T. Greve

Open pulled straw (OPS) vitrification: A new way to reduce cryoinjuries of bovine ova and embryos

Although cryopreservation of certain mammalian embryos is now a routine procedure, considerable differences of efficiency exist depending on stage, species and origin (in vivo or in vitro produced). Factors that are suspected to cause most of these differences are the amount of the intracellular lipid droplets and the different microtubular structure leading to chilling injury as well as the volume/surface ratio influencing the penetration of cryoprotectants. A new approach, the Open Pulled Straw (OPS) method, which renders very high cooling and warming rates (over 20,000°C/min) and short contact with concentrated cryoprotective additives (less than 30 sec over −180°C) offers a possibility to circumvent chilling injury and to decrease toxic and osmotic damage. In this paper we report the vitrification by the OPS method of in vitro produced bovine embryos at various stages of development. Embryos cryopreserved from Day 3 to Day 7 (Day 0 = day of fertilization) exhibited development into blastocysts at rates equivalent to those of control embryos; even those cryopreserved on Day 1 or 2 exhibited only somewhat reduced survival. Eighty‐one percent of Day 8 hatched blastocysts also survived the procedure. The method was also successfully used for bovine oocytes; of 184 vitrified oocytes, 25% developed into blastocysts after fertilization and culture for 7 days. Pregnancies were achieved following transfer after vitrification at both the oocyte and blastocyst stage. The OPS vitrification offers a new way to solve basic problems of reproductive cryobiology and may have practical impact on animal biotechnology and human assisted reproduction. Mol. Reprod. Dev. 51:53–58, 1998.

HIGH BOVINE BLASTOCYST DEVELOPMENT IN A STATIC IN VITRO PRODUCTION SYSTEM USING SOFAA MEDIUM SUPPLEMENTED WITH SODIUM CITRATE AND MYO-INOSITOL WITH OR WITHOUT SERUM-PROTEINS

We describe a bovine embryo culture system that supports repeatable high development in the presence of serum or BSA as well as under defined conditions in the absence of those components. In the first experiment, embryo development in SOF with amino acids (SOFaa), sodium citrate (SOFaac) and myo-inositol (SOFaaci) and with BSA or polyvinyl alcohol (PVA) was compared with that in a M199 granulosa cell co-culture (M199 co-culture). Subsequently, development and cell numbers of blastocysts cultured under defined conditions in SOFaaci with PVA (SOFaaci-PVA), or under undefined conditions in SOFaaci with 5% cow serum (SOFaaci-CS) or M199 co-culture were compared. The repeatability of culture results in SOFaaci-CS was checked by weekly replicates (n = 30) spread over 11 months. The viability of embryos developed in SOFaaci-PVA was estimated by transfer of morphologically good blastocysts (n = 10) to synchronized recipients. In the second experiment, the effect of omitting CS or BSA from IVM and IVM-IVF on subsequent embryo development in SOFaaci-PVA or in SOFaaci-CS was investigated. Blastocyst development in SOFaa-PVA, SOFaac-PVA, SOFaa-BSA and M199 was 16 +/- 3b, 23 +/- 2ab, 30 +/- 8a and 36 +/- 7a%, respectively (Pab < 0.05). Additional inclusion of myoinositol resulted in 42 +/- 1a% blastocysts in SOFaaci-PVA vs 19 +/- 3b% in SOFaac-PVA, 47 +/- 7a% in SOFaac-BSA, and 36 +/- 7a% in M199 co-culture, respectively (Pab < 0.01). In 30 replicates, the average cleavage and blastocyst rates of oocytes in SOFaaci-CS were 87 +/- 4 and 49 +/- 5%, respectively. Five normal calves were produced after transfer of 10 blastocysts developed in defined culture medium (i.e., SOFaaci-PVA). Defined IVM or IVM-IVF (i.e., in absence of CS and BSA) reduced cleavage rates (83 +/- 3 and 55 +/- 3% vs 90 +/- 1% in presence of CS; P < 0.01). Subsequent embryo development in SOFaaci-CS was not affected in either of these defined conditions. However, cleavage and blastocyst rates under completely defined IVP conditions were 54 +/- 7 and 19 +/- 4%, respectively. It was concluded that under defined culture conditions, addition of citrate and myo-inositol improved blastocyst development to rates comparable to those obtained with serum, BSA or co-culture and that the quality of blastocysts was not affected by the absence of serum or BSA. However, serum was essential during IVM/IVF for normal fertilization and subsequent high blastocyst development.

Oocyte growth, capacitation and final maturation in cattle

Abstract The oocyte growth phase includes a series of modulations of organelles and inclusions, as well as a period of oocyte transcription, which are necessary for the oocyte to achieve meiotic and developmental competence. Oocyte transcription including nucleolar function (rRNA-synthesis) is activated in the secondary follicle and is maintained up to an oocyte diameter of about 110 μm in the 3 mm tertiary follicle. At a diameter of 100 to 110 μm, the oocyte gradually achieves the competence to undergo meiotic maturation and sustain embryonic development. In the dominant follicle the oocyte undergoes further ultrastructural modifications and attains full developmental competence through a process that may be termed “capacitation”. The final oocyte maturation up to metaphase II after LH stimulation of the ovulatory follicle is the culmination of the previous processes and equips the oocyte with a haploid chromosomal compartment and the cell biological apparatus specialized for fertilization and initial embryonic development.

New method for culture of zona-included or zona-free embryos: the Well of the Well (WOW) system.

Culture of mammalian zygotes individually and in small groups results in lower developmental rates than culture of large groups. Zona‐free zygotes also have impaired developmental potential in current culture systems. This paper describes a new approach to resolve the problems, the Well of the Well (WOW) system. Small wells (WOWs) were formed in four‐well dishes by melting the bottom with heated steel rods. The WOWs were then rinsed, the wells were filled with medium, and the embryos were placed into the WOWs. To test the value of the WOW system a 3 × 3 factorial experiment was performed. Bovine presumptive zygotes were cultured from day 1 to day 7 (day 0: day of insemination) using three modules (single embryos, embryo groups of five, or single zona‐digested embryos) and three different culture systems (400 μl medium, 200 μl drops, or WOWs). An additional control group consisted of 40 to 50 embryos cultured in 400 μl medium. The WOW system resulted in higher blastocyst/oocyte rates for all three modules (single: 59%; group of five: 61%; single zona‐digested: 53%) than the culture in drops or in wells (P < 0.05 for all). The developmental rate was independent of the number of WOWs per well. The cell number of blastocysts cultured in the WOW system did not differ from that of the controls. Apart from its theoretical value in revealing the role of different factors influencing embryo development in vitro, the WOW system may have immediate practical consequences in certain areas of mammalian embryo production. Mol Reprod Dev 55:256–264, 2000.

Sex and development in bovine in-vitro fertilized embryos

In vitro fertilized bovine embryos were karyotyped at Day 7 and Day 8 post insemination. The results showed that the percentage of males (sex ratio) was dependent on the developmental stage. Among expanded blastocysts (the most advanced embryos), the sex ratio was 100%, followed by 89% for expanding blastocysts, 75% for blastocysts, and 40% for young blastocysts, all analyzed at Day 7. For embryos karyotyped at Day 8, the sex ratio was 20%. The average mitotic index for all in vitro fertilized embryos was 3.5%. These results suggest that the apparent relationship between sex and developmental rate could be used as a method for noninvasive sexing of in vitro fertilized embryos.

Oocyte ultrastructure in bovine primordial to early tertiary follicles.

Abstract The aim of the present study was to describe in detail the changes occurring in the cytoplasmic ultrastructure of the bovine oocyte from the onset of growth in the primordial follicle until the completion of growth in the tertiary follicle. Bovine oocytes from primordial, primary, secondary and early to mid-antral follicles were processed and analysed by light and transmission electron microscopy. The primordial follicular oocyte was characterized by numerous coated pits on the oolemma and the accumulation of free and organelle-related smooth (SER) and rough (RER) endoplasmic reticulum, round mitochondria and Golgi complexes around the nucleus, which was located slightly off centre. Up to the secondary follicular stage the oocyte displayed an increase in the number of microvilli, elongated mitochondria and Golgi complexes. During the secondary follicular stage, formation of the zona pellucida, development of gap junctions between the oocyte and the granulosa cells, formation of the cortical granules in the oocyte and reduction in the number of coated pits on the oolemma were seen. In the tertiary follicular oocyte up to 100 μm in diameter, the number of Golgi complexes and lipid droplets increased and the organelles were dislocated to the deep cortical region. During the final growth of the oocyte up to >120 μm, the organelles were dislocated further to the peripheral region, the extent of the free SER and RER compartments were reduced, the number of individual cortical granules increased, hooded mitochondria became abundant and the perivitelline space developed. In conclusion, the growth of the bovine oocyte is associated with the relocation and modulation of a number of cytoplasmic organelles as well as the development of oocyte specific structures such as the zona pellucida and cortical granules.

Handmade somatic cell cloning in cattle: analysis of factors contributing to high efficiency in vitro.

Abstract Widespread application of somatic cell cloning has been hampered by biological and technical problems, which include complicated and time-consuming procedures requiring skilled labor. Recently, zona-free techniques have been published with limited or no requirement for micromanipulators. The purpose of the present work was to optimize certain steps of the micromanipulator-free (i.e., handmade) procedure, to analyze the morphology of the developing blastocysts, and to explain factors involved in the high efficiencies observed. Optimization of the procedure included selection of the appropriate medium for enucleation, orientation of pairs at fusion, timing of fusion, and culture conditions. As a result of these improved steps, in vitro efficiency as measured by blastocysts per reconstructed embryo and blastocysts per working hour was among the highest described so far. The cattle serum used in our experiments was superior to other protein sources for in vitro embryo development. One possible explanation of this effect is the considerable mitogenic activity of the cattle serum compared with that of commercially available fetal calf serum. Morphological analysis of blastocysts by inverted microscopy, inner cell mass-trophoblast differential staining, and transmission electron microscopy revealed high average quality. A high initial pregnancy rate was achieved after the transfer of single blastocysts derived by aggregation of two nuclear transfer embryos into recipients. The improved handmade somatic cell nuclear transfer method may become a useful technology as a simple, inexpensive, and efficient alternative to traditional somatic cell nuclear transfer.

The effect of media, serum and temperature on in vitro survival of bovine blastocysts after Open Pulled Straw (OPS) vitrification.

The recently introduced Open Pulled Straw (OPS) vitrification technique has successfully been used for cryopreserving porcine embryos as well as for bovine embryos and oocytes. The aim of this work is to investigate several factors on the in vitro survival of bovine blastocysts. In 5 experiments, a total of 862 in vitro produced blastocysts and expanded blastocysts was vitrified and warmed using the OPS technology, then cultured in vitro for an additional 3 days. The culture medium in Experiments 1 to 4 was SOFaa with supplements and 5% calf serum (CS). In Experiment 1, the replacement of TCM-199 + 20% CS with PBS + 20% CS in the holding medium during vitrification and warming did not result in significant differences in the re-expansion (92 vs 95%) and hatching rates (79 vs 72%). In Experiment 2, the PBS holding medium was supplemented with either 20% CS, 5 mg/mL bovine serum albumin (BSA) or 3 mg/mL polyvinylalcohol (PVA). Although the re-expansion rates did not differ (98, 95 and 93%, respectively), there was a decrease in the hatching rate after vitrification with PVA (77 and 78 vs 51%, respectively). In Experiment 3, the influence of temperature of equilibration media prior to and rehydration media after the vitrification was investigated. When the temperature of these media was adjusted to 20 degrees C instead of the standard 35 degrees C, both the re-expansion and the hatching rates decreased markedly. However, increasing the time of equilibration with the diluted cryoprotectant solution at 20 degrees C eliminated these differences. In Experiment 4, the ethylene-glycol and dimethyl sulfoxide cryoprotectant mixture was replaced with ethylene glycol-ficoll-trehalose solution. No difference in the re-expansion (89 vs 96%, respectively) or hatching rate (79 vs 84%, respectively) was detected. In Experiment 5, the vitrified-warmed blastocysts were cultured in SOFaa medium supplemented with 5% CS or 5 mg/mL BSA. Although the re-expansion rates were identical in the 2 groups (95%), the hatching rates were lower when embryos were cultured in BSA (71 and 47%, respectively). These findings indicated the possible broader application for OPS, as they demonstrated that the physical advantages of rapid cooling and warming may be accompanied by different chemical composition (holding media, cryoprotective additives) according to the requirements of the biological structure. Our study also shows the need for serum supplementation of the medium for hatching to occur after OPS vitrification.

The effects of exogenous gonadotropins on oocyte and embryo quality in cattle

Abstract It is well documented and unfortunately accepted that approximately 15 to 20% of all donor cattle superstimulated with eCG or FSH yield no transferable embryos. In the present paper, some factors leading to reduced oocyte and embryo quality are discussed. We have focused firstly on certain endocrine and oocyte maturational features which take place during the period of luteal regression, i.e. the period from PGF2α administration until the preovulatory LH surge, and secondly, on the relationship between the superovulatory response and the embryo quality on Day 7. We conclude that: 1) treatment with eCG or FSH causes increased estradiol-17β plasma levels, suppressed episodic LH secretion, earlier occurrence of the LH surge and the nucleoli of oocytes from undergoing the normal vacuolization in a certain proportion of donor cattle, 2) although subtle and hardly measurable, these deviations have a profound effect on the subsequent embryonic developmental capacity, 3) the superovulatory response does not affect the subsequent viability of embryos transferred on Day 7 and 4) optimization of the donors reproductive physiology is the only way to reduce the incidence of non-transferable embryos.

Transcriptional activity in in vitro produced bovine two- and four-cell embryos

The objectives of this study on in vitro produced bovine two‐ and four‐cell embryos were (1) to investigate the uptake of 3H‐uridine through the plasma membrane, (2) to characterize the pattern of RNA synthesis during the second cell cycle, and (3) to measure the incorporation of 3H‐uridine into de novo synthesized RNA. A total of 200 embryos were incubated with 3H‐uridine for 15, 30, 60 (two‐ and four‐cell embryos), 120 (four‐cell embryos), 180 (two‐cell embryos), and 240 min (two‐ and four‐cell embryos), respectively. 3H‐uridine uptake reached a maximum by 30 min in two‐cell embryos, whereas four‐cell embryos reached a maximum at 120 min. A total of 440 two‐cell embryos were isolated 27–33 hr postinsemination (hpi), and 90 of these were incubated for 10 hr with 3H‐uridine (200 μCi/ml). The remainder were incubated with 3H‐uridine for 3 hr starting at 0–3 (n = 54), 3–6 (n = 75), 6–9 (n = 77), or 9–12 (n = 77) hr after cleavage to the two‐cell stage. Control two‐cell embryos (n = 67) were incubated with 3H‐uridine supplemented with 5 mg/ml of unlabelled uridine for 10 hr (inhibition control), or they were incubated with 3H‐uridine for 10 hr and RNase treated (100 μg/ml post fixation (RNase control). Subsequently, the embryos were processed for autoradiography. The long‐term incubation revealed transcription (autoradiographically labelled nuclei) in a total of 77% of the two‐ and four‐cell embryos. No transcription was observed in any of the 3 hr incubation groups. The RNase control embryos lacked labelling of the nuclei, whereas the inhibition control embryos only showed markedly reduced labelling. Finally, total RNA extraction was performed on a total of 336 two‐cell embryos that were incubated with 3H‐uridine or 3H‐uridine supplemented with unlabelled uridine for 2, 5, or 10 hr. It was possible to detect an increasing amount of labelled RNA after the 2, 5, and 10 hr incubation periods, and it was possible to inhibit this incorporation competitively. Together the data demonstrate a low level of transcription during the second cell cycle without a well‐defined transcriptional peak.