Development of early bovine embryos in co-culture with ksom and taurine, superoxide dismutase or insulin

Bioactive supplements influencing bovine in vitro embryo development

Ovum pickup and in vitro production (IVP) of bovine embryos are replacing traditional multiple ovulation embryo transfer (MOET) as the primary means for generating transferable embryos from genetically elite sires and dams. However, inefficiencies in the IVP process limit the opportunities to produce large numbers of transferable embryos. Also, the post-transfer competency of IVP embryos is inferior to embryos produced by artificial insemination or MOET. Numerous maternal, paternal, embryonic, and culture-related factors can have adverse effects on IVP success. This review will explore the various efforts made on describing how IVP embryo development and post-transfer competency may be improved by supplementing hormones, growth factors, cytokines, steroids and other bioactive factors found in the oviduct and uterus during early pregnancy. More than 40 of these factors, collectively termed as embryokines, are reviewed here. Several embryokines contain abilities to promote embryo development, including improving embryo survivability, improving blastomere cell numbers, and altering the distribution of blastomere cell types in blastocysts. A select few embryokines also can benefit pregnancy retention after IVP embryo transfer and improve neonatal calf health and performance, although very few embryokine-supplemented embryo transfer studies have been completed. Also, supplementing several embryokines at the same time holds promise for improving IVP embryo development and competency. However, more work is needed to explore the post-transfer consequences of adding these putative embryokines for any adverse outcomes, such as large offspring syndrome and poor postnatal health, and to specify the specific embryokine combinations that will best represent the ideal conditions found in the oviduct and uterus.

Effects of changing culture medium on preimplantation embryo development in rabbit

Many studies have focused on the optimization of the composition of embryo culture medium; however, there are few studies involving the effect of a culture medium changing procedure on the preimplantation development of embryos. In this study, three groups were designed: a non-renewal group, a renewal group and a half-renewal group. The levels of reactive oxygen species (ROS), apoptotic index, blastocyst ratio and blastocyst total cell number were analyzed in each group. The results showed that the ROS level and the apoptotic index of blastocyst in the non-renewal group were significantly higher than in the renewal group and the half-renewal group (P < 0.05). The blastocyst ratio and blastocyst total cell number were significantly higher in the half-renewal group than that in non-renewal group and the renewal group (P < 0.05). These results demonstrated that the procedure of changing the culture medium influenced ROS level, apoptotic index, blastocyst ratio and total cell number of blastocysts. In addition, the result suggested that changing the culture medium may lead to a loss of important regulatory factors for embryos, while not changing the culture medium may lead to the accumulation of toxic substances. Half-renewal can alleviate the defects of both no renewal and renewal, and benefit embryo development. This study will be of high value as a reference for the optimization of embryo culture in vitro, and is very significant for assisted reproduction.

Effect of evaporation-induced osmotic changes in culture media in a dry-type incubator on clinical outcomes in in vitro fertilization-embryo transfer cycles

OBJECTIVE

This study investigated whether adding outer-well medium to inhibit osmotic changes in culture media in a dry-type incubator improved the clinical outcomes of in vitro fertilization-embryo transfer (IVF-ET) cycles.

METHODS

In culture dishes, the osmotic changes in media (20 µL)-covered oil with or without outer-well medium (humid or dry culture conditions, respectively) were compared after 3 days of incubation in a dry-type incubator. One-step (Origio) and G1/G2 (Vitrolife) media were used.

RESULTS

The osmotic changes in the dry culture condition (308 mOsm) were higher than in the humid culture conditions (285-290 mOsm) after 3 days of incubation. In day 3 IVF-ET cycles, although the pregnancy rate did not significantly differ between the dry (46.2%) and humid culture (52.2%) groups, the rates of abortion and ongoing pregnancy were significantly better in the humid culture group (2.3% and 50.2%, respectively) than in the dry culture group (8.3% and 37.8%, respectively, p<0.05). In day 5 IVF-ET cycles, the abortion rate was significantly lower in the humid culture group (2.2%) than in the dry culture group (25.0%, p<0.01), but no statistically significant difference was observed in the rates of clinical and ongoing pregnancy between the dry (50.0% and 25.0%, respectively) and humid culture groups (59.5% and 57.3%, respectively) because of the small number of cycles.

CONCLUSION

Hyperosmotic changes in media occurred in a dry-type incubator by evaporation, although the medium was covered with oil. These osmotic changes were efficiently inhibited by supplementation of outer-well medium, which resulted in improved pregnancy outcomes.

Kinetin enhances in vitro development of parthenogenetic and nuclear transfer porcine embryos

Culture conditions affect the development of mammalian embryos in vitro. Kinetin belongs to the family of N(6)-substituted adenine derivates and promotes cell division, synthesis of DNA repair enzymes, superoxide dismutase activity, and ribosomal RNA transcription. We investigated the effects of kinetin on in vitro development of parthenogenetic and nuclear transfer (NT) porcine embryos. These embryos were cultured with or without kinetin in either BSA- or polyvinyl alcohol-containing medium for 7 days. mRNA expression of three developmentally important genes, HSP70, Glut-1, and poly[A] polymerase in NT embryos was analyzed. Regardless of kinetin supplementation, the proportion of blastocysts and blastocyst cells were not significantly different in parthenogenetic embryos. However, kinetin supplementation increased expansion and hatching rates in all groups. In somatic cell NT embryos, kinetin increased the proportion of embryos developed to blastocysts from 7.5% to 15.4% in medium supplemented with PVA. However, gene expression levels of HSP70, poly[A] polymerase and Glut-1 mRNA were not significantly different in NT blastocysts. The present study indicates that kinetin not only improves blastocyst expansion and cell number of parthenogenetic porcine embryos but also enhances NT porcine embryo development in a completely defined culture condition in vitro.

Effect of taurine and melatonin in the culture medium on buffalo in vitro embryo development

This study was carried out to investigate the effect of supplementing culture medium with different concentrations of taurine and melatonin, on buffalo oocyte in vitro meiotic maturation and embryo development. In experiment 1, oocytes were matured in vitro and the cleaved embryos were cultured in the same following seven culture medium; (i) control (TCM 199 + 10% SS); (ii) control + 0.5 mM taurine; (iii) control + 1 mM taurine; (iv) control + 3 mM taurine; (v) control + 5 microM melatonin; (vi) control + 10 microM melatonin and (vii) control + 50 microM melatonin. In experiment 2, based on the results of experiment 1, to examine the synergistic effect of antioxidants, the oocytes were matured in culture medium (TCM199 + 10% SS), supplemented with both taurine at 1 mM and melatonin at 10 microM concentration and the cleaved embryos were cultured in the same medium. Supplementation of taurine at 1 mM concentration in the culture medium resulted in a higher (p < 0.05) transferable embryo (TE) yield when compared with control (20.6% vs 14.1%). Supplementation of melatonin at 10 and 50 microM concentration in the culture medium resulted in a higher (p < 0.05) meiotic maturation rate (90.3% and 88.8% respectively) and TE yield (28.4% and 27.2% respectively), than the other treatments. In experiment 2, the TE yield did not improve by supplementing the culture medium with both taurine and melatonin, when compared with melatonin alone. In conclusion, the results of this study demonstrated that, enriching the culture medium with taurine and melatonin, improves in vitro embryo production efficiency in buffaloes. In particular, a high TE yield was obtained by enriching the culture medium with 10 microM melatonin.

Beta-alanine but not taurine can function as an organic osmolyte in preimplantation mouse embryos cultured from fertilized eggs

Early preimplantation mouse embryos are susceptible to the detrimental effects of increased osmolarity and, paradoxically, their in vitro development is significantly compromised by osmolarities near that of oviductal fluid. In vitro development can be restored, however, by several compounds that are accumulated by 1-cell embryos to act as organic osmolytes, providing intracellular osmotic support and cell volume regulation. Taurine, a substrate of the beta-amino acid transporter that functions as an organic osmolyte transporter in other cells, had been proposed to function as an organic osmolyte in mouse embryos. Here, however, we found that taurine is neither able to provide protection for in vitro embryo development against increased osmolarity nor is it accumulated to higher intracellular levels as osmolarity is increased, indicating that it cannot function as an organic osmolyte in early preimplantation embryos. In contrast, beta-alanine, the other major substrate of the beta-amino acid transporter, both protects against increased osmolarity and is accumulated to somewhat higher levels as osmolarity is increased, indicating that it is able to function as an organic osmolyte in embryos. However, we also found that beta-alanine is displaced from embryos by glycine-the most effective organic osmolyte in embryos previously identified-and beta-alanine does not increase protection above that afforded by glycine at concentrations near those in vivo. Thus, the beta-amino acid transporter is likely present in early preimplantation embryos to supply beta-amino acids such as taurine for purposes other than to serve as organic osmolytes.

Taurina no desenvolvimento de embriões bovinos fecundados in vitro

O objetivo deste trabalho foi avaliar o efeito de diferentes concentrações de taurina no desenvolvimento de embriões bovinos fecundados in vitro em meio de cultivo com diferentes fontes de soro. No experimento 1, zigotos (n=440) fecundados in vitro foram distribuídos aleatoriamente nos tratamentos com 0, 3, 7 ou 14 mM de taurina em meio de cultivo acrescido de 10% de soro fetal bovino (SFB) e 3g/l de albumina sérica bovina (BSA). No experimento 2, os zigotos (n=940) foram divididos nos tratamentos com 0, 3 ou 14 mM de taurina em meio acrescido de 10% de SFB ou 3g/l de BSA. No experimento 3, os zigotos (n=191) foram divididos nos tratamentos com 0 ou 3 mM de taurina em meio de cultivo sem fonte de soro, porém adicionado de 3 g/l de álcool polivinil. Nos experimentos 1 e 2 não se observou diferença (P>0,05) na taxa de clivagem, na produção de blastocistos e no número de células entre as concentrações de taurina avaliadas. No experimento 3 encontraram-se maior (P<0,05) taxa de clivagem (68,5% vs. 16,9%) e produção de blastocistos (8,3% vs. 0%) na presença de taurina. O cultivo de zigotos em meio adicionado de SFB produziu maior (P<0,01) taxa de blastocistos no sétimo (25,6% vs. 6,7%) e oitavo (30,8% vs. 13,9%) dia pós-fecundação e número de células/blastocistos (104,8± 2,63 vs. 84,7± 3,86) do que no cultivo com BSA, apesar de menor (P<0,01) taxa de clivagem (58,1% vs. 71,3%). Conclui-se que o efeito benéfico da taurina no desenvolvimento embrionário somente é observado na ausência de SFB e BSA. O SFB produz menor taxa de clivagem mas melhora o desenvolvimento embrionário após as primeiras divisões celulares.

Prevalence of apoptosis and inner cell allocation in bovine embryos cultured under different oxygen tensions with or without cysteine addition

Supraphysiological oxygen tension during embryo culture can generate reactive oxygen species (ROS), which can induce apoptosis. Antioxidants such as thiol compounds (cysteine, cysteamine) can be used to prevent ROS damage to the embryo. The purpose of this study was to evaluate the prevalence of apoptosis during bovine embryo development and to evaluate the effect of the presence or absence of cysteine 0.6 mM in modified synthetic oviduct fluid (mSOF) on in vitro produced cattle embryos cultured under two different oxygen tensions (5% O2 versus 20% O2). Effects were assessed by checking embryo development at Days 7, 8 and 9 and by evaluating Day 9 hatched blastocysts for differentiation by means of differential staining and for apoptosis by means of TUNEL-assay. Apoptotic cells were present in 94% of Day 7 blastocysts and in 100% of Days 8 and 9 blastocysts. Cysteine addition affected Day 8 blastocyst rates in a negative way (P < 0.05) regardless of the oxygen tension. In fact, cysteine addition to the mSOF culture medium had a negative effect upon embryo development in terms of blastocyst rates, hatching rates and apoptotic cell ratio. Embryos cultured under 5% O2 in the presence of cysteine, however, possessed significantly higher numbers of ICM cells. This finding corroborates the theoretical assumption that antioxidants are beneficial for ICM development.

Osmoregulation and cell volume regulation in the preimplantation embryo

The early preimplantation mammalian embryo possesses mechanisms that regulate intracellular osmolarity and cell volume. While transport of osmotically active inorganic ions might play a role in this process in embryos, the major mechanisms that have been identified and studied are those that employ organic osmolytes. Organic osmolytes provide a substantial portion of intracellular osmotic support in embryos and are required for their development under in vivo conditions. The main osmolytes that have been identified in cleavage stage embryos are accumulated via two transport systems of the neurotransmitter transporter family active in early preimplantation embryos--the glycine transport system (GLY) and the beta-amino acid transport system (system beta). While system beta has been established to have a similar role in many other cells, this is a novel function for the GLY transport system. The intracellular concentration of organic osmolytes such as glycine in early preimplantation embryos is regulated by tonicity, allowing the embryo to regulate its volume against shrinkage and to control its internal osmolarity. In addition, the cells of the embryo can regulate against an increase in volume via controlled release of osmolytes from the cytoplasm. This is mediated by a swelling-activated anion channel that is also highly permeable to a range of organic osmolytes, and which closely resembles similar channels found in many other cell types (VSOAC channels). Together, these mechanisms appear to regulate cell volume in the egg through the early cleavage stages of embryogenesis, after which there are indications that the mechanisms of osmoregulation change.

Protection against reactive oxygen species during mouse preimplantation embryo development: role of EDTA, oxygen tension, catalase, superoxide dismutase and pyruvate

Oxidative damage due to the production of reactive oxygen species (ROS) is one of a number of culture-induced stresses which may compromise preimplantation embryo development in vitro. Ethylenediaminetetraacetic acid (EDTA), reduced oxygen tension, superoxide dismutase (SOD) and catalase (CAT) offer protection against oxidative stress, but few attempts have been made to determine which of these agents, or which combination, is the most effective. In particular, no systematic investigation of their actions and interactions has been made using a multifactorial experimental design. Murine zygotes were cultured in the presence or absence of 10 miccroM EDTA, SOD (100-7,000 U/ml) and CAT (50-100 U/ml) at atmospheric (20%) and reduced (5%) oxygen tensions. Blastocyst formation and hatching rates (at various time points), and cell numbers were recorded, whilst parallel groups of embryos had their consumption of pyruvate, a hydrogen peroxide scavenger, measured. All parameters interacted significantly and affected blastocyst formation, hatching rate and cell numbers but the effect of EDTA was the most pronounced. There were beneficial effects of 5% O2, CAT and SOD, while 20% O2 had a deleterious effect on development. EDTA improved blastocyst formation and hatching rates but paradoxically led to a reduction in cell number. 5% O2 was the next most significant parameter to enhance embryo development and also increased cell numbers. No differences in pyruvate uptake were apparent between the various treatment groups. The results suggest that embryo culture in EDTA-free medium under 5% O2 provides the most practical and physiological conditions for in vitro murine embryo culture.

Effect of protein supplementation and presence of an antioxidant on the development of bovine zygotes in synthetic oviduct fluid medium under high or low oxygen tension

The aim of this study was to investigate the effect of protein supplementation of culture medium and the presence of a putative antioxidant on bovine zygote development under 5% (low) and 20% (high) O2. In Experiment 1, presumptive zygotes (n=992) were cultured in synthetic oviduct fluid (SOF) alone or supplemented with 3 mg/mL PVP, 3 mg/mL BSA (SOFB), and/or 10% FCS (SOFBF) in 5% CO2, 5% O2, 90% N2. In Experiment 2, zygotes (n=1916) were cultured in SOF, SOFB or SOFBF with or without taurine under high and low O2. In Experiment 1, presence of BSA or BSA plus FCS significantly increased the speed of development compared to SOF or SOF+PVP. Blastocyst quality was also improved, as evidenced by increased hatching rate and cell numbers. In Experiments 2, taurine had no effect on development irrespective of oxygen concentration or protein supplementation. In conclusion, the presence of protein in the culture medium and culture under reduced O2 significantly improved embryo development. Taurine had no effect on development.

Allopurinol, an inhibitor of xanthine oxidase, improves the development of IVM/IVF bovine embryos (>4 cell) in vitro under certain culture conditions

To determine the origin of free oxygen radicals in the culture medium of bovine embryos, the effect of allopurinol, an inhibitor of xanthine oxidase, on the development of embryos (>4 cell) in modified synthetic oviduct fluid (m-SOF) medium was examined. When embryos were cultured in the presence of 0.2 mM allopurinol under high oxygen tension (5% CO2 in air), the blastocyst rate significantly (P<0.05) increased compared with the absence of allopurinol (allopurinol (+) 42 vs. (-) 25%; Day 6, 63 vs. 51%; Day 7, 69 vs. 58%; Day 8). However, allopurinol had no effect on embryo development under low oxygen tension (5% CO2, 5% O2, 90% N2). Moreover, it was found that the developmental rate and the total cell number of blastocysts decreased (development rate: 60 vs. 28%, cell number: 132 vs. 74) when the embryos were cultured in medium containing 0.01 U/mL xanthine oxidase (XOD) and 0.1 mM hypoxanthine (HXT), and the damaging effect of XOD and HXT was removed by the addition of 0.2 mM allopurinol. The beneficial effect of allopurinol was also observed when the glucose concentration was increased to 4.5 mM from 1.5 mM (control: 22% vs. allopurinol: 34%; Day 8), but no beneficial effects were observed in the media without glucose (control: 55% vs. allopurinol: 59%). Taken together, these results suggested that a portion of the free oxygen radicals are generated from the XOD and HXT reactions under culture conditions, and this generation is enhanced by high oxygen tension in the gas atmosphere or by high glucose concentrations in the medium.

Effects of antioxidants on the development of bovine IVM/IVF embryos in various concentrations of glucose

This study was undertaken to determine the effects of glucose, antioxidants and different oxygen tensions on the development of bovine embryos cultured in modified synthetic oviduct fluid (m-SOF) medium. In vitro matured (IVM) and fertilized (IVF) oocytes were incubated for 48 h. Embryos reaching at least the 4-cell stage were selected for further culture under various conditions for 6 d. Supplementing the m-SOF media with 4.5 mM glucose resulted in a significantly lower (P < 0.01) embryo developmental rate (21%; Day 8) than was obtained with 1.5 mM glucose (58%; Day 8) or no glucose (53%; Day 8). Antioxidants such as SOD, catalase and mannitol had no positive effect on embryo development in m-SOF medium supplemented with 1.5 mM glucose. However, in m-SOF medium supplemented with 4.5 mM glucose, SOD and mannitol significantly (P < 0.05) improved embryo development: SOD increased the developmental rate from 19 to 35% (Day 8), while mannitol increased it from 13 to 30% (Day 8). Low oxygen concentration improved embryo development significantly (P < 0.05) in m-SOF medium supplemented with 4.5 mM glucose (low O2: 31% vs high O2: 14%; Day 8) but not 0 mM glucose (low O2: 58% vs high O2: 55%; Day 8). Our data suggest that low concentration of glucose during culture of bovine embryos is beneficial, and that generation of free oxygen radicals is partly caused by a high concentration of glucose in the medium.

Effects of glutamine, glycine and taurine on the development of in vitro fertilized bovine zygotes in a chemically defined medium

The effects of glutamine, glycine and taurine on the development of bovine zygotes derived from IVM/IVF were determined using a protein-free chemically defined medium. After the cumulus cells were removed at 18 hr post-insemination, the presumptive zygotes were cultured for 4 or 6 days (about 104 or 154 hr) under a gas atmosphere of 5% O2: 5% CO2: 90% N2. A modified synthetic oviduct fluid medium supplemented with 20 amino acids (1 mM glutamine, essential amino acids for basal medium Eagle and non-essential amino acids for minimum essential medium), insulin, and PVA was used as a basic medium (mSOFai). Omitting 1 mM glutamine from mSOFai did not affect the embryonic development after 4 and 6 days of culture. After 4 days of culture, no significant effects of glycine and taurine on the development of zygotes to the morula stage were observed. However, supplementation with glycine or taurine significantly (P < 0.05) affected, with no interaction, the embryonic development to blastocysts after 6 days of culture. Addition of 5 mM glycine and 2 or 10 mM taurine significantly (P < 0.05) increased the percentage of blastocysts. The mean cell number in the blastocysts was affected by the glycine level, and was increased by the addition of 10 mM glycine (P < 0.001). These results demonstrate that glycine and taurine in a chemically defined medium containing a group of essential and non-essential amino acids improve the development of bovine zygotes to the blastocyst stage under 5% O2.

Effect of superoxide dismutase(SOD) on pronucleus formation of porcine oocytes fertilized in vitro

This study was undertaken to evaluate the effects of superoxide dismutase (SOD) on pronucleus formation in porcine oocytes fertilized in vitro by frozen-thawed spermatozoa. No differences were found in penetration rates when SOD was added to maturation or fertilization medium at any level tested in first and second experiments. Pronucleus formation rates were higher (P < 0.05) when SOD at 10 and 100 units was added to the maturation medium (46 and 53%, respectively) compared with the controls (26%). On the other hand, when the fertilization medium was supplemented with SOD at different concentrations (1, 10 and 100 units/ml), pronucleus formation rates (55, 52 and 50%) were significantly higher (P < 0.05) than in the control group. In third experiment, the oocytes were cultured in medium with (1 unit/ml) or without SOD for 8, 16, 24 and 32 h after insemination. The penetration rates had a tendency to increase as time of sperm-oocyte culture was prolonged. No significant differences, however, were observed in penetration rates between groups with and without SOD. On the other hand, the pronucleus formation rates were higher in medium with than without SOD at 8 (7 vs 0%), 16 (14 vs 3%), 24 (48 vs 16%; P < 0.01) and 32 h (49 vs 22%; P < 0.05). These findings demonstrate the advantage of culture with SOD on pronucleus formation in porcine oocytes penetrated by spermatozoa. However, SOD does not affect penetration rates and polyspermy.

Development of rabbit zygotes into blastocysts in defined protein-free medium and offspring born following culture and embryo transfer

We report here on an improved, completely defined culture system for producing embryos in vitro which mimics development in vivo. This system avoids the confounding effects of the many unknowns introduced by the multivariate components of the serum or by unknowns attached to bovine serum albumin (BSA). Zygotes were obtained from superovulated rabbits and cultured in modified defined RPMI 1640:Dulbecco's MEM, 1:1 (RD) medium. The effect of a novel and potentially ideal antioxidant, tempol, was tested (20 to 0.001 mM) but found to be either toxic or ineffective. In the presence of 20% O(2), 600 units of Superoxide dismutase or 2.5 mM of taurine increased embryo hatching after 72 h of culture in RD medium to 75 and 76%, respectively, compared with 46% in the control (P < 0.05). The need for antioxidants was reduced with 5% O(2). The beneficial effects of RD medium were demonstrated when 60 zygotes cultured for 48 h to the early blastocyst stage in this medium were transferred and resulted in 30 young (50%) compared with 35/60 (58%) young from uncultured control transfers. Only 12% of the young were obtained from slower developing morulae. Thus, high viability was established for rapidly growing embryos in culture, but fewer slow growing embryos survived after transfer. A further comparison of embryos cultured in RD medium with a high potassium simple, optimized, defined medium (KSOM), revealed that both yielded results approaching those of direct transfer without culture. Simple defined media may also be useful for the culture of embryos of other species.

Cell allocation to the inner cell mass and the trophectoderm in bovine embryos cultured in two different media

Data from other laboratories have shown that speed of bovine blastocyst development is higher when Ménézo B2 is used for coculture compared to TCM199. It was our purpose to investigate whether this early blastocyst formation was also indicative of embryo quality by studying the allocation of inner cells in embryos generated by B2-coculture and by TCM199-coculture. For this purpose, a differential staining technique was used. General embryo development was similar for TCM199- and B2-embryos expressed as rate of cleavage at day 3 and morula-blastocyst formation at day 8 (P > 0.05), but significantly different when expressed as number of eight-cell stages at day 3 and expanded or hatched blastocysts at day 8 (P < 0.01). B2-embryos cultured until day 5, 6, and 7 post insemination, had total cell numbers of 24, 65, and 109 respectively, which was significantly higher than the cell number of TCM199-embryos cultured over the same time period (18, 41, and 71 respectively, P < 0.001). Morphological differentiation was significantly more advanced for B2-embryos at day 7 and 8 (P < 0.0001 and P < 0.001, respectively). First presumptive inner cells appeared in eight- to 16-cell stages at day 3. Because the determination of inner cells by differential staining is depending upon the presence of functional tight junctions, we concluded that the establishment of the tight junction seal in B2-embryos differed from that in TCM199-embryos: Inner cells appeared 0.56 cell cycle later in B2-embryos (P < 0.001) and a larger variation existed in the number of ICM-cells in B2-blastocysts (P < 0.001). The higher total cell number of B2-expanded blastocysts was mainly acquired by trophectoderm growth (P < 0.06). These data indicate that the apparent better quality of B2-embryos (faster cleavage, earlier blastocyst formation) is not reflected in a reliable number of inner cells of B2-blastocysts.

Effect of high molecular weight factors present in bovine oviductconditioned medium on in vitro bovine embryo development

To investigate the presence of embryotrophic factors in bovine oviduct-conditioned medium (BOCM), the high molecular weight fraction (> 10 KDa) from BOCM was added to 3 chemically defined embryo culture media (TCM199, DMEM/F12 and modified synthetic oviduct fluid [mSOF]). Zygotes were obtained by in vitro maturation and fertilization of oocytes. Conditioning of TCM199 with oviduct cells increased both cleavage to the 5- to 8-cell stage (59 vs 37%) and further development to the blastocyst stage (19 vs 4%). The low molecular weight fraction (< 10 KDa) of BOCM maintained development to the 5- to 8-cell stage but did not allow development to the blastocyst stage. Adding the high molecular weight fraction to the inactive low molecular weight fraction restored bovine embryo development up to the blastocyst stage. This embryotrophic effect of the high molecular weight fraction was not observed when this fraction was added to TCM199 or DMEM/F12 medium. Whereas adding this fraction to mSOF medium significantly (P<0.05) increased embryo development up to the blastocyst stage (36%) in comparison with that of mSOF (15%) or BOCM (14%). These results show that BOCM contains high molecular weight factors promoting embryo development up to the blastocyst stage. Some chemically defined media mask the effect of these embryotrophic factors.