Effects of estrogen receptor alpha- and beta-selective substances in the metaphysis of the tibia and on serum parameters of bone and fat tissue metabolism of ovariectomized rats

The functions of estrogen receptors (ER) alpha and beta (ER-alpha and beta) in bone and fat tissue are not precisely described. Therefore we studied the effects of a specific ERalpha and ERbeta agonist in bone and fat of ovariectomized (ovx) rats and compared them with the effects of estradiol (E2). Animals were s.c. injected for 4-weeks with 3 doses of the ERalpha agonist 16alpha-LE2 or the ERbeta agonist 8beta-VE2 or with E2. The intermediate doses were antagonized by an additional daily treatment with ICI (1.53mg). Bone and fat parameters were evaluated by quantitative computer tomography (qCT). Estrogen regulated hormones were also measured. Uterine weights were stimulated; serum LH and leptin levels suppressed E2 and the ERalpha agonist. Density of the cancellous metaphyseal structures of the tibia was reduced in the controls which was prevented by E2 and the ERalpha agonist. Endosteal surface, endosteal, periosteal circumferences and fat depots were largest in the controls and the ERbeta treated animals and lowest in the E2 and the 16alpha-LE2 injected ovx rats. Osteocalcin and the CrossLaps were highest in the ovx controls and reduced by E2 and the ERalpha agonist. Serum osteocalcin was stimulated by the ERbeta agonist. The strain strength index (SSI) in relation to the bodyweight - an indicator of bone elasticity - was lowest in controls and increased dose dependently in the E2 and in the ERalpha treated animals. Most effects in the uterus, serum and bone were antagonized by ICI. Most effects in the bone and fat were exerted by mechanisms involving the ERalpha but the ERbeta agonist appears to stimulate osteoblasts.

329 A NOVEL SUSPENSION CULTURE SYSTEM FOR BOVINE OVIDUCT EPITHELIAL CELLS

Bovine oviduct epithelial cells (BOEC) are difficult to culture without dedifferentiation. Frequently observed changes in morphology during culture suggest that gene expression patterns are affected as well. We explored a novel short-term culture system for BOEC – suitable for co-culture experiments with embryos – and evaluated the cells with respect to morphological criteria, candidate gene expression, and hormone responsiveness. Simmental heifers were slaughtered on Day 3.5 after standing heat and BOEC were obtained by squeezing along the ampulla with forceps. The cell sheets were separated mechanically by repeated passages through syringes and pipetting, and recovered by sedimentation. Cells from the ipsi- and contralateral oviduct were cultured separately at a density of 106 cells per well in 24-well plates with 800 μL TCM-199 supplemented with 2% OCS (estrous cow serum, as used in embryo culture) or CS 3.5 (cow serum, Day 3.5 after standing heat, adequate to the cycle stage in which cells were obtained) and 0.25 mg/mL gentamicin. For cell counting, an aliquot was further disaggregated by passing 15 times through a 30-gauge needle to achieve a single-cell suspension. Culture took place at 38°C in a humidified atmosphere of 5% CO2 in air. Cells were examined by light microscopy at seeding and after 6, 12, 24, and 48 h. Cell aggregates showed a worm-like structure, displaying numerous vigorously beating cilia on their surfaces throughout the culture period. Trypan blue staining indicated that cells contained in aggregates were viable while single cells stained predominantly positive (non-viable). The purity of the epithelial cell culture was >95%, as determined by immunohistochemistry using antibodies against vimentin and cytokeratin. For electron microscopic investigations, BOEC were sampled at seeding and after 24 h in culture. Cultured BOEC showed a morphology highly similar to that of BOEC in vivo. Both secretory cells with numerous secretory granules and mitochondria, and ciliated cells with long, well developed and actively moving kinocilia were visible. RT-PCR data for candidate genes (ERα, ERβ, HMGCR, PHGPx, PR) obtained from BOEC samples at seeding and after 6, 12, 24, and 48 h in culture showed that gene expression was stable for the majority of transcripts after 6 h in culture. There was no significant difference between cells cultured with OCS or CS 3.5 and no difference between cells obtained from the ipsi- or contralateral oviduct. Estradiol-17β (E2, 10 pg/mL) or progesterone (P4, 10 ng/mL) stimulation showed that the cultured BOEC are able to respond to hormonal signals in a manner similar to their reaction in vivo (Ulbrich et al. 2003 J. Steroid. Biochem. Mol. Biol. 84, 279–89). Progesterone receptor mRNA was up-regulated by E2 and estrogen receptor β mRNA was up-regulated by P4. The culture system for bovine oviduct epithelial cells thus provides an adequate tool to investigate mechanisms of the embryo-maternal communication in cattle. This work was supported by the Deutsche Forschungsgemeinschaft (Research Unit “Mechanisms of Embryo-Maternal Communication”; FOR 478/1).

Monitoring gene expression changes in bovine oviduct epithelial cells during the oestrous cycle

The oviduct epithelium undergoes marked morphological and functional changes during the oestrous cycle. To study these changes at the level of the transcriptome we did a systematic gene expression analysis of bovine oviduct epithelial cells at oestrus and dioestrus using a combination of subtracted cDNA libraries and cDNA array hybridisation. A total of 3072 cDNA clones of two subtracted libraries were analysed by array hybridisation with cDNA probes derived from six cyclic heifers, three of them slaughtered at oestrus and three at dioestrus. Sequencing of cDNAs showing significant differences in their expression levels revealed 77 different cDNAs. Thirty-seven were expressed at a higher level at oestrus, for the other 40 genes expression levels were higher at dioestrus. The identified genes represented a variety of functional classes. During oestrus especially genes involved in the regulation of protein secretion and protein modification, and mRNAs of secreted proteins, were up-regulated, whereas during dioestrus particularly transcripts of genes involved in transcription regulation showed a slight up-regulation. The concentrations of seven selected transcripts were quantified by real-time RT-PCR to validate the cDNA array hybridisation data. For all seven transcripts, RT-PCR results were in excellent correlation (r>0.92) with the results obtained by array hybridisation. Our study is the first to analyse changes in gene expression profiles of bovine oviduct epithelial cells during different stages of the oestrous cycle, providing a starting point for the clarification of the key transcriptome changes in these cells.

230TRANSCRIPTOMICS ANALYSIS OF CHANGES IN GENE EXPRESSION IN BOVINE OVIDUCT EPITHELIAL CELLS DURING THE ESTROUS CYCLE

The oviduct epithelium undergoes marked morphological and functional changes during the estrous cycle. It has been shown that a dramatic change in the frequencies of ciliated and non-ciliated cells occurs during the estrous cycle. At estrus the epithelium consists of secretory and ciliated cells and at diestrus mainly of ciliated cells. The oviduct provides the microenvironment for sperm capacitation, fertilization, and early cleavage-stage embryonic development. At the molecular level, only a few genes or proteins are known that change during the estrous cycle and which may be important for fertility, so as the bovine oviduct-specific glycoprotein, the major secretory protein in the oviduct. Therefore, we studied systematically the changes in gene expression in bovine ipsilateral oviduct epithelial cells at estrus and diestrus. To identify differentially expressed genes, a combination of subtracted cDNA libraries and cDNA array hybridization was used. Two subtracted libraries were produced to enrich cDNAs of upregulated genes at estrus and at diestrus. A total of 1536 cDNA clones of each library were analyzed with radioactively (33-P) labeled probes generated from the oviduct epithelial cells of six Simmental heifers, three of them slaughtered at Day 0 (estrus) and three at Day 12 after standing heat (diestrus). After normalization of the raw data and statistical analysis, all cDNAs showing significant differences in their expression levels at estrus compared to diestrus were sequenced. Sequencing revealed 84 different cDNAs;; 42 of them matched bovine genes or their human/mouse homologs with known functions, and 42 matched genes without a known function. Half of the genes (n=42) were expressed at a higher level at estrus;; for the other (n=42) expression levels were higher at diestrus. The regulated genes or their products represented a variety of functional classes, such as genes of the secretory pathway, genes involved in transcription regulation, cell-surface proteins, cell–cell interaction proteins, secreted proteins, members of signal transduction pathways, immune-related proteins, and some enzymes. The identification of genes differentially regulated in ipsilateral oviduct epithelial cells at estrus v. diestrus is the first step of a systematic analysis of differential gene expression during the estrous cycle. Further studies will follow, focusing on different compartments of the bovine oviduct and additional times of the estrous cycle.

Embryo-maternal communication in bovine - strategies for deciphering a complex cross-talk

Early embryonic development, implantation and maintenance of a pregnancy are critically dependent on an intact embryo-maternal communication. So far, only few signals involved in this dialogue have been identified. In bovine and other ruminants, interferon tau is the predominant embryonic pregnancy recognition signal, exhibiting antiluteolytic activity. However, this is just one aspect of the complex process of embryo-maternal signalling, and a number of other systems are more likely to be involved. To gain a more comprehensive understanding of these important mechanisms, integrated projects involving specialists in embryology, reproductive biotechnology and functional genome research are necessary to perform a systematic analysis of interactions between pre-implantation stage embryos and oviduct or uterine epithelial cells, respectively. State-of-the-art transcriptomic and proteomic technologies will identify reciprocal signals between embryos and their maternal environment and the respective downstream reaction cascades. For in vivo studies, the use of monozygotic twins as recipient animals provides elegant model systems, thus eliminating genetic variability as a cause of differential gene expression. In addition, suitable systems for the co-culture of oviduct epithelial or endometrium cells with the respective embryonic stages need to be established for functional validation of candidate genes potentially involved in the dialogue between embryos and their maternal environment. The knowledge of these mechanisms should help to increase the pregnancy rate following embryo transfer and to avoid embryonic losses. Candidate genes involved in embryo-maternal communication will also be used to define new quality criteria for the selection of embryos for transfer to recipients. Another application is the supplementation of embryotrophic factors or components of embryo-maternal signalling in optimized formulations, such as bioartificial matrices. As a long-term goal, signalling mechanisms identified in bovine will also be functionally evaluated in other species, including the human.

Nucleolar proteins and ultrastructure in bovine in vivo developed, in vitro produced, and parthenogenetic cleavage-stage embryos

In the present study, ribosomal RNA (rRNA) gene activation, monitored through nucleolus development, was studied by autoradiography following (3)H-uridine incubation, transmission electron microscopy, and immunofluorescence confocal laser scanning microscopy of key nucleolar proteins involved in rRNA transcription (topoisomerase I, upstream binding factor, and RNA polymerase I) and processing (fibrillarin, nucleolin, and nucleophosmin) in in vivo developed, in vitro produced, and parthenogenetic bovine embryos. In general, in vivo developed embryos displayed formation of fibrillo-granular nucleoli during the 4th post-fertilization cell cycle. During the previous stages of development, nucleolus precursor bodies (NPBs) were observed. However, on some occasions the initial steps of nucleolus formation were observed already at the 2- and 4-cell stage in cases where such embryos were collected from superovulated animals together with later embryonic stages presenting nucleolar development and autoradiographic labeling. The in vitro produced embryos displayed very synchronous formation of fibrillo-granular nucleoli and autoradiographic labeling during the 4th cell cycle. In vivo developed and in vitro produced embryos displayed allocation of nucleolar proteins to fibrillar and granular compartments of the developing nucleoli during the 4th cell cycle. The parthenogenetic embryos typically displayed formation of fibrillo- granular nucleoli during the 5th cell cycle and autoradiographic labeling was not observed until the morula stage. Moreover, the 1-, 2-, and 4-cell parthenogenetic embryos practically lacked NPBs. On the other hand, parthenogenetic embryos displayed allocation of nucleoar proteins to nuclear entities during the 4th cell cycle. In conclusion, both in vivo developed and in vitro produced bovine embryos displayed activation of transcription and nucleolar development during the 4th cell cycle. However, in vivo developed embryos flushed together with later developmental stages displayed premature activation of these processes. Parthenogenetic bovine embryos, on the other hand, displayed a delayed activation.

Effects of a novel co-culture system on development, metabolism and gene expression of bovine embryos produced in vitro

An in vitro model using co-culture of bovine in vitro-produced (IVP) embryos and bovine oviduct epithelial cells (bOECs) was established to study embryo-maternal interactions in the oviductal environment. In vitro conditions maintaining differentiated growth of oviductal cells were determined by evaluating several media supplemented with different sera at various concentrations. Morphological features were used as indicators of physiological growth, and it became obvious that synthetic oviduct fluid (SOF) supplemented with either oestrous cow serum (OCS) or dextran-coated charcoal-treated fetal calf serum (DCC-FCS) helped to prevent dedifferentiation of bOECs (Expt 1). RT-real-time-PCR analysis revealed an increased mRNA content of the oviduct-specific glycoprotein GP 85-97 when using lower serum concentrations (2 and 5% compared with 10%; Expt 2). In subsequent experiments in which cell-free cultured controls and co-cultured embryos were compared, co-cultured embryos showed an increased rate of cleavage (P < 0.05) after 3 days. Successive cell-free culture until day 8 resulted in a lower rate of blastocyst development (P < 0.05) and reduced ATP content (P < 0.05) of co-cultured versus control embryos (Expt 3). Long-term co-culture (8 days) in SOF with 5% OCS increased the expression of developmentally relevant genes (glucose transporter 1 (Glut-1) and heat shock protein (HSP 70)) in co-cultured versus control embryos (Expt 4). Higher embryonic Glut-1 mRNA expression after co-culture was obvious when using 10% DCC-FCS, but was not significant when culture medium was supplemented with 10% rather than 5% OCS (Expt 5). In conclusion, SOF with 5% OCS supports differentiated growth of bOECs. Co-culture under these conditions improves early cleavage rate, but not blastocyst development, and increases the expression of developmentally relevant genes influenced by type of serum and serum concentration.

Effects of a novel co-culture system on development, metabolism and gene expression of bovine embryos produced in vitro

An in vitro model using co-culture of bovine in vitro-produced (IVP) embryos and bovine oviduct epithelial cells (bOECs) was established to study embryo-maternal interactions in the oviductal environment. In vitro conditions maintaining differentiated growth of oviductal cells were determined by evaluating several media supplemented with different sera at various concentrations. Morphological features were used as indicators of physiological growth, and it became obvious that synthetic oviduct fluid (SOF) supplemented with either oestrous cow serum (OCS) or dextran-coated charcoal-treated fetal calf serum (DCC-FCS) helped to prevent dedifferentiation of bOECs (Expt 1). RT-real-time-PCR analysis revealed an increased mRNA content of the oviduct-specific glycoprotein GP 85-97 when using lower serum concentrations (2 and 5% compared with 10%; Expt 2). In subsequent experiments in which cell-free cultured controls and co-cultured embryos were compared, co-cultured embryos showed an increased rate of cleavage (P < 0.05) after 3 days. Successive cell-free culture until day 8 resulted in a lower rate of blastocyst development (P < 0.05) and reduced ATP content (P < 0.05) of co-cultured versus control embryos (Expt 3). Long-term co-culture (8 days) in SOF with 5% OCS increased the expression of developmentally relevant genes (glucose transporter 1 (Glut-1) and heat shock protein (HSP 70)) in co-cultured versus control embryos (Expt 4). Higher embryonic Glut-1 mRNA expression after co-culture was obvious when using 10% DCC-FCS, but was not significant when culture medium was supplemented with 10% rather than 5% OCS (Expt 5). In conclusion, SOF with 5% OCS supports differentiated growth of bOECs. Co-culture under these conditions improves early cleavage rate, but not blastocyst development, and increases the expression of developmentally relevant genes influenced by type of serum and serum concentration.

Immunocytochemical analysis of vimentin expression patterns in porcine embryos suggests mesodermal differentiation from day 9 after conception

The expression of the intermediate filament proteins vimentin and keratin in porcine embryos was studied by whole-mount immunocytochemistry between day 7 and day 11 after conception. Expression of vimentin was first detected in the inner cell mass of about 50% of the 9-day-old embryos. In elongated 11-day-old embryos, cells expressing vimentin were observed in the epiblast (after disappearance of Rauber's membrane) and in cells migrating from the epiblast between the trophoblast and the underlying hypoblast layer. A keratin-positive response was observed in trophectoderm cells at all stages. These findings suggest that inner cell mass cells in the pig start differentiating into mesodermal cells not later than day 9 after conception. While the delamination of the mesodermal germ layer is known to correlate with the loss of pluripotency of the inner cell mass cells, the early onset of mesodermal differentiation in the porcine embryo, characterized by vimentin expression and in contrast to the mouse, could in part be responsible for the lack of success in establishing pluripotent embryonic stem cell lines in this species. Our results suggest that further attempts to isolate inner cell mass-derived pluripotent cells should be attempted well before day 9 after conception.

First identification of caldesmon transcripts in bovine oviduct epithelial cells in vitro by means of an RNA differential display technique examining culture-induced expression changes

Innovative molecular biology techniques enable the quick evaluation of distinct gene expression pattern of cells or tissues. Hitherto, a cell-type-specific behaviour has been difficult to evaluate. In addition to standard morphological and immunological criteria in this study the expression of in vitro-cultured bovine oviduct epithelial cells (BOECs) was compared with fresh cells by RNA arbitrarily primed polymerase chain reaction (RAP-PCR). The cultured cells showed mitotic activity during the whole culture period (6 days) until they had reached about 80% confluency. Remarkable results of a random transcript screening using fresh versus cultured BOECs were reported, in which a single PCR product appeared during culture, but was absent in fresh cells. Sequence analysis of the culture-induced 522 bp fragment revealed a high homology (87%) to caldesmon (CaD) of various species and a 92% homology to a short cDNA fragment of a bovine non-muscle CaD. Specific, cross-species PCR primers were used to elongate this partial sequence (1,036 bp). This resulting cDNA showed an open reading frame and was identified as a bovine non-muscle CaD isoform. When compared with human non-muscle CaDs (89% homology) a deletion of 2 codons was observed. According to sequential culture experiments, CaD expression was not found in fresh BOECs but specific transcripts appeared within 48-113 h under specific culture conditions. It is likely that augmented CaD expression in cultured BOECs may reflect the cell effort adapting to specific culture conditions. The hypothesis that increased CaD levels could be important to facilitate adherence and spreading by formation of new stress fibres can be favoured. This first identification of caldesmon expression being specifically induced during in vitro culture demonstrates the potential of RAP-PCR for the analysis and validation of cell culture techniques.

Growth Hormone (GH)/GH Receptor Expression and GH-Mediated Effects During Early Bovine Embryogenesis1

Pituitary growth hormone (GH) stimulates postnatal growth and metabolism. The role of GH and its receptor (GHR) during prenatal development, however, is still controversial. As shown by reverse transcription polymerase chain reaction (RT-PCR), bovine in vitro fertilization embryos synthesized the transcript of GHR from Day 2 of embryonic life onwards. Real time RT-PCR revealed that synthesis of GHR mRNA was increased 5.9-fold in 6-day-old embryos compared with 2-day-old embryos. Using in situ hybridization, the mRNA encoding GHR was predominantly localized to the inner cell mass of blastocysts. The GHR protein was first visualized 3 days after fertilization. GH-specific transcripts were first detected in embryos on Day 8 of in vitro culture. As shown by transmission electron microscopy, GH treatment resulted in elimination of glycogen storage in 6- to 8-day-old embryos and an increase in exocytosis of lipid vesicles. These results suggest that a functional GHR able to modulate carbohydrate and lipid metabolism is synthesized during preimplantation development of the bovine embryo and that this GHR may be subject to activation by embryonic GH after Day 8.

Insulin-like growth factor I (IGF-I) and long R(3)IGF-I differently affect development and messenger ribonucleic acid abundance for IGF-binding proteins and type I IGF receptors in in vitro produced bovine embryos

The insulin-like growth factor (IGF) system is a complex network, including ligands (IGF-I and -II), binding proteins (IGFBP-1 to -6), and receptors, of which the type I IGF receptor (IGF-I-R) is important for transmission of most biological effects of IGFs. As IGFs are secreted in large amounts by the female reproductive tract, it has been hypothesized that maternal IGFs may affect embryonic growth and differentiation in a fine-tuned manner, involving modulation of IGF effects by embryonic IGFBP and IGF-I-R expression. To address this point, we cultured in vitro produced bovine embryos in a chemically defined culture system in the presence (100 ng/ml) of recombinant human IGF-I, long R(3)IGF-I (LR(3)), or without IGF supplementation (control). The affinity of LR(3) to IGFBPs measured by competition assays and Western ligand blots is at least 3 orders of magnitude lower than that of IGF-I. LR(3) was most efficient in stimulating early embryonic cleavage, whereas further development was most potently supported by IGF-I. Total cell numbers of blastocysts were highest in the presence of LR(3) (105 +/- 4), followed by IGF-I (96 +/- 5), and the control group (91 +/- 3; P < 0.05). Differential cell staining of blastocysts revealed that these differences were mainly represented by trophectoderm cell numbers. Analysis of messenger RNA (mRNA) expression for IGFBPs and IGF-I-R was performed by RT-real-time PCR, using expression of the nonregulated housekeeping gene glyceraldehyde-3-phosphate dehydrogenase for normalization. Embryonic IGFBP-2 mRNA levels in the LR(3) treatment group were 1.7-fold (P < 0.001) and 2.8-fold (P < 0.001) higher than those in the IGF-I and control groups, respectively. IGFBP-5 mRNA levels were about 2-fold (P < 0.001) elevated in both IGF treatment groups, with slightly (P < 0.05) higher levels in IGF-I- than in LR(3)-treated embryos. Similarly, IGFBP-3 mRNA abundance was increased (P < 0.05) in embryos from the IGF-I vs. the LR(3) culture system. IGF-I-R mRNA levels were reduced by IGF-I (80% of control; P < 0.01), but increased by LR(3) (1.3-fold vs. control; P < 0.001). These data show that the affinity for IGFBPs of IGF peptides is relevant for their effects on preimplantation embryos and affects different parameters, i.e. development, cell numbers, and mRNA expression for components of the IGF system, in different directions.

Overexpression of insulin-like growth factor-II in mouse embryonic stem cells promotes myogenic differentiation

Embryonic stem (ES) cells derived from androgenetic or parthenogenetic mouse embryos are important tools for studying the roles of imprinted genes in early development. Androgenetic ES cells have been shown to preferentially differentiate into the myogenic lineage both in vitro and after formation of teratocarcinomas in vivo. To clarify if the maternally imprinted Igf2 gene which is expected to be overexpressed in androgenetic ES cells is sufficient to induce myogenic differentiation, R1 ES cells were transfected with human IGF-II expression vectors. Stable ES cell clones exhibiting human IGF-II mRNA and protein expression were studied vs ES cell clones without IGF-II overexpression in a standard in vitro differentiation system involving culture in "hanging drops" and observation of differentiation of the recovered embryoid bodies (EBs). EBs derived from IGF-II overexpressing ES cells showed stimulated myogenic differentiation evident by the appearance of myoblasts already 3 days after plating and by higher levels of skeletal muscle-specific transcripts (myf5, myoD, myogenin) at earlier stages. Our study demonstrates for the first time that overexpression of IGF-II enhances and accelerates myogenic differentiation of ES cells, which has implications for ES cell-derived tissue engineering.

Transgenic technology in farm animals--progress and perspectives

Current applications of gene transfer in farm animals include the improvement of product quality and quantity, disease resistance, the production of valuable proteins in the mammary gland or other organs, the genetic modification of pigs for xenotransplantation and the generation of new animal models in cases where rodent models are not sufficient for studying the problem under evaluation. Although DNA microinjection into pronuclei of zygotes from various farm animal species has happened since 1985, the efficiency of this method is low. Further drawbacks are related to the random integration process which may cause mosaicism, insertional mutations and varying expression due to position effects. Sperm-mediated gene transfer is not routinely established yet, although the mechanisms of binding and internalisation of DNA by sperm cells is becoming increasingly clearer. New protocols for the use of retroviral vectors to infect metaphase II oocytes which are subsequently fertilised resulted in efficient production of transgenic cattle. In spite of extensive efforts to establish pluripotent stem cells from farm animal species, no germ-line competent cells have been reported in mammalian species other than mouse so far. However, recent success in cloning sheep, cattle, goats and pigs from cultured cells provides an alternative route for efficient and targeted genetic modifications of farm animals.

Establishment of pluripotent cell lines from vertebrate species--present status and future prospects

Pluripotent embryonic stem (ES) cells are undifferentiated cell lines derived from early embryos and are capable of unlimited undifferentiated proliferation in vitro. They retain the ability to differentiate into all cell types including germ cells in chimeric animals in vivo, and can be induced to form derivatives of all three germ layers in vitro. Mouse ES cells represent one of the most important tools in genetic research. Major applications include the targeted mutation of specific genes by homologous recombination and the discovery of new genes by gene trap strategies. These applications would be of high interest for other model organisms and also for livestock species. However, in spite of tremendous research activities, no proven ES cells colonizing the germ line have been established for vertebrate species other than mouse and chicken thus far. This review summarizes the current status of deriving pluripotent embryonic stem cell lines from vertebrates and recent developments in nuclear transfer technology, which may provide an alternative tool for genetic modification of livestock animals.

Chimeric pigs following blastocyst injection of transgenic porcine primordial germ cells

Porcine primordial germ cell (PGC) derived cell lines of WAPhGH-transgenic pigs have been established that were able to contribute to chimeras. PGCs were isolated from day 25 to 28 genital ridges of more than 30 individual transgenic fetuses in order to have an easy to follow marker gene. To support undifferentiated growth, cell lines were derived and stable maintained on STO no. 8 feeder cells, a murine embryonic fibroblast cell line expressing recombinant, membrane-bound porcine stem cell factor (SCF). Fifteen lines proliferated in an undifferentiated state up to passage 13; two lines were maintained for more than 23 passages. Cell staining experiments for differentiation markers in several cell lines, indicated the presence of pluripotent cells in prolonged cultures. Further characterization using karyotyping revealed a normal, euploid set of chromosomes in cells of passages 15 and higher. Pluripotency of freshly isolated, short-term (up to 24 hr before injection) and long-term cultured, frozen/thawed cells was tested by injection into day 6 recipient blastocysts to give rise to chimeric piglets. The injected embryos (n = 209) were endoscopically transferred into the uterine horns of 11 recipient gilts. Tissue analysis from 49 fetuses and eighteen liveborn piglets for PGC contribution in chimeras was carried out using PCR analysis for the presence of the marker transgene. Thirty-two fetuses showed detectable chimerism in up to five out of 12 tissues analyzed. Skin samples from eight piglets were positive for the transgene, four of them displayed coat colour chimerism.

Adult cloning in cattle: potential of nuclei from a permanent cell line and from primary cultures

Nuclear transfer was used to evaluate the developmental potential of nuclei from a spontaneously immortalized bovine mammary gland epithelial cell line (MECL) and from primary cultures of mammary gland cells (PMGC) and ear skin fibroblasts (PESF) established from 3-year-old cows. Cell proliferation was investigated by incorporation and detection of 5-bromo-2'-deoxyuridine (BrdU). The proportion of cells in S-phase was significantly (P < 0.05) higher for MECL cells than for PMGC and PESF, both in the presence of serum (90% vs. 28% and 15%) and following serum starvation (27% vs. 6% and 3%). Nuclei from PESF supported the development of reconstructed embryos to the blastocyst stage significantly better than those of PMGC (60% vs. 26%; P < 0.05). Embryos reconstructed with cells from MECL failed to develop to blastocysts. After transfer of embryos derived from PMGC and PESF, respectively, 2/2 and 5/12 recipients were pregnant on day 42. On day 90, the corresponding pregnancy rates were 2/2 and 3/12. One live calf derived from a PMGC was born at day 287 of gestation. Another live PESF-derived calf was delivered by caesarean section at day 286 of gestation. Our study suggests that nuclei from primary cultures of adult cells can be successfully reprogrammed by nuclear transfer, whereas nuclei from a permanent cell line failed to support the development of nuclear transfer embryos.

Factors affecting proliferation and dedifferentiation of primary bovine oviduct epithelial cells in vitro

The oviduct is the physiological site for key events in reproduction, such as capacitation of spermatozoa, fertilization and early embryonic development. Interactions between oviduct epithelial cells and gametes or embryos cannot sufficiently be studied in vivo. Therefore, model systems are needed which mimic in vivo conditions most closely. In this study we optimised the method for isolating bovine oviduct cells and compared different cell support materials as well as two culture systems (perfusion vs static culture) for their ability to maintain characteristic morphological and functional features of oviduct cells. Out of nine different cell support materials tested, cellulose nitrate (0.45 micron pore size) was the most suitable to maintain cells in a manner similar to freshly isolated oviduct epithelial cells. Comparing static vs perfusion culture by electron microscopy, morphological differences of the cells were insignificant in the first days of culture, while they became more evident after 8 days. The cells in the static system lost typical characteristics such as columnar shape, cilia and secretory protrusions, while these features were still present in perfusion culture. In addition, intense ciliogenesis and cytoplasmic organelles for protein synthesis were found under perfusion conditions. These findings were underlined by differences in expression of the oviduct-specific oestrus-associated glycoprotein 85-97 kDa (GP 85-97) gene as revealed by semi-quantitative reverse transcription-polymerase chain reaction (RT-PCR). The RNA levels of this specific gene were significantly higher in perfusion compared to the static culture system. Our data show clear advantages of perfusion vs static culture for primary bovine oviduct epithelial cells.

Potential of fetal germ cells for nuclear transfer in cattle

The developmental potential of bovine fetal germ cells was evaluated using nuclear transfer. Male and female germ cells at three stages of fetal development from 50- to 57-, 65- to 76- or 95- to 105-day-old fetuses were fused to enucleated oocytes 2 to 4 hr prior to activation with 7% ethanol (5 min) followed by 5 hr culture in 10 microg/ml cycloheximide and 5 microg/ml cytochalasin B. The in vitro development of nuclear transfer embryos derived from germ cells was compared with those derived from embryonic cells (blastomeres from day 5 or day 6 embryos). Blastocyst rate (38%) obtained with germ cells from 50- to 57-day-old fetuses tended to be higher than when using germ cells from 65- to 76- or 95- to 105-day-old fetuses (23% and 20%, respectively). Within each stage of fetal development, the proportion of blastocysts derived from male germ cells tended to be higher than that obtained with female germ cells, but due to the high variation between individual fetuses this difference was not significant. With the post activation procedure used in this study, germ cells from 50- to 57-day-old fetuses supported the development of nuclear transfer embryos to the blastocyst stage significantly (P<0.05) better than nuclei of embryonic cells (38% vs. 3%). After transfer of blastocysts derived from germ cells of 50-to 57- and 65- to 76-day fetuses, respectively, 45% (5/11) and 50% (3/6) recipients were pregnant on day 30. The corresponding pregnancy rates on day 90 were 36% (4/11) and 17%(1/6). One live male calf was delivered by cesarean section at day 277 of gestation. Our results show that nuclei of bovine fetal germ cells may successfully be reprogrammed to support full-term development of nuclear transfer embryos.

Effects of serum starvation and re-cloning on the efficiency of nuclear transfer using bovine fetal fibroblasts

The developmental potential of bovine fetal fibroblasts was evaluated using nuclear transfer. Fibroblasts from a 37-day-old fetus were fused to enucleated oocytes before activation. Nuclei of starved (cultured for 8 days in medium containing 0.5% serum) fibroblasts supported the development of reconstructed embryos to the blastocyst stage significantly better than those of non-starved fibroblasts (39% versus 20%; P < 0.05). When nuclear transfer morulae derived from starved or non-starved fibroblasts were used for re-cloning, the proportion of blastocysts (52 and 55%, respectively) obtained with these embryonic nuclei was significantly higher than it was with fibroblast nuclei used in the first round of nuclear transfer (P < 0.05 and P < 0.001, respectively). After transfer of blastocysts derived from non-starved and starved fibroblasts, respectively, 33% (1/3) and 78% (7/9) of recipients were pregnant on day 30 as assessed by ultrasonography. On day 90, the corresponding pregnancy rates were 33% (1/3) and 63% (5/8). Two live male twin calves, derived from non-starved fibroblasts, were delivered by Caesarean section at day 281 of gestation. This study demonstrates a positive effect of serum starvation on the efficiency of nuclear transfer using bovine fetal fibroblasts. The efficiency of nuclear transfer could be further increased by recloning.

[Isolation and long-term cultivation of rabbit embryonic stem cells]

A cell line similar to embryonic stem cells has been isolated from 5-day rabbit embryos. After the disruption of zona pellucida, embryos were mechanically separated into cel aggregates, which were then cultivated on a feeder layer of primary mouse embryonic fibroblasts. Cells similar to embryonic stem cells had high nuclear-to-cytoplasm ratio. It has been demonstrated for the first time that the inner cell mass and embryonic stem cells of rabbits expressed the activity of alkaline phosphatase. Between 10 and 30% of cells retained this expression and pluripotent characteristics up to the 23rd transfer. After 14-17 transfers the obtained embryonic cells could be induced to differentiation in vitro, which resulted in the formation of embryoid bodies. After the 23rd transfer, the line of rabbit embryonic cells was lost as a result of its differentiation.

Primary culture of porcine PGCs requires LIF and porcine membrane-bound stem cell factor

We studied the effect of murine leukaemia inhibitory factor (LIF), human basic fibroblast growth factor (bFGF) and porcine stem cell factor (SCF) on the survival and/or proliferation of porcine primordial germ cells (PGCs) obtained from 27-day-old embryos in vitro. PGCs were cultured in embryonic stem cell (ESC) medium supplemented with or without either LIF (1000 IU/ml) alone or LIF together with bFGF (10 ng/ml). They were seeded on mitotically inactivated feeder cells, either STO or transfected STO cells (STO#8), expressing the membrane-bound form of porcine SCF. PGCs were identified by their alkaline phosphatase (AP) activity and counted after 1, 3 and 5 days in culture. After 1 day of culture, PGCs cultured on STO#8 cells showed significantly higher survival than PGCs cultured on STO cells (p < 0.05). The combined effect of SCF and LIF caused a significant increase in PGC number by day 3 of culture when PGCs were cultured on either STO cells (p < 0.01) or STO#8 (p < 0.001). When SCF and LIF were used together with bFGF no increase in the PGC number was observed. Our results suggest that the membrane-bound form of porcine SCF plays a pivotal role in the primary culture of porcine PGCs and that bFGF is not required in vitro.

Comparison of ultrasound-guided vs laparoscopic transvaginal ovum pick-up (OPU) in simmental heifers

Transvaginal ovum pick-up (OPU) offers several advantages over standard embryo transfer procedures. For a systematic comparison of the ultrasound-guided (U-OPU) and the laparoscopic OPU (L-OPU) method, groups of Simmental heifers were subjected to 1 of the 2 OPU-methods for 8 wk (15 sessions) followed by a treatment-free interval of 11 wk and then another 8-wk period of OPU using the alternative method. Parameters that were evaluated included the number of follicles aspirated, number and morphology of recovered cumulus-oocyte complexes (COCs), and developmental capacity of oocytes after in vitro maturation (IVM) and fertilization (IVF). Blood samples were also taken from the donors twice a wk for progesterone measurement. To evaluate effects of long-term OPU on subsequent fertility of donors, all heifers (n = 14) were inseminated during the first natural estrus after the OPU experiment. The proportion of Class I oocytes was significantly (P < 0.001) higher after U-OPU than after L-OPU (38.7% vs 21.0%). Following IVM/IVF, this difference in oocyte quality was reflected by the cleavage rate (U-OPU: 58.1%; L-OPU: 52.1%; P < 0.05) and the rate of development to morulae and blastocysts (U-OPU: 27.1%; L-OPU: 13.9%; P < 0.001). Among other factors, the greater changes in vacuum pressure during L-OPU vs U-OPU might be responsible for the difference in oocyte quality. This problem may be overcome by a more flexible system for regulating the vacuum. Progesterone levels were higher during the L-OPU than the U-OPU periods. Seven donors (50%) were diagnosed pregnant by ultrasonography on Day 28 and by palpation per rectum on Day 42.