Transgenic farm animals: applications in agriculture and biomedicine

The Presence or Absence of Alkaline Phosphatase Activity to Discriminate Pluripotency Characteristics in Porcine Epiblast Stem Cell-Like Cells

Porcine embryonic stem cells (pESCs) would provide potentials for agricultural- and biotechnological-related applications. However, authentic pESCs have not been established yet because standards for porcine stem cell-specific markers and culture conditions are not clear. Therefore, the present study reports attempts to derive pluripotent epiblast stem cells either from in vitro or in vivo derived porcine embryos. Nine epiblast cell lines (seven lines from Berkshire and two lines from Duroc) could only be isolated from day 9- to 9.5-old in vivo derived early conceptuses. Pluripotency features were analyzed in relation to the presence or absence of alkaline phosphatase (AP) activity. Interestingly, the mRNA expression of several marker genes for pluripotency or epiblast was different between putative epiblast stem cells of the two groups [AP-positive (+) pEpiSC-like cell 2 line and AP-negative (-) pEpiSC-like cell 8 line]. For example, expressions of OCT-3/4, NANOG, SOX2, c-MYC, FGF2, and NODAL in AP-negative (-) porcine epiblast stem cell (pEpiSC)-like cells were higher than those in AP-positive (+) pEpiSC-like cells. Expression of surface markers differed between the two groups to some extent. SSEA-1 was strongly expressed only in AP-negative (-) pEpiSC-like cells, whereas AP-positive (+) pEpiSC-like cells did not express. In addition, we report to have some differences in the in vitro differentiation capacity between AP-positive (+) and AP-negative (-) epiblast cell lines. Primary embryonic germ layer markers (cardiac actin, nestin, and GATA 6) and primordial germ cell markers (Dazl and Vasa) were strongly expressed in embryoid bodies (EBs) aggregated from AP-negative (-) pEpiSC-like cells, whereas EBs aggregated from AP-positive (+) pEpiSCs did not show expression of primary embryonic germ layers and primordial germ cell markers except GATA 6. These results indicate that pEpiSC-like cells display different pluripotency characteristics in relation to AP activity.

The creation of transgenic pigs expressing human proteins using BAC-derived, full-length genes and intracytoplasmic sperm injection-mediated gene transfer

In most transgenic (Tg) animals created to date, a transgene consisting of the minimum promoter region linked to a cDNA has been used. However, transgenes on small plasmids are susceptible to the position effect, increasing the difficulty of controlling transgene expression. In this study, we attempted to create Tg pigs by intracytoplasmic sperm injection-mediated gene transfer (ICSI-MGT) using two large genomic transgenes derived from a bacterial artificial chromosome (BAC) containing the full genomic region encoding two human proteins, type I collagen and albumin. The production efficiencies (Tg piglets/live offspring) of type I collagen and albumin Tg pigs were 11.8% (6/51) and 18.2% (2/11), respectively. In all of the Tg pigs examined by real-time PCR analysis, tissue-specific expression of the transgene was confirmed (type I collagen: skin, tendon, vessels, genitalia; albumin: liver). The production of human proteins derived from BAC transgenes was also confirmed. Fluorescence in situ hybridization analysis indicated that the BAC transgenes transferred into porcine oocytes by ICSI-MGT were integrated into single or multiple sites on the host chromosomes. These data demonstrate that Tg pigs expressing human proteins in a tissue-specific manner can be created using a BAC transgenic construct and the ICSI-MGT method.

Expression analysis of pluripotency factors in the undifferentiated porcine inner cell mass and epiblast during in vitro culture

Limited understanding of the importance of known pluripotency factors in pig embryonic stem cells (ESC) impedes the establishment and validation of porcine ESC lines. This study evaluated the expression of known mouse ESC and human ESC (hESC) pluripotency markers in in vivo inner cell mass (ICM) and in vitro-cultured undifferentiated porcine epiblast cells isolated from 8-day porcine blastocysts, primary cultures of epiblast-derived neuroprogenitor cells, and endoderm cells. The expression profile of common pluripotency markers (POU domain 5 transcript factor 1, SRY-box containing gene 2, and Nanog homeobox), species-specific markers, ESC-associated factors, and differentiation markers was evaluated. The mRNA of uncultured ICMs, cultured epiblast cells, epiblast-derived neuroprogenitor cells, and endoderm cells was amplified prior to expression analysis of candidate genes by real-time RT-PCR. ESC factors whose expression correlated best with the undifferentiated epiblast state were identified by comparative mRNA expression analysis between porcine epiblast-derived somatic cell lines, fetal fibroblasts, and adult tissues. Across tissue types Nanog homeobox exhibited ubiquitous expression, whereas POU domain 5 transcript factor 1, teratocarcinoma-derived growth factor 1, and RNA exonuclease homolog 1 transcript expression was restricted primarily to undifferentiated epiblasts. Our results suggested that expression of pluripotency markers in undifferentiated pig epiblast cells more closely resembled that observed in hESC. Expression alterations of ESC-associated factors in epiblast cells were also observed during in vitro culture. Our data demonstrate the potential use of some pluripotency factors as markers of porcine epiblast stem cells and indicate that the in vitro environment may influence the cultured epiblast's developmental state.

Hydrogen peroxide homeostasis and signaling in plant cells

The increases of H2O2 concentrations in plant cells often occur under biotic and abiotic stress conditions (e.g. light, environmental stresses and plant hormone abscisic acid). Atmospheric H202 as an ancient signal molecule not only plays the key role in inducing evolution of oxygenic photosynthesis, but also modulates many physiological events, such as stomatal movement, hypersensitive responses, programmed cell death and gene expressions. H2O2 levels in cells must sustain a fine equilibrium between production and scavenging. H2O2 enters cells from the apoplast or generated sources, and in turn is distributed in sub-cellular compartments. H202 can modulate the activities of many components in signaling, such as protein phosphatases, protein kinases, transcription factors (TFs), and calcium channels. Elevated cytosolic calcium concentrations will initiate further downstream responses, via the action of calcium-binding proteins. On the other hand, the research of H2O2 as a signal molecule is still in a comparatively juvenile stage, for example, little is known about how the cells sense H2O2, what the rate-limiting steps and most important cellular events are in cell signaling and what kind of genes is specific or necessary to H2O2 signaling. The answers to all the questions depend on the functional genomic and molecular genetics analysis.

Production of porcine cloned transgenic embryos expressing green fluorescent protein by somatic cell nuclear transfer

In the present study, nuclear transferred embryos (NTEs) were reconstructed by using pig fetal fibroblasts as donors and in vitro matured oocytes as recipients. The effects of G418 selection on donor cells, duration of IVM of prepubertal gilt oocytes and oxygen tension in IVM of oocytes were investigated. The results were as follows: (i) When G418 selected cells expressing GFP were used as donors, the cleavage rate of NTEs decreased drastically in comparison to NTEs derived from donors without antibiotic selection (47.5% vs. 71.6%, p < 0.05). For the blastocyst rate, no significant difference was observed between two groups (10% vs. 10.4%, p > 0.05). (ii) The rate of nuclear maturation of oocytes increased significantly when IVM duration time was extended from 36 to 42 h (83.6% vs. 96.7%, p < 0.05). However, no statistical difference was observed between NTEs derived from oocytes of 36 h IVM group and NTEs from oocytes of 42 h IVM group in the rates of cleavage (59.3% vs. 73.6%, p > 0.05) and blastocyst formation (9.3% vs. 13.2%, p > 0.05); (iii) no significant difference was observed between NTEs reconstructed from oocytes matured under lower oxygen (7% O2) tension and NTEs derived from oocytes matured under higher oxygen tension (20% O2) in cleavage rate (70.6% vs. 67.1%, p > 0.05) and blastocyst rate (11.8% vs. 12.3%, p > 0.05). These results suggest that: (i) G418 selection does not have a significant effect on cleavage rate of NTEs expressing GFP. (ii) Nuclear maturation is greatly improved by prolonging IVM duration from 36 to 42 h, while no significant differences were observed for developmental potential of transgenic embryos. Thus IVM 42 h is the better choice in order to obtain maximum number of M II oocytes as recipients. (iii) Lower oxygen tension and higher oxygen tension in IVM have no significant effect on development of cloned embryos.

Bovine Embryonic Stem Cells

Bovine embryonic stem (bES) cell lines reported to date vary in morphology and marker expression, such as alkaline phosphatase (ALPL), stage-specific embryonic antigen 4 (SSEA4), and octamer-binding transcription factor-4 (OCT4), that normally are associated with the undifferentiated, pluripotent state. This chapter introduces the methods of isolating and maintaining bovine ES cells. These bovine ES cells grow in large, multicellular colonies resembling the mouse ES and embryonic germ (EG) cells, as well as human EG cells. Throughout the culture period, most of the cells within the colonies stain positive for ALPL and cell surface markers SSEA4 and OCT4. The staining patterns of the bES cells are identical to those of the blastocysts fertilized in vitro (IVF), yet different from most previously reported bovine ES cell lines, which are either negative or not detected. After undifferentiated culture for more than 1 year, these cells maintained the ability to differentiate into embryoid bodies and derivatives of all three EG layers, thus demonstrating their pluripotency. In addition to bES from IVF, this chapter introduces two methods of generating blastocyst stage embryos other than in vitro fertilization, which are parthenogenetic activation and somatic cell nuclear transfer for the potential application of generation "patient-specific" ES cells.

Goat uromodulin promoter directs kidney-specific expression of GFP gene in transgenic mice

BACKGROUND

Uromodulin is the most abundant protein found in the urine of mammals. In an effort to utilize the uromodulin promoter in order to target recombinant proteins in the urine of transgenic animals we have cloned a goat uromodulin gene promoter fragment (GUM promoter) and used it to drive expression of GFP in the kidney of transgenic mice.

RESULTS

The GUM-GFP cassette was constructed and transgenic mice were generated in order to study the promoter's tissue specificity, the GFP kidney specific expression and its subcellular distribution. Tissues collected from three GUM-GFP transgenic mouse lines, and analyzed for the presence of GFP by Western blotting and fluorescence confirmed that the GUM promoter drove expression of GFP specifically in the kidney. More specifically, by using immuno-histochemistry analysis of kidney sections, we demonstrated that GFP expression was co-localized, with endogenous uromodulin protein, in the epithelial cells of the thick ascending limbs (TAL) of Henle's loop and the early distal convoluted tubule in the kidney.

CONCLUSION

The goat uromodulin promoter is capable of driving recombinant protein expression in the kidney of transgenic mice. The goat promoter fragment cloned may be a useful tool in targeting proteins or oncogenes in the kidney of mammals.

Insulin-Like Growth Factor-I and Binding Proteins 1, 2, and 3 in Bovine Nuclear Transfer Pregnancies1

In cloned pregnancies, placental deficiencies, including increased placentome size, reduced placentome number, and increased accumulation of allantoic fluid, have been associated with low cloning efficiency. To assess differences in paracrine and endocrine growth regulation in cloned versus normal bovine placentomes and pregnancies, we have examined the expression of insulin-like growth factor (IGF)-I and -II and their binding proteins (IGFBP)-1 through -3 in placentomes of artificially inseminated (AI), in vitro-produced (IVP), and nuclear transfer (NT) pregnancies at Days 50, 100, and 150 of gestation. Fetal, maternal, and binucleate cell counts in representative placentomes were performed on Days 50-150 of gestation in all three groups. Increased numbers of fetal, maternal, and binucleate cells were present in NT placentomes at all stages of gestation examined. Immunolocalization studies showed that spatial and temporal patterns of expression of IGFBP-2 and -3 were markedly altered in the placentomes of NT pregnancies compared to AI/IVP controls. Concentrations of IGF-I in fetal plasma, as determined by RIA, were significantly higher (P = 0.001) in NT pregnancies (mean +/- SEM, 30.3 +/- 2.3 ng/ml) compared with AI (19.1 +/- 5.5 ng/ml) or IVP (24.2 +/- 2.5 ng/ml) pregnancies on Day 150 of gestation. Allantoic fluid levels of IGFBP-1 were also increased in NT pregnancies. These findings suggest that endocrine and paracrine perturbations of the IGF axis may modulate placental dysfunction in NT pregnancies. Furthermore, increased cell numbers in NT placentomes likely have significant implications for fetomaternal communication and may contribute to the placental overgrowth observed in the NT placentomes.

Transgenic animals in biomedicine and agriculture: outlook for the future

Transgenic animals are produced by introduction of 'foreign' deoxyribonucleic acid (DNA) into preimplantation embryos. The foreign DNA is inserted into the genetic material and may be expressed in tissues of the resulting individual. This technique is of great importance to many aspects of biomedical science including gene regulation, the immune system, cancer research, developmental biology, biomedicine, manufacturing and agriculture. The production of transgenic animals is one of a number of new and developing technologies that will have a profound impact on the genetic improvement of livestock. The rate at which these technologies are incorporated into production schemes will determine the speed at which we will be able to achieve our goal of more efficiently producing livestock, which meets consumer and market demand.

Specific genetic modifications of domestic animals by gene targeting and animal cloning

The technology of gene targeting through homologous recombination has been extremely useful for elucidating gene functions in mice. The application of this technology was thought impossible in the large livestock species until the successful creation of the first mammalian clone "Dolly" the sheep. The combination of the technologies for gene targeting of somatic cells with those of animal cloning made it possible to introduce specific genetic mutations into domestic animals. In this review, the principles of gene targeting in somatic cells and the challenges of nuclear transfer using gene-targeted cells are discussed. The relevance of gene targeting in domestic animals for applications in bio-medicine and agriculture are also examined.

High level expression of the bioactive human interleukin-10 in milk of transgenic mice

Human interleukin-10 (hIL-10) has wide spectrum of anti-inflammatory activities and has shown a potential to be used for treatment of inflammatory or immune illness. In this study, transgenic mice that over-express human interleukin-10 (IL-10) in their milk were generated using a bovine beta-casein/human IL-10 hybrid gene. After cloning of the IL-10 gene, a 22 kb hybrid gene was constructed by linking a 10 kb promoter sequence of the bovine beta-casein gene to the cloned 12 kb IL-10 gene. In six of the eight transgenic mice, the transgene RNA was expressed only in the mammary gland and in the other two mice, it was also slightly expressed in the lung. The highest human IL-10 level in milk was 1620 microg x ml(-1). Notably, transgenes in all the eight transgenic mice were expressed regardless of the integration site even though no correlation was shown between the copy numbers of the transgene and expression level. These results suggest that the genomic sequence of the human IL-10 gene can induce the IL-10 expression at high levels under the control of the bovine beta-casein promoter.

Transgenic goats produced by DNA pronuclear microinjection of in vitro derived zygotes

This study was undertaken to investigate various factors affecting the outcomes of in vitro fertilization (IVF) of oocytes retrieved by laparoscopic ovum pick-up (LOPU) technique from prepubertal and adult goats, as well as to evaluate the developmental competence of in vitro produced embryos. Oocyte-cumulus complexes recovered by LOPU from donors stimulated with gonadotrophins were matured in vitro. Fresh semen was used for IVF following various capacitation treatments. In vitro produced zygotes were either cultured to assess in vitro development or were transferred into recipients for full term development. The results indicated that successful IVF of the goat oocytes was affected by factors such as sperm capacitation treatment, oocyte quality, and abundance of cumulus cells on zona pellucida. Oocytes from both prepubertal and adult goats demonstrated similar full term developmental competence despite the fact that in vitro developmental rates were lower for prepubertal goats. The births of transgenic offspring demonstrated that the established LOPU-IVF technology combined with pronuclear microinjection can be successfully used to produce transgenic goats.

Expression of a reporter gene after microinjection of mammalian artificial chromosomes into pronuclei of bovine zygotes

The introduction of mammalian artificial chromosomes (ACs) into zygotes represents an alternative, more predictive technology for the production of recombinant proteins in transgenic animals. The aim of these experiments was to examine the effects of artificial chromosome microinjection into bovine pronuclei on embryo development and reporter gene expression. Bovine oocytes aspirated from 2-5 mm size follicles were matured in vitro for 22 hr. Mature oocytes were fertilized in vitro with frozen- thawed bull spermatozoa. Artificial chromosome carrying either beta-galactosidase (Lac-Z) gene or green fluorescence protein (GFP) gene were isolated by flow cytometry. A single chromosome was microinjected into one of the two pronuclei of bovine zygotes. Sham injected zygotes served as controls. Injected zygotes were cultured in G 1.2 medium for 7 days. Hatched blastocysts were cultured on blocked STO cell feeder layer for attachment and outgrowth of ICM and trophectoderm cells. The results showed a high zygote survival rate following LacZ-ACs microinjection (74%). However, the blastocyst development rate after 7 days of culture was significantly lower than that of sham injected zygotes (7.5 vs. 22%). Embryonic cells positive for Lac-Z gene were detected by PCR in three of nine outgrowth colonies. In addition, GFP gene expression was observed in 15 out of 85 (18%) embryos at the arrested 2-cell stage to blastocyst stage. Six blastocysts successfully outgrew, three outgrowths were GFP positive for up to 3 weeks in culture. We conclude that the methodology for artificial chromosome delivery into bovine zygotes could lead to viable blastocyst development, and reporter gene expression could be sustained during pre-implantation development.