with largely reduced endogenous CYP counterparts is recognized as an ideal strategy to correct CYP species difference. CYP3A is the most abundant CYP subfamily both in human and mammals. In this study, we designed a microRNA-based shRNA (miR-shRNA) simultaneously targeting four members of mouse CYP3A subfamily (CYP3A11, CYP3A16, CYP3A41 and CYP3A44), and transgenic mice expressing the designed miR-shRNA were generated by lentiviral transgenesis. Results showed that the CYP3A expression level in transgenic mice was markedly reduced compared to that in wild type or unrelated miR-shRNA transgenic mice, and was inversely correlated to the miR-shRNA expression level. The CYP3A expression levels in transgenic offspring of different generations were also remarkably lower compared to those of controls, and moreover the inhibition rate of CYP3A expression remained comparable over generations. The ratio of the targeted CYP3A transcriptional levels was comparable between knockdown and control mice of the same gender as detected by RT-PCR DGGE analysis. These data suggested that transgenic miR-shRNA suppressed CYP3A expression in a dose-dependent and inheritable manner, and transcriptional levels of the targeted CYP3As were suppressed to a similar extent. The observed knockdown efficacy was further confirmed by enzymatic activity analysis, and data showed that CYP3A activities in transgenic mice were markedly reduced compared to those in wild-type or unrelated miR-shRNA transgenic controls (1.11±0.71 vs 5.85±1.74, 5.9±2.4; P<0.01). This work laid down a foundation to further knock down the remaining murine CYP3As or CYPs of other subfamilies, and a basis to generate CYP knockdown animals of other species.

Successful suppression of endogenous α-1,3-galactosyltransferase expression by RNA interference in pig embryos generated in vitro

RNA interference (RNAi) technology using small interfering RNAs (siRNA) has been widely used as a powerful tool to knock down gene expression in various organisms. In pig preimplantation embryos, no attempt to suppress the target gene expression with such technology has been made. The purpose of this study is to demonstrate that the RNAi technology is useful for suppression of endogenous target gene expression at an early stage of development in pigs. Alpha-1,3-Galactosyltransferase (α-GalT) is an enzyme that creates the Galα1-3Gal (α-Gal) epitope on the cell surface in some mammalian species, and removal of the epitope is considered to be a prerequisite for pig-to-human xenotransplantation. We decided to suppress the endogenous α-GalT mRNA expression in pig early embryos, since reduction of α-GalT synthesis is easily monitored by cytochemical staining with Bandeiraea simplicifolia isolectin-B(4), a lectin that specifically binds to the α-Gal epitope, and by RT-PCR analysis. Cytoplasmic microinjection of double-stranded RNA and pronuclear injection of an siRNA expression vector into the embryos generated in vitro resulted in a significant reduction in expression of the α-GalT gene and α-Gal epitope in blastocysts, at which stage the α-Gal epitope is abundantly expressed. Somatic cell nuclear transfer of embryonic fibroblasts stably transfected with an siRNA expression vector also led to a significant reduction in the level of α-GalT mRNA synthesis together with decreased amounts of the α-Gal epitope at the blastocyst stage. These results indicate that the RNAi technology is useful for efficient suppression of a target gene expression during embryogenesis in pigs and suggest the possibility of production of siRNA-expressing pigs for use in xenotransplantation.

[An update on the development of transgenic animal technology]

The animal transgenic technology has increasingly turned mature over several decades and promoted the research of transgenic technology to a new developmental phase. In this review, various kinds of transgenic technologies, including somatic cell nuclear transfer, gene transfer mediated by transposon, gene knockout mediated by RNA interference, and zinc-finger nucleases-gene targeting technology, are summarized. Recently, the success of induced pluripotent stem cells (iPS cells), which has provided an alternative way to derive pluripotent stem cells of large animals, will extend the field of transgenic animal studies. Here, we summarized the latest trends on the basis of previous studies. In addition, the characteristics of different kinds of transgenic methods in detail are discussed.

Regulation of mucosal mast cell activation by short interfering RNAs targeting syntaxin4

Mucosal mast cells (MMCs) have an important role in allergic inflammation, and effective antagonists are required for their regulation. To discover a possible mechanism of controlling the activation of MMCs, we investigated the expression and function of syntaxin4, one of the soluble membrane N-ethylmaleimide-sensitive factor attachment protein receptor (SNARE) proteins, in RBL-2H3 cells, which is a rat mucosal mast cell line. Syntaxin4 silencing was induced by transfection of short interfering RNAs (siRNAs). Syntaxin4 was knocked down in mast cells at both the mRNA and protein levels. The release of granule contents that are involved in inflammation, such as histamine and hexosaminidase, was significantly suppressed by the gene silencing of syntaxin4. Silencing of this gene was also induced in the trachea and bronchi of rats by intratracheal application of the siRNAs using an atelocollagen delivery system. The activation of MMCs, which was monitored by the level of rat mast cell protease-II (RMCPII) in the bronchoalveolar lavage fluid (BALF), was inhibited, and asthmatic airway constriction was prevented by administration of the syntaxin/atelocollagen complex. These results indicate that siRNAs targeting syntaxin4 can stabilize mucosal mast cells and may have beneficial therapeutic effects on the asthmatic response.

Aldose reductase deficiency protects sugar-induced lens opacification in rats

Aldose reductase (AKR1B1), which catalyzes the reduction of glucose to sorbitol and lipid aldehydes to lipid alcohols, has been shown to be involved in secondary diabetic complications including cataractogenesis. Rats have high levels of AKR1B1 in lenses and readily develop diabetic cataracts, whereas mice have very low levels of AKR1B1 in their lenses and are not susceptible to hyperglycemic cataracts. Studies with transgenic mice that over-express AKR1B1 indicate that it is the key protein for the development of diabetic complications including diabetic cataract. However, no such studies were performed in genetically altered AKR1B1 rats. Hence, we developed siRNA-based AKR1B1 knockdown rats (ARKO) using the AKR1B1-siRNA-pSuper vector construct. Genotyping analysis suggested that more than 90% of AKR1B1 was knocked down in the littermates. Interestingly, all the male animals were born dead and only 3 female rats survived. Furthermore, all 3 female animals were not able to give birth to F1 generation. Hence, we could not establish an AKR1B1 rat knockdown colony. However, we examined the effect of AKR1B1 knockdown on sugar-induced lens opacification in ex vivo. Our results indicate that rat lenses obtained from AKR1B1 knockdown rats were resistant to high glucose-induced lens opacification as compared to wild-type (WT) rat lenses. Biochemical analysis of lens homogenates showed that the AKR1B1 activity and sorbitol levels were significantly lower in sugar-treated AKR1B1 knockdown rat lenses as compared to WT rat lenses treated with 50mM glucose. Our results thus confirmed the significance of AKR1B1 in the mediation of sugar-induced lens opacification and indicate the use of AKR1B1 inhibitors in the prevention of cataractogenesis.

FGF4-dependent stem cells derived from rat blastocysts differentiate along the trophoblast lineage

Differentiated trophoblast cell lineages arise from trophoblast stem (TS) cells. To date such a stem cell population has only been established in the mouse. The objective of this investigation was to establish TS cell populations from rat blastocysts. Blastocysts were cultured individually on a feeder layer of rat embryonic fibroblasts (REFs) in fibroblast growth factor-4 (FGF4) and heparin supplemented culture medium. Once cell colonies were established REF feeder layers could be replaced with REF conditioned medium. The blastocyst-derived cell lines, in either proliferative or differentiated states, did not express genes indicative of ICM-derived tissues. In the proliferative state the cells expressed established stem cell-associated markers of TS cells. Cells ceased proliferation and differentiated when FGF4, heparin, and REF conditioned medium were removed. Differentiation was characterized by a decline of stem cell-associated marker gene expression, the appearance of large polyploid cells (trophoblast giant cells), and the expression of trophoblast differentiation-associated genes. Collectively, the data indicate that the rat blastocyst-derived cell lines not only possess many features characteristic of mouse TS cells but also possess some distinct properties. These rat TS cell lines represent valuable new in vitro models for analyses of mechanisms controlling TS cell renewal and differentiation.

Combination of the somatic cell nuclear transfer method and RNAi technology for the production of a prion gene-knockdown calf using plasmid vectors harboring the U6 or tRNA promoter

By combining RNAi technology with SCNT method, we attempted to produce transgenic calves with knocked down bPRNP for technological assessments. The respective utilities of type II (tRNA) and type III (hU6) Pol III promoters in mediating plasmid vector-based RNAi for the production of a bPRNP-knockdown calf were compared. Plasmid harboring DNA for siRNA expression was introduced stably into the genome of primary cultured bovine cells. By inserting the transgenic cell into an enucleated bovine egg, SCNT embryos were produced. The ability for SCNT embryos to develop to blastocysts was higher in hU6 based vector groups (44-53%) than in a tRNA group (32%). In all, 30 hU6-embryos and 12 tRNA-embryos were transferred to 11 recipients. Only tRNA-embryos were able to impregnate recipients (6 out of 11 transfers), resulting in four aborted fetuses, one stillbirth, and one live-born calf. The expression of EGFP, a marker, was detected in all six. The bPRNP transcript levels in the nervous tissues (brain, cerebellum, spinal bulb, and spinal cord) from the calf, which was killed 20 days after birth, were reduced to 35% of those of the control calf on average, as determined by qRT-PCR. The PrPC levels, as estimated by western blot were reduced to 86% on average in the nervous tissues. These findings suggest that SCNT technology remains immature, that the tRNA promoter is useful, and that RNAi can significantly reduce PRNP mRNA levels, but insufficient reduction of PrPC levels exists in cattle under these conditions.

Stable suppression of gene expression by short interfering RNAs targeted to promoter in a mouse embryonal carcinoma stem cell line

RNA interference (RNAi) can induce gene silencing via two pathways: post-transcriptional gene silencing (PTGS) and transcriptional gene silencing (TGS). The mediators of gene inactivation in both pathways are 21-bp small interfering RNAs (siRNAs) generated from longer double-stranded RNA (dsRNA). PTGS involves siRNA-mediated targeting and degradation of mRNA. However, siRNAs induce TGS via DNA methylation at the targeted promoter. Synthetic siRNAs can induce loss of gene activity comparable to long dsRNA. The limitation of this method is that the transfected synthetic siRNA works for only a few days. In this study, we tested the RNAi response to siRNA (PTGS pathway) by using a plasmid containing an enhanced green fluorescent protein (eGFP) gene as a target as well as a plasmid creates siRNA transcript, in a form of a hairpin, against eGFP gene. To investigate TGS pathway via RNAi, we also used a plasmid creates hairpin siRNA transcript against pgk-1 promoter. The data presented here indicated long-lasting inhibition in expression of eGFP and puromycin genes, both under the control of the murine Pgk-1 promoter. However, Southern blot analysis showed no methylation in pgk-1 promoter.

Conditional RNAi in mice

RNA interference (RNAi)-mediated gene knockdown has developed into a routine method to assess gene function in cultured mammalian cells in a fast and easy manner. For the use of RNAi in mice, short hairpin (sh) RNAs expressed stably from the genome are a fast alternative to conventional knockout approaches. We developed a strategy for complete or conditional gene knockdown in mice, where the Cre/loxP system is used to activate RNAi in a time and tissue dependent manner. Alternatively doxycycline controlled shRNA expression vectors can be used for conditional gene silencing. Single copy RNAi constructs are placed into the Rosa26 locus of ES cells by recombinase mediated cassette exchange and transmitted through the germline of chimeric mice. The shRNA transgenic offspring can be either directly used for phenotypic analysis or are further crossed to a Cre transgenic strain to activate conditional shRNA vectors. The site specific insertion of single copy shRNA vectors allows the expedite and reproducible production of knockdown mice and provides an easy and fast approach to assess gene function in vivo.

Transplacental RNAi: deciphering gene function in the postimplantation-staged embryo

RNAi offers the opportunity to examine the role in postimplantation development of genes that cause preimplantation lethality and to create allelic series of targeted embryos. We have delivered constituitively expressed short hairpin (sh) RNAs to pregnant mice during the early postimplantation period of development and observed gene knockdown and defects that phenocopy the null embryo. We have silenced genes that have not yet been “knocked out” in the mouse (geminin and Wnt8b), those required during earlier cleavage stages of development (nanog), and genes required at implantation (Bmp4, Bmp7) singly and in combination (Bmp4 + Bmp7), and obtained unique phenotypes. We have also determined a role in postimplantation development of two transcripts identified in a differential display RT-PCR screen of genes induced in ES cells by noggin exposure, Aggf1 and an Est (GenBank AK008955). Systemic delivery of shRNAs provides a valuable approach to gene silencing in the embryo.

Interference RNA for in vivo Knock-down of gene expression or genome-wide screening using shRNA

With the lack of tools available to manipulate the rat genome, alternative technologies have been investigated to generate loss-of-function rat models by gene invalidation. The recent demonstration that RNA interference (RNAi)-mediated gene silencing occurs in rodents has opened new opportunities for rat functional genetics. In this chapter, we provide some practical guidelines for RNAi working in rat, based on the recent design and development of mice and rat Knock down models.

Genetically modified mice-successes and failures of a widely used technology

Genetically modified mice, created by random integration of a transgene into the genome or by targeted mutation of a specific gene, have proven to be extremely powerful tools for studying gene function in vivo. In this article, we give (1) a short overview of the traditional methods in mouse transgenesis and (2) a discussion of the problems with these methods, (3) more recent methods that were developed to overcome these problems, and (4) an outlook on future directions in gene targeting.

Small interfering RNA targeting heme oxygenase-1 (HO-1) reinforces liver apoptosis induced by ischemia-reperfusion injury in mice: HO-1 is necessary for cytoprotection

We have shown that overexpression of heme oxygenase-1 (HO-1) prevents the liver inflammation response leading to ischemia and reperfusion injury (IRI). This study was designed to explore the precise function and mechanism of HO-1 cytoprotection in liver IRI by employing a small interfering RNA (siRNA) that effectively suppresses HO-1 expression both in vitro and in vivo. Using a partial lobar liver warm ischemia model, mice were injected with HO-1 siRNA/nonspecific control siRNA or Ad-HO-1/Ad-beta-gal. Those treated with HO-1 siRNA showed increased serum glutamic-oxaloacetic transaminase levels, significant liver edema, sinusoidal congestion/cytoplasmic vacuolization, and severe hepatocellular necrosis. In contrast, Ad-HO-1-pretreated animals revealed only minimal sinusoidal congestion without edema/vacuolization or necrosis. Administration of HO-1 siRNA significantly increased local neutrophil accumulation and the frequency of apoptotic cells. Mice treated with HO-1 siRNA were characterized by increased caspase-3 activity and reduced HO-1 expression, whereas those given Ad-HO-1 showed decreased caspase-3 activity and increased HO-1/Bcl-2/Bcl-x(L), data confirmed by use of an in vitro cell culture system. Thus, by using an siRNA approach this study confirms that HO-1 provides potent cytoprotection against hepatic IRI and regulates liver apoptosis. Indeed, siRNA provides a powerful tool with which to study gene function in a wide range of liver diseases.

Engineering the mouse genome to model human disease for drug discovery

Genetically engineered mice (GEM) have become invaluable tools for human disease modeling and drug development. Completion of the mouse genome sequence in combination with transgenesis and gene targeting in embryonal stem cells have opened up unprecedented opportunities. Advanced technologies for derivation of GEM models will be introduced and discussed.

Gene knockdown in the mouse through RNAi

RNA interference (RNAi)-mediated gene knockdown has developed into a routine method to assess gene function in cultured mammalian cells in a fast and easy manner. For the use of RNAi in mice, short hairpin (sh) RNAs expressed from transgenic vectors are a fast alternative to conventional knockout approaches. We describe our strategy to elicit body-wide, cell type-specific, or inducible gene silencing in mice by control of shRNA expression through Cre recombinase or doxycycline. For reproducible expression of shRNAs, vectors are placed into the Rosa26 locus of ES cells by recombinase-mediated cassette exchange and transmitted through the germ line of chimeric mice. The site specific insertion of single copy shRNA vectors allows to expedite and reproducible production of knockdown mice and provides a simple approach to assess gene function in vivo.

Transgenic RNAi applications in the mouse

Within the past 10 years, RNA interference has emerged as a powerful experimental tool as it allows rapid gene function analysis. Unique features such as reversibility of gene silencing and simultaneous targeting of several genes characterize the approach. In this chapter, transgenic RNAi techniques in reverse mouse genetics are discussed and protocols are provided.

U6 promoter-driven siRNA injection has nonspecific effects in zebrafish

RNA interference (RNAi) is a posttranscriptional gene silencing mechanism triggered by double-stranded RNA (dsRNA), which causes degradation of homologous mRNAs. RNAi has been observed in a wide range of eukaryotes, including fungi, plants and animals. In vertebrates, long dsRNA activates the interferon response and yields nonspecific degradation of mRNA. In contrast, small interference RNA (siRNA) duplexes with a length of 21-23 nucleotides trigger specific gene silencing and thus are widely used in gene function studies. The use of siRNA for gene silencing in zebrafish has rarely been reported. In this report, we studied mammalian U6 promoter-driven siRNA-mediated RNA interference in zebrafish. The well characterized genes Myf5, Dlg3 and Nacre were selected as targets. Two to four target siRNAs were synthesized with incorporation of the U6 promoter. Constructs were introduced into early zebrafish embryos through microinjection, followed by in situ hybridization and embryonic development was monitored to determine whether U6 promoter-driven siRNAs could efficiently suppress specific gene expression. We showed that these siRNAs could partially suppress endogenous gene expression and that the siRNA efficiency varied at different targeted positions. However, the U6 promoter-driven siRNAs may also have induced nonspecific gene suppression (off-target effects). It appears that, despite the findings of previous reports, the current methodology of siRNA interference is not practical for studying gene function during early zebrafish development.

Animal transgenesis: an overview

Transgenic animals are extensively used to study in vivo gene function as well as to model human diseases. The technology for producing transgenic animals exists for a variety of vertebrate and invertebrate species. The mouse is the most utilized organism for research in neurodegenerative diseases. The most commonly used techniques for producing transgenic mice involves either the pronuclear injection of transgenes into fertilized oocytes or embryonic stem cell-mediated gene targeting. Embryonic stem cell technology has been most often used to produce null mutants (gene knockouts) but may also be used to introduce subtle genetic modifications down to the level of making single nucleotide changes in endogenous mouse genes. Methods are also available for inducing conditional gene knockouts as well as inducible control of transgene expression. Here, we review the main strategies for introducing genetic modifications into the mouse, as well as in other vertebrate and invertebrate species. We also review a number of recent methodologies for the production of transgenic animals including retrovirus-mediated gene transfer, RNAi-mediated gene knockdown and somatic cell mutagenesis combined with nuclear transfer, methods that may be more broadly applicable to species where both pronuclear injection and ES cell technology have proven less practical.

The multicopy gene Sly represses the sex chromosomes in the male mouse germline after meiosis

Small-interfering RNAs have been used to disrupt the function of the more than 100 copies of the Sly gene on the mouse Y chromosome, leading to defective sex chromosome repression during spermatid differentiation and, as a consequence, sperm malformations and near-sterility.

Studies of mice with Y chromosome long arm deficiencies suggest that the male-specific region (MSYq) encodes information required for sperm differentiation and postmeiotic sex chromatin repression (PSCR). Several genes have been identified on MSYq, but because they are present in more than 40 copies each, their functions cannot be investigated using traditional gene targeting. Here, we generate transgenic mice producing small interfering RNAs that specifically target the transcripts of the MSYq-encoded multicopy gene Sly (Sycp3-like Y-linked). Microarray analyses performed on these Sly-deficient males and on MSYq-deficient males show a remarkable up-regulation of sex chromosome genes in spermatids. SLY protein colocalizes with the X and Y chromatin in spermatids of normal males, and Sly deficiency leads to defective repressive marks on the sex chromatin, such as reduced levels of the heterochromatin protein CBX1 and of histone H3 methylated at lysine 9. Sly-deficient mice, just like MSYq-deficient mice, have severe impairment of sperm differentiation and are near sterile. We propose that their spermiogenesis phenotype is a consequence of the change in spermatid gene expression following Sly deficiency. To our knowledge, this is the first successful targeted disruption of the function of a multicopy gene (or of any Y gene). It shows that SLY has a predominant role in PSCR, either via direct interaction with the spermatid sex chromatin or via interaction with sex chromatin protein partners. Sly deficiency is the major underlying cause of the spectrum of anomalies identified 17 y ago in MSYq-deficient males. Our results also suggest that the expansion of sex-linked spermatid-expressed genes in mouse is a consequence of the enhancement of PSCR that accompanies Sly amplification.

During meiosis in the male mouse, the X and Y chromosomes are transcriptionally silenced, and retain a significant degree of repression after meiosis. Postmeiotically, X and Y chromosome–encoded genes are consequently expressed at a low level, with the exception of genes present in many copies, which can achieve a higher level of expression. Gene amplification is a notable feature of the X and Y chromosomes, and it has been proposed that this serves to compensate for the postmeiotic repression. The long arm of the mouse Y chromosome (MSYq) has multicopy genes organized in clusters over several megabases. On the basis of analysis of mice carrying MSYq deletions, we proposed that MSYq encodes genetic information that is crucial for postmeiotic repression of the sex chromosomes and for sperm differentiation. The gene(s) responsible for these functions were, however, unknown. In this study, using transgenically delivered small interfering RNA, we disrupted the function of Sly, a gene that is present in more than 100 copies on MSYq. Sly-deficient males have major sperm differentiation problems together with a remarkable postmeiotic derepression of genes encoded on the X and Y chromosomes. Furthermore, the epigenetic modifications normally associated with sex chromosome repression are altered. Our data thus show that the SLY protein is required to mediate postmeiotic repression of the X and Y chromosomes. It is likely that the sperm differentiation problems in Sly-deficient males are largely a consequence of the derepression of the sex chromosomes in spermatids. We propose that the postmeiotic repressive effect of Sly on genes encoded on the X and Y chromosomes drove their massive amplification in the mouse.

In vivo genetic manipulation of the rat trophoblast cell lineage using lentiviral vector delivery

In this report, we have adapted a lentiviral gene delivery technique for genetic modification of the rat trophoblast cell lineage. Blastocysts were incubated with lentiviral particles and transferred into the uteri of pseudopregnant female rats, harvested at various times during gestation, and then analyzed. Two test systems were evaluated: (1) delivery of an enhanced green fluorescent protein (EGFP) gene under the control of constitutive promoters to rat blastocysts; (2) delivery of EGFP short hairpin RNA (shRNA) to rat blastocysts constitutively expressing EGFP. Lentiviral packaged gene constructs were efficiently and specifically delivered to all trophoblast cell lineages. Additionally, lentiviral mediated transfer of shRNAs was an effective strategy for modifying gene expression in trophoblast cell lineages. This technique will permit the in vivo evaluation of "gain-of-function" and "loss-of-function" manipulations in the rat trophoblast cell lineage.

An efficient method for generating transgenic mice using NaOH-treated spermatozoa

Transgenic (Tg) animals are widely used in researching the characteristics of exogenous genes. Intracytoplasmic sperm injection (ICSI)-mediated transgenesis (ICSI-Tr) has been a useful method for generating Tg animals, especially in the mouse. However, the original methods using freeze-thawed spermatozoa showed severe chromosomal damage and low offspring rates after embryo transfer. Herein, we describe an improved method to generate Tg mice efficiently using a simple pretreatment of spermatozoa with 10 mM NaOH. These spermatozoa lost their plasma membrane and tail, while still maintaining nuclear integrity. Sperm heads were mixed with 0.5-5 ng/microl of the transgene for enhanced green fluorescent protein (EGFP) for 3 min to 1 h at room temperature and were then microinjected into oocytes by ICSI. The best results were obtained when treated spermatozoa were incubated with 2 ng/microl of EGFP for 10 min; 55.6% of injected embryos developed to the blastocyst stage, and more than half (56.9%) of them displayed EGFP fluorescence. Under these conditions, 12 pups of 34 offspring were positive for the transgene after transfer at the 2-cell stage into pseudopregnant recipient mice (a high rate [10.2%] from manipulated embryos). This method was found to be suitable for hybrid and inbred strains of mouse such as C57BL/6 and 129X1/Sv. Thus, a simple sperm pretreatment with NaOH before ICSI-Tr resulted in an efficient insertion of an exogenous gene into the host genome. This method allows for easy production of Tg mice, requiring fewer oocytes for micromanipulation than classical methods.

Cholesterol-modified superporous poly(2-hydroxyethyl methacrylate) scaffolds for tissue engineering

Modifications of poly(2-hydroxyethyl methacrylate) (PHEMA) with cholesterol and laminin have been developed to design scaffolds that promote cell-surface interaction. Cholesterol-modified superporous PHEMA scaffolds have been prepared by the bulk radical copolymerization of 2-hydroxyethyl methacrylate (HEMA), cholesterol methacrylate (CHLMA) and the cross-linking agent ethylene dimethacrylate (EDMA) in the presence of ammonium oxalate crystals to introduce interconnected superpores in the matrix. With the aim of immobilizing laminin (LN), carboxyl groups were also introduced to the scaffold by the copolymerization of the above monomers with 2-[(methoxycarbonyl)methoxy]ethyl methacrylate (MCMEMA). Subsequently, the MCMEMA moiety in the resulting hydrogel was hydrolyzed to [2-(methacryloyloxy)ethoxy]acetic acid (MOEAA), and laminin was immobilized via carbodiimide and N-hydroxysulfosuccinimide chemistry. The attachment, viability and morphology of mesenchymal stem cells (MSCs) were evaluated on both nonporous and superporous laminin-modified as well as laminin-unmodified PHEMA and poly(2-hydroxyethyl methacrylate-co-cholesterol methacrylate) P(HEMA-CHLMA) hydrogels. Neat PHEMA and laminin-modified PHEMA (LN-PHEMA) scaffolds facilitated MSC attachment, but did not support cell spreading and proliferation; the viability of the attached cells decreased with time of cultivation. In contrast, MSCs spread and proliferated on P(HEMA-CHLMA) and LN-P(HEMA-CHLMA) hydrogels.

Development of CRTEIL and CETRIZ, Cre-loxP-based systems, which allow change of expression of red to green or green to red fluorescence upon transfection with a cre-expression vector

We developed Cre-loxP-based systems, termed CRTEIL and CETRIZ, which allow gene switching in a noninvasive manner. Single transfection with pCRTEIL resulted in predominant expression of red fluorescence. Cotransfection with pCRTEIL and Cre-expression plasmid (pCAG/NCre) caused switching from red to green fluorescence. Similarly, cotransfection with pCETRIZ and pCAG/NCre resulted in change of green to red fluorescence. These noninvasive systems will be useful in cell lineage analysis, since descendants of cells exhibiting newly activated gene expression can be continuously monitored in noninvasive fashion.