393 CHARACTERIZATION OF PORCINE EMBRYONIC GERM CELL LINES DERIVED FROM DANISH LANDRACE AND YUCATAN MINI PIG EMBRYOS AT DAYS 20 TO 24 OF PREGNANCY

The establishment of pluripotent embryonic stem cells (ESC) in farm animals would benefit animal health and provide meaningful models for regenerative therapies and for studying embryonic development. However, long-term porcine ESC with preserved stem cell characteristics have not yet been established. Porcine embryonic germ cells (pEGC), which are pluripotent stem cell-like cells derived from primordial germ cells, have been established with high efficiency and, therefore, are an alternative to porcine ESC. Here we report the establishment of pEGC from Danish Landrace and Yucatan mini pig embryos at Day 20-24 of pregnancy, an embryonic stage that is significantly younger than reported previously (Day 25-28). The derived pEGC lines were characterized by morphological evaluation, scanning and transmission electron microscopy, RT-PCR for the expression of pluripotency markers, and immunostaining. In addition, molecular signaling pathways that might be involved in maintenance of pluripotency were investigated. We were successful in the derivation of pEGC lines from embryos at Day 20-21 (2/2 pooled, 9/15 individual; lines derived/PGC cultured from pooled or individual embryos, respectively) and Day 23-24 (3/3 pooled, 9/11 individual), but not from Day 17-18 (0/1 pooled, 0/14 individual) in the Danish Landrace. In addition, we successfully derived pEGC lines fromYucatan mini pig embryos at Day 23-24 of pregnancy (9/9 individual). All of the established pEGC lines proliferated robustly and were maintained for at least 8 passages (maximum 11 passages) without showing signs of senescence. The pEGC colonies had ESC-like morphology, and electron microscopy revealed the presence of cilia on the cell surfaces, similar to human ESC. The cells expressed at various levels OCT4, SOX2, NANOG, TERT, C-MYC, KLF4, CDH1, REX1, and other pluripotency markers. Receptors for leukemia inhibitory factor (LIF) (LIFr and gp130) and basic fibroblast growth factor (bFGF) (FGFr1 and FGFr2, isoform 2) were present at passages 0-7, whereas C-KIT was expressed at high levels only in primary cultures and down-regulated by passage 6. To determine which growth factors are relevant in maintaining pluripotency gene expression, we established and maintained pEGC lines for 10 passages in serum-free conditions in medium supplemented either with LIF, stem cell factor (SCF), or bFGF. Compared with nontreated controls, OCT4, SOX2, NANOG, and STAT3 were significantly up-regulated in LIF-treated pEGC lines (P < 0.01). In SCF-treated pEGC, NANOG and STAT3 were significantly higher than in control lines (P < 0.01), whereas in bFGF-treated pEGC, only STAT3 was significantly up-regulated (P < 0.01). Our results suggest that the LIF signaling pathway is active in pEGC; therefore, it is currently under further investigation. The pluripotency of 12 established cell lines is being tested by teratoma formation. These results will help to improve the culture of pluripotent stem cells in the pig.

85 DEOXYRIBONUCLEIC ACID METHYLATION IN PORCINE PARTHENOGENETIC PREIMPLANTATION EMBRYOS

DNA methylation is one of the most important epigenetic mechanisms involved in gene silencing. Waves of DNA de- and re-methylation occur during mammalian preimplantation development. Whether the same happens in porcine parthenogenetic embryos has never been determined, and we set out to investigate this question. Porcine oocytes were aspirated from antral follicles, matured in vitro for 42 h, parthenogenetically activated and fixed in 4% paraformaldehyde at the 1-, 2-, 4-, and 8-cell stage as well as at the early and late blastocyst stage. The degree of DNA methylation was assessed by immunocytochemical staining (Anti-5MetC mouse monoclonal; Abcam, Copenhagen, Denmark) and DNA was counterstained with Hoechst 33258. Porcine fetal fibroblasts were used as standard. The fluorescent signals were detected using an epifluorescence microscope (Leica) and a Leica camera set at fixed exposure times. Signals were quantified using NIH ImageJ sofware. Total means of intensities (methylation and DNA) were calculated and exponential curves were obtained using Microsoft Excel-based statistics. DNA methylation and DNA content were highly correlated in porcine fetal fibroblasts demonstrating the effect of an immediate maintenance methylation taking place during the DNA S-phase of the cell cycle. A similar correlation was observed in the parthenogenetic embryos at all the developmental stages. The level of DNA methylation increased slightly from the early to the late 1-cell stage, and a pronounced increase in DNA methylation level was noted at the 2-cell stage. At the late 1-cell stage, the DNA methylation level of the two pronuclei was similar probably due to the maternal origin of both pronuclei. At the 4-cell stage, DNA methylation had decreased again but was higher compared with other developmental stages, except the 2-cell stage, and at the 8-cell stage, the level of DNA methylation reached a minimum. Subsequently, the level of DNA methylation increased slightly at the blastocyst stages. In conclusion, DNA methylation and DNA content were correlated in porcine fetal fibroblasts and parthenogenetic embryos. Furthermore, the levels of DNA methylation in parthenogenetic embryos exhibited an increase to the 2-cell stage followed by a decrease to the 8-cell stage and a final increase to the blastocyst stage. The initial increase in methylation to the 2-cell stage is different from what has been reported previously for in vivo derived porcine embryos. We are thankful to H. Holm and J. Nielsen for excellent technical assistance. This project was supported by Marie Currie Action project MRTN-CT-2006-35468 (CLONET).

107 EARLY EMBRYONIC SURVIVAL IN THE PIG IS HIGHER THAN CONVENTIONALLY REPORTED

It is generally accepted that 30% of the embryos in a porcine litter die within the first 40 days of pregnancy (Pope WP and First NL 1985 Theriogenology 23, 91–105). The aim of the study was to investigate the dynamics of embryonic mortality from the 2nd to the 7th week of pregnancy in a homogeneous pig population in order to test whether this dogma holds true. A total of 141 pregnant Danish Landrace × Yorkshire gilts were divided into three groups dependent on gestational length: Group 1 (Days 9 to 24 post insemination (p.i.)): At Days 9 to 18 p.i., embryos were collected by flushing the uterine horns with PBS containing 1% serum. At Days 19 to 24, embryos were identified in situ by opening of the horns along the anti-mesometrial side. All embryos were staged according to the morphological appearance of embryo proper. Pre-somite stage embryos were categorized as either: Hatched blastocysts, pre-streak 1, pre-streak 2, primitive streak, or neural groove stage embryos (Vejlsted M et al. 2006 Mol. Reprod. Dev. 73, 709–718). Somite stage embryos were staged according to the number of somites. All embryos in Group 2 (Days 24.5 to 33 p.i.) and Group 3 (Days 40.5 to 47 p.i.) were identified in situ by opening the uterine horns as described above. The localization in the uterus and the Crown Rump Length (CRL) was recorded for all embryos in these groups. The average embryo recovery rate, (i.e. the ratio between the numbers of recovered embryos and the CL numbers) was 82%. Moreover, there were no significant differences between the groups with respect to the embryo recovery rate, signaling the absence of continued embryonic mortality. No significant correlations were obtained between the location of the embryos in the uterus and the CRL (only measured for Groups 2 and 3). Our data indicate that (1) the level of embryonic mortality was less than 10 to 15% and (2) there was no continued embryonic mortality occurring between Days 9 to 47 p.i. This is in great contrast to previous reports. Furthermore, there is no evidence that the location in the uterine horn has any influence on the embryonic development. Table 1.The average numbers of corpora lutea (CL), embryos, and the embryo recovery rates in gilts at different time points after insemination The Danish Research Council for Technology and Production Sciences.

286 ESTABLISHMENT OF PORCINE EMBRYONIC STEM CELL-LIKE CULTURES USING DIFFERENT MEDIA

Porcine embryonic stem cells (pESC) have the potential of becoming an invaluable model for cell-based therapy. However, stable pESC lines are still lacking. We aimed at evaluating various culture media containing growth factors known to support the growth of murine and human ESC for generation of pESC. A total of 186 zona pellucida enclosed (ZPE) and 8 zona pellucida hatched (ZPH) blastocysts were isolated by flushing of sow uteri 5 days post insemination. A total of 122 of the ZPE blastocysts were selected for culture on mouse embryonic fibroblasts (MEF) using either culture of whole blastocyst or immunosurgery. Six types of media were tested: (1) Pig ESC medium [pESCm; DMEM/F10 (1:1), 10% Knockout Serum (KSR), 5% Fetal Bovine Serum and 0.1% leukaemia inhibitory factor (LIF)], (2) pESCm supplemented with 20 ng mL–1 stem cell factor (SCF) (pESCm+SCF), (3) pESCm supplemented with 4 ng mL–1 basic fibroblast growth factor (bFGF; pESCm+bFGF), (4) Human ESC medium (hESCm; Knockout DMEM, 15% KSR and 4 ng mL–1 bFGF), (5) hESCm supplemented with 0.1% LIF (hESCm+LIF) and (6) a commercial LIF containing medium (Resgro; Millipore A/S, Copenhagen, Denmark) used for derivation of murine ESC. At Day 7 of culture, outgrowth colonies (OC) were morphologically examined and attachment rates as well as number of ES-like colonies were noted. ES-like colonies were defined as delineated colonies containing cells with a high nucleo-cytoplasmic ratio and one or two distinct nucleoli. This morphology was verified by nuclear immunocytochemical OCT4-staining (Santa Cruz Biotechnology, Santa Cruz, CA, USA) upon 4% paraformaldehyde fixation. Manual passaging was performed on Day 8 to 10 and RT-PCR was performed on pieces of colonies to evaluate OCT4, Nanog and SOX2 expression. Attachment rates were similar across media groups using whole blastocyst culture and immunosurgery (46 v. 39%, respectively) as were the rates of ES-like OC (80 v. 74%). The highest attachment rates were obtained in pESCm+SCF (60%), hESCm+LIF (55%) and pESCm+bFGF (54%), whereas rates were significantly lower in pESCm (36%), Resgro (33%) and hESCm (22%). High numbers of ES-like colonies were obtained in hESCm (100%) and pESCm+bFGF (100%) though not significantly different from pESCm (89%), hESC+LIF (83%) and pESCm+SCF (66%). Culture in Resgro medium, on the contrary, resulted exclusively in differentiated OC. The maximum number of passages was obtained in pESCm (7 passages) and hESCm (4 passages) after which the colonies started to differentiate into an epithelial-like morphology or became quiescent. RT-PCR analyses showed that most of the ES-like OC were positive for all the pluripotency markers tested, but the passages were, in general, either negative or inconsistently positive for Oct4, Nanog and/or Sox2. In conclusion, supplementation of media with growth factors used for culture of human and murine ESC had a positive effect on the attachment rate of pESC, whereas an effect on the rate of ES-like OC was lacking. The commercial murine ESC medium, Resgro, did not yield ES-like OC at all. Further optimization is needed in order to maintain pluripotency after passage.

96 AN IMMUNOHISTOCHEMICAL STUDY ON MARKERS OF PLURIPOTENCY AND DNA METHYLATION IN THE DEVELOPING PORCINE GERM LINE

Reprogramming of the germ line genome is a fundamental molecular process involving DNA demethylation. This has been demonstrated in the mouse (Seki Y et al. 2005 Dev. Biol. 278, 440–458), but has not yet been studied in the pig. From a large collection of porcine embryos/fetuses 2 to 7 weeks post-insemination (p.i.), a total of 35 randomly selected specimens from the end of the second (n = 10), third (n = 10), fourth (n = 5), and seventh (n = 10) gestational week were selected for an immunohistochemical study on pluripotency markers and DNA methylation in the developing germ line. Intact embryos and isolated developing gonads were paraffin embedded, sectioned (5 to 15 μm) and evaluated for the expression of markers of pluripotency [OCT4 (sc-8628, Santa Cruz Biotech., Santa Cruz, CA), Nanog (500-P236, PeproTech EC, Rocky Hill, NJ), and SOX2 (MAB2018, R&D Systems, Wiesbaden, Germany)], DNA methylation [5-methyl cytidine (ab10805, Abcam, Cambridge, MA)], and meiosis [SCP-3 (generous gift from C. Heyting)]. Heat-induced epitope retrieval (HIER) in an alkaline (pH 8.2) EDTA buffer (Shi SR et al. 2001 J. Histochem. Cytochem. 49, 931–937) and confocal laser scanning microscopy allowed for the evaluation of germ cells co-expressing OCT4 and 5-methyl cytidine. The expression of Nanog and SOX2 was found to be better visualized using HIER in an acidic (pH 6.0) citrate buffer. Isolated and clustered primordial germ cells (PGC) were identified by OCT4 labeling early during gastrulation in embryos around 2 weeks of age p.i. The amount of methylated DNA in PGC appeared similar to that in the nuclei of neighboring somatic cells at this stage. During colonization of the genital ridges, in embryos at the end of the third gestational week, this global DNA methylation status seemed to markedly decrease in PGC, remaining low in the gonadal maturing germ cells. Around onset of meiosis, in fetuses at the seventh gestational week, germ cells in 3 out of 5 female specimens studied had ceased to express markers of pluripotency. In contrast, such markers appeared to be retained in germ cells of male siblings. In conclusion, expression of pluripotency markers during porcine germ line development appears similar to what has been described in the mouse with expression ceasing at the beginning of meiosis in the female but not in the male fetus. Further, the timing of germ line DNA demethylation appears similar between the 2 species. In the mouse, PGC entering the genital ridges soon initiate meiosis, whereas in the pig, these events are separated by a 3-week period. The connection between porcine germ line pluripotency and DNA methylation status during the third to fourth week of development p.i. is presently being thoroughly investigated.

185 THE PORCINE EPIBLAST AND NOT THE INNER CELL MASS HAS DEVELOPED CONVENTIONAL PATHWAYS FOR REGULATION OF PLURIPOTENCY

Pluripotency in mice and human embryonic stem cells is regulated by a number of transcription factors, notably including Oct-4, Sox-2, and Nanog. However, in the pig, previous research indicates that Oct-4 protein and mRNA is not specifically localized to the inner cell mass (ICM) of the zona-intact (ZI) blastocyst. Levels of expression of Nanog mRNA, on the other hand, appear to be low in the ZI blastocyst, and protein has not been detected. Similarly, Sox-2 expression in the ZI blastocyst is relatively low and not specific to the ICM. In this study, we investigated the mRNA expression of Oct-4, Sox-2, and Nanog in D6/D7-derived ZI porcine in vivo-derived blastocysts compared with epiblasts mechanically isolated from hatched D10/D11 in vivo-derived blastocysts. We then investigated components involved in pathways important for regulating pluripotency, including JAK/STAT (i.e. gp130, LIFr), FGF (i.e. bFGF, FGFr1, FGFr2), and BMP (bmp4, smad4) signaling pathways and their downstream targets, stat3, c-myc, c-fos, by using RT-PCR. Sows were artificially inseminated, and embryos were flushed from uteri following slaughter. Single D6/D7 blastocysts (n = 3), single mechanically isolated D10/D11 epiblasts (n = 3), endometrium, and oviduct total RNA was isolated using the RNeasy Micro Kit (Qiagen, Valencia, CA, USA). Total RNA from the blastocysts and epiblasts was then amplified to form cDNA using the QuantiTect Whole Transcriptome kit (Qiagen). Positive control tissues (oviduct and endometrium) were reverse transcribed using the RevertAid First Strand cDNA synthesis kit (Fermentas, Burlington, Ontario, Canada). Primers were designed to span introns in highly homologous sequences to human mRNA. Primers were tested in both oviduct and endometrium tissue, and products were sequenced to confirm specificity. PCR was performed at 55°C for 35 cycles. Results indicate that D6/D7 blastocysts only expressed Oct-4 and not Nanog and Sox-2. In contrast, all 3 transcripts were expressed in D10/D11 epiblasts. The D10/D11 epiblasts also expressed LIFr, bFGF, FGFr1, FGFr2, bmp4, smad4, stat3, c-myc, and c-fos. The cytokine receptor gp130 was only weakly expressed in a single epiblast. In contrast, the earlier stage D6/D7 blastocysts failed to express these messengers with the exception of weak expression of gp130 in all 3 blastocysts, and only a single blastocyst expressed LIFr, smad4, c-myc, and c-fos. In conclusion, this study indicates that the ICM of the porcine D6/D7 ZI blastocyst has not developed pluripotency signaling as observed in mice and humans at this developmental stage. Furthermore, without expression of gp130, the JAK/STAT pathway is unlikely to play a role in regulating pluripotency in the epiblast. It is likely that the later stage epiblast may be more amenable for the derivation of porcine embryonic stem cells.

20 IMMUNOCYTOCHEMICAL CHARACTERIZATION OF DAYS 17 AND 19 OVINE IN VIVO AND SOMATIC CELL NUCLEAR TRANSFER EMBRYOS

The present study aimed to characterize development of in vivo and somatic cell nuclear transfer (SCNT) Merino ovine embryos on Days 17 and 19 using the mesoderm marker vimentin, the neuroectoderm marker β-tubulin III, and the pluripotency marker OCT4 for primordial germ cells. In vivo embryos were obtained by transferring 10 to 20 zygotes to each of 20 intermediate recipient ewes. On Day 6, 4 final recipients were used to obtain embryos for recovery at Day 17 (n = 2) and at Day 19 (n = 2). SCNT embryos were constructed from in vitro-matured oocytes and adult granulosa cells. On Day 6, 9 embryos (with intact inner cell masses) were transferred to each recipient for collection at Day 17 (n = 2) and Day 19 (n = 2). Ewes were euthanazed with phenobarbitone and excised reproductive tracts flushed with saline. A total of 24 embryos at Day 17 (14 in vivo and 10 SCNT) and 23 embryos at Day 19 (11 in vivo and 12 SCNT) were collected and processed for immunohistochemistry. On Day 17, length of embryo proper for in vivo and SCNT embryos was 6.2 and 5.6 mm, width of allantois was 9.3 and 3.8 mm, and number of somites was 19 and 13, respectively. On Day 19, length of embryo proper for in vivo and SCNT embryos was 11.5 and 7.3 mm, width of allantois was 70.6 and 13.7 mm, and number of somites was 28 and 22, respectively. On both Day 17 and Day 19, in vivo embryos had a much larger allantois, more somites, and were longer in length. Vimentin staining was observed in all in vivo embryos at Day 17 and Day 19; however, in 75% of Day 17 SCNT embryos, differentiation of the somites into dermatome with underlying sclerotome was either delayed or absent. Similarly, at both Day 17 and Day 19, a larger proportion of embryos did not stain for β-tubulin III, and of those that did, only a small amount was found in the neural tube. The intensity of both stains was much weaker in the SCNT embryos compared to in vivo embryos. Oct-4 was initially found in the splanchnic mesoderm lining the endoderm in the wall of the yolk sac and later in the dorsal mesentery and medial aspect of the mesonephros with in vivo embryos having double the number of positively stained cells than SCNT embryos. The delay in mesoderm compartments of SCNT embryos could imply future problems in the musculoskeletal system. However, lack of any neuroectoderm staining in more than half SCNT embryos could point to neurological problems being more of an issue in terms of survival and well-being. Equally, the smaller allantois could induce later placental abnormalities. The current project was funded by the Co-operative Research Centre for Innovative Dairy Products (CRC-IDP), Australia.

276 CHARACTERIZATION OF BOVINE EPIBLAST OUTGROWTH COLONIES DERIVED FROM DAY 12 BLASTOCYSTS

Isolation and culture of mouse embryonic stem (ES) cells has been performed for many years, and the improvements achieved throughout the last decade in the human field has evoked great hopes for future cell replacement therapies. However, despite certain similarities in the molecular regulation of pluripotency between man and mouse, there is a need for developing large animal models. The aim of our study was to isolate, culture, and characterize bovine ES-like cell colonies derived from the epiblast. Embryos were produced by in vitro maturation, fertilization, and culture. After 6 days of in vitro culture, blastocysts were transferred to synchronized heifers and allowed to develop for an additional 6 days in vivo. At Day 12 after insemination, embryos were collected by nonsurgical flushing. Embryonic discs were isolated from 15 blastocysts by microsurgery and cultured on mitomycin-inactivated mouse embryonic fibroblasts (SLN cells) in DMEM/F12 medium supplemented with 15% fetal calf serum (FCS), 5% knockout serum replacement (KSR), 106UmL–1 leukemia inhibitory factor (LIF), basic fibroblast growth factor (bFGF), nonessential amino acids (NEAA), and nucleosides. After 4 (n = 6), 6 (n = 4), and 8 days (n = 5) of culture, the primary outgrowth colonies were fixed in 4% paraformaldehyde, embedded in paraffin, sectioned, and exposed to antisera recognizing Oct-4 (pluripotency marker; Santa Cruz Biotechnology, Santa Cruz, CA, USA), Vimentin (mesenchyme marker; Zymed Laboratories, South San Francisco, CA, USA), Cytokeratin-8 (trophectoderm marker; Becton, Dickinson and Co., Franklin Lakes, NJ, USA), and α-1-Fetoprotein (hypoblast marker; DakoCytomation, Glostrup, Denmark). The site of antigen-antibody reaction was revealed using the ABC-AEC-method and counterstained with hematoxylin. At Day 4, all colonies had developed a compact central core of cells with a low cytoplasm-to-nucleus ratio, surrounded by a monolayer of squamous cells. At Days 6 and 8, 3 out of 4 and 3 out of 5 colonies, respectively, still presented the compact core which occasionally was encapsulated by a squamous or cuboidal cell sheet. In the remaining colonies, a compact core was less defined. Oct-3/4 staining was observed in the nuclei of the compact core in 5 out of 6 colonies on Day 4, and in all colonies presenting a compact core on Days 6 and 8. However, whereas all nuclei in the core were stained on Days 4 and 6, only scattered nuclei were stained on Day 8. Vimentin staining was observed in the cytoplasm of cells in the compact core in 3 out of 6 Day 4 colonies, in all Day 6 colonies presenting a compact core, but not in any Day 8 colonies. In contrast, α-1-Fetoprotein staining intensity increased with culture period and was mostly observed in squamous monolayer portions. Cytokeratin-8 staining was weak and restricted to the cytoplasm of the cells encapsulating and surrounding the core in 2 Day 6 colonies and a single Day 8 colony. In conclusion, epiblasts isolated from Day 12 bovine blastocysts efficiently attach to feeder cells and develop outgrowth colonies with cores containing presumptive pluripotent cells (Oct-4). However, these cells to some degree lost Oct-4 expression toward Day 8 and were, in parallel, to some degree overgrown by cells of hypoblast (α-1-Fetoprotein) and trophectoderm (Cytokeratin-8) origin.

57 GENOME ACTIVATION IN MOUSE EMBRYOS OF DIFFERENT ORIGIN

Major genome activation is a key event in early embryonic development occurring at the late 2-cell stage in the mouse. Concomitantly occurring molecular and ultrastructural changes in the nucleolus, where the ribosomal RNA genes are transcribed and their transcripts processed, enable the use of this organelle as a sensitive marker of genome activation in embryos produced by different techniques. The aim of this study was to evaluate and compare the genome activation in mouse embryos of different origin using the nucleolus as a marker. Early and late 2-cell- and late 4-cell-stage embryos, prepared by in vitro fertilization (IVF), parthenogenetic activation (PG), and somatic cell nuclear transfer of mouse embryonic fibroblast (MEF), and mouse HM1 embryonic stem cells (HM1) were processed for autoradiography following 3H-uridine incubation and transmission electron microscopy (5 embryos per group) and for immunofluorescence for detection of nucleolar proteins involved in rRNA synthesis (upstream binding factor; UBF) and processing (nucleophosmin; B23) (10–21 embryos per group). Early 2-cell embryos in all groups showed transcriptional activity in the nucleoplasm, but not over nucleolar precursor bodies (NPBs). UBF was localized diffusely in the cytoplasm. B23 was, likewise, localized in the cytoplasm and, in 30% of embryos, in the nucleoplasm. Late 2-cell IVF and PG embryos displayed transcriptional labelling over nucleoplasm and NPBs, which, ultrastructurally, were in the process of transformation into fibrillo-granular nucleoli presenting fibrillar centers, a dense fibrillar component, and a granular component. MEF and HM1 embryos displayed transcriptional labelling over nucleoplasm, but not over NPBs, and the transformation into functional nucleoli was never observed at this stage of development. UBF and B23 were in all groups localized in the nucleoplasm and, in 40–50% of cases, distinctly in the developing nucleoli. At the late 4-cell stage, all embryos presented transcriptional labelling over nucleoplasm and NPBs, which were at different levels of transformation into fibrillo-granular nucleoli. UBF and B23 were distinctly localized in these developing nucleoli. However, whereas fully transformed reticulated fibrillo-granular nucleoli without remnants of NPBs were found in IVF and PG embryos, despite the distinct localization of nucleolar proteins, the nucleoli in MEF and HM1 embryos were not reticulated and still displayed remnants of NPBs. Conclusively, embryos reconstructed by nuclear transfer, independent of cell origin, displayed well-timed extranucleolar genomic activation, but delayed transformation of NPBs into reticulated fibrillo-granular nucleoli. Moreover, the proper nucleolar activation noted in PG embryos activated in the same manner as MEF and HM1 embryos demonstrate that somatic and embryonic stem cell factors exert an influence on nucleolar activation and may cause reduced embryo viability. This work was supported by the Specific Targeted Project (MED-RAT; contract LSHG-CT-2006-518240) and Marie Curie ResearchTraining Networks (CLONET; contract 035468-2).

49 EARLY ASPECTS OF NUCLEAR REPROGRAMMING FOLLOWING BOVINE SOMATIC CELL NUCLEAR TRANSFER

This study was designed in order to evaluate the global transcription and morphology of reprogramming during somatic cell nuclear transfer (SCNT). Following 20–22 h of IVM, couplets of MII cytoplasts and starved bovine fibroblasts were, after 2 h co-culture, electrically fused, chemically activated by 5 µm ionomycin for 5 min, followed by a 3–4 h incubation in 2 mm 6-DMAP, and fixed at 0.5, 1, 1.5, 2, 3, 4, 8, 12, and 16 h post-activation (hpa). The reconstructed embryos were processed for lacmoid staining, autoradiography following [3H]uridine incubation, transmission electron microscopy (TEM), and immunofluorescence (4 and 12 hpa) in order to evaluate chromatin dynamics, transcriptional activity, nuclear and nucleolar ultrastructure, and localization of nucleolar proteins (upstream binding factor (UBF) and fibrillarin), respectively, during the first cell cycle. Likewise, starved fibroblasts were fixed and processed for autoradiography and TEM. The fibroblasts displayed strong transcriptional activity and active fibrillo-granular nucleoli. None of the reconstructed embryos, however, displayed transcriptional activity. During first 3 hpa, the majority of the embryos displayed a single block of condensed chromatin surrounded by a more or less complete nuclear envelope (NE) and an abundant population of elongated somatic cell mitochondria. This somatic cell complex was located peripherally in the ooplasm. At the subsequent time points, the embryos displayed pronuclear-like structures, which from 8 hpa were located centrally in the ooplasm. From about 4 hpa, the somatic cell complex had dispersed and the elongated mitochondria could no longer be tracked. The first nucleolus-related structures were observed at 1.5 hpa and only in nuclei with a complete NE. At 1.5 to 4 hpa, the nucleolus-related structures appeared either as bodies presenting a large fibrillar center and presumptive dense fibrillar component, but no granular component, or as electron-dense nucleolus precursor bodies (NPBs). From 4 hpa and onward, only compact NPBs were observed. At 4 and 12 hpa, UBF was localized into small discrete clusters of foci enclosed in a shell-like structure labeled by fibrillarin in the nucleus. In conclusion, at SCNT, the somatic cell cytoplasm remains structurally organized in a somatic cell complex over the initial 3–4 hpa. During the same period, the somatic cell chromatin undergoes condensation and the NE is partially dissolved. Subsequently, pronucleus-like euchromatic nuclei with typical NPBs are formed, although somatic cell nucleolar components may be temporarily seen. Throughout the process, transcription is repressed. This work was supported by Marie Curie Intra-European Fellowships (MEIF-CT-2006-021629), and by grant VEGA 1/3255/06 and DFG.

293 EMBRYONIC STEM-LIKE CELLS DERIVED FROM PORCINE INNER CELL MASS CELLS ISOLATED BY DIFFERENT METHODS

The aim was to examine isolation methods and culture conditions for the establishment of embryonic stem-like cells derived from the inner cell mass (ICM) of porcine embryos. A total of 83 zona pellucida-enclosed (ZPE) and 88 hatched (ZPH) porcine in vivo Days 5–7 blastocysts were assigned for ICM isolation by: (A) manual dissection by needles (ZPE: n = 10; ZPH, n = 15), (B) immunosurgical isolation (ZPE: n = 30; ZPH: n = 10), (C) immunosurgery and manual cleaning (ZPE: n = 11; ZPH: n = 40), and (D) culture of whole blastocysts (ZPE: n = 42; ZPH: n = 23). Culture was done on mouse embryonic fibroblasts (MEF) at 5% O2 (for A–C) and 20% O2 (for D) in DMEM with fetal calf serum (FCS), serum replacement, and leukemia inhibitory factor (LIF). Outgrowth colonies (OC) were evaluated by phase contrast and subjected to either (1) physical passage and RT-PCR for Oct-4, Nanog, and Sox2; or (2) immunocytochemical localization of Oct-4 at Days 6–7. Five OC categories were defined: (I) epiblast-like colonies (multilayered ICM-like with homogeneous nuclear Oct-4 staining), (II) ES-like colonies with few surrounding cells (ES-like cells with homogeneous nuclear Oct-4 staining surrounded by few cells), (III) clearly delineated ES-like colonies (ES-like cells with homogeneous or heterogeneous nuclear Oct-4 staining and clear demarcation to many differentiated cells), (IV) poorly delineated ES-like colonies (ES-like cells with homogeneous or heterogeneous nuclear Oct-4-staining and poor demarcation to many differentiated cells), and (V) differentiated colonies (heterogeneous cell populations lacking nuclear Oct-4 staining). Oct-4 staining was supported by expression of Oct-4, often associated with Nanog and Sox2. The attachment rates were similar for methods A, B, and C, being higher for ZPH (75–80%) than for ZPE (40–50%) blastocysts. Method D gave 42% attachment for ZPE, but only 23% for ZPH blastocysts at 5% O2, whereas the figures at 20% O2 were 63% and 80%, respectively. Methods B and C gave the highest proportion of OCs in categories II–IV (ES-like cell-containing), and the ZPE-derived OCs exhibited a more homogeneous nuclear Oct-4 staining than the ZPH-derived. Method D gave the highest proportion of category II colonies. Passage was performed from OC categories II–IV (with ES-like cells). For method C, 24 OCs resulted in 18 (75%) passage 1 (P1) colonies. In 11, 6, 3, and 2 cases, they were passed to P2, P3, P4, and P5, respectively, maintaining ES-like morphology before they went into quiescence or differentiation. However, most colonies attained cytoplasmic Oct-4 staining and lost Oct-4, Nanog, and Sox2 expression at P1 or P2; only a single colony maintained Nanog and Sox2 expression up to P3. For isolation method D, 10 OCs resulted in 3 (30%) P1 colonies, but only one continued to P2 before differentiation. In conclusion, all methods consistently gave ES-like OCs. Whole blastocysts at 20% O2 gave the highest attachment rates. However, immunosurgery, eventually followed by manual cleaning, tended to result in the highest proportion of OCs presenting ES-like cells, with the ZPE-derived OCs exhibiting the most homogeneous Oct-4 staining. When subjected to passage, a few colonies maintained ES-like morphology up to P5, but expression of pluripotency markers was lost during the initial passages.

Ribosomal RNA and nucleolar proteins from the oocyte are to some degree used for embryonic nucleolar formation in cattle and pig

The nucleolus is the site of ribosomal RNA (rRNA) and ribosome production. In the bovine primordial follicle oocyte, this organelle is inactive, but in the secondary follicle an active fibrillo-granular nucleolus develops and proteins involved in rDNA transcription (topoisomerase I, RNA polymerase I and upstream binding factor) and early (fibrillarin) or late rRNA processing (nucleolin and nucleophosmin) localize to it. At the end of the oocyte growth phase, the nucleolus is inactivated again and transforms into a solid remnant. The nucleolar remnant is dissolved when meiosis is resumed. Upon fertilization, structures resembling the nucleolar remnant, now referred to as nucleolus precursor bodies (NPBs), are established in the pronuclei. These entities are engaged in the re-establishment of fibrillo-granular nucleoli at the major activation of the embryonic genome. This nucleolar formation can be classified into two different modes: one where nucleolus development occurs inside NPBs (internal; e.g. cattle) and the other where it occurs on the surface of NPBs (external; e.g. pig). Oocyte derived proteins engaged in late rRNA processing (nucleolin and nucleophosmin) may to some degree be re-used for nucleolar formation in the embryo, while the other nucleolar proteins require de novo embryonic transcription in order to be allocated to the developing nucleoli. Moreover, unprocessed rRNA inherited from the oocyte targets to the developing embryonic nucleoli. In conclusion, the nucleolus is important for the development of oocytes and embryos and may serve as a marker for the completion of oocyte growth and the normality of activation of the embryonic genome.

5 NUCLEOLAR DEVELOPMENT REQUIRES TRANSCRIPTIONAL ACTIVITY DURING PORCINE EMBRYONIC GENOME ACTIVATION

The development of a functional nucleolus accompanying the major embryonic genome activation (EGA) is considered a marker for embryo quality and viability. However, the use of this marker is limited by the lack of accurate knowledge of the biology of embryonic nucleologenesis. The objective of this study was to elucidate the role of RNA polymerase I (RPI) and total transcriptional activity, reflecting EGA, for nucleologenesis in in vivo-developed porcine embryos. Late 4-cell-stage embryos were cultured in the absence (control) or presence of actinomycin D (AD; 0.2 �g mL-1, 3 h for RPI inhibition; 2.0 �g mL-1, 3 h for total transcriptional inhibition). Late 2-cell-stage embryos were cultured to the late 4-cell stage with 0.2 �g mL-1 AD (long-term inhibition) to prevent EGA. Embryos were fixed at the late 4-cell stage and processed for RT-PCR (de novo synthesized rRNA), autoradiography (ARG, following culture with 3H-uridine for the last 20 min before fixation), TEM, FISH (probe-labeling rRNA and rDNA), silver staining of nucleolar proteins, and immunofluorescence for RPI. Control embryos displayed typical extranucleolar and nucleolar ARG labeling, fibrillo-granular nucleoli, and focal RPI localization signaling de novo rRNA synthesis in functional nucleoli, confirmed by RT-PCR. All nuclei showed large FISH clusters (rRNA and rDNA) that in 88% of the cases were co-localized with large foci of silver-stained nucleolar proteins. After RPI inhibition, only extranucleolar ARG labeling was detected and, instead of fibrillo-granular nucleoli, a segregated dense-fibrillar component and a granular component, but no fibrillar centers, were observed. RPI was dispersed in all nuclei, the number of nuclei presenting large FISH clusters decreased to 40%, and only 42% of nuclei showed nucleolar proteins localized to large foci. After total transcriptional inhibition and long-term inhibition, the nuclei did not display any ARG labeling and presented inactive nucleolus precursor bodies indicating lack of rRNA (RT-PCR) and total RNA synthesis. However, 40% of the nuclei in both groups presented large FISH clusters of rRNA. This rRNA is considered as partially processed residues of maternally inherited molecules, and their clustering is most likely independent of EGA. Inhibition of transcriptional activity at the time of EGA caused the dispersion of RPI (de novo synthesized) but did not influence the localization of silver-stained nucleolar proteins to large foci (41%). On the other hand, EGA inhibition caused the lack of RPI labeling and hampered the localization of nucleolar proteins to foci. Differences between these 2 groups could be due to the activation of RNA polymerase II before the 3-h AD treatment. In conclusion, RPI transcription and de novo protein synthesis are required for formation of functional nucleoli. However, the clustering of maternally inherited nucleolar transcripts is independent on transcriptional activity at the time of EGA. Failure in constituent RNA polymerase activation during EGA leads to pattern-specific changes in nucleologenesis, which may serve as a marker for early embryo quality.

140 LOCALIZATION OF PRIMORDIAL GERM CELLS IN DAY 21 BOVINE EMBRYOS

In most animal species, germ cell precursors, i.e., primordial germ cells (PGCs), arise from the epiblast and then migrate to the future gonadal ridge during development. At least in the mouse, PGCs may be cultured as embryonic germ cells that remain pluripotent. PGCs are the only cells in which OCT4 expression is maintained after gastrulation. The present study aimed at identifying the localization of PGCs in Day 21 in vivo-derived bovine embryos by immunohistochemical staining against OCT4. Six embryos were obtained after slaughter of superovulated heifers 21 days after insemination. The uterine tracts were flushed and embryos fixed, paraffin-embedded, and processed for immunohistochemistry. Embryos were sagitally sectioned, and selected serial sections were immunohistochemically stained for OCT4 to identify potential PGCs. Two embryos were at the neural groove stage. At this stage of development, the primitive gut had not yet been abstricted from the yolk sac and the allantois was not visible. A weak homogeneous OCT4 staining was localized to nuclei in a well-defined region of the epiblast, which was in the process of a gradual anterior to posterior differentiation into neural and surface ectoderm. Moreover, a strong OCT4 staining was localized to a few scattered cells found in the visceral mesoderm associated with the yolk sac in the region of the endoderm-hypoblast transition at some distance from the embryo proper. Four embryos were at the neural tube/somite stage. At this stage of development, the primitive gut had been defined and only the midgut was connected to the yolk sac. Furthermore, the allantois was visible as an anchor-shaped structure at the posterior end of the embryo. A strong OCT4 staining was found in nuclei of solitary cells in the endoderm and its associated visceral mesoderm of the ventral aspect of the mid and hindgut. The described OCT4 staining corresponds well with previous findings in the pig, in which presumptive PGCs are found in the endoderm epithelium during the neural groove stage. Later, during the early somite stages, they are localized in the endoderm and visceral mesoderm of the yolk sac and allantois, and in later somite stages, they are found in the developing genital ridge. This is, however, the first study to demonstrate the localization of these cells, at least by OCT4 staining, in bovine embryos at the neural groove and neural tube/somite stages.

153 IMMUNOCYTOCHEMICAL STUDIES OF OCT-4, SOX-2, AND β-TUBULIN III EXPRESSION IN EARLY PORCINE EMBRYOS

In the mouse, the transcription factor SOX-2 is known to have at least 2 roles: (1) it acts as a co-factor of the transcription factor OCT-4, the key regulator of pluripotency essential for the development of the inner cell mass/epiblast; and (2) it is involved in the direction of neural development. In this study, we elucidate the localization of SOX-2 in early porcine embryos in relation to that of OCT-4 and the early neuronal marker β-tubulin III. Embryos were flushed from uteri, fixed in 4% paraformaldehyde, and processed for paraffin sectioning. Sections (5 �m) were stained with anti-OCT-3/4 (Santa Cruz Biotechnology, Santa Cruz, CA, USA) using the ABC-AEC-method and counterstained with hematoxylin, or processed for double immunofluorescent staining using antibodies against SOX-2 (R&amp;D Systems Europa, Ltd., Abington, Oxon, UK) and β-tubulin III (Sigma-Aldrich Denmark A/S, Copenhagen, Denmark) and counterstaining with Hoechst. The embryos were classified as pre-streak (n = 8), primitive streak (n = 4), neural groove (n = 5), and somite (n = 4) stage (Vejlsted et al. 2006 Mol. Reprod. Dev. 73, 709–718). At the early pre-streak stage, SOX-2 and OCT-4 staining was found in the nuclei and a weak β-tubulin III staining in the cytoplasm of all epiblast cells. At the late pre-streak and the primitive streak stage, SOX-2 staining became polarized to the nuclei in the anterior epiblast region, whereas OCT-4 staining was found in all nuclei of the epiblast and of the forming meso- and endoderm. The β-tubulin III staining was restricted to the epiblast and showed no anterior-posterior polarization. At the primitive streak, when cells were involuting to form the meso- and endoderm, SOX-2 staining of nuclei was absent. At the neural groove stage, the SOX-2 and β-tubulin III staining was localized to nuclei and cytoplasm, respectively, of the same cells and observed in the neural plate and groove. A polarization in SOX-2 staining was observed in an anterior-posterior direction. At the somite stage, the SOX-2 and β-tubulin III staining was again localized to the same cells and observed in the neuropores and neural tube. The SOX-2 staining of the neural tube was polarized in a dorso-ventral direction. At the neural groove and somite stage, the OCT-4 staining gradually disappeared from the epiblast, mesoderm, and endoderm except from scattered cells, presumably primordial germ cells, localized in the endoderm. Our results suggest that also in the porcine embryo SOX-2 plays a dual role, being involved in regulation of both pluripotency and neural development.

Morphological characterization of pre- and peri-implantation in vitro cultured, somatic cell nuclear transfer and in vivo derived ovine embryos

The processes of cellular differentiation were studied in somatic cell nuclear transfer (SCNT), in vitro cultured (IVC) and in vivo developed (in vivo) ovine embryos on days 7, 9, 11, 13, 17 and 19. SCNT embryos were constructed from in vitro matured oocytes and granulosa cells, and IVC embryos were produced by in vitro culture of in vivo fertilized zygotes. Most SCNT and IVC embryos were transferred to recipients on day 6 while some remained in culture for day 7 processing. In vivo embryos were collected as zygotes, transferred to intermediate recipients and retransferred to final recipients on day 6. All embryos were processed for examination by light and transmission electron microscopy or immunohistochemical labelling for alpha-1-fetoprotein and vimentin. Overall, morphological development of in vivo embryos was superior to IVC and SCNT embryos. Day 7 and particularly day 9 IVC and SCNT embryos had impaired hypoblast development, some lacking identifiable inner cell masses. On day 11, only in vivo and IVC embryos had developed an embryonic disc, and gastrulation was evident in half of in vivo embryos and one IVC embryo. By day 13, all in vivo embryos had completed gastrulation whereas IVC and SCNT embryos remained retarded. On days 17 and 19, in vivo embryos had significantly more somites and a more developed allantois than IVC and SCNT embryos. We conclude that IVC and particularly SCNT procedures cause a retardation of embryo development and cell differentiation at days 7-19 of gestation.

147 IDENTIFICATION OF PRIMORDIAL GERM CELLS IN PORCINE EMBRYOS FROM THE PRIMITIVE STREAK STAGE

In embryonic stem cell research, Oct-4 is one of the most widely used markers of pluripotency. Moreover, at least in the mouse, this marker is restricted to primordial germ cells (PGCs) after gastrulation. Vimentin is often used as a marker of mesoderm/mesenchyme in embryonic tissues and appears to localize to the same embryonic cells as Oct-4, at least in the bovine epiblast. The expression of neither of these markers has been completely addressed in the pig. Therefore, the purpose of the present study was to examine the expression of Oct-4 and vimentin in the porcine epiblast during differentiation and establishment of the three germ layers, i.e. the process of gastrulation. A total of 410 porcine embryos were collected at 8 to 17 days post-insemination from 29 sows of the Danish Landrace breed. Embryos were categorized based on stereo-microscopic observations into the following stages: pre-streak stages 1 and 2, primitive streak stage, neural groove stage, and somite stage. Specimens were fixed at all stages, dehydrated and embedded in paraffin wax. Selected embryos at each stage (n = 28) were completely cut into serial sections for immunohistochemical evaluation of Oct-4 and vimentin. Pre-streak stage 1 embryos were defined by lack of polarization of the embryonic disk, whereas in pre-streak stage 2 embryos a crescent shaped thickening was seen at the posterior pole of the disk. This thickening, marking the first morphological anterior-posterior polarization of the embryo proper, was shown to be a site of incipient ingression of cells from the epiblast. Immunohistochemical analyses localized Oct-4 to nuclei and vimentin to cytoplasm of both founding and ingressing epiblast cells. During formation of mesoderm and endoderm, at the primitive streak stage, solitary Oct-4 positive cells, i.e. potential PGCs, were seen scattered in the endoderm. Cells of the epiblast displayed positive labeling for Oct-4 until specification for the ectoderm cell lineage at the subsequent neural groove stage. In mesoderm, Oct-4 likewise disappeared by the time of formation of the first somites, defining the following somite stage. Thus, at this stage the only cells labeled for Oct-4, i.e. potential PGCs, were seen solitarily scattered in the endoderm. By the 15-somite stage, such cells were no longer visible in the endoderm but were seen located in the mesoderm, spreading from the stalk of the yolk sac and allantois and extending through the mid- and hindgut areas into the incipient genital ridge. Vimentin localized to the mesenchyme and most other derivatives of neural crest and mesodermal origin. In conclusion, based on Oct-4 labeling and distribution pattern, we strongly believe that we have identified the porcine PGCs from the primitive streak stage.

204 SPONTANEOUS DIFFERENTIATION OF PORCINE INNER CELL MASS-DERIVED CELLS INTO CELLS DISPLAYING NEURAL AND GLIAL MARKERS

The pig is needed as a model for human embryonic stem (ES) cell therapy. Our aims were to isolate, culture, and characterize porcine inner cell mass (ICM) derived cells. Porcine blastocysts (n = 22) were flushed from sows on Day 8 after insemination and two blastocysts were immediately fixed. A total of 18 (90%) ICMs were microsurgically isolated from the remaining blastocysts and cultured on mitomycin-inactivated mouse embryonic fibroblasts (SLN cells) in a human ES cell medium without (n = 9) or with 106 U/mL leukemia inhibitory factor (LIF, n = 9). The colonies were inspected by stereomicroscopy every second day. After approximately one week, ES-like portions of the primary outgrowth colonies were passaged physically. Subsequently, passages were performed approximately once a week. Colonies from different passages were fixed in 4% paraformaldehyde and processed for immunocytochemistry together with the blastocysts. LIF had no apparent effect on rates of attachment and growth during initial outgrowth and after passages, or on differentiation patterns. A total of 15 (83%) ICMs attached during the outgrowth culture and 12 (80%) of these developed ES-like portions, i.e. compact masses of small tightly packed cells. In blastocysts, nuclei of the ICM stained exclusively for Oct-4. After 6 days of culture, however, Oct-4 staining was lacking in outgrowth colonies. After 14 days of culture, 6 out of 13 passage (P) 1 colonies had developed morphological characteristics compatible with neural differentiation, i.e. large bipolar perikarya and long axon-like structures; after one month, 15 out of 17 P2-4 colonies displayed neural differentiation. Cells in such colonies displayed cytoplasmic staining for �-III-tubulin in the perikarya and axon-like extensions. After 2-3 months of culture, cell populations in colonies with neural differentation displayed cytoplasmic staining for the intermediate filaments nestin (marker for neural progenitor cells) and vimentin (in the nervous system a marker for glial cells), and cytoplasmic staining for �-III-tubulin and TUC-4 (markers of post-mitotic neurons). Double-immunostaining revealed a co-localization pattern suggesting the existence of a heterogeneous neural cell population that included neural progenitor cells (staining for nestin only), maturing neural progenitor cells (staining for nestin throughout the cytoplasm combined with �-III tubulin in the axon-like extensions only), early neurons (staining for �-III-tubulin, TUC-4, and nestin in the complete cytoplasm), and glial cells (staining for vimentin alone or in combination with nestin). At no time point studied so far were the neural transcription factors Pax6 and Sox2 detected. In conclusion, ICMs were efficiently isolated from Day 8 porcine blastocysts and attached to feeder cells. However, during initial outgrowth culture they lost their Oct-4 expression, and over the subsequent passages they developed into a heterogeneous population of cells at different stages of neural differentiation.

236 NUCLEAR AND CYTOPLASMIC MODIFICATIONS OF GERMINAL VESICLE BOVINE OOCYTES IN RELATION TO CHROMATIN REMODELING

We previously reported that germinal vesicle (GV) bovine oocytes can be classified on the basis of their chromatin organization and that increased chromatin condensation is accompanied by a major incidence of gap junction-mediated coupling interruption between germ and cumulus cells and by an increase in oocyte developmental competence (Lodde et al. 2005 Reprod. Fertil. Dev. 17(2), 294-295). The aim of this study was to characterize, at the ultrastructural level, both nuclear and cytoplasmic compartments of bovine oocytes classified according to their chromatin configuration because key structural modifications, such as nucleolar inactivation and remodeling of specific ooplasmic structures, take place during the later phases of oocyte growth. Cumulus-oocyte complexes collected from 0.5-2-mm early antral (EA) and 2-6-mm mid-antral (MA) follicles were freed of cumulus cells. Denuded oocytes were stained with Hoechst 33342, classified according to the degree of chromatin condensation, and processed for light microscopy of semi-thin sections (LM; n = 10 in each class) and transmission electron microscopy (TEM; n = 5 in each class). Four classes of oocytes were identified by the Hoechst staining: GV0 with filamentous chromatin diffused in the nuclear area, GV1 with few foci of condensed chromatin, GV2 with chromatin further condensed into distinct clumps, and GV3 with chromatin condensed into a single clump. Almost all oocytes collected from EA follicles were classified as GV0. Oocytes of this class were absent in MA follicles, whereas class GV1, GV2, and GV3 oocytes occurred at similar frequency. LM confirmed the chromatin condensation found by the Hoechst staining and revealed that in class GV2 and GV3 oocytes the chromatin was mainly located close to the nucleolus. Ultrastructurally, the nucleolus was fibrillo-granular in GV0 oocytes; the oocytes in the other classes displayed an electron dense fibrillar sphere with the remnant of a fibrillar center on the surface. Organelles were dispersed in the cytoplasm at GV0 while at GV1 and GV2 most organelles were homogenously distributed in the oocyte cortex. At GV3 most organelles were found in clusters in the oocyte cortex. Typical features of completion of the oocyte growth phase, like undulation of the nuclear envelope and reduction of the size of Golgi complex, were found at GV2 and GV3. Moreover, GV3 oocytes presented cortical granules that displayed varying degrees of degeneration. Our findings indicate that the process of chromatin remodeling is strictly related to structural modifications that characterize the later stages of the oocyte growth phase. Because the highest degree of chromatin condensation was combined with degenerative features of cortical granules, we hypothesize that this class of oocytes (GV3) originated from early atretic follicles, as also suggested in other species. The evaluation of oocytes on the basis of chromatin configuration may be useful for the development of new strategies for manipulating fertility in mammals. This work was supported by a COFIN Grant.

Chronological Appearance of Apoptosis in Bovine Embryos Reconstructed by Somatic Cell Nuclear Transfer from Quiescent Granulosa Cells

Efficiency of cloning has remained low and in spite of attempts to improve this technology, many reconstructed embryos do not implant or are lost during early pregnancy. Chromosomal aberrations, deviant gene expression patterns and abnormal regulation of cell death may be involved in this increased early embryonic loss. Here, we investigate the chronological onset of both apoptotic changes in nuclear morphology and DNA degradation [detected by transferase-mediated dUTP nick-end labelling (TUNEL) reaction] in bovine two-cell- to blastocyst-stage embryos. Such embryos were generated either by reconstruction with nuclear transfer from quiescent granulosa cells or by regular in vitro embryo production. Nuclear condensation was observed from the two-cell stage and TUNEL labelling was observed from the six-cell stage in reconstructed embryos, whereas nuclear condensation was evident from the eight-cell stage and TUNEL labelling from the 13-cell stage in embryos derived in vitro. Furthermore, reconstructed embryos displayed elevated ratios of embryos containing apoptotic nuclei at pre-compaction stages and higher indices of apoptotic nuclei in morula and blastocyst stages when compared with in vitro-produced embryos.

Renal Lipofuscinosis in Danish Slaughter Cattle

A study was performed to characterize dark brown or black discoloured kidneys ("black kidneys") in Danish slaughter cattle and to investigate the aetiology and pathogenesis. In 133 939 cattle entering four abattoirs, 359 cases of "black kidneys" were recorded. Of these, 57 cases were submitted for macroscopical, microscopical, and ultrastructural examination. A pigment with characteristics similar to those of lipofuscin was found in secondary lysosomes in epithelial cells of the proximal tubules. Pigment accumulation was the cause of discoloration, with a positive correlation between the discoloration of the renal cortex and the degree of pigment accumulation. Cases occurred only in cattle of the Holstein breed or the Red Danish Dairy breed and mainly in animals aged 3 years or older. In these breeds, prevalences of 0.44% and 2.51% were found, respectively. Epidemiological analyses indicated that affected animals aged 4.5 to 6.5 years or 7.5 to 8.5 years were culled more frequently than unaffected cattle. Epidemiological and genealogical analyses strongly indicated a genetic aetiology with simple autosomal recessive inheritance.

181 Oct-4: A POTENTIAL MARKER FOR PLURIPOTENCY IN CATTLE

The POU (Pit-Oct-Unc) domain transcription factor Oct-4 is one of the most acknowledged markers for pluripotency in murine and primate embryonic cells. At the blastocyst stage, expression of Oct-4 has been shown to remain high in the inner cell mass (ICM) while being rapidly down regulated in the trophectoderm (TE). Furthermore, in these species, expression of Oct-4 is maintained in pluripotent derivatives of the ICM and in embryonic stem (ES) cells, but lost upon differentiation. In the bovine embryo, a marker with similar qualities has long been sought. The aim of this study was to investigate, using a commercially available antibody for immunohistochemistry (IHC), whether Oct-4 might serve this role. In vitro produced (IVP) embryos were transferred to synchronized recipients at Day 6 post insemination (p.i) and flushed at Day 12; in vivo-derived embryos were flushed at Day 14. Day 8 IVP embryos (n = 20) were fixed and processed for IHC in paraffin sections together with Day 12 (n = 18) and Day 14 (n = 3) embryos. From Day 8 IVP embryos, outgrowth colonies (OCs) were formed by intact blastocyst culture on mouse SNL feeder cells. OCs were photographed using a stereomicroscope on Days 12, 14, and 16 p.i., and were examined for Oct-4 expression by in situ IHC at Day 16 p.i. (n = 94). From isolated embryonic discs of Day 12 embryos, OCs were derived by similar culture and were either processed for IHC on paraffin sections at Days 16, 18, and 20 p.i. (n = 9) or used for establishment of ES-like cell lines. Of colonies formed, representative specimens from each of the initial 5 passages (n = 18) were examined for Oct-4 expression either in paraffin sections or in situ. In Day 8 embryos, Oct-4 expression was demonstrated in all nuclei of both ICM and TE cells except for presumptive apoptotic ones. Approximately one-fifth of the OCs presented a substantial amount of Oct-4 positive cells of putative ICM, but also of TE origin. Apparently, the formation of Oct-4 positive OCs was favored by initial attachment of the embryonic pole to the feeder cells. In Day 12 and 14 embryos, specific and exclusive Oct-4 staining of nuclei of the complete epiblast, but not the hypoblast and the TE, was revealed. All OCs derived from Day 12 embryonic discs showed specific staining for Oct-4 in nuclei of putative epiblast origin only. On subsequent culture of these isolated epiblast derivatives, loss of Oct-4 staining from colonies was observed by passage 3. This study has, for the first time, shown expression of Oct-4 to be limited to pluripotent cells of bovine Day 12 and 14 embryos. Compared with murine and primate embryos, down-regulation of Oct-4 expression in bovine TE cells appears to be delayed. Findings indicate that Oct-4 may be used as a marker for pluripotency in bovine ES-like cells, although TE derivatives may maintain Oct-4 expression when isolated from Day 8 embryos.

212 HETEROGENEITY OF RIBOSOMAL RNA GENE ACTIVATION AMONG CELLS OF IN VITRO-PRODUCED PORCINE EMBRYOS

In vitro production (IVP) of porcine embryos by in vitro maturation of oocytes followed by fertilization and culture in vitro is hampered by great deficiencies. Initiation of at least the major embryonic genome transcription, which includes activation of ribosomal RNA (rRNA) genes and the associated formation of a fibrillo-granular nuclealus, is normally seen during the 4-cell stage in pigs. We have investigated the activation of rRNA synthesis and the presence of silver staining nucleolar proteins in porcine IVP embryos as a marker of transcriptional activity and, thus, developmental competence. A total of 205 porcine IVP embryos from the 2-cell to the blastocyst stage were examined using sequential fluorescent in situ hybridization (FISH) to the rRNA genes and their transcripts and silver staining of nucleolar proteins as previously described (Viuff et al. 2002 Biol. Reprod. 66, 629–634). Briefly, cumulus-oocyte complexes with at least three cumulus cell layers and evenly granulated ooplasm were isolated from 2–5 mm ovarian follicles with stereomicroscopic evaluation. Subsequently, oocytes were matured in NCSU-37 and mechanically denuded followed by fertilization using frozen-thawed epididymal semen. Presumptive zygotes were then cultured in NCSU-23 at 39°C, 5% CO2. Around the time of expected cleavage, the embryos were examined every second hour to determine the time of cleavage. Embryos at the 2-cell stage were harvested at 5 h post-cleavage (hpc), 4-cell embryos late during the third cell cycle at 30 hpc, and tentative 8- and 16-cell embryos at 10 hpc. Blastocysts were harvested at Day 5 post-insemination. In general, nuclei of 2-cell embryos displayed 4 small foci of FITC labelling (presumably the rDNA), but no specific silver staining, and were consequently categorized as transcriptionally inactive. At the late 4-cell stage, 58% of the embryos resembled the 2-cell stage. However, in the remaining embryos (42%), some or all nuclei displayed large areas of FISH labelling (presumptive rDNA and rRNA) co-localized with silver staining, and were catagorized as transcriptionally active. Among the 8-cell embryos, 64% displayed a majority of transcriptionally active nuclei, whereas this was the case in 83% and 92% of the embryos in the 16-cell embryos and the blastocysts, respectively. In general, the majority of the embryos contained a mixture of transcriptionally active and inactive cells. These findings show that the porcine IVP embryos are often delayed and asynchronous with respect to activation of the rRNA genes. Table 1. Categorization of nuclei according to transcriptional activity This work was supported by grants from “Disease models, disease prevention and animal welfare improvement: The pig embryo as a model.” Danish Research Agency (Grant: 9901178), NATO (Grant: 978658), and Deutsche Forschungsgemeinschaft (DFG).

27 MORPHOLOGICAL AND IMMUNOHISTOCHEMICAL CHARACTERIZATION OF DAY 21 IVP AND NT BOVINE EMBRYOS

A major limitation of somatic cell nuclear transfer (NT) for the production of cloned calves is that only 1–5% of cloned embryos produce viable calves. The high rate of mortality is attributed to both pre- and post-natal losses and is primarily due to incomplete reprogramming of donor cells. Almost 50% of the pregnancy losses occur in the first trimester of pregnancy, indicating a major disruption in normal embryo development at NT. The aim of this study was to analyze germ layer formation by stereomicroscopy and immunohistochemical techniques for both NT embryos and their in vivo counterparts on Day 21 and to compare deviations from normal embryonic development as a measure of developmental capacity. Blastocyts derived by IVF (n = 20), conventional NT (n = 20), or hand made cloning (HMC; n = 20) were non surgically transferred to each synchronized recipient cow (n = 3). Each group of twenty embryos was transferred to one recipient. Cows were slaughtered on Day 21 and uterine tracts recovered and flushed with phosphate-buffer solution with 10% serum. Recovered Day 21 embryos were fixed in 4% paraformaldehyde, and embedded in paraffin; serial sections were stained with hematoxylin and eosin and evaluated by light microscopy. Immunohistochemical localization of cytokeratin 8 was used as a marker for potential ectoderm, alphafetoprotein for potential endoderm, and vimentin for potential mesoderm. Four IVF (20%; 4/20) embryos, six NT (30%; 6/20) embryos, and ten HMC (50%; 10/20) embryos were recovered following flushing. No obvious morphological differences were seen in the formation of a neural tube, differentiation of mesoderm, and number of somites among IVF (25%; 1/4), NT (33.3%; 2/6), and HMC (20%; 2/10) embryos. Delayed development with respect to the formation of neural groove and mesoderm differentiation was observed in 25% (1/4) of IVF, 16.7% (1/6) of NT, and 30% (3/10) of HMC embryos. In addition, 25% (1/4) of IVF, 16.7% (1/6) of NT, and 33.3% (2/6) of HMC embryos had not initiated gastrulation (i.e. displayed hypoblast and epiblast), suggesting a more substantial developmental delay. The remaining embryos showed gross abnormalities compared to their in vivo counterparts, including degenetration of epiblast and hypoblast cells. Cytokeratin was detected in the trophoblast, ectoderm, hypoblast, and endoderm. Alpha-fetoprotein was detected in the hypoblast while vimentin was seen in the mesoderm. In conclusion, although localization of staining in IVF and cloned embryos was consistent with that of in vivo embryos, the intensity was weaker, suggesting compromised or delayed development. It is also possible that the differences observed were due to the recipient and not to the treatment group. This work was supported by Genetics Australia Cooperative Limited, Victoria, Australia.

71 DEVELOPMENTAL DELAY OF PRE-IMPLANTATION OVINE IN VITRO CULTURED AND SOMATIC CELL NUCLEAR TRANSFER EMBRYOS

Despite advances in the production of somatic cell nuclear transfer (SCNT) embryos, significant embryo losses are persistent, particularly around implantation. Malformations of the placenta and in a variety of organs are seen, and have been linked to deviant epigenetic reprogramming. The aim of the present study was to examine the formation of germ layers, which are prerequisites for formation of the embryo proper and placenta, in invivo-derived (in vivo), partly in vitro-cultured (IVC), and SCNT ovine embryos. Embryos were derived as follows: In vivo embryos (n = 27) were flushed from the uterus on Days 7, 9, 11, and 13. For IVC embryos (n = 22) in vivo zygotes were flushed, followed by culture in the presence of 20% human serum, transfer to the uterus on Day 6, and flushing as in vivo embryos. SCNT embryos (n = 41) were produced by fusion of serum starved granulosa cells with enucleated oocytes, followed by activation, culture in SOF, transfer to the uterus on Day 6, and flushing as described for in vivo embryos. Recovered embryos were processed for light microscopy (LM) and transmission electron microscopy (TEM), and paraffin sections were immunohistochemically labelled for the germ layers: alpha-1-fetoprotein for potential endoderm, cytokeratin-8 for potential ectoderm, and vimentin for potential mesoderm. A consistent delay of the IVC and particularly the SCNT embryos was noted throughout all time points: On Days 7 and 9, differentiation of the inner cell mass into hypoblast and epiblast was evident in 7 out of 12 in vivo embryos, whereas this phenomenon was less prominent or absent in 9 out of 13 IVC and 13 out of 15 SCNT embryos. Furthermore, 6 of the IVC and 12 of the SCNT embryos lacked an identifiable embryonic disc. On Day 11, half of the in vivo embryos had initiated gastrulation, evidenced by localization of endoderm and mesoderm precursor cells between the hypoblast and the epiblast. This feature was noted in only a single IVC and in none of the SCNT embryos. On Day 13, all in vivo embryos had completed gastrulation including the formation of somatic and visceral mesoderm. This feature was noted in only 1 out of 3 IVC and in none of the SCNT embryos. Likewise, amniotic folds were seen in one third of the in vivo embryos at this stage, but not observed in any IVC or SCNT embryos. The immunohistochemical markers displayed the same cell lineage localization in all three groups of embryos, but a developmental delay in the IVC and in particular the SCNT embryos was evident. In conclusion, ovine IVC and SCNT embryos develop at a slower rate than in vivo embryos at least up until Day 13 of gestation.

Regulation of ribosomal RNA gene expression in porcine oocytes

In vitro production (IVP) of porcine embryos including in vitro maturation (IVM) of oocytes followed by in vitro fertilization (IVF) and in vitro culture (IVC) of the resultant embryos may result in live offspring, but it is still associated with great inefficiencies probably due to incomplete cytoplasmic maturation of the oocytes in vitro. Therefore, fundamental knowledge on the regulation of transcription during the oocyte growth phase when the messengers and protein synthetic machinery necessary for oocyte developmental competence are formed, is of great importance. In mammals, synthesis of RNA, up to 60-70% of which is ribosomal (rRNA), increases during oocyte growth and reaches a peak at the beginning of follicular antrum formation. In oocytes at the end of the growth phase, acquisition of full meiotic competence coincides with a markedly decreased rRNA transcriptional activity in the gametes. Our recent studies on the porcine oocyte growth phase have revealed a deeper molecular and biological insight into the complex regulation of rRNA transcription at different stages of follicular development. The data indicate that the so-called pocket protein, p130, is involved in the down-regulation of rRNA transcription at the end of the oocyte growth phase through an inhibition of the action of upstream binding factor (UBF). The latter protein is necessary for the function of RNA polymerase I (RNA Pol I), which is the actual enzyme driving rRNA gene transcription. Moreover, rRNA transcription also appears to be down-regulated by a decrease in the expression of mRNA encoding PAF53, an RNA Pol I-associated factor also required for the polymerase to exert its action. At the ultrastructural level, these molecular changes are paralleled by marginalization of the fibrillar centres of the oocyte nucleolus followed by compaction of the nucleolus into an inactive sphere of fibrils.

Nucleolar ultrastructure and protein allocation in in vitro produced porcine embryos

The nucleolus formation was studied as an indirect marker of the ribosomal RNA (rRNA) genes activation in porcine embryos following oocyte maturation, fertilization, and culture in vitro. Nucleologenesis was assessed by transmission electron microscopy (TEM), light microscopical autoradiography following 20 min of 3H-uridine incubation, and immunocytochemical localization of key nucleolar proteins involved in rRNA transcription (upstream binding factor (UBF), topoisomerase I, and RNA polymerase I) and processing (fibrillarin, nucleophosmin, nucleolin) by confocal laser scanning microscopy. During the first four post-fertilization cell cycles, TEM revealed spherical nucleolus precursor bodies (NPBs), consisting of densely packed fibrils, as the most prominent intra-nuclear entities of the blastomeres. Fibrillo-granular nucleoli were observed in some blastomeres in a single embryo during the 5th cell cycle, i.e., the tentative 16-cell stage, where formation of fibrillar centres (FC), a dense fibrillar component, and a granular component on the surface of the NPBs was seen. In this embryo, autoradiographic labeling was detected over the nucleoplasm and in particular over the nucleoli. Fibrillarin was immunocytochemically localized in the presumptive NPBs of the pronuclei. This protein was again localized to the presumptive NPBs together with nucleolin from late during the 3rd cell cycle, i.e., the four-cell stage in some embryos. UBF, RNA polymerase I, and nucleophosmin were localized to the presumptive NPBs in a proportion of the embryos at the 4th cell cycle, i.e., the tentative eight-cell stage and onwards. Toposiomerase I was not localized to intra-nuclear entities even during the 5th post-fertilization cell cycle. Moreover, a considerable proportion of the blastomere nuclei apparently did not show localization of other nucleolar proteins. In conclusion, porcine embryos produced in vitro display a substantial delay in or even lack of the development of functional nucleoli.

2POSTHATCHING DEVELOPMENT SYSTEM: A NOVEL IN VITRO CULTURE OF BOVINE EMBRYOS

Although high blastocyst rates can be achieved in somatic cell nuclear transfer, abortions and developmental abnormalities still hamper advancement. Reliable and practical methods to evaluate early embryonic development and differentiation are required to understand and overcome the problem. Our aim was to establish an in vitro culture system for monitoring posthatching development (PHD). Slaughterhouse-derived bovine oocytes were matured in vitro, fertilized (Day 0) and cultured (Holm et al., 1999, Theriogenology, 52, 683–700). On Day 8, degenerated embryos were removed from each well and 400L of modified culture medium (SOFaaci plus 0.5% glucose and 10% fetal bovine serum) were added. At Day 11, hatched blastocysts were selected by scoring them as Quality 1 (Q1: &gt;1.0mm, clear trophoblast, compact inner cell mass), Quality 2 (Q2: 0.5mm, dark spots in the trophoblast, less compact inner cell mass), or Quality 3 (Q3: &lt;0.5mm, many dark spots in the trophoblast, spread inner cell mass). The resulting 304 blastocysts in 12 replicates were then loaded into 15mm×1.2 gel tunnels of 2.4% agarose in PBS, supplemented with either 5% (Agar5) or 10% (Agar10) fetal bovine serum, covered with the modified culture medium, and then incubated at 38.5°C in 5% CO2, 5% O2, 90% N2. Embryo morphology and length were evaluated using a stereomicroscope on Days 12, 13, 14 and 15. On Day 14, 75 embryos were removed, biopsed (1mm) for sex determination of each embryo, and processed for light and transmission electron microscopy. Qualitative and quantitative data were analyzed by χ2 test and GLM procedure of SAS, respectively, with P level of 0.05. A total of 170 embryos (56% of total) initiated elongation. This percentage was higher (LSmeansSD, n=12; P&lt;0.05) in Agar10 v. Agar5 in both Q1 (889 v. 637), Q2 (667 v. 485) and Q3 embryos (529 v. 278). Mean embryo length (mm; LSmeansSEM) on Day 13 was higher (P&lt;0.05) in Q1 (2.10.2, n=49) and Q2 (1.71.4, n=98) than Q3 (1.20.3, n=23). On Day 14, Q1 embryos (3.50.2) were longer (P&lt;0.01) than Q2 and Q3 embryos (2.70.1 and 2.00.3). On Day 15, Q1, Q2 and Q3 embryos (4.40.5, n=24, 4.00.3, n=45 and 2.90.6, n=14, respectively) had similar length, probably influenced by the low number of Q3 embryos. The percentage of males was higher (P&lt;0.001) in Q1 (95%; n=40), but similar in Q2 (39%; n=26) and Q3 (71%; n=7). Light microscopy confirmed hypoblast and epiblast formation. Ultrastructural analysis revealed that the latter had penetrated the trophoblast (Rauber’s layer), forming an embryonic disc including many degenerative cells. In conclusion, this culture system represents the first model for rapid growth, elongation, and initial differentiation of bovine posthatching embryos.

127APOPTOSIS IN BOVINE BLASTOCYSTS FROM FIVE DIFFERENT PRODUCTION SYSTEMS

Regulation of apoptosis may be affected by factors during preimplantation development, and this is possibly related to embryo developmental potential. Here we investigate differences in the incidence of apoptotic nuclei in Day 7 bovine blastocysts produced by two different in vivo and three different in vitro methods. In vivo embryos were produced either by a regular superovulation procedure (reg group; n=29; Laurincik et al., 2003, Mol. Reprod. Dev. 65, 73–85), or by postponement of the LH surge (pp group; n=35; van de Leemput et al., 2001, Therio. 55, 573–592). In vitro embryos were derived from systems using either co-culture (cc group; n=30, Avery and Greve 2000, Mol. Reprod. Dev. 55, 438–445), or culture in synthetic oviduct fluid (SOF) with (S+group; n=35) or without serum (S− group; n=38; Holm et al., 1999, Theriogenology, 52, 683–700). Embryos were collected at approx. 168h post ovulation/insemination and subjected to chromatin staining and detection of DNA degradation by TUNEL reaction. The total number of nuclei, number of nuclei displaying apoptotic morphology (+M), number of nuclei displaying TUNEL reaction (+T), and number of nuclei displaying both markers simultaneously (M&amp;T) were scored according to J.O. Gjørret et al. (2003 Biol. Reprod. 69. in press). Only M&amp;T nuclei were regarded as apoptotic, and +M, +T, and apoptotic (M&amp;T) indices (%) were calculated for the trophoblast (tb), inner cell mass (i) and the total blastocysts (t) in each group. Significant differences were observed for all parameters when all groups were compared (ANOVA, P ranging from 0.024 to&lt;0.0001). Highest number of total nuclei were observed in the S+ group, whereas the lowest indices were observed in the pp group, which had significant lower indices in the i and t than in the reg., S+ and S− groups P&lt;0.05; Tukey’s post test for ANOVA). Highest indices were generally observed in the S− group. The results demonstrate that not only embryo cell numbers but also incidences of apoptotic markers are affected by the mode of production. However, in Day 7 bovine blastocysts high cell number is not consistent with a low incidence of apoptosis. Even though cell numbers appeared comparable in the two in vivo groups, their incidences of apoptosis were different, and the reg group displayed indices comparable to the in vitro groups, highlighting the importance of ovulation protocols when in vivo embryos are used as reference material in general. Table 1

96ULTRASTRUCTURE AND CELL DEATH OF VITRIFIED PORCINE BLASTOCYSTS

Cryopreservation of porcine embryos by the simple open pulled straw (OPS) method was recently reported to result in live offspring (Berthelot et al., 2000, Cryobiology 41; 116–124,) and is evaluated in the present study by light (LM) and transmission electron microscopy (TEM) as well as by TUNEL staining in order to detect morphological and molecular signs of cell death and subsequent regeneration. Blastocysts were collected from gilts on Day 5 (Day 0=1st AI) and were randomly assigned to one of three groups: Fresh controls (FC) were fixed immediately after collection, and vitrified embryos were fixed either immediately after vitrification and warming (V0) or after 24h of culture upon warming after vitrification (V24). In each of the three groups, embryos were fixed and processed for LM/TEM (FC, n=13; V0, n=20; V24, n=18) or TUNEL staining (counter staining with propidium iodide) and confocal laser scanning microscopy (FC, n=32; V0, n=31; V24, n=33). At LM, the FC embryos displayed a well-defined trophoblast (Tb) and inner cell mass (ICM), expanded blastocoele cavity and a narrow or no perivitelline space. In V0 embryos, collapse of the blastocoele cavity and cell swelling was detected. At the TEM level, the V0 embryos showed extensive injuries including a general distension or shrinkage of mitochondria and massive increase in the amount of membrane-bound vesicles, vacuoles and secondary lysosomes. In both FC and V0 embryos, the presence of dead or phagocytozed cells in the ICM and Tb was occasional. A few extruded cells were often noticed in the perivitelline space or in the blastocoele cavity, and such cells ranged from being rather normal to showing typical morphological features of apoptosis. TUNEL staining confirmed the presence of a few apoptotic cells in both groups of embryos. Approximately 2/3 of the V24 embryos had, as evaluated by LM, partially recovered, re-expanded or even hatched whereas the remaining 1/3 had degenerated. At the TEM level, the recovered embryos displayed almost normal blastocyst morphology, except for a widening of the perivitelline space, accumulation of debris, increased electron-lucidity of the ICM and partial distension of mitochondria. The degenerated embryos had disintegrated into a poorly defined mass of cells and debris including cells with either decreased or increased electron-density of the cytoplasm and with abundant degeneration of mitochondria and other organelles. Both recovered and degenerated embryos displayed persistent abundant presence of small membrane-bound vesicles, vacuoles and secondary lysosomes. All V24 embryos displayed increased occurrence of dead or phagocytozed cells in the ICM and Tb as well as increased occurrence of extruded cells showing typical morphological features of apoptosis or secondary necrosis. TUNEL staining confirmed the increased occurrence of apoptotic cells in this group of embryos. In conclusion, immediately after vitrification and warming, porcine embryos displayed severe subcellular damages, but during 24h of culture the majority of the embryos were able to regenerate. Along with the regenerative process, apoptosis became evident. Supported by CRAFT EC contract no. QLK5-CT-2002-70983.

125MORPHOLOGICAL CHARACTERIZATION OF DAY 14 AND DAY 21 IVP AND CLONED BOVINE EMBRYO DEVELOPMENT

The establishment of viable embryonic development following in vitro production (IVP) or nuclear transfer by SUZI (subzonal injection) and handmade cloning (HMC) methods is pivotal for practical implementation of embryo technology. The development of cloned embryos is currently impeded by the high rate of pre- and postnatal losses. This project is aimed at developing screening methods using both ultra-structural and molecular markers of development of post-hatching/pre-implantation stage embryos to enable selection of embryos with greater developmental competence. Initially twenty embryos derived by IVP or nuclear transfer (SUZI or HMC) were transferred to six recipient cows on Day 7 (n=120). Embryos were collected on Days 14 and 21 by flushing the uterine tracts of slaughtered cows. Embryos were fixed in 4% paraformaldehyde and processed for paraffin embedding. Serial sections were stained with haematoxylin and eosin and evaluated by light microscopy. On each day of collection, certain characteristics were expected to be observed according to normal in vivo development (Maddox-Hyttel et al., 2003, Reproduction 125, 607–623). On Day 14, IVP embryos (n=6) were ovoid to filamentous in shape. Three embryos had extensive foldings of trophoblast in the process of forming an amniotic cavity. NT-SUZI embryos (n=4) had a mainly round uneven shape. No NT-HMC embryos were recovered. On Day 21, IVP embryos (n=4) more closely resembled in vivo embryos than any other group and formed either a neural groove or a neural groove with somites. NT-SUZI embryos (n=6) were mainly filamentous, with one embryo showing complete development of the neural tube and 5 somite pairs. NT-HMC (n=17) development ranged from ovoid to multi-protrusions of the yolk sac. One embryo displayed the formation of a neural tube. Embryos, irrespective of production method, which had an abnormal morphology, presented only an incomplete hypoblast and severe degeneration of the epiblast. Those embryos that were morphologically comparable to in vivo embryos also displayed developmental stages which ranged from presentation of a primitive streak and formation of a neural tube to having a neural tube, differentiation of mesoderm and somites. At present, the low number of embryos recovered as well as their abnormal development clearly reflect the low success rate to term of live calves. It is possible that no Day 14 NT-HMC embryos were recovered due to collection efficiency not being optimal. It is apparent that IVP and cloned embryos have different developmental time lines as compared to that of in vivo embryos.

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.

Immunohistochemical and ultrastructural characterization of the initial post-hatching development of bovine embryos

The problems of sustaining placenta formation in embryos produced by nuclear transfer have emphasized the need for basic knowledge about epiblast formation and gastrulation in bovine embryos. The aims of this study were to define stages of bovine post-hatching embryonic development and to analyse functional mechanisms of germ-layer formation. Embryos developed in vivo were collected after slaughter from superovulated cows on days 9, 11, 14 and 21 after insemination and processed for transmission electron microscopy (n = 26) or immunohistochemistry (n = 27) for potential germ-layer characterization (cytokeratin 8 for potential ectoderm; alpha-1-fetoprotein for potential endoderm; and vimentin for potential mesoderm). On day 9, the embryos were devoid of zona pellucida and presented a well-defined inner cell mass (ICM), which was covered by a thin layer of trophoblast cells (the Rauber's layer). Formation of the hypoblast from the inside of the ICM was ongoing. On day 11, the Rauber's layer was focally interrupted and adjacent underlying ICM cells formed tight junctions. The hypoblast, which formed a thin confluent cell layer, was separated from the ICM and the tropho-blast by intercellular matrix. The embryos were ovoid to tubular and displayed a confluent hypoblast on day 14. The epiblast was inserted into the trophoblast epithelium and tight junctions and desmosomes were present between adjacent epiblast cells as well as between peripheral epiblast and trophoblast cells. In some embryos, the epiblast was more or less covered by foldings of trophoblast in the process of forming the amniotic cavity. Cytokeratin 8 was localized to the trophoblast and the hypoblast underlying the epiblast; alpha-1-fetoprotein was localized to most hypoblast cells underlying the trophoblast; and vimentin was localized to most epiblast cells. On day 21, the smallest embryos displayed a primitive streak and formation of the neural groove, whereas the largest embryos presented a neural tube, up to 14 somites and allantois development. These embryos depicted the gradual formation of the endoderm, mesoderm and ectoderm as well as differentiation of paraxial, intermediate and lateral plate mesoderm. Cytokeratin 8 was localized to the trophoblast, the hypoblast and the surface and neural ectoderm; and alpha-1-fetoprotein was localized to the hypoblast, but not the definitive endoderm, the intensity increasing with development. Vimentin was initially localized to some, but not all, cells positioned particularly in the ventral region of the primitive streak, to presumptive definitive endoderm cells inserted into the hypoblast, and to mesoderm. In conclusion, within 2 weeks of hatching, bovine embryos complete formation of the hypoblast and the epiblast, establishment of the amniotic cavity, ingression of epiblast cells for primitive streak formation, involution of cells through the node and the streak for endoderm and mesoderm fomation, neurulation and differentiation of the mesoderm. The recruitment of cells from the epiblast to form the primitive streak as well as the endoderm and mesoderm is associated with expression of the intermediate filament vimentin.

Immunohistochemical and ultrastructural characterization of the initial post-hatching development of bovine embryos

The problems of sustaining placenta formation in embryos produced by nuclear transfer have emphasized the need for basic knowledge about epiblast formation and gastrulation in bovine embryos. The aims of this study were to define stages of bovine post-hatching embryonic development and to analyse functional mechanisms of germ-layer formation. Embryos developed in vivo were collected after slaughter from superovulated cows on days 9, 11, 14 and 21 after insemination and processed for transmission electron microscopy (n = 26) or immunohistochemistry (n = 27) for potential germ-layer characterization (cytokeratin 8 for potential ectoderm; alpha-1-fetoprotein for potential endoderm; and vimentin for potential mesoderm). On day 9, the embryos were devoid of zona pellucida and presented a well-defined inner cell mass (ICM), which was covered by a thin layer of trophoblast cells (the Rauber's layer). Formation of the hypoblast from the inside of the ICM was ongoing. On day 11, the Rauber's layer was focally interrupted and adjacent underlying ICM cells formed tight junctions. The hypoblast, which formed a thin confluent cell layer, was separated from the ICM and the tropho-blast by intercellular matrix. The embryos were ovoid to tubular and displayed a confluent hypoblast on day 14. The epiblast was inserted into the trophoblast epithelium and tight junctions and desmosomes were present between adjacent epiblast cells as well as between peripheral epiblast and trophoblast cells. In some embryos, the epiblast was more or less covered by foldings of trophoblast in the process of forming the amniotic cavity. Cytokeratin 8 was localized to the trophoblast and the hypoblast underlying the epiblast; alpha-1-fetoprotein was localized to most hypoblast cells underlying the trophoblast; and vimentin was localized to most epiblast cells. On day 21, the smallest embryos displayed a primitive streak and formation of the neural groove, whereas the largest embryos presented a neural tube, up to 14 somites and allantois development. These embryos depicted the gradual formation of the endoderm, mesoderm and ectoderm as well as differentiation of paraxial, intermediate and lateral plate mesoderm. Cytokeratin 8 was localized to the trophoblast, the hypoblast and the surface and neural ectoderm; and alpha-1-fetoprotein was localized to the hypoblast, but not the definitive endoderm, the intensity increasing with development. Vimentin was initially localized to some, but not all, cells positioned particularly in the ventral region of the primitive streak, to presumptive definitive endoderm cells inserted into the hypoblast, and to mesoderm. In conclusion, within 2 weeks of hatching, bovine embryos complete formation of the hypoblast and the epiblast, establishment of the amniotic cavity, ingression of epiblast cells for primitive streak formation, involution of cells through the node and the streak for endoderm and mesoderm fomation, neurulation and differentiation of the mesoderm. The recruitment of cells from the epiblast to form the primitive streak as well as the endoderm and mesoderm is associated with expression of the intermediate filament vimentin.

Gene expression during pre- and peri-implantation embryonic development in pigs

Embryo technological procedures such as in vitro production and cloning by nuclear transfer are not as advanced in pigs as in cattle and cannot yet be applied under field conditions. The present paper focuses on genome activation in in vivo-derived, in vitro-produced and nuclear transfer pig embryos with special emphasis on the development of embryonic nucleoli, where the ribosomal RNA (rRNA) genes transcribed can be used as markers for genome activity. In addition, contemporary data on gene expression in in vivo-derived pig embryos are reviewed. In in vivo-derived pig embryos, pronounced transcription is initiated at the four-cell stage (the third cell cycle after fertilization), when nucleoli develop. In parallel with the development of the nucleoli as a result of rRNA gene activation, a cascade of other genes is also likely to be transcribed. However, apart from identification of transcripts for the oestrogen receptor at the blastocyst stage, reports on mRNAs resulting from initial transcription of the pig embryonic genome are lacking, in contrast to the situation in cattle and, in particular, mice. More information is available on gene expression during elongation of pig conceptuses, when the genes for steroidogenic enzymes, extracellular matrix receptors, oestrogen receptors, growth factors and their receptors, as well as retinol binding protein and retinoic acid receptors, are expressed. Nucleolus development appears to be disturbed in in vitro-produced pig embryos and in pig embryos reconstructed by nuclear transfer of granulosa cells to enucleated metaphase II oocytes produced by oocyte maturation in vivo or in vitro, which is indicative of disturbances in activation of rRNA genes.

Nucleolar protein allocation and ultrastructure in bovine embryos produced by nuclear transfer from granulosa cells

In the present study immunofluorescence confocal laser scanning microscopy, autoradiography following (3)H-uridine incubation and transmission electron microscopy were used to evaluate the nucleolar protein localization, transcriptional activity, and nucleolar ultrastructure during genomic re-programming in bovine embryos reconstructed by nuclear transfer from granulosa cells into non-activated cytoplasts followed by activation. During the 1st cell cycle (1-cell embryos), no autoradiographic labelling was detected. Ultrastructurally, nucleoli devoid of a granular component were observed. During the 2nd cell cycle (2-cell embryos) autoradiographic labelling was also lacking and the embryos displayed varying degrees of nucleolar inactivation. During both the 3rd (4-cell embryos) and 4th (tentative 8-cell embryos), cell cycles autoradiographic labelling was lacking in some embryos, while others displayed labelling and associated formation of fibrillo-granular nucleoli. During the 5th cell cycle (tentative 16-cell embryos), all embryos displayed autoradiographic labelling and fibrillo-granular nucleoli. In some blastomeres, however, deviant nucleolar ultrastructure was observed. During the first cell cycle labelling of RNA polymerase I, fibrillarin, upstream binding factor (UBF) and nucleolin (C23) was localized to nuclear entities. During the 2nd cell cycle, only labelling of RNA polymerase I and fibrillarin persisted. During the 3rd and 4th cell cycle labelling of fibrillarin persisted, labelling of nucleophosmin (B23) appeared and that of nucleolin re-appeared. During the 5th cell cycle almost all embryos showed complete labelling of all proteins except for UBF, which lacked in more than half of the embryos. In conclusion, bovine granulosa cell nuclear transfer embryos showed re-modelling of the nucleoli to an inactive form followed by re-formation of fibrillo-granular nucleoli. The re-formation of fibrillo-granular nucleoli was initiated already during the 3rd cell cycle, which is one cell cycle earlier than in in vivo- and in vitro-derived bovine embryos. Moreover, in more than half of the embryos, UBF could not be immunocytochemically localized to the nucleolar compartment during the 5th cell cycle indicating lack of developmental potentials.