Importance of cumulus cells and insemination intervals for development of bovine oocytes into morulae and blastocysts in vitro

Nuclear transfer improves the developmental potential of embryos derived from cytoplasmic deficient oocytes

Embryo development after fertilization is largely determined by the oocyte quality, which is in turn dependent on the competence of both the cytoplasm and nucleus. Here, to improve the efficiency of embryo development from developmentally incompetent oocytes, we performed spindle-chromosome complex transfer (ST) between in vitro matured (IVM) and in vivo matured (IVO) oocytes of the non-human primate rhesus monkey. We observed that the blastocyst rate of embryos derived from transferring the spindle-chromosome complex (SCC) of IVM oocytes into enucleated IVO oocytes was comparable with that of embryos derived from IVO oocytes. After transferring the reconstructed embryos into the uterus of surrogate mothers, two live rhesus monkeys were obtained, indicating that the nuclei of IVM oocytes support both the pre-and post-implantation embryo development of non-human primates.

Cumulus cells during in vitro fertilization and oocyte vitrification in sheep: Remove, maintain or add?

The objective was to evaluate the developmental competence of immature and matured ovine oocytes after removing, maintaining or adding cumulus cells (CC) associated to vitrification by Cryotop method. Three experiments were performed involving 3,144 oocytes. In Experiment 1, CC were removed from immature, matured or fertilized oocytes subjected to in vitro embryo production. In Experiment 2, oocytes were vitrified either in MI or MII stage with or without CC, while a control group with CC remained unvitrified. In Experiment 3, oocytes partially denuded from CC were vitrified either in MI or MII stage, and a co-culture of fresh CC was added or not soon after warming to complete in vitro maturation (IVM) and in vitro fertilization (IVF), or IVF, respectively, while a control group remained unvitrified. In Experiment 1, the cleavage rate, development rate on Day 6 and blastocyst rate on Day 8 were improved when CC were maintained until the end of IVF (P < 0.05). In Experiment 2, vitrification of oocytes with enclosed CC showed a tendency to increase cleavage (P = 0.06) and improved blastocyst rate (P < 0.05). In Experiment 3, adding CC as co-culture after vitrification-warming tended to improve cleavage rate (P = 0.06) and increased hatching rate (P < 0.05). Regarding oocyte stage, vitrification of in vitro matured oocytes resulted in greater developmental competence than immature stages (P < 0.05). In conclusion, CC seems to have a relevant role for in vitro embryo development in either fresh or vitrified oocytes.

Failure to launch: aberrant cumulus gene expression during oocyte in vitro maturation

In vitro maturation (IVM) offers significant benefits for human infertility treatment and animal breeding, but this potential is yet to be fully realised due to reduced oocyte developmental competence in comparison with in vivo matured oocytes. Cumulus cells occupy an essential position in determining oocyte developmental competence. Here we have examined the areas of deficient gene expression, as determined within microarrays primarily from cumulus cells of mouse COCs, but also other species, between in vivo matured and in vitro matured oocytes. By retrospectively analysing the literature, directed by focussing on downregulated genes, we provide an insight as to why the in vitro cumulus cells fail to support full oocyte potential and dissect molecular pathways that have important roles in oocyte competence. We conclude that the roles of epidermal growth factor signalling, the expanded extracellular matrix, cumulus cell metabolism and the immune system are critical deficiencies in cumulus cells of IVM COCs.

Effects of co-culture of cumulus oocyte complexes with denuded oocytes during in vitro maturation on the developmental competence of cloned bovine embryos

This study evaluated the effects of co-culture of immature cumulus oocyte complexes (COCs) with denuded immature oocytes (DO) during in vitro maturation on the developmental competence and quality of cloned bovine embryos. We demonstrated that developmental competence, judged by the blastocyst formation rate, was significantly higher in the co-cultured somatic cell nuclear transfer (SCNT+DO, 37.1 ± 1.1%) group than that in the non-co-cultured somatic cell nuclear transfer (SCNT-DO, 25.1 ± 0.9%) group and was very similar to that in the control IVF (IVF, 38.8 ± 2.8%) group. Moreover, the total cell number per blastocyst in the SCNT+DO group (101.7 ± 6.2) was higher than that in the SCNT-DO group (81.7 ± 4.3), while still less than that in the IVF group (133.3 ± 6.0). Furthermore, our data showed that mRNA levels of the methylation-related genes DNMT1 and DNMT3a in the SCNT+DO group were similar to that in the IVF group, while they were significantly higher in the SCNT-DO group. Similarly, while the mRNA levels of the deacetylation-related genes HDAC2 and HDAC3 were significantly higher in the SCNT-DO group, they were comparable between the IVF and SCNT+DO groups. However, the mRNA levels of HDAC1 and DNMT3B were significantly higher in the SCNT+DO group than in the other groups. In conclusion, the present study demonstrated that co-culture of COCs with DO improves the in vitro developmental competence and quality of cloned embryos, as evidenced by increased total cell number.

Glucose requirement at different developmental stages of in vitro fertilized bovine embryos cultured in semi-defined medium

Three experiments were conducted in which 2-cell bovine embryos were prepared from oocytes, obtained from abattoir ovaries, by in-vitro maturation for 22 to 24 hours, followed by exposure to spermatozoa for 8 hours and culture for 40 hours within the cumulus. The cumulus cells were then removed, and the cleaved embryos were cultured for a further 120 hours or longer, in the presence or absence of glucose, pyruvate and lactate. Very few embryos developed in the complete absence of energy substrates. Lactate and pyruvate, alone or combined, supported development to the 8-cell stage, but pyruvate was required to support development to the morula stage (Experiment 1). When present throughout culture or when added at 48 or 96 hours postinsemination, 5.56 mM glucose was detrimental to development (Experiments 1 and 2). However, when added at 120 hours postinsemination, 5.56 mM glucose improved development to the blastocyst and expanded blastocyst stages, compared with no glucose or 11.12 mM glucose (Experiment 3).

Coculturing denuded oocytes during the in vitro maturation of bovine cumulus oocyte complexes exerts a synergistic effect on embryo development

The present study examined the effect of coculturing cumulus oocyte complexes (COCs) and denuded oocytes (DOs) during in vitro maturation (IVM) on nuclear and cytoplasmic maturation, zona pellucida (ZP) hardening, the pattern of fertilization and glutathione peroxidase 1 (GPX1) gene expression in the oocyte. Furthermore, the rate of embryonic development and the quality of blastocysts were examined for both COCs and DOs. Three IVM conditions were studied: 1) the coculture of 12 COCs and 60 DOs, 2) COC control with 12 COCs, and 3) DO control with 60 DOs. The IVM was performed in a 120-μl droplet of TCM199-based IVM medium. Following IVM, in vitro fertilization (IVF) and in vitro culture (IVC) were conducted separately for the COCs and DOs (DO coculture) from the IVM coculture group. Coculturing COCs and DOs increased the percentage of oocytes reaching the blastocyst stage and the total number of cells per blastocyst in both the COC coculture (44.4 ± 8.6 vs 26.7 ± 9.7%, P < 0.01, and 137.9 ± 24.9 vs 121.7 ± 21.1, P < 0.05) and the DO coculture (20.5 ± 5.0 vs 11.1 ± 2.5%, P < 0.01, and 121.9 ± 27.5 vs 112.3 ± 33.2, P < 0.05) compared to their respective control groups. The synergistic effects of coculturing were detected as increased nuclear and cytoplasmic maturation, the prevention of ZP hardening, increased monospermic fertilization and increased expression of GPX1 in the oocytes in response to endogenous oocyte-secreted factors. In conclusion, coculturing COCs and DOs may be an effective culture system for both intact COCs and immature DOs.

The influence of sperm concentration, length of the gamete co-culture and the evolution of different sperm parameters on the in vitro fertilization of prepubertal goat oocytes

The aims of the present study were: (1) to evaluate the influence of sperm concentration (ranging from 0.5 × 106 to 4 × 106 spermatozoa/ml) and length of the gamete co-incubation time (2, 4, 6, 8, 10, 12, 16, 20, 24 or 28 h) on in vitro fertilization (IVF), assessing the sperm penetration rate; (2) to investigate the kinetics of different semen parameters as motility, viability and acrosome status during the co-culture period; and (3) to analyse the effect of the presence of cumulus–oocytes complexes (COCs) on these parameters. To achieve these objectives, several experiments were carried out using in vitro matured oocytes from prepubertal goats. The main findings of this work are that: (1) in our conditions, the optimum sperm concentration is 4 × 106 sperm/ml, as this sperm:oocyte ratio (approximately 28,000) allowed us to obtain the highest penetration rate, without increasing polyspermy incidence; (2) the highest percentage of viable acrosome-reacted spermatozoa is observed between 8–12 h of gamete co-culture, while the penetration rate is maximum at 12 h of co-incubation; and (3) the presence of COCs seems to favour the acrosome reaction of free spermatozoa on IVF medium, but not significantly. In conclusion, we suggest that a gamete co-incubation for 12–14 h, with a concentration of 4 × 106 sperm/ml, would be sufficient to obtain the highest rate of penetration, reducing the exposure of oocytes to high levels of reactive oxygen species produced by spermatozoa, especially when a high sperm concentration is used to increase the caprine IVF outcome.

Development of vitrified–thawed bovine oocytes after in vitro fertilization and somatic cell nuclear transfer

Cryopreservation could be a useful technique for providing a steady source of oocytes for nuclear transfer and in vitro embryo production. The purpose of this study was to develop a method for cryopreservation of bovine oocytes while maintaining the developmental potential following subsequent in vitro fertilization (IVF) or somatic cell nuclear transfer (SCNT). Following vitrification-thawing, the surviving oocytes were (a) used for parthenogenetic activation, (b) examined for pronuclear formation after IVF, (c) examined for embryo development after IVF, and (d) used for SCNT employing fetal fibroblasts transfected with green fluorescent protein (GFP) gene. While most of the oocytes survived vitrification when the microdrop method was used (92.50%), the cleavage and blastocyst formation rates after parthenogenetic activation were lower (46.5% and 11.1%) than that in the non-vitrified control (86.6% and 13.5%). After IVF, the pronuclear formation (2PN) of fertilized embryos was lower in the vitrified group than in the control (21.7% and 59.9%). After SCNT, fusion rates were similar in control (58.33%) and vitrified-thawed oocytes (53.19%). However, the cleavage (73.1% and 46.3%) and blastocyst formation rates (22.2%, 7.4%; p<0.05) differed between control and vitrified-thawed oocytes. In vitrified-thawed or control oocytes, all embryos reconstructed using fetal fibroblasts transfected with GFP gene showed GFP expression. To evaluate the complete developmental potential, embryos derived from vitrified-thawed and fresh control oocytes were non-surgically transferred to 27 recipients (16 for control and 11 for vitrified-thawed). In the vitrified-thawed group, two pregnancies were detected at day 60, and one of them lasted until day 222. While in the fresh group, one pregnancy maintained to term. In conclusion, vitrified-thawed bovine oocytes could support development into the subsequent stages after IVF and SCNT. In addition, this study showed the possibility of the vitrified-thawed bovine oocytes in the production of transgenic cloned animals. In addition, further studies are required to increase the efficiency of oocyte vitrification for the practical uses and production of live offspring.

Comparison of hybrid and purebred in vitro-derived cattle embryos during in vitro culture

Frozen-thawed spermatozoa collected from a beef bull (Japanese Black) were used for in vitro fertilization (IVF) of matured oocytes obtained from dairy (Holstein) and beef (Japanese Black) females. Embryos were examined for fertilization, cleavage rate, interval between insemination and blastocyst production (experiment I), total cell number per embryo and sex ratio during blastocyst formation (experiment II), and blastocyst production rate of zygotes that developed to 2-, 4-, and 8-cell stages at 48h post-fertilization (experiment III). Fertilized oocytes were cultured in vitro on a cumulus cell co-culture system. The fertilization and cleavage rate of oocytes groups were similar, however, the blastocyst production rate was greater (P<0.05) in hybrid than from purebred embryos (27% versus 20%). Development of blastocysts produced from hybrid embryos developed at a faster rate than blastocysts produced from the straightbred embryos. In hybrid embryos, blastocyst production was significantly greater on day 7 (56%) and gradually decreased from 20% on day 8 to 17% on day 9. In contrast, blastocyst production rate from the purebred embryos was lower on day 7 (17%), increasing on day 8 to 59% and then decreased on day 9 to 24%. The total number of cells per embryo and sex ratio of in vitro-produced blastocysts were not different between hybrid and purebred embryos. The number of blastocysts obtained from embryos at the 8-cell stage of development by 48h post-fertilization (94%) was greater (P<0.01) than the number of zygotes producing blastocysts that had developed to the 4-cell stage (4%) and the 2-cell stage (2%) during the same interval. These results show that the blastocyst production rate and developmental rate to the blastocyst stage were different between hybrid and purebred embryos, and that almost all of the in vitro-produced blastocysts were obtained from zygotes that had developed to the 8-cell stage 48h post-fertilization.

Cumulus contributions during bovine fertilization in vitro

A mandatory step in performing micromanipulation techniques, studying sperm-oocyte interactions and evaluating morphological aspects of oocyte quality is the removal of cumulus cells from oocytes or zygotes at various stages. In cattle, cumulus removal shortly before fertilization in vitro strongly decreases sperm penetration rates. This study was conducted to evaluate the function of the cumulus oophorus during bovine fertilization in vitro. The importance of cumulus secretions during IVF was investigated by inseminating cumulus-denuded oocytes (CDOs) in fertilization medium supplemented with individual cumulus secretions, such as progesterone or hyaluronic acid. None of these substances increased the fertilization rate of CDOs. However, fertilizing CDOs in cumulus-conditioned medium or on a cumulus monolayer partially restored the reduction in fertilization rate (P<0.05). The fertilization rate of CDOs inseminated on a cumulus monolayer further increased when physical contact between the gametes and the monolayer was prevented by fertilizing them inside a culture plate insert placed on the monolayer (P<0.05). Finally, the importance of reactive oxygen species (ROS) generation and O(2) concentration during IVF was studied. Luminol-dependent chemiluminescence revealed a higher ROS load in conditioned medium of cumulus-enclosed oocytes (CEOs) than in that of CDOs after sperm-oocyte co-incubation (P<0.05). Furthermore, lowering the external O(2) concentration from 20 to 5% decreased the fertilization rate of both CEOs and CDOs, but had a higher impact on CEOs (P<0.05). In conclusion, this study provides evidence that the cumulus oophorus benefits the fertilizing ability of penetrating spermatozoa by creating a complex microenvironment of both cumulus secretions and metabolic products around the oocyte. Gap junctional communication between the oocyte and corona cells as well as sperm trapping by the cumulus oophorus seem to be essential factors in supporting fertilization.

Effect of cumulus cell removal of in vitro matured bovine oocytes prior to in vitro fertilization on subsequent cleavage rate

The aim of this study is to identify the effect of cumulus cells removal prior to the in vitro fertilization of matured bovine oocytes on cleavage rate. Denuded, matured oocytes were fertilized in presence or absence of loose cumulus cells, cumulus cell conditioned IVF medium (CCCM), charcoal-treated CCCM and charcoal-treated CCCM supplemented with progesterone at a final concentration of 150 ng/ml. After 18 h of incubation with sperm, the presumptive embryos were cultured on a BRL monolayer and the percentage of cleaved embryos was evaluated on Day 4. Removal of cumulus cells prior to IVF significantly reduced the cleavage rate (25% for denuded oocytes versus 56% for cumulus-oocyte complexes (COCs)). The addition of loose cumulus cells partially restored the effect of denudation (cleavage rate: 37% for denuded oocytes supplemented with loose cumulus cells versus 27% for denuded oocytes and 58% for COCs). CCCM also had a positive effect on the cleavage rate of oocytes denuded prior to IVF (36% for denuded oocytes fertilized in CCCM versus 14% for denuded oocytes). Treating the CCCM with charcoal resulted in complete loss of its effect on cleavage rate (18% for denuded oocytes fertilized in charcoal-treated CCCM versus 34% for denuded oocytes fertilized in CCCM). The addition of progesterone to charcoal-treated CCCM partially restored the reduction of the cleavage rate caused by charcoal treatment (27% for denuded oocytes fertilized in charcoal-treated CCCM supplemented with progesterone versus 14% for denuded oocytes fertilized in charcoal-treated CCCM and 36% for denuded oocytes fertilized in CCCM). In conclusion, removal of cumulus cells prior to IVF adversely affects the cleavage rate through loss of a factor secreted by these cells. This factor probably is progesterone.

Cysteine, glutathione, and Percoll treatments improve porcine oocyte maturation and fertilization in vitro

Several factors have been examined to improve in vitro fertilization and development of porcine oocytes. Cysteine is known to be beneficial for oocyte maturation and male pronuclear formation in pigs and glutathione is known to help prevent membrane disruption of sperm in other species, including human. It has also been reported that the presence of cumulus cells influences the outcome of in vitro fertilization in cattle. The objectives of the present study were to investigate the effects of several factors involved in porcine in vitro maturation (IVM) and fertilization (IVF) procedures on oocyte embryogenic competence. The following factors were examined: the effects of different concentrations (0, 0.285, 0.57, 1.14, 2.28 microM) and exposure duration (22 and 44 hr) of cysteine during IVM, glutathione inclusion and of cumulus presence during IVF, and the use of gradient Percoll (45%/90%) during sperm preparation. The presence of cysteine in maturation medium improved blastocyst development significantly regardless of the duration of exposure when compared to the control (11--16% vs. 4%, P < 0.01). However, no dose-responsive effect was observed at the concentrations tested. The use of gradient Percoll during sperm preparation significantly improved cleavage (85% vs. 57%, P < 0.01) and blastocyst development (24% vs. 6%, P < 0.01) over conventional sperm preparation. Significant improvement was also achieved by the addition of glutathione to Percoll gradient (30% vs. 20%, P < 0.05). In conclusion, cysteine and glutathione as well as Percoll and cumulus were beneficial to embryogenic competence of porcine oocytes in this study. Mol. Reprod. Dev. 59:330-335, 2001.

Influence of cumulus cells and sperm concentration on cleavage rate and subsequent embryonic development of buffalo (Bubalus bubalis) oocytes matured and fertilized in vitro

The objective of the present study was to investigate the effects of sperm concentration and presence or absence of cumulus cells on fertilization, cleavage rate and subsequent embryonic development upto the blastocyst stage in buffalo. Cumulus-oocyte-complexes (COCs) obtained from slaughterhouse ovaries were matured in vitro in TCM-199 + 10% FBS + 5 micrograms/mL FSH-P for 24 h. After maturation the COCs were either used as such (cumulus-intact) or freed from attached cumulus cells by repeated pipetting (cumulus-free). Frozen-thawed buffalo spermatozoa were treated with 10 micrograms/mL heparin and 2.5 mM caffeine for sperm capacitation. Oocytes were fertilized in vitro with 1 to 2, 4 to 5 or 9 to 10 million sperm/mL and the cleavage rate was recorded 42 to 44 h post insemination. The cleaved embryos were co-cultured with buffalo oviductal epithelial cells for 10 d post insemination, and the uncleaved oocytes were fixed and stained with aceto-orcein for determination of the penetration rate. The cleavage rate and the proportion of cleaved embryos that developed to morula and blastocyst stages were significantly higher (P < 0.05) whereas the proportion of degenerated oocytes and those that became arrested at the 2 to 16-cell stage were significantly lower (P < 0.05) with cumulus-intact than with cumulus-free oocytes at the 3 sperm concentrations. Increasing the sperm concentration increased the cleavage rate significantly (P < 0.05) from 1 to 2 million through 9 to 10 million sperm/mL but had no effect on the proportion of cleaved embryos that developed to morula and blastocyst stages. In conclusion, the results of the present study suggest that cumulus cells have a positive influence on fertilization, cleavage and subsequent embryonic development. Increase in sperm concentration increases cleavage rate without affecting subsequent embryonic development.

Hyaluronidase activity of macaque sperm assessed by an in vitro cumulus penetration assay

A model system consisting of cynomolgus macaque sperm and ovulated hamster ova-cumulus complexes (OCCs) was utilized to study the role of the sperm protein PH-20 in cumulus penetration. The hyaluronidase activity of solubilized macaque sperm PH-20 was evaluated using an ELISA-like microplate assay prior to and following the addition of the hyaluronidase inhibitors heparin (0-100 microg/ml) and apigenin (250 microM), as well as the Ig fraction of a polyclonal antibody raised against purified recombinant macaque PH-20 (R10; 10-400 microg/ml). Sperm motility following exposure to enzyme inhibitors was evaluated using computer-aided sperm motility analysis. Macaque sperm were labeled with the permeant fluorescent nuclear dye, Hoechst 33342, and were coincubated with ovulated hamster OCCs for 30 min at 37 degrees C. The addition of heparin, apigenin, or R10 antibody to solubilized sperm extracts resulted in a linear dose-dependent decrease in hyaluronidase activity (P < .01). In the heterologous cumulus penetration assay, fluorescently labeled macaque sperm that were pretreated with heparin (1-100 microg/ml), apigenin (250 microM), or R10 antibody (Ig fraction, 10-400 microg/ml) demonstrated a dose-dependent decrease in the ability to penetrate hamster OCCs (P < 0.01), in the absence of effects on sperm motility. In the homologous assay, experiments using macaque OCCs and fluorescently labeled macaque sperm confirmed that the same concentrations of heparin and R10 antibody similarly suppressed spermatozoal cumulus penetration (P < .01). These results suggest that macaque sperm PH-20-derived hyaluronidase participates in cumulus penetration in this species, and that this model system is useful for further studies into primate gamete interaction.

Growth of preimplantation bovine embryos

Development of mammalian embryos in vitro is functionally and temporally inferior to embryo development as it occurs inside the female reproductive tract. The deficiencies of cultured embryos range from slow cleavage rates to complete developmental arrests or blocks, occurring at particular stages in many species. A variety of approaches have been used to overcome the blocks, including most extensively the coculture of preimplantation embryos with various somatic cells. However, even with coculture, development of embryos in vitro is still not equivalent to that in vivo. In most laboratories, only 25-40% of inseminated oocytes develop into morulae and blastocysts in spite of numerous variations on the basic technique. A better understanding of the factors governing embryonic growth is required before we can hope to achieve results comparable with those occurring in vivo.

Cumulus cell function during bovine oocyte maturation, fertilization, and embryo development in vitro

Several contemporary micromanipulation techniques, such as sperm microinjection, nuclear transfer, and gene transfer by pronuclear injection, require removal of cumulus cells from oocytes or zygotes at various stages. In humans, the cumulus cells are often removed after 15-18 hr of sperm-oocyte coincubation to assist the identification of the fertilization status. This study was designed to evaluate the function of cumulus cells during oocyte maturation, fertilization, and in vitro development in cattle. Cumulus cells were removed before and after maturation and after fertilization for 0, 7, 20, and 48 hr. The cumulus-free oocytes or embryos were cultured either alone or on cumulus cell monolayers prepared on the day of maturation culture. Percentages of oocyte maturation, fertilization, and development to cleavage, morula, and blastocyst stages and to expanding or hatched blastocysts were recorded for statistical analysis by categorical data modeling (CATMOD) procedures. Cumulus cells removed before maturation significantly reduced the rate of oocyte maturation (4-26% vs. 93-96%), fertilization (0-9% vs. 91-92%), and in vitro development at all stages evaluated. Cumulus cells removed immediately prior to in vitro fertilization (IVF) or 7 hr after IVF reduced the rates of fertilization (58-60% and 71%, respectively, vs. 91-92% for controls), cleavage development (40-47% and 53-54% vs. 74-78% for controls), and morula plus blastocyst development (15% and 24% vs. 45%, P < 0.05). Cumulus cell co-culture started at various stages had no effect on fertilization and cleavage development but significantly improved rates of embryo development to morula or blastocyst stages (P < 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)

Use of F1 progeny of Holstein × Zebu cross cattle as oocyte donors for in vitro embryo production and gene microinjection

This study was designed to determine the possibility of using F1 crossbreed cattle (HolsteinxZebu) as donors of oocytes for in vitro fertilization (IVF) and for pronuclear gene microinjection into in vitro-produced embryos. In the first part of the experiment oocytes from Bos taurus (Holstein), Bos indicus (Zebu) and F1 crossbred Bos taurusxBos indicus (HolsteinxZebu) genotypes were inseminated with Bos taurus (Holstein) semen and were allocated for in vitro embryo production using conventional IVF procedures. No differences were observed on the in vitro maturation (IVM) rates between breeds (HolsteinxHolstein:85%, ZebuxHolstein:84% and ZebuxHolsteinxHolstein:88%). Holstein cows yielded the highest number of cumulus oocyte complexes (6.8 per ovary) for in vitro maturation, differing (P<0.05) from ZebuxHolstein and ZebuxHolsteinxHolstein F1 by 5.1 and 5.8, respectively. However, the Holstein breed also yielded the lowest percentage of cleavage (45.1 vs 71.9% for ZebuxHolstein and 65.1% for ZebuxHolsteinxHolstein). Of the 3 genotypes, the hybrid F1 breed was the most efficient source of oocytes for the production of embryos capable of reaching morulae and blastocyst stages (76/250; P<0.001). In the second part of the study, 599 oocytes from the F1 breed were fertilized in vitro, 1 group of 150 oocytes was used for the determination of the optimal pronuclear visualization period. The highest number of oocytes with 2 pronuclei was observed between 24 to 28 h after IVF (27 to 42%). The remaining 399 oocytes were microinjected with a gene construct bearing the bacterial lacZ gene as the reporter for gene expression. Survival of embryos to microinjection was 73.8%, and 45.5% of them (50/110) cleaved in culture. Of the microinjected embryos, 1 out of 50 showed beta-galactosidase activity. These findings indicate that a tropical crossbreed of cattle (ZebuxHolsteinxHolstein) can be used as a source of oocytes for IVF programs and gene microinjection studies.

Evaluation of culture systems containing bovine oviduct epithelial cells or granulosa cells to mature and maintain the developmental competence of bovine oocytes in vitro

The effects of estrous cow serum (ECS), bovine oviduct epithelial cells (BOEC), and bovine granulosa cells (GC) on in vitro maturation (IVM) of immature oocyte-cumulus complexes (OCCs) were evaluated. Selected OCCs were cultured for 24 to 26 h in microdroplets of culture medium (CM; TCM 199 + 25 mM HEPES + 100 mug gentamicin sulfate/ml) or in CM medium supplemented or conditioned with 20% ECS, BOEC +/- 20% ECS or GC + 20% ECS. Supplemented media were incubated for 2 h before addition of OCCs, whereas media were conditioned by incubation with 20% ECS or BOEC +/- 20% ECS for 6 d, or with 20% ECS +/- GC for 24 or 48 h before addition of OCCs. The developmental competence of oocytes after TVM was assessed by insemination with glass wool separated, frozen-thawed bovine spermatozoa in microdroplets of modified medium (TALP) containing heparin (5 mug/ml) and BOEC for 18 h. The presumptive zygotes were cultured in microdroplets of CM medium + 20% ECS + BOEC for 7 to 9 d to assess embryo development to morula and blastocyst stages. The percentages of OCCs undergoing IVM (85 to 94%) and in vitro fertilization (IVF) (66 to 80%) were high, irrespective of the IVM conditions. Only after the IVM of OCCs in CM medium alone was the percentage of oocytes undergoing IVF significantly lower (66%; P<0.05). The proportion of IVF oocytes developing to blastocysts with a normal complement of cells (126 to 138) increased significantly (P<0.05) when the OCCs were matured in supplemented or conditioned CM medium containing ECS and/or somatic cells (18 to 28%) compared with those in CM medium alone (9%). When the CM medium was supplemented or conditioned with GC + 20% ECS, the proportion of fertilized oocytes developing to blastocysts increased significantly (28%; P<0.05). These results indicate that the potential of immature OCCs to be fertilized and to complete embryonic development to the blastocyst stage in vitro is enhanced by maturation in CM medium containing 20% ECS and/or BOEC or GC.

In vitro development up to hatching of bovine in vitro-matured and fertilized oocytes with or without support from somatic cells

To verify the importance of somatic cells upon in vitro embryo development, in vitro-matured (IVM) and -fertilized (IVF) bovine oocytes were cultured in TCM 199 supplemented with estrous cow serum (10% v/v) and 0.25 mM sodium pyruvate (ECSTCM) under the following treatments: 1) ECSTCM alone; 2) together with bovine oviduct epithelial cells (BOEC); 3) with cumulus cells (CC); 4) in fresh BOEC conditioned ECSTCM; or 5) in frozen-thawed BOEC conditioned ECSTCM. Culturing zygotes encased in cumulus cells significantly reduced the cleavage rate (P<0.05). There was no difference between culture systems in the proportions of embryo development through the 8-cell stage (P=0.42) up to the morula/blastocyst stages (P=0.50) at Day 7 post insemination. However, co-culture with BOEC yielded the highest percentage (21.2% of zygotes; P<0.05) of quality Grade-1 and Grade-2 embryos with the number of blastomeres per embryo (114.4) comparable to that of 7-day-old in vivo-developed embryos of similar grades (102.5), and higher (P<0.05) than those of the other treatments. The ratio of blastocysts to total morulae/blastocysts obtained from frozen-thawed conditioned medium was lower (P<0.05) than that from ECSTCM or after co-culture with BOEC at Day 7 post insemination. On average, 7.5 to 17.5% of the zygotes developed to blastocyst, expanded blastocyst and hatched blastocyst stages by Day 10 post insemination, depending upon the culture system. The difference between treatments, however, was not significant (P=0.68). The results indicate that chronological development up to hatching of bovine IVM-IVF embryos is not favored by somatic cells; however, the presence of viable oviduct epithelial cells in culture significantly improves the quality of 7-day-old embryos.

Bovine oocyte development following different oocyte maturation and sperm capacitation procedures

Various procedures have been reported for successful in vitro maturation and in vitro fertilization (IVM/IVF) of bovine follicular oocytes. Direct comparisons of these different recommended procedures have been rare. In this research, involving a total of 5,128 oocytes, a series of experiments were conducted to compare oocyte maturation, fertilization, and development in vitro with 2 maturation systems (with or without added hormones) and 3 types of sperm treatment procedures. Oocytes were collected from ovarian antral follicles (2-7 mm in diameter) within 3 hr after slaughter of cows or heifers. Those with intact or at least 4 layers of cumulus cells were selected for IVM/IVF. Oocytes were incubated for 22 hr in either Medium 199 with 7.5% fetal calf serum (M199 + FCS) alone or M199 + FCS with added hormones (M199 + FCS + H; oFSH 0.5 micrograms/ml, oLH 5.0 micrograms/ml, and E2 1.0 micrograms/ml) at 39 degrees C in 5% CO2 and 95% air. For IVF, frozen-thawed sperm were treated with either 0.1 microM calcium ionophore A23187 (A23187) for 1 min, or 10 or 100 micrograms/ml heparin (H10 or H100) for 15 min.(ABSTRACT TRUNCATED AT 250 WORDS)

Current status and potential of embryo transfer and reproductive technology in dairy cattle

Significant use of embryo transfer in dairy cattle commenced with the introduction of nonsurgical embryo recovery in the mid-1970s and developed with the use of nonsurgical transfers in the late 1970s. Numbers of registered Holstein calves from embryo transfer doubled yearly through 1980, after which the rate of increase slowed; the total reached nearly 19,000 calves in 1990. However, the efficacy of superovulation procedures and commercial success rates of transferred fresh embryos have not improved the past 10 to 15 yr. Fertilization rates in superovulated donors remain low. Although embryo-splitting techniques were perfected in the early 1980s, they are not used widely. A practical, commercial embryo-sexing procedure remains unavailable. Recent significant improvement is apparent in the technology of ultrasound-guided oocyte collection and in vitro oocyte maturation, fertilization, and embryo culture. In the future, this technology may be used in conjunction with sperm separated by sex with a flow cytometer. Modest numbers of embryo clones have been produced in several commercial programs via nuclear transfer techniques. However, the efficiency of gene transfer experiments involving ova of cattle and other domestic species has been low. Recently, DNA probe technology has begun to provide genotype information for cattle and will ultimately be applied to embryos.