Impact of embryonic expression of enhanced green fluorescent protein on early mouse development

Low-temperature tolerances of tropical fish with potential transgenic applications in relation to winter water temperatures in Canada

Application of fluorescent protein transgenes in tropical freshwater fish is used in research (e.g., in zebrafish) and in the commercial ornamental aquarium trade. To assess the overwinter potential of such fish in Canada, we examined the minimum temperature tolerance of three wild-type species (zebrafish, Danio rerio (Hamilton, 1822); black tetra, Gymnocorymbus ternetzi (Boulenger, 1895); tiger barb, Puntius tetrazona (Bleeker, 1855)) used as fluorescent models in the aquarium trade, as well as four lines of green fluorescent protein (GFP) transgenic and wild-type zebrafish used in research. Both tetra and barb had lower temperature tolerance limits that were higher than surveyed winter temperatures in Canada, and the lower tolerance limits of zebrafish lines was only within the range of a few surveyed lakes in some years. One line of GFP zebrafish had a lower temperature tolerance limit that was significantly higher than those of other lines, suggesting that some fluorescent transgene constructs may alter tolerance to extreme temperatures. When lines of zebrafish were reared at 8, 10, or 28 °C for 4 months, all lines were capable of producing viable embryos after cold rearing. These results indicate that tropical transgenic fish models used in research and in the aquarium trade are not expected to persist over winter in Canadian water systems.

An improved Akt reporter reveals intra- and inter-cellular heterogeneity and oscillations in signal transduction

Akt is a key node in a range of signal transduction cascades and play a critical role in diseases such as cancer and diabetes. Fluorescently-tagged Akt reporters have been used to discern Akt localisation, yet it has not been clear how well these tools recapitulate the behaviour of endogenous Akt proteins. Here, we observed that fusion of eGFP to Akt2 impaired both its insulin-stimulated plasma membrane recruitment and its phosphorylation. Endogenous-like responses were restored by replacing eGFP with TagRFP-T. The improved response magnitude and sensitivity afforded by TagRFP-T-Akt2 over eGFP-Akt2 enabled monitoring of signalling outcomes in single cells at physiological doses of insulin with subcellular resolution and revealed two previously unreported features of Akt biology. In 3T3-L1 adipocytes, stimulation with insulin resulted in recruitment of Akt2 to the plasma membrane in a polarised fashion. Additionally, we observed oscillations in plasma membrane localised Akt2 in the presence of insulin with a consistent periodicity of 2 min. Our studies highlight the importance of fluorophore choice when generating reporter constructs and shed light on new Akt signalling responses that may encode complex signalling information.This article has an associated First Person interview with the first author of the paper.

Non-destructive monitoring of mouse embryo development and its qualitative evaluation at the molecular level using Raman spectroscopy

Current research focuses on embryonic development and quality not only by considering fundamental biology, but also by aiming to improve assisted reproduction technologies, such as in vitro fertilization. In this study, we explored the development of mouse embryo and its quality based on molecular information, obtained nondestructively using Raman spectroscopy. The detailed analysis of Raman spectra measured in situ during embryonic development revealed a temporary increase in protein content after fertilization. Proteins with a β-sheet structure—present in the early stages of embryonic development—are derived from maternal oocytes, while α-helical proteins are additionally generated by switching on a gene after fertilization. The transition from maternal to embryonic control during development can be non-destructively profiled, thus facilitating the in situ assessment of structural changes and component variation in proteins generated by metabolic activity. Furthermore, it was indicated that embryos with low-grade morphology had high concentrations of lipids and hydroxyapatite. This technique could be used for embryo quality testing in the future.

Aromatase-null mice expressing enhanced green fluorescent protein in germ cells provide a model system to assess estrogen-dependent ovulatory responses

Enhanced green fluorescent protein (EGFP) has provided us with valuable approaches for tracking living cells. We established a novel line of transgenic mice, which express EGFP in the testis and ovary. Histological analysis demonstrated that spermatids in the testis and oocytes in ovarian follicles beyond preantral stages were positive for EGFP. By exploiting these features, we evaluated ovulatory responses of aromatase-gene (Cyp19a) knockout mouse expressing the EGFP transgene, which is totally anovulatory due to 17β-estradiol (E2) deficiency. Ovulation in the knockout mice was induced by sequential injections of E2 on days 1, 4 and 5, pregnant mare serum gonadotropin on day 4 and human chorionic gonadotropin on day 6. Fluorescent oocytes were readily detectable at 15 h after the last gonadotropin injection in the oviduct under a fluorescence stereomicroscope, even when only one oocyte was present. However, when E2 supplementation on day 4 or day 5 in the regimen was omitted, no ovulated oocytes were detected, indicating that exogenous E2 supplementation at the time of gonadotropin stimulation is necessary to induce ovulation in aromatase-gene knockout mice. Our results further demonstrated that the current mouse line can provide an alternative tool to study germ cell biology, including oogenesis, ovulation and senescence.

Characterization of stable fluorescent transgenic marine medaka (Oryzias dancena) lines carrying red fluorescent protein gene driven by myosin light chain 2 promoter

Stable transgenic germlines carrying the red fluorescence protein (RFP) gene (rfp) driven by fast skeletal myosin light chain-2 gene (mlc2f) promoter were established in a truly euryhaline fish species, the marine medaka (Oryzias dancena; Beloniformes). Transgenic lines contained transgene copy numbers varying from a single copy to more than 230 copies per genome. Although the transgenic founders displayed mosaic and/or ectopic expression of the RFP signal, the resultant F1 transgenics and their progeny showed consistently stable transmission of the transgenic locus and uniform RFP signal through several subsequent generations. In adult transgenics, an authentic brilliant red fluorescence was achieved over the skeletal muscles of the transgenic individuals, which might be sufficient for ornamental display. Expression analysis of the transgenic mRNAs indicated that rfp transcripts were predominantly expressed in the skeletal muscles. Different transgenic lines displayed different levels of transgene expression at the mRNA, protein, and phenotypic levels. However, the efficiency of transgene expression was independent of the transgene copy number. The RFP protein levels were consistently stable in the transgenic fish muscles through several generations, up to F5. The results of this study suggest that transgenic marine medaka that acquire strong fluorescent signals in their skeletal muscles can be developed as a promising, novel ornamental fish for display in both freshwater and seawater aquaria.

Long-term live-cell imaging of mammalian preimplantation development and derivation process of pluripotent stem cells from the embryos

Mammalian fertilization is a process in which two highly specialized haploid gametes unite and endow totipotency to the resulting diploid zygote. This is followed by cell proliferation and the onset of differentiation during the brief period leading up to implantation. In these processes, a number of cellular components and structures are regulated spatially and temporally, as seen in repeated cell division, cell cycle progression, and epigenetic reprogramming. In mammals, the numbers of oocytes and embryos that can be collected are very limited. Therefore, analyses of molecular mechanisms are hampered because of difficulties in conducting biochemical analyses on such limited material. Furthermore, immunostaining methods require cell fixation and are insufficient for understanding ontogeny, because the processes observed in fertilization and early embryonic development progress in time-dependent manners and each phenomenon is connected with others by cause-and-effect relationships. Consequently, it is important to develop an experimental system that enables molecular imaging without affecting embryonic development. To achieve the above advantages, especially retrospective and prospective analyses, we have established a live-cell imaging system that enables observations under minimally invasive conditions. Using this approach, we have succeeded in visualizing and predicting the developmental potential of embryos after various perturbations. We also succeeded in imaging embryonic stem (ES) cell derivation in natural conditions. In this review, we describe a brief history of embryonic imaging and detailed protocols. We also discuss promising aspects of imaging in the fields of developmental and stem cell biology.

Green fluorescent protein alters the transcriptional regulation of human mitochondrial genes after gamma irradiation

Green fluorescent proteins (GFP), extensively used as reporters in biological and imaging studies, are assumed to be mostly biologically inert. Here, we test the assumption in regard to the transcriptional regulation of 18 mitochondrially encoded genes in GFP expressing human T-cell line (JURKAT cells) exposed to gamma radiation. Using quantitative polymerase chain reaction, we demonstrate that wild type and GFP expressing JURKAT cells have different baseline mitochondrial transcript expression (10 out of the 18 tested genes) and after a single dose of radiation (100 Gy) show a significantly different transcriptional regulation of their mitochondrial genes. While in wild type cells, ten of the tested genes are up-regulated in response to radiation exposure, GFP expressing cells show less transcriptional regulation with a small down-regulation in five genes. Our results indicate that the presence of GFP in the cytoplasm can alter the cellular response to ionizing radiation.

Functional ability of cytoskeletal β-actin regulator to drive constitutive and ubiquitous expression of a fluorescent reporter throughout the life cycle of transgenic marine medaka Oryzias dancena

Marine medaka Oryzias dancena, a candidate model organism, represents many attractive merits as a material for experimental transgenesis and/or heterologous expression assay particularly in the field of ecotoxicology and developmental biology. In this study, cytoskeletal β-actin gene was characterized from O. dancena and the functional capability of its promoter to drive constitutive expression of foreign reporter protein was evaluated. The O. dancena β-actin gene possessed a conserved genomic organization of vertebrate major cytoplasmic actin genes and the bioinformatic analysis of its 5'-upstream regulatory region predicted various transcription factor binding motifs. Heterologous expression assay using a red fluorescent protein (RFP) reporter construct driven by the O. dancena β-actin regulator resulted in stunningly bright expression of red fluorescence signals in not only microinjected embryos but also grown-up transgenic adults. Although founder transgenics exhibited mosaic patterns of RFP expression, transgenic offspring in subsequent generations displayed a vivid and uniform expression of RFP continually from embryos to adults. Based on the blot hybridization assays, two transgenic lines established in this study were proven to possess high copy numbers of transgene integrants (approximately 240 and 34 copies, respectively), and the transgenic genotype in both lines could successfully be passed stably up to three generations, although the rate of transgene transmission in one of the two transgenic lines was significantly lower than expected Mendelian ratio. Significant red fluorescence color could be ubiquitously observable in all the tissues or organs of the transgenics. Quantitative real-time RT-PCR represented that the expression pattern of transgene under the regulation of β-actin promoter would resemble, in overall, the regulation of endogenous β-actin gene in adult tissues, although putative mechanism for competitive or independent regulation between transgene and endogenous gene could also be found in several tissues. Results from this study undoubtedly indicate that the O. dancena β-actin promoter would be powerful enough to fluorescently visualize most cell types in vivo throughout its whole lifespan. This study could be a useful start point for a variety of transgenic experiments with this species concerning the constitutive expression of living fluorescent color reporters and other foreign proteins.

Effect of fluorescent mercury light irradiation on in vitro and in vivo development of mouse oocytes after parthenogenetic activation or sperm microinjection

The detection of specific cellular components using fluorescent agents such as green fluorescent protein (GFP), red fluorescent protein or Hoechst dyes provides a powerful tool for studying cell biology. However, specimens must be exposed to high-intensity light, which might cause cellular damage. Here, we exposed mouse metaphase stage (M) II oocytes to fluorescent mercury vapor light at three wavelengths (539 nm, 488 nm and 341 nm) to determine the maximum exposure time that would avoid damage. When oocytes were activated parthenogenetically after exposure to these wavelengths for more than 20 min, 5 min or 4 sec, respectively, the percentages of dead oocytes after activation increased, and none of the surviving embryos developed to blastocysts. However, embryos fertilized by intracytoplasmic sperm injection (ICSI) were more tolerant to light damage, even though the quality of blastocysts, judged by cell number and cell allocation to the inner cell mass and trophectoderm measured by immunostaining for Oct4 and Cdx2, was reduced as exposure times increased. Live, healthy offspring were obtained when these exposed embryos were transferred into recipient pseudopregnant females at the 2-cell stage. In addition, MII oocytes collected from GFP-expressing transgenic mice after 5 min of irradiation with 488-nm light were also able to develop to full term following ICSI. Thus, we determined the safe period of exposure to several wavelengths for oocyte manipulation or observation that would permit subsequent development.

Understanding paternal genome demethylation through live-cell imaging and siRNA

Identification of a DNA demethylase responsible for zygotic paternal DNA demethylation has been one of the most challenging goals in the field of epigenetics. Several candidate molecules have been proposed, but their involvement in the demethylation remains controversial, partly due to the difficulty of preparing a sufficient quantity of materials for biochemical analysis. In this review, we utilize a recently developed method for live-cell imaging of mouse zygotes combined with RNA interference (RNAi) to search for factors that affect zygotic paternal DNA demethylation. The combined use of various fluorescent probes and RNAi is a useful approach for the study of not only DNA demethylation but also the spatiotemporal dynamics of histone depositions in zygotes, although it is not appropriate for large-scale screening or knockdown of genes that are abundantly expressed before fertilization. This new technique enables us to understand the epigenetic hierarchy during cellular response and differentiation in preimplantation embryos.

Liver fatty acid-binding protein and obesity

While low levels of unesterified long chain fatty acids (LCFAs) are normal metabolic intermediates of dietary and endogenous fat, LCFAs are also potent regulators of key receptors/enzymes and at high levels become toxic detergents within the cell. Elevated levels of LCFAs are associated with diabetes, obesity and metabolic syndrome. Consequently, mammals evolved fatty acid-binding proteins (FABPs) that bind/sequester these potentially toxic free fatty acids in the cytosol and present them for rapid removal in oxidative (mitochondria, peroxisomes) or storage (endoplasmic reticulum, lipid droplets) organelles. Mammals have a large (15-member) family of FABPs with multiple members occurring within a single cell type. The first described FABP, liver-FABP (L-FABP or FABP1), is expressed in very high levels (2-5% of cytosolic protein) in liver as well as in intestine and kidney. Since L-FABP facilitates uptake and metabolism of LCFAs in vitro and in cultured cells, it was expected that abnormal function or loss of L-FABP would reduce hepatic LCFA uptake/oxidation and thereby increase LCFAs available for oxidation in muscle and/or storage in adipose. This prediction was confirmed in vitro with isolated liver slices and cultured primary hepatocytes from L-FABP gene-ablated mice. Despite unaltered food consumption when fed a control diet ad libitum, the L-FABP null mice exhibited age- and sex-dependent weight gain and increased fat tissue mass. The obese phenotype was exacerbated in L-FABP null mice pair fed a high-fat diet. Taken together with other findings, these data suggest that L-FABP could have an important role in preventing age- or diet-induced obesity.

DNA methylation profiling using live-cell imaging

Changes in DNA methylation status at specific gene loci are key epigenetic modifications, which regulate corresponding gene expression patterns. During embryogenesis, de novo methylation takes place in particular genes and this is thought to be associated with cellular differentiation. In contrast, genome-wide changes in DNA methylation are known to occur at particular developmental stages, such as global DNA demethylation during preimplantation development and germ cell formation. These alterations are considered to be the erasure of epigenetic memory or genomic reprogramming. Conventionally, immunostaining using an antibody against 5'-methylcytosine has been performed to analyze global DNA methylation status in situ. We developed a live-cell imaging technique that allows the capture of long-term dynamic changes in DNA methylation three-dimensionally. This technique consists of the construction of a fluorescent probe that can bind specifically to methylated DNA using human methyl-CpG binding domain protein 1, expression of the probe in the cell and prolonged three-dimensional imaging. Using this technique, we were able to observe time-dependent changes in DNA methylation status in living preimplantation mouse embryos. Other groups have used this approach to analyze the drastic differentiation of embryonic stem cells. In this review, I describe the theoretical basis of this imaging and discuss its usefulness and potential for studies on epigenetic regulation, especially in early mammalian development.

Green fluorescent protein as indicator of nonviral transient transfection efficiency in endometrial and testicular biopsies

In the last years, physical and chemical methods of plasmid delivery have revolutionized the efficiency of nonviral gene transfer, and the success of gene therapy is largely dependent upon the development of gene-delivery methods. The nonviral techniques that lead to a direct transfer of DNA into tissue fragments, like electroporation (EP) and lipofection delivery systems are still insufficiently investigated. Our aim was to test the efficiency of EP and lipofection protocols in endometrial and testicular tissue fragments, using a naked plasmid DNA encoding green fluorescent protein (GFP). Because the transfection efficiency depends upon several factors, we tried to optimize the transfection conditions by testing different lipofectamine 2000 and plasmid ratios, electrical parameters, and culture after transfection. Our results show that these two nonviral methods of gene delivery are feasible and efficient in gene transfection of endometrial and testicular tissue biopsies. We found that the most performing ratio of plasmid:lipofectamine was 10:50 for transient lipofection, whereas two pulses for 10 s at 960 microF of capacitance, 200 V of voltage were the most favorable electrical parameters for EP efficiency in the presence of 5 microL of phMGFP plasmid. After lipofection and EP, the highest GFP intensity was observed respectively after 48 and 72 h of tissue fragment culturing. In conclusion, nonviral methods are attractive for an improvement of the gene therapy and our protocol could provide useful indications for in vivo gene therapy applications.

Elevated expression of MeCP2 in cardiac and skeletal tissues is detrimental for normal development

MeCP2 plays a critical role in interpreting epigenetic signatures that command chromatin conformation and regulation of gene transcription. In spite of MeCP2's ubiquitous expression, its functions have always been considered in the context of brain physiology. In this study, we demonstrate that alterations of the normal pattern of expression of MeCP2 in cardiac and skeletal tissues are detrimental for normal development. Overexpression of MeCP2 in the mouse heart leads to embryonic lethality with cardiac septum hypertrophy and dysregulated expression of MeCP2 in skeletal tissue produces severe malformations. We further show that MeCP2's expression in the heart is developmentally regulated; further suggesting that it plays a key role in regulating transcriptional programs in non-neural tissues.

Hepatic phenotype of liver fatty acid binding protein gene-ablated mice

Although the function of liver fatty acid binding protein in hepatic fatty acid metabolism has been extensively studied, its potential role in hepatic cholesterol homeostasis is less clear. Although hepatic cholesterol accumulation was initially reported in L-FABP-null female mice, that study was performed with early N2 backcross generation mice. To resolve whether the hepatic cholesterol phenotype in these L-FABP(-/-) mice was attributable to genetic inhomogeneity, these L-FABP(-/-) mice were further backcrossed to C57Bl/6 mice up to the N10 (99.9% homogeneity) generation. Hepatic total cholesterol accumulation was observed in female, but not male, L-FABP(-/-) mice at all (N2, N4, N6, N10) backcross generations examined. The greater total cholesterol was due to increased hepatic levels of both unesterified (free) cholesterol and esterified cholesterol. Altered hepatic cholesterol accumulation correlated directly with L-FABP's ability to bind cholesterol with high affinity as shown by direct L-FABP binding of fluorescent cholesterol analogs (NBD-cholesterol, dansyl-cholesterol), a photoactivatable cholesterol analog [free cholesterol benzophenone (FCBP)], and free cholesterol (circular dichroism, isothermal titration microcalorimetry). One mole of fluorescent sterol was bound per mole of L-FABP. This was confirmed by photo-cross-linking studies with the photoactivatable cholesterol analog FCBP and by isothermal titration calorimetry with free cholesterol, which showed that L-FABP bound only one sterol molecule per L-FABP molecule. In contrast, the hepatic phenotype of male, but not female, L-FABP(-/-) mice was characterized by decreased hepatic triacylglycerol levels at all backcross generations examined. Taken together, these data support the hypothesis that L-FABP plays a role in physiological regulation of not only hepatic fatty acid metabolism, but also that of hepatic cholesterol.

Development of cloned embryos from porcine neural stem cells and amniotic fluid-derived stem cells transfected with enhanced green fluorescence protein gene

We assessed the developmental ability of embryos cloned from porcine neural stem (NS) cells, amniotic fluid-derived stem (AFS) cells, fetal fibroblast cells, adult fibroblast, and mammary gland epithelial cells. The five cell lines were transfected with enhanced green fluorescence protein gene respectively using lipofection. NS and AFS cells were induced to differentiate in vitro. Stem cells and their differentiated cells were harvested for analysis of the markers using RT-PCR. The five cell lines were used for nuclear transfer. The two-cell stage-cloned embryos derived from each cell line were transferred into the oviducts of surrogate mothers. The results showed that both NS and AFS cells expressed POU5F1, THY1 and SOX2, and they were both induced to differentiate into astrocyte (GFAP+), oligodendrocyte (GalC+), neuron (NF+, ENO2+, and MAP2+), adipocyte (LPL+ and PPARG-D+), osteoblast (osteonectin+ and osteocalcin+), myocyte (MYF6+ and MYOD+), and endothelium (PECAM1+, CD34+, CDH5+, and NOS3+) respectively. Seven cloned fetuses (28 days and 32 days) derived from stem cells were obtained. The in vitro developmental ability (morula-blastocyst rate was 28.26-30.07%) and in vivo developmental ability (pregnancy rate were 1.67-2.17%) of the embryos cloned from stem cells were higher (P<0.05) than that of the embryos cloned from somatic cells (morula-blastocyst rate was 16.27-19.28% and pregnancy rate was 0.00%), which suggests that the undifferentiated state of the donor cells increases cloning efficiency.

Lentiviral transfection of ependymal primary cultures facilitates the characterisation of kinocilia-specific promoters

Ependymal primary cultures (EPCs) are an established model for studying ependymal cell biochemistry and the biology of kinocilia-bearing cells. However, the difficulty in causing them to express transgenes at high efficiency has been an important drawback of the system. Indeed plasmid-based transfection attempts remain at an efficiency below 1% and fail to elicit reporter gene expression, namely green fluorescent protein (GFP) synthesis, in any of the kinocilia-bearing cells of the cultures. Human immunodeficiency virus pseudotyped with the vesicular stomatitis virus envelope glycoprotein (HIV/VSV-G) and encoding GFP under the control of the ubiquitously recognised promoter of elongation factor 1 alpha (EF1alpha) also does not cause transgene expression in the kinocilia-bearing cells of an EPC when applied at multiplicities of infection (MOIs) of up to 40 and destroys the culture when the MOI is increased further. In contrast, HIV/VSV-G encoding GFP under the control of a promoter specifically active in kinocilia-bearing cells leads to transgene expression in up to 79% of the kinociliated cells of an EPC when applied at an MOI of 20. This has permitted the initial characterisation of the promoter for the gene specifically transcribed in kinocilia-bearing cells, wdr16. The results have identified two regions of 100 nucleotides length each, which are critical for promoter activity and contain putative binding sites for the transcription factors Foxd1, Sox17 and Spz1. It appears that wdr16 is controlled by a bidirectional promoter also responsible for regulating the syntaxin 8 gene.

Expression of EGFP and NPTII protein is not associated with organ abnormalities in deceased transgenic cloned cattle

Both enhanced green fluorescence protein (EGFP) and neomycin phosphotransferase type II enzyme (NPTII) are widely used in transgenic studies, but their side effects have not been extensively investigated. In this study, we evaluated the expression profiles of the two marker genes and the relationship between their expression and organ abnormalities. Eight transgenic cloned cattle were studied, four harboring both EGFP and NPTII, and four harboring only the NPTII gene. Four age-matched cloned cattle were used as controls. EGFP and NPTII expression were measured and detected by Q-PCR, Western blot, ELISA, and RIA in heart, liver, and lungs, and the values ranged from 0.3 to 5 microg/g. The expression profiles exhibited differential or mosaic pattern between the organs, the pathologic symptoms of which were identified, but were similar to those of age-matched cloned cattle. All data indicated that the expression of EGFP and NPTII is not associated with organ abnormalities in transgenic cloned cattle.

[Exogenous DNA influencing fertilization of goat sperm cells and expression in early embryos]

Our early study found that goat spermatozoa could spontaneously take up foreign DNA and vary in capabilities of spermatozoa from different donors to bind and internalize exogenous DNA. In this study, three goats with considerable differences of capability were used to investigate the effect of exogenous DNA on goat spermatozoa, and feasibility and efficiency of transgenic embryo production by sperm-mediated gene transfer method. The viability, acrosomal reaction frequencies and cleavages were decreased in the groups co-cultured with exogenous DNA, compared with the control groups, and the range of decrease was correlated with the capability of sperm cells up-take foreign DNA. After fertilizing with co-cultured spermatozoa, GFP gene was introduced into oocytes and expressed in early embryos. However, different efficiencies of transgenic embryos appeared in sperm donors (P<0.05). GFP gene was detected in 16.2% (25/154), 5.3% (4/76), and 0% (0/36) embryos, respectively, when high, middle and low capability of sperm donors were used. But only 6.5% (10/154) embryos from high capability sperm donor expressed GFP. Our results demonstrate that selecting high capability of sperm donor is a key step for improving efficiency of sperm mediated-gene transfer method. However, the adverse influence of foreign DNA on spermatozoa needs to be further studied.

Localization of green fluorescent protein in mouse preimplantation embryos

The localization of enhanced green fluorescent protein (EGFP) was studied in preimplantation embryos obtained from reciprocal mating of hemizygous C57Bl/6-Tgn (ACTbEGFP)1Osb/J mice with C57Bl/6 mice. Specific fluorescence of EGFP was observed in all oocytes and embryos obtained from transgenic females during all preimplantation stages and in embryos inheriting the EGFP gene from transgenic males starting from the 8 blastomere stage during the compactization period. EGFP mRNA or EGFP synthesized during oogenesis can be retained in embryos during the entire preimplantation period, while expression of EGFP gene transferred from the father coincides with the onset of compactization. The possibility of using these embryos in experimental mammalian embryology is discussed.

Isolation of progenitor cells from GFP-transgenic pigs and transplantation to the retina of allorecipients

Work in rodents has demonstrated that progenitor transplantation can achieve limited photoreceptor replacement in the mammalian retina; however, replication of these findings on a clinically relevant scale requires a large animal model. To evaluate the ability of porcine retinal progenitor cells to survival as allografts and integrate into the host retinal architecture, we isolated donor cells from fetal green fluorescent protein (GFP)-transgenic pigs. Cultures were propagated from the brain, retina, and corneo-scleral limbus. GFP expression rapidly increased with time in culture, although lower in conjunction with photoreceptor markers and glial fibrillary acid protein (GFAP), thus suggesting downregulation of GFP during differentiation. Following transplantation, GFP expression allowed histological visualization of integrated cells and extension of fine processes to adjacent plexiform layers. GFP expression in subretinal grafts was high in cells expressing vimentin and lower in cells expressing photoreceptor markers, again consistent with possible downregulation during differentiation. Cells survived transplantation to the injured retina of allorecipients at all time points examined (up to 10 weeks) in the absence of exogenous immune suppression without indications of rejection. These findings demonstrate the feasibility of allogeneic progenitor transplantation in a large mammal and the utility of the pig in ocular regeneration studies.

Development of porcine transgenic nuclear-transferred embryos derived from fibroblast cells transfected by the novel technique of nucleofection or standard lipofection

The aim of our study was to determine the in vitro developmental potential of porcine nuclear-transferred (NT) embryos that had been reconstructed with Tg(pWAPhGH-GFPBsd) transgene-expressing fibroblast cells. The gene construct was introduced into fibroblast cells by the novel method of nucleofection or standard lipofection. NT oocytes derived from foetal and adult dermal fibroblast cells were stimulated by either simultaneous fusion and electrical activation (Groups IA and IB) or sequential electrical and chemical activation (Groups IIA and IIB). The percentages of cloned embryos that reached the morula and blastocyst stages were 152/254 (59.8%) and 77/254 (30.3%) or 139/276 (50.4%) and 45/276 (16.3%) in Groups IA or IB, respectively. The rates of NT embryos that developed to the morula and blastocyst stages were 103/179 (57.5%) and 41/179 (22.9%) or 84/193 (43.5%) and 27/193 (14.0%) in Groups IIA and IIB, respectively. In conclusion, the in vitro developmental competences of porcine transgenic NT embryos that had been reconstructed with the Tg(pWAPhGH-GFPBsd) gene-transfected fibroblast cells were relatively high. Further, the nucleofection efficiency of all the porcine fibroblast cell lines as estimated by intra-vitam fluorescent evaluation based on the index of reporter eGFP transgene expression was nearly 100%. However, PCR analysis for transgene screening confirmed the absence of Tg(pWAPhGH-GFPBsd) fusion gene in some of the nucleofected cell lines. To our knowledge, the novel method of nucleofection is the first to transfect nuclear donor cells in the production of transgenic cloned embryos.

The commonly used beta-actin-GFP transgenic mouse strain develops a distinct type of glomerulosclerosis

Green fluorescent protein (GFP) transgenic animals are widely used in biomedical research. We observed that the commonly used beta-actin-GFP transgenic mouse has renal defects with proteinuria starting as early as 5 weeks of age. Histological analysis reveals a widespread increase in glomerular extracellular matrix, occasional mesangiolysis, and secondary tubulointerstitial injury. Electron microscopic (EM) analysis reveals dramatic thickening of the glomerular basement membrane (GBM). Several other transgenic strains with GFP on ubiquitous promoters including beta-actin (with insertion in a different location) and ubiquitin C show no renal abnormalities. Western blot analysis on crude glomerular preparations from several GFP transgenic strains revealed that higher levels of GFP expression might be responsible for the observed pathogenesis. Mapping of the transgene insertion site by inverse PCR indicates that the beta-actin GFP transgene does not cause insertional mutagenesis nor does it modify the transcription level of adjacent genes. Taken together, this strain of beta-actin-GFP transgenic mouse may be used to study the mechanism of GBM expansion. Moreover, experiments using this strain of GFP mouse should be hereafter carefully planned because its renal pathology may interfere with data interpretation.

Expression and loss of alleles in cultured mouse embryonic fibroblasts and stem cells carrying allelic fluorescent protein genes

Background

Loss of heterozygosity (LOH) contributes to many cancers, but the rate at which these events occur in normal cells of the body is not clear. LOH would be detectable in diverse cell types in the body if this event were to confer an obvious cellular phenotype. Mice that carry two different fluorescent protein genes as alleles of a locus would seem to be a useful tool for addressing this issue because LOH would change a cell's phenotype from dichromatic to monochromatic. In addition, LOH caused by mitotic crossing over might be discernable in tissues because this event produces a pair of neighboring monochromatic cells that are different colors.

Results

As a step in assessing the utility of this approach, we derived primary embryonic fibroblast populations and embryonic stem cell lines from mice that carried two different fluorescent protein genes as alleles at the chromosome 6 locus, ROSA26. Fluorescence activated cell sorting (FACS) showed that the vast majority of cells in each line expressed the two marker proteins at similar levels, and that populations exhibited expression noise similar to that seen in bacteria and yeast. Cells with a monochromatic phenotype were present at frequencies on the order of 10^-4 and appeared to be produced at a rate of approximately 10^-5 variant cells per mitosis. 45 of 45 stably monochromatic ES cell clones exhibited loss of the expected allele at the ROSA26 locus. More than half of these clones retained heterozygosity at a locus between ROSA26 and the centromere. Other clones exhibited LOH near the centromere, but were disomic for chromosome 6.

Conclusion

Allelic fluorescent markers allowed LOH at the ROSA26 locus to be detected by FACS. LOH at this locus was usually not accompanied by LOH near the centromere, suggesting that mitotic recombination was the major cause of ROSA26 LOH. Dichromatic mouse embryonic cells provide a novel system for studying genetic/karyotypic stability and factors influencing expression from allelic genes. Similar approaches will allow these phenomena to be studied in tissues.

Differentiation of mouse p19 embryonic carcinoma stem cells injected into an empty zebrafish egg chorion in a microfluidic device

Mouse P19 embryonic carcinoma (EC) stem cells were xenotransplanted into the emptied chorion, the transparent envelope of a fertilized zebrafish egg (rather than mouse native zona pellucida) combined with a microfluidic device to study P19 EC cell differentiation in the chorion biomaterial. A distilled-water jet was used to remove the innate yolk and perivitelline inner mass from the chorion. P19 EC cells were injected into the emptied chorion using a micropipette, and they were subsequently cultured until the inner space of the chorion became completely occupied by cells. A simple microfluidic device was used for handling convenience and effective experiment. At d15, we found neural cells in the outer layer of the cell mass and beating cardiomyocytes in the inner layer of the large embryoid body. We propose that even though the species are different, the external innate membranes developed for embryo protection represent a useful type of ECM.

Mice with the enhanced green fluorescent protein gene knocked in to chromosome 11 exhibit normal transmission ratios

Meiotic recombination between homologous chromosomes can be suppressed within a chosen segment by a regional inversion. In mice, this feature can be engineered and conveniently used in genetic screens to maintain chemically induced mutations within the homologous chromosome. The efficiency of an inversion-based mutagenesis screen can be substantially enhanced provided that the inversion chromosome and its wild-type (WT) homologue are both visibly tagged by two different coat color markers. Dual tagging eliminates labor associated with molecular genotyping. Previously, we reported the generation of the In(11)10Brd strain of mice carrying K14-agouti tagging a 30-cM inversion between the Trp53 and Egfr loci on mouse chromosome 11. Since K14-agouti causes yellowing of ears and tails, the In(11)10Brd mice are easily distinguishable from their WT littermates. In this paper, we describe the construction of a second strain of mice that carry the enhanced green fluorescent protein (EGFP) transgene at the Egfr locus. The EGFP carriers are visually recognizable by emitting green fluorescent light upon UV illumination. We found that the EGFP function was transmitted from one generation to another with expected Mendelian frequencies, and no detrimental effects of EGFP expression were detected in hemizygous or homozygous animals. The EGFP mice together with the previously generated In(11)10Brd inversion carriers constitute a complete set of reagents required for initiation of a regional ENU mutagenesis screen to address functionally more than one-third of mouse chromosome 11.

Using the chorions of fertilized zebrafish eggs as a biomaterial for the attachment and differentiation of mouse stem cells

The development of proper biomaterials is critical for the success of cell therapy and modern tissue engineering. Here, we extruded the yolk and remaining inner mass from fertilized zebrafish eggs and used the resulting chorions as a biomaterial for the differentiation and attachment of mouse P19 embryonic carcinoma (EC) cells. Cells inserted into the chorion showed the spontaneous formation of embryoid body due to the repulsive cell adhesion of the chorion and differentiated specifically into neural cells and cardiomyocytes. In contrast, dissolved chorion extracellular matrix (ECM) conferred enhanced cell attachment on it, suggesting that a unique property of the zebrafish chorion with nanoporous structure appears to be responsible for the simple and controllable embryoid formation for stem cell differentiation. These results indicate that chorions from fertilized zebrafish eggs may be used as an extracellular matrix alternative and applied for stem cell differentiation to specific cell lineages.

Noninvasive visualization of molecular events in the mammalian zygote

Following fertilization, a number of molecular events are triggered in the mammalian zygote. As biochemical studies using mammalian gametes and zygotes have inherent difficulties, the molecular nature of these processes is currently unclear. We have developed a method to visualize these events. In vitro transcribed mRNAs encoding for proteins fused with green fluorescent protein were microinjected into oocytes or embryos and fluorescence signals were observed. Using this technique we succeeded in obtaining images of the DNA methylation status in living mouse and rabbit embryos. Moreover, time-lapse images were acquired of spindle and nuclear formation during second meiosis and first mitosis. Importantly, the microinjected embryos developed to the normal offspring even after observation, suggesting that the technique is relatively noninvasive. Thus, our method may help elucidate the molecular aspects of fertilization and preimplantation development and, based on the real-time genetic and epigenetic status, could become a tool to select "good quality" embryos before implantation.