The effects of group size on development and interferon-tau secretion by in-vitro fertilized and cultured bovine blastocysts

Individual culture and atmospheric oxygen during culture affect mouse preimplantation embryo metabolism and post-implantation development

RESEARCH QUESTION

Does single embryo culture under atmospheric or reduced oxygen alter preimplantation metabolism and post-implantation development compared with culture in groups?

DESIGN

Mouse embryos were cultured under 5% or 20% oxygen, individually or in groups of 10. Spent media were analysed after 48, 72 and 96 h of culture. Blastocysts were assessed by outgrowth assay or transferred to pseudo-pregnant recipients, and fetal and placental weight, length and morphology were assessed.

RESULTS

Compared with group culture, individually cultured blastocysts had lower net consumption of glucose and aspartate and higher glutamate production. Atmospheric oxygen reduced uptake of glucose and aspartate and increased production of glutamate and ornithine compared with 5% oxygen. Combining 20% oxygen and single culture resulted in further metabolic changes: decreased leucine, methionine and threonine consumption. Under 5% oxygen, individual culture decreased placental labyrinth area but had no other effects on fetal and placental development or outgrowth size compared with group culture. Under 20% oxygen, however, individual culture reduced outgrowth size and fetal and placental weight compared with group-cultured embryos.

CONCLUSIONS

Preimplantation metabolism of glucose and amino acids is altered by both oxygen and individual culture, and fetal weight is reduced by individual culture under atmospheric oxygen but not 5% oxygen. This study raises concerns regarding the increasing prevalence of single embryo culture in human IVF and adds to the existing evidence regarding the detrimental effects of atmospheric oxygen during embryo culture. Furthermore, these data demonstrate the cumulative nature of stress during embryo culture and highlight the importance of optimizing each element of the culture system.

Blastocyst-induced changes in the bovine endometrial transcriptome

The objectives of this study were (i) to determine whether blastocyst-induced responses in endometrial explants were detectable after 6- or 24-h co-culture in vitro; (ii) to test if direct contact is required between embryos and the endometrial surface in order to stimulate endometrial gene expression; (iii) to establish the number of blastocysts required to elicit a detectable endometrial response; (iv) to investigate if upregulation of five interferon-stimulated genes (ISGs) in the endometrium was specific to the blastocyst stage and (v) to test if alterations in endometrial gene expression can be induced by blastocyst-conditioned medium. Exposure of endometrial explants to Day 8 blastocysts in vitro for 6 or 24 h induced the expression of ISGs (MX1, MX2, OAS1, ISG15, RSAD2); expression of IFNAR1, IFNAR2, NFKB1, IL1B, STAT1, LGALS3BP, LGALS9, HPGD, PTGES, ITGB1, AKR1C4, AMD1 and AQP4 was not affected. Culture of explants in the presence of more than five blastocysts was sufficient to induce the effect, with maximum expression of ISGs occurring in the presence of 20 blastocysts. This effect was exclusive to blastocyst stage embryos; oocytes, 2-cell embryos or Day 5 morulae did not alter the relative abundance of any of the transcripts examined. Direct contact between blastocysts and the endometrial surface was not required in order to alter the abundance of these transcripts and blastocyst-conditioned medium alone was sufficient to stimulate a response. Results support the notion that local embryo-maternal interaction may occur as early as Day 8 of pregnancy in cattle.

A microwell culture system that allows group culture and is compatible with human single media

PURPOSE

A microwell culture system that facilitates group culture, such as well-of-the-well (WOW), improves embryonic development in an individual culture. We examined the effect of WOW on embryonic development in vitro with commercially available human single culture media.

METHODS

Using four different commercial human single culture media, in vitro development and imprinted gene expression of bovine embryos cultured in WOW were compared to droplet culture (one zygote per drop). To determine the effects of microwell and group culture on embryonic development, different numbers of embryos were cultured in droplet or WOW. Diffusion simulation of accumulating metabolites was conducted using the finite volume method.

RESULTS

WOW had a positive effect on bovine embryonic development, regardless of the type of single culture media. Imprinted gene expression was not different between droplet- and WOW-derived blastocysts. The microwell and group cultures in WOW showed a significant positive effect on the rate of total blastocysts and the rate of development to the expanded and hatching blastocyst stages. The assumed cumulative metabolite concentration of WOW with one embryo was 1.47 times higher than that of droplet culture with one embryo. Furthermore, the concentration of WOW with three embryos was 1.54 times higher than that of WOW with one embryo.

CONCLUSIONS

In using human single culture media, a microwell culture system that allows group culture could be a powerful clinical tool for improving the success of assisted reproductive technologies.

Interferon-tau and fertility in ruminants

Establishment of pregnancy in domestic ruminants includes pregnancy recognition signalling by the conceptus, implantation and placentation. Despite the high fertilisation success rate in ruminants, a significant amount of embryo loss occurs, primarily during early gestation. Interferon-tau (IFNT), a type I interferon that is exclusively secreted by the cells of the trophectoderm of the ruminant conceptus, has been recognised as the primary agent for maternal recognition of pregnancy in ruminants. It produces its antiluteolytic effect on the corpus luteum by inhibiting the expression of oxytocin receptors in the uterine epithelial cells, which prevents pulsatile, luteolytic secretion of prostaglandin F2α by the uterine endometrium. While the importance of IFNT in maternal recognition of pregnancy and prevention of luteolysis in ruminants is unequivocal, important questions, for example, relating to the threshold level of IFNT required for pregnancy maintenance, remain unanswered. This paper reviews data linking IFNT with measures of fertility in ruminants.

Embryo density may affect embryo quality during in vitro culture in a microwell group culture dish

PURPOSE

Culturing embryos in groups is a common practice in mammalian embryology. Since the introduction of different microwell dishes, it is possible to identify oocytes or embryos individually. As embryo density (embryo-to-volume ratio) may affect the development and viability of the embryos, the purpose of this study was to assess the effect of different embryo densities on embryo quality.

METHODS

Data of 1337 embryos from 228 in vitro fertilization treatment cycles were retrospectively analyzed. Embryos were cultured in a 25 μl microdrop in a microwell group culture dish containing 9 microwells. Three density groups were defined: Group 1 with 2-4 (6.3-12.5 μl/embryo), Group 2 with 5-6 (4.2-5.0 μl/embryo), and Group 3 with 7-9 (2.8-3.6 μl/embryo) embryos.

RESULTS

Proportion of good quality embryos was higher in Group 2 on both days (D2: 18.9 vs. 31.5 vs. 24.7%; p < 0.001; D3: 19.7 vs. 27.1 vs. 21.2%; p = 0.029; Group 1. vs. Group 2. vs. Group 3). Cell number on Day 3 differed between Groups 1 and 2 (6.8 ± 2.2; 7.3 ± 2.1; p = 0.004) and Groups 2 and 3 (7.3 ± 2.1 vs. 7.0 ± 2.0; p = 0.014).

CONCLUSIONS

Culturing 5-6 embryos together in a culture volume of 25 μl may benefit embryo quality. As low egg number, position, and distance of the embryos may influence embryo quality, results should be interpreted with caution.

Selection of viable in vitro-fertilized bovine embryos using time-lapse monitoring in microwell culture dishes

Conventionally, in vitro-fertilized (IVF) bovine embryos for transfer are morphologically evaluated at day 7–8 of embryo culture. This method is, however, subjective and results in unreliable selection. We previously described a novel selection system for IVF bovine blastocysts for transfer that traces the development of individual embryos with time-lapse monitoring in our specially developed microwell culture dishes (LinKID micro25). The system can noninvasively identify prognostic factors that reflect viability after transfer. By assessing a combination of identified prognostic factors —timing of the first cleavage; number of blastomeres at the end of the first cleavage; and number of blastomeres at the onset of lag-phase, which results in temporary developmental arrest during the fourth or fifth cell cycle— the pregnancy rate was improved over using conventional morphological evaluation. Time-lapse monitoring with LinKID micro25 could facilitate objective and reliable selection of healthy IVF bovine embryos. Here, we review the novel bovine embryo selection system that allows for prediction of viability after transfer.

In vitro culture of individual mouse preimplantation embryos: the role of embryo density, microwells, oxygen, timing and conditioned media

Single embryo culture is suboptimal compared with group culture, but necessary for embryo monitoring, and culture systems should be improved for single embryos. Pronucleate mouse embryos were used to assess the effect of culture conditions on single embryo development. Single culture either before or after compaction reduced cell numbers (112.2 ± 3.1; 110.2 ± 3.5) compared with group culture throughout (127.0 ± 3.4; P < 0.05). Reduction of media volume from 20 µl to 2 µl increased blastocyst cell numbers in single embryos cultured in 5% oxygen (84.4 ± 3.2 versus 97.8 ± 2.8; P < 0.05), but not in 20% oxygen (55.2 ± 2.9 versus 57.1 ± 2.8). Culture in microwell plates for the EmbryoScope and Primo Vision time-lapse systems changed cleavage timings and increased inner cell mass cell number (24.1 ± 1.0; 23.4 ± 1.2) compared with a 2 µl microdrop (18.4 ± 1.0; P < 0.05). Addition of embryo-conditioned media to single embryos increased hatching rate and blastocyst cell number (91.5 ± 4.7 versus 113.1 ± 4.4; P < 0.01). Single culture before or after compaction is therefore detrimental; oxygen, media volume and microwells influence single embryo development; and embryo-conditioned media may substitute for group culture.

Combined effects of individual culture and atmospheric oxygen on preimplantation mouse embryos in vitro

Embryos are routinely cultured individually, although this can reduce blastocyst development. Culture in atmospheric (20%) oxygen is also common, despite multiple detrimental effects on embryos. Although frequently occurring together, the consequences of this combination are unknown. Mouse embryos were cultured individually or grouped, under physiological (5%) or atmospheric (20%) oxygen. Embryos were assessed by time-lapse and blastocyst cell allocation. Compared with the control group (5% oxygen group culture), 5-cell cleavage (t5) was delayed in 5% oxygen individual culture and 20% oxygen group culture (59.91 ± 0.23, 60.70 ± 0.29, 63.06 ± 0.32 h post-HCG respectively, P < 0.05). Embryos in 20% oxygen individual culture were delayed earlier (3-cell cleavage), and at t5 cleaved later than embryos in other treatments (66.01 ± 0.40 h, P < 0.001), this delay persisting to blastocyst hatching. Compared with controls, hatching rate and cells per blastocyst were reduced in 5% oxygen single culture and 20% oxygen group culture (134.1 ± 3.4, 104.5 ± 3.2, 73.4 ± 2.2 cells, P < 0.001), and were further reduced in 20% oxygen individual culture (57.0 ± 2.8 cells, P < 0.001), as was percentage inner cell mass. These data indicate combining individual culture and 20% oxygen is detrimental to embryo development.

Use of a novel polydimethylsiloxane well insert to successfully mature, culture and identify single porcine oocytes and embryos

The objective of this study was to evaluate the efficacy of a novel polydimethylsiloxane (PDMS) well-insert system for oocyte in vitro maturation (IVM) and in vitro embryo culture (IVC) in pigs. The PDMS well inserts, consisting of multiple microwells with connecting microchannels, resulted in equivalent blastocyst development compared with standard microdrop culture for IVC. These PDMS well inserts were then evaluated for IVM or IVC in a rocking versus static environment. The rocking environment during both oocyte IVM and embryo culture had detrimental effects on oocyte and embryo development compared with a static environment. Importantly, blastocyst development of oocytes and embryos cultured in the PDMS well inserts in the static environment was equivalent to that of standard microdrops. Further analysis of transcript abundance in blastocysts produced from these different environments revealed that the PDMS well-insert system may produce more viable embryos. In conclusion, this PDMS well-insert system can successfully mature oocytes and culture embryos in an individually-identifiable manner without compromising, and perhaps enhancing, developmental potential.

Effect of co-culture with intact embryos on development of bovine separated blastomeres

To improve embryo development in bovine separated blastomeres, we evaluated applicability of co-culture with intact embryos. The morphological quality of blastocysts derived from separated blastomeres and rate of blastocyst formation were only slightly increased when the cells were co-cultured with intact embryos, which did not provide significant differences when statistically analyzed. However, the cell count of inner cell mass (ICM), trophectoderm (TE) and total number of cells in Day 8 blastocysts were significantly higher when the cells were co-cultured with the intact embryos than those with the cells cultured individually (P<0.05). Transfer of four monozygotic pairs of blastocysts derived from the cells co-cultured with intact embryos led to three pregnancies even when the blastomeres were produced by in vitro maturation and in vitro fertilization of oocytes collected by ovum pick-up from elite cows. These results suggest that co-culturing with intact embryos may enhance development of bovine separated blastomere.

Beneficial effect of two culture systems with small groups of embryos on the development and quality of in vitro-produced bovine embryos

Currently, in vitro-produced embryos derived by ovum pick up (OPU) and in vitro fertilization (IVF) technologies represent approximately one-third of the embryos worldwide in cattle. Nevertheless, the culture of small groups of embryos from an individual egg donor is an issue that OPU-IVF laboratories have to face. In this work, we tested whether the development and quality of the preimplantation embryos in vitro cultured in low numbers (five embryos) could be improved by the addition of epidermal growth factor, insulin, transferrin and selenium (EGF-ITS) or by the WOW system. With this aim, immature oocytes recovered from slaughtered heifers were in vitro matured and in vitro fertilized. Presumptive zygotes were then randomly cultured in four culture conditions: one large group (LG) (50 embryos/500 μl medium) and three smaller groups [five embryos/50 μl medium without (control) or with EGF-ITS (EGF-ITS) and five embryos per microwell in the WOW system (WOW)]. Embryos cultured in LG showed a greater ability to develop to blastocyst stage than embryos cultured in smaller groups, while the blastocyst rate of WOW group was significantly higher than in control. The number of cells/blastocyst in LG was higher than control or WOW, whereas the apoptosis rate per blastocyst was lower. On the other hand, the addition of EGF-ITS significantly improved both parameters compared to the control and resulted in similar embryo quality to LG. In conclusion, the WOW system improved embryo development, while the addition of EGF-ITS improved the embryo quality when smaller groups of embryos were cultured.

Effect of embryo density on in vitro development and gene expression in bovine in vitro-fertilized embryos cultured in a microwell system

To identify embryos individually during in vitro development, we previously developed the well-of-the-well (WOW) dish, which contains 25 microwells. Here we investigated the effect of embryo density (the number of embryos per volume of medium) on in vitro development and gene expression of bovine in vitro-fertilized embryos cultured in WOW dishes. Using both conventional droplet and WOW culture formats, 5, 15, and 25 bovine embryos were cultured in 125 µl medium for 168 h. The blastocysts at Day 7 were analyzed for number of cells and expression of ten genes (CDX2, IFN-tau, PLAC8, NANOG, OCT4, SOX2, AKR1B1, ATP5A1, GLUT1 and IGF2R). In droplet culture, the rates of formation of >4-cell cleavage embryos and blastocysts were significantly lower in embryos cultured at 5 embryos per droplet than in those cultured at 15 or 25 embryos per droplet, but not in WOW culture. In both droplet and WOW culture, developmental kinetics and blastocyst cell numbers did not differ among any groups. IFN-tau expression in embryos cultured at 25 embryos per droplet was significantly higher than in those cultured at 15 embryos per droplet and in artificial insemination (AI)-derived blastocysts. Moreover, IGF2R expression was significantly lower in the 25-embryo group than in the 5-embryo group and in AI-derived blastocysts. In WOW culture, these expressions were not affected by embryo density and were similar to those in AI-derived blastocysts. These results suggest that, as compared with conventional droplet culture, in vitro development and expression of IFN-tau and IGF2R in the microwell system may be insensitive to embryo density.

Development of a single bovine embryo improved by co-culture with trophoblastic vesicles in vitamin-supplemented medium

To improve the development of singly cultured bovine embryos, we developed a co-culture method with trophoblastic vesicles. The growth of trophoblastic cells was markedly increased in vitamin-supplemented medium 199 compared with medium 199. Upon co-culture of a single embryo with trophoblastic vesicles in vitamin-supplemented medium 199, embryo development to the blastocyst stage was significantly higher than in embryos co-cultured with trophoblastic vesicles in RPMI 1640 or with cumulus cells in medium 199 (control). In the absence of the vitamin cocktail, co-culture with trophoblastic vesicles in medium 199 did not improve embryo development compared with that of the control. The vitamin cocktail was effective in embryo development when co-cultured with trophoblastic vesicles, but not with cumulus cells. Embryo development was not improved in the absence of co-cultured trophoblastic vesicles, even in the presence of vitamin cocktail. In conclusion, the co-culture system with trophoblastic vesicles in vitamin-supplemented medium 199 efficiently enhances the development of singly cultured embryos.

Effect of culture medium volume and embryo density on early mouse embryonic development: tracking the development of the individual embryo

PURPOSE

To determine the optimal volume or density of embryos for the well-of-the-well (WOW) system in order to track the development of individual embryos and to determine whether the WOW system can reverse the negative impact of culturing embryos singly.

METHODS

(1) Mouse embryos (groups of nine at the 2-cell stage) were cultured in 6.25 μl, 12.50 μl, 25.00 μl and 50.00 μl of droplets of culture medium under paraffin oil; (2) Groups of three, six, nine and twelve embryos at the 2-cell stage were cultured in 50 μl of droplet of culture medium under paraffin oil; (3) Groups of nine embryos at the 2-cell stage were cultured in 50 μl of droplet under paraffin oil with or without nine micro-wells made on the bottom of the Petri dish into each of which were placed one of the nine embryos (WOW system). Also single 2-cell stage embryos was cultured individually in 5.5 μl of droplet of culture medium under paraffin oil with or without a single micro-well made on the bottom of the Petri dish (WOW system for single culture). At the end of culture, the percentages of blastocyst development, hatching and hatched blastocysts were compared in each group. The blastocysts were fixed for differential staining.

RESULTS

The blastocyst development was significantly higher (P < 0.05) when nine embryos were cultured in 50 μl of droplet of culture medium compared with other volumes. The blastocyst development was significantly reduced (P < 0.05) in single embryo culture compared to group embryo culture with or without the WOW system. The blastocyst development was not improved when single embryo cultured individually in a micro-well was compared to single embryo cultured individually without micro-well. The total cell numbers of blastocysts were significantly higher in group embryo culture than single embryo culture regardless of whether the WOW system was used. In addition, the total cell numbers of blastocysts were significantly higher (P < 0.05) in single embryo culture with the WOW system than without.

CONCLUSIONS

Group embryo culture is superior to single embryo culture for blastocyst development. The WOW system with 50 μl of droplet of culture medium can be used to track the individual development of embryo cultured in groups while preserving good embryonic development. The reduced embryonic development with single embryo culture cannot be ameliorated by the WOW system.

Culture systems: embryo density

Embryo density is defined as the embryo-to-volume ratio achieved during in vitro culture; in other words, it is the number of embryos in a defined volume of culture medium. The same density can be achieved by manipulating either the number of embryos in a given volume of medium, or manipulating the volume of the medium for a given number of embryos: for example, a microdrop with five embryos in a 50 μl volume under oil has the same embryo-to-volume ratio (1:10 μl) as a microdrop with one embryo in a 10 μl volume under oil (1:10 μl). Increased embryo density can improve mammalian embryo development in vitro; however, the mechanism(s) responsible for this effect may be different with respect to which method is used to increase embryo density.Standard, flat sterile plastic petri dishes are the most common, traditional platform for embryo culture. Microdrops under a mineral oil overlay can be prepared to control embryo density, but it is critical that dish preparation is consistent, where appropriate techniques are applied to prevent microdrop dehydration during preparation, and results of any data collection are reliable, and repeatable. There are newer dishes available from several manufacturers that are specifically designed for embryo culture; most are readily available for use with human embryos. The concept behind these newer dishes relies on fabrication of conical and smaller volume wells into the dish design, so that embryos rest at the lowest point in the wells, and where putative embryotrophic factors may concentrate.Embryo density is not usually considered by the embryologist as a technique in and of itself; rather, the decision to culture embryos in groups or individually is protocol-driven, and is based more on convenience or the need to collect data on individual embryos. Embryo density can be controlled, and as such, it can be utilized as a simple, yet effective tool to improve in vitro development of human embryos.

Single or Group Culture of Mammalian Embryos: The Verdict of the Literature

During infertility treatment with IVF, embryos are cultured either in groups or individually. Each approach has potential benefits and detriments, and the purpose of this review is to try to come to a consensus based on the literature as to which approach yields superior results. Group culture of embryos may produce better quality embryos via secretion of embryotrophic factors, while opponents of the approach argue that embryos cultured together may either deplete the media of substrates or negatively affect nearby embryos via the transmission of other secreted factors. In these cases, quantity of embryos, volume of media and proximity and quality of companion embryos are also important factors to consider. While it has long been accepted that group culture is beneficial for embryos from various animal species, emerging data also suggest a similar benefit in the human. Conversely, embryos cultured individually avoid potential substrate depletion, negative impact from factors secreted from companion embryos, while more practically permitting the ability to monitor and track the embryo for identification via morphology or molecular analysis to select and transfer potentially superior embryos. Importantly, advancements in embryo culture platforms now permit tracking of individual embryos, while also offering ability to reap the benefits of group culture. These approaches utilize confined microenvironments immediately surrounding the embryos that may be conducive for periodic sampling/analysis, while also allowing access to a larger media reservoir to avoid substrate depletion. Thus, though questions remain as to optimal embryo density and volume of culture media, group embryo culture in the correct culture platform is likely to be superior to individual embryo culture.

Towards the use of microfluidics for individual embryo culture

Mammalian embryo development is still relatively inefficient in vitro. Much research has been conducted on the chemical environment, or culture medium, surrounding the embryo, but little attention has been given to the actual physical culture environment, which has changed very little over the years. The application of microfluidics to embryo production in vitro is a tantalising approach that may alleviate some of the limits that traditional microdrop culture places on embryo development and research into gamete and embryo physiology. These devices may lead to enhanced in vitro embryo development and quality by more closely mimicking the in vivo environment. Initial work in this area is promising and gives us proof-of-principle that these unique microfluidic systems may indeed be applicable to in vitro culture of gametes and embryos. The present paper reviews the advantages of microfluidics for in vitro embryo production: how the platforms are manufactured, the current uses of microfluidics in assisted reproduction, static v. dynamic culture environments, individual gamete and embryo culture and the future directions of microfluidic application to in vitro embryo production and manipulation. Finally, preliminary data from our laboratory using a new microfluidic well insert for porcine, bovine and murine embryo culture is discussed.

Effect of the association of IGF-I, IGF-II, bFGF, TGF-beta1, GM-CSF, and LIF on the development of bovine embryos produced in vitro

This study examined the influence of the following growth factors and cytokines on early embryonic development: insulin-like growth factors I and II (IGF-I, IGF-II), basic fibroblast growth factor (bFGF), transforming growth factor (TGF-beta), granulocyte-macrophage colony-stimulating factor (GM-CSF), and leukemia inhibitory factor (LIF). Synthetic oviduct fluid (SOF) was used as the culture medium. We studied the development of bovine embryos produced in vitro and cultured until Day 9 after fertilization. TGF-beta1, bFGF, GM-CSF, and LIF used on their own significantly improved the yield of hatched blastocysts. IGF-I, bFGF, TGF-beta1, GM-CSF, and LIF significantly accelerated embryonic development, especially the change from the expanded blastocyst to hatched blastocyst stages. Use of a combination of these growth factors and cytokines (GF-CYK) in SOF medium produced higher percentages of blastocysts and hatched blastocysts than did use of SOF alone (45% and 22% vs. 24% and 12%; P<0.05) on Day 8 after in vitro fertilization and similar results to use of SOF+10% fetal calf serum (38% and 16%, at the same stages, respectively). The averages of total cells, inner cell mass cells, and trophectoderm cells of exclusively in vitro Day-8 blastocysts for pooled GF-CYK treatments were higher than those for SOF and similar to those for fetal calf serum. The presence of these growth factors and cytokines in the embryo culture medium therefore has a combined stimulatory action on embryonic development; in particular through an increase in hatching rate and in the number of cells of both the inner cell mass and trophoblast. These results are the first to demonstrate that use of a combination of recombinant growth factors and cytokine, as IGF-I, IGF-II, bFGF, TGF-beta1, LIF, and GM-CSF, produces similar results to 10% fetal calf serum for the development of in vitro-produced bovine embryos. This entirely synthetic method of embryo culture has undeniable advantages for the biosecurity of embryo transfer.

Effect of the microenvironment and embryo density on developmental characteristics and gene expression profile of bovine preimplantative embryos cultured in vitro

The Well of the Well (WOW) system has been developed to culture embryos in small groups or to track the development of single embryos. In the present study, we aimed to examine the effects of the microenvironment provided by the WOW system and embryo density on developmental rates, embryo quality and preimplantative gene expression profile of the resulting embryos. Embryos cultured in a group of 16 reached the blastocyst stage at a significantly lower level than zygotes cultured in a group of 50 (22.2 vs 30.3%), whereas zygotes cultured in WOW were able to compensate against low embryo densities, reaching a blastocyst rate as high as embryos cultured in a group of 50 (31.3 vs 30.3%). Moreover, embryos derived from WOW culture did not differ in terms of differential cell counts and apoptotic cell index compared with controls. The gene expression analysis revealed 62 transcripts to be upregulated and 33 transcripts to be downregulated by WOW culture. Comparing the in vivo derived blastocysts with the blastocysts derived from WOW culture, and group culture, expression of ATP5A1, PLAC8 and KRT8 was more similar to the embryos derived from WOW culture, whereas expression of S100A10 and ZP3 genes was more similar to blastocysts cultured in a group. In conclusion, microenvironment as well as embryo density significantly affected developmental rates. While subsequent blastocysts did not differ in terms of differential cell counts and apoptotic cell index, significant differences were observed in terms of the relative abundance of transcripts in the resulting embryos.

Direct Evidence for the Action of Phosphatidylinositol (3,4,5)-Trisphosphate-Mediated Signal Transduction in the 2-Cell Mouse Embryo1

Paf (1-o-alkyl-2-acetyl-sn-gylcero-3-phosphocholine) is a putative autocrine survival factor for the preimplantation embryo. It acts to induce receptor-mediated calcium transients in the early embryo. Inhibitors of 1-o-phosphatidylinositol-3-kinase (PI3kinase), such as wortmannin and LY 294002, blocked these calcium transients, implicating the generation of phosphatidylinositol (3,4,5)-trisphosphate (PIP3) in autocrine signal transduction in the early embryo. Perfusion of the embryo cytoplasm with a blocking antibody to PIP3 inhibited paf-induced calcium transients and hyperpolarization of the membrane potential. Furthermore, direct infusion of PIP3 into the embryo induced a nifedipine (10 micromol/L)- and diltiazem (10 micromol/L)-sensitive calcium current in the 2-cell embryo. PIP3 acts as a docking site on membranes for proteins that contain pleckstrin homology domains, such as the thymoma viral proto-oncogene protein (AKT) and phospholipase C gamma. The 2-cell embryo expressed three genes for AKT (Akt 1-3) and two genes for phospholipase C gamma (Plcg1 and Plcg2), and we confirmed the expression of both AKT and phospholipase C gamma 1 by immunolocalization. Paf induced increased accumulation of serine 473-phosphorylated AKT in the region of the plasma membrane, consistent with its recruitment to membrane PIP3. Inhibitors of PI3kinase, such as LY294002, and of AKT, e.g., deguelin and AKT-inhibitor, reduced zygote development in a dose-dependent manner, and this inhibition was partially reversed by the addition of paf to the culture medium. These results provide the first direct evidence that PIP3 and its responsive signaling pathways act in the 2-cell embryo. Since signal transduction via PI3kinase has important roles in governing the cell survival pathways, these results support the hypothesis that autocrine embryotropins, such as paf, act as survival factors.

In vitro-produced bovine embryos: dealing with the warts

Bovine in vitro embryo production is an inefficient process; while maturation and fertilization proceed apparently normally, the proportion of embryos reaching the transferable (blastocyst) stage is rarely over 40% and those that do reach this stage are often compromised in quality and competence. There is considerable evidence of a significant influence of follicular origin on oocyte developmental potential and it appears that once the oocyte is removed from the follicle its developmental capacity is capped. Evidence suggests that while culture conditions during bovine in vitro embryo production can impact somewhat the developmental potential of the early embryo, the intrinsic quality of the oocyte is the key factor determining the proportion of oocytes developing to the blastocyst stage. This paper highlights some of the problems associated with in vitro production of embryos and discusses some of the ways of overcoming these problems.

The Effects of Blastomere Biopsy and Oxygen Tension on Bovine Embryo Development, Rate of Apoptosis and Interferon-? Secretion

A series of experiments was performed to examine the effects of blastomere biopsies on subsequent development of IVF-derived bovine embryos. The first experiment was designed to assess the optimal time for blastomere removal. One blastomere was removed either 48 or 72 h after IVF. Biopsy at 48 h resulted in 17.2% of embryos proceeding to the blastocyst stage, which was lower than when biopsies were performed at 72 h (37.5%, p < 0.05). In the second experiment, embryos were cultured either under atmospheric or 5% O(2) following blastomere removal. Biopsies had no effect on rate of blastocyst formation with 36% of controls and 33.7% of biopsied embryos proceeding to that stage. However, culture under 5% O(2) significantly increased the number of blastocysts from 29.9% to 40.3% (p < 0.05). This effect was significant in both biopsied and control embryos. In the final experiment, biopsied embryos were again cultured under different oxygen tension. Blastocysts were collected and cultured individually for 48 h in medium droplets in their respective O(2) concentration after which time the medium was assayed for concentration of interferon-tau (IFN-tau). Reduced O(2) concentration again significantly increased blastocyst formation from 24.9% to 41.9% (p < 0.05). IFN-tau secretion was not affected by biopsies, but culture under atmospheric O(2) resulted in significantly increased IFN-tau concentration in medium droplets (12274.0 +/- 2825.9 pM vs 5046.5 +/- 2562.2 pM; p < 0.05).

Effect of inclusion of serum and granulocyte-macrophage colony stimulating factor on secretion of interferon-tau during the in vitro culture of ovine embryos

In each of three experiments, in vitro-matured and -fertilised zygotes were cultured to Day 7 post insemination in synthetic oviductal fluid (SOF). In Experiment 1, zygotes were cultured in groups in either SOF plus albumin (SOFA) or serum (SOFS) and then blastocysts were cultured individually for a further 24 h without a change of media. In Experiment 2, zygotes were cultured in groups using a 2 x 2 factorial design in SOFA or SOFS, with or without recombinant ovine granulocyte-macrophage colony stimulating factor (GM-CSF; 5 ng mL(-1)). Blastocysts were then cultured individually using a split-plot design in SOFA or SOFS with or without GM-CSF. In Experiment 3, zygotes were cultured in SOFA in which GM-CSF was absent (A) or present (P) during Days 1-3, Days 3-5 or Days 5-7 of IVC in six combinations as follows: AAA, AAP, APP, PPP, PPA and PAA. Serum or GM-CSF increased secretion of interferon (IFN)-tau in Experiments 1 and 2 both between Days 5 and 7 of group culture and during individual culture. Secretion of IFN-tau during individual culture was determined by the medium in which embryos were group cultured and the effects of GM-CSF and serum were not additive. In Experiment 3, the presence of GM-CSF between Days 1 and 3 of culture was responsible for stimulation of secretion of IFN-tau between Days 5 and 7; IFN-tau secretion was detected as early as Day 3 post insemination.

The effect of paracrine/autocrine interactions on the in vitro culture of bovine preimplantation embryos

Bovine preimplantation embryos develop more successfully when cultured in groups, proibably because of the increased production of, and exposure to, embryotrophic autocrine and paracrine factors. Using a novel embryo culture technique, this study had two aims: 1. to determine the distance over which potential paracrine interactions affect bovine embryo development in terms of blastocyst and hatching rates, cell counts and carbohydrate metabolism; 2. to investigate the effect of platelet-activating factor (PAF) supplementation on bovine embryo development and metabolism. Groups of 16 presumptive zygotes were attached to the bottom of a culture dish by the cell adhesive Cell-Tak in a 4 × 4 equidistant array. The distance between individual embryos in each group was 0–689 μm. Optimal blastocyst formation rate occurred when embryos were cultured 165 μm apart compared with control non-attached zygotes (Kruskal–Wallis followed by Mann–Whitney U test post-hoc; P < 0.05). Increasing the distance between embryos resulted in a further decline in blastocyst rate, which reached zero at 540 μm apart. Blastocyst cell number, pyruvate/glucose uptake and lactate production decreased as the interembryo distance increased from 240 to 465 μm (P < 0.05). Supplementation with PAF during conventional group culture enhanced blastocyst cell number, hatching rates and the oxidative metabolism of pyruvate and glucose. The data indicate that the distance between individual bovine embryos in culture influences preimplantation development, in particular blastocyst formation, cell number and metabolism. It is suggested that diffusible paracrine/autocrine factors, such as PAF, are in part responsible for the regulation of early embryo development.

In vivo expression of interferon tau mRNA by the embryonic trophoblast and uterine concentrations of interferon tau protein during early pregnancy in the cow

In this study, we have measured uterine concentrations of interferon tau and intensity of embryonic interferon tau mRNA expression between day 14 and 18 in cows. While interferon tau concentrations rose dramatically (P < 0.001) from day 14 to 18, there was no significant increase in the intensity of expression of interferon tau mRNA by the trophoblast. When results were analyzed on the basis of embryo size, well elongated embryos (>10 cm) produced significantly (P < 0.001) more interferon tau than smaller embryos but showed similar levels of interferon tau mRNA expression. These results demonstrate that the increase in interferon tau concentrations responsible for the maternal recognition of pregnancy results from the increase in embryo size during elongation and not from any upregulation of mRNA expression.

Comparison of Gene Expression in Male and Female Mouse Blastocysts Revealed Imprinting of the X-Linked Gene, Rhox5/Pem, at Preimplantation Stages

Mammalian male preimplantation embryos develop more quickly than females . Using enhanced green fluorescent protein (EGFP)-tagged X chromosomes to identify the sex of the embryos, we compared gene expression patterns between male and female mouse blastocysts by DNA microarray. We detected nearly 600 genes with statistically significant sex-linked expression; most differed by 2-fold or less. Of 11 genes showing greater than 2.5-fold differences, four were expressed exclusively or nearly exclusively sex dependently. Two genes (Dby and Eif2s3y) were mapped to the Y chromosome and were expressed in male blastocysts. The remaining two (Rhox5/Pem and Xist) were mapped to the X chromosome and were predominantly expressed in female blastocysts. Moreover, Rhox5/Pem was expressed predominantly from the paternally inherited X chromosome, indicating sex differences in early epigenetic gene regulation.

Development of porcine embryos in vivo and in vitro; evidence for embryo 'cross talk' in vitro

The in vitro development of zygotes of domestic species to the blastocyst stage is facilitated by culture in groups, suggesting a role for autocrine/paracrine factors. A novel method was used to investigate the potential role of such factors using in-vitro-produced and in-vivo-derived porcine embryos. The development of individual zygotes to the blastocyst stage was optimal when they were cultured 81-160 mum apart. As the distance between the embryos was increased, blastocyst rates declined significantly, reaching zero beyond 640 mum. Blastocyst volume and cell number (both inner cell mass and trophectoderm) were also increased when the distance apart was between 81 and 160 mum. Culturing embryos in groups at different stages of development suggested that group culture confers a greater advantage to development after the activation of the genome. Group culture of in-vivo-derived embryos showed a weak distance effect. The results suggest a role for as yet unknown diffusible paracrine/autocrine factors released by early porcine embryos in promoting the growth of neighbouring embryos in vitro. This advantage is observed to a lesser extent by in-vivo-derived zygotes which are likely to have been better conditioned for development in vitro by being conceived in the female reproductive tract.

Gene expression and developmental competence of bovine embryos produced in vitro under varying embryo density conditions

The objective of this study was to determine the effects of oocyte/embryo density (embryo number:medium volume ratio) on developmental competence and relative transcription of developmentally important genes in in vitro-produced bovine embryos. Using standard procedures, bovine oocytes were matured, fertilized and cultured in vitro in groups of 5, 10, 20 or 30 oocytes/embryos per 100 microL medium drop (embryo number/medium volume ratios of 1:20, 1:10, 1:5 and 1:3.3, respectively). A semi-quantitative RT-PCR assay was used to determine the relative abundance of Hsp 70.1 and Glut-1 transcripts in Day-6 morulae, and in Day-7 and Day-8 blastocysts and expanded blastocysts. Cleavage rates (55.9, 49.1, 47.1 and 34.6%, respectively) and blastocyst developmental rates (24.1, 18.9, 20.4 and 12.6%, respectively) were higher in groups containing 5, 10 and 20 embryos versus 30 embryos per drop, but there were no significant differences among groups in hatching rates. The relative abundance of Hsp 70.1 transcripts in Day-7 blastocysts was higher in embryos produced in the 20-embryo than in the 5-embryo groups. There were no differences among embryos from all groups in the amount of Glut-1 mRNA (regardless of embryonic stage). However, there were differences in the pattern of Hsp 70.1 gene expression between distinct stages of embryo development and embryo density; these dissimilarities appeared to be associated with compromised development at higher embryo densities. In conclusion, the increase in embryo density during IVM, IVF, and IVC phases of in vitro embryo production might negatively affect embryo development and the pattern of gene expression of in vitro-produced bovine embryos.

Influence of antral follicle size on oocyte characteristics and embryo development in the bovine

The developmental competence of bovine oocytes isolated from antral follicles of different sizes was assessed in three European laboratories (Belgium, UCL; Denmark, DIAS; France, INRA). Using the same protocol for in vitro production of embryos, the oocytes isolated from follicles with a diameter > or = 6 mm always gave a higher blastocyst rate than oocytes from follicles < 4 mm (UCL: 42% versus 14%, DIAS: 50% versus 35%, INRA: 39% versus 22%; P < 0.05). Blastocyst cell number was not affected by follicle size. Several parameters were investigated for these oocytes. The energy metabolism of cumulus-oocyte-complexes and of denuded oocytes was assessed by the oxygen and pyruvate uptake and by lactate release both at the beginning and the end of the maturation. No effect of follicle size could be detected but lactate release increased after maturation. The global profile of transcripts, the pattern of protein neosynthesis and the kinetics of meiosis resumption were not affected by follicle size. The developmental kinetics of derived embryos was also analysed. Whatever the follicle size, viable embryos had a shorter first and third embryonic cell cycle. Among the viable embryos, the size of the follicle interfered with the fourth cell cycle duration. A higher percentage of blastocysts issued from large follicle presented a short fourth cell cycle (9h) (35% versus 6%; P < 0.05). Beside, blastocysts derived from small follicles had a delayed cavitation and expansion. Thereby, a higher developmental competence for oocytes from follicle > or = 6 mm versus < 4 mm was demonstrated in three laboratories although no differences could be displayed directly at the oocyte level.

Sexual dimorphism in interferon-tau production by in vivo-derived bovine embryos

Interferon-tau (IFN-tau) is an anti-luteolytic factor responsible for preventing regression of the maternal corpus luteum (CL) during early pregnancy of cattle. In vitro-produced (IVP) bovine embryos first produce IFN-tau as blastocysts. In the present study, we have examined whether sexually dimorphic production of IFN-tau, which is observed among IVP blastocysts, also occurs among in vivo-produced blastocysts, and whether this difference between the sexes persists to day 14 when silencing of one of the X-chromosomes in the trophectoderm is complete. Embryos were flushed from cattle that had been superovulated and bred by AI. Blastocysts (63 male, 62 female) recovered between days 8.5 and 9.5 of pregnancy, were cultured individually. No differences were observed between males and females in either their developmental stage or quality at the beginning, during, and at the end of culture. Female embryos produced more IFN-tau than males by 24 hr (mean values, males: 16.6 +/- 3.7, females: 49.4 +/- 9.0 pg per embryo; P < 0.05) and 48 hr (male: 189.8 +/- 37.1, female: 410.9 +/- 66.6 pg per embryo; P < 0.05). However, the variability in IFN-tau production between individual blastocysts was so great that IFN-tau secretion is unlikely to be of value as a non-invasive means to predict embryo sex. When conceptuses were recovered at day 14, elongating males (n = 25) and females (n = 24) were similar in dimension and did not differ in their IFN-tau production after 4.5 hr (male: 2,550 +/- 607, female: 2,376 +/- 772 ng per conceptus) and 24 hr (male: 12,056 +/- 2,438, female: 8,447 +/- 1,630 ng per conceptus) of culture. Thus, sexual dimorphism in IFN-tau production is observed in both IVP and in vivo-produced expanded blastocysts, but is lost by day 14 of in vivo development.

Effects of Developmental Stage, Embryonic Interferon-tau Secretion and Recipient Synchrony on Pregnancy Rate after Transfer of in vitro Produced Bovine Blastocysts

Three separate trials of bovine embryo transfers were performed consisting of 32, 41 and 33 transfers, respectively, to examine the effects of (a) the developmental stage of in vitro-derived blastocysts, (b) the amount of interferon-tau (IFN-tau) they secreted during culture and (c) the cyclic stage of the recipient at the time of transfer on the probability of establishment of pregnancy. One blastocyst was transferred into the ipsilateral uterine horn to the CL. At the time of transfer, blastocysts were classified into one of three developmental stages (early blastocyst, blastocyst and expanded blastocyst) and the cyclic stage of each cow was assessed (-12 h, on time, +12 h, +24 h, >24 h). Prior to the second and third trials, blastocysts were individually cultured for 24 h in 50 microl medium droplets and the IFN-tau concentration in the droplet was determined. Logistic regression analyses revealed that expanded blastocysts had a significantly higher likelihood of establishing pregnancy (p = 0.009), and that there was a significant interaction with the cyclic stage of the recipient in this group with lower rates of pregnancy resulting from decreasing synchrony with the recipient (p = 0.033). IFN-tau secretion during culture was significantly higher in expanded blastocysts than in the other two groups (p < 0.05). A significant effect of the pre-transfer level of IFN-tau secretion was found only in the 'Blastocyst' group where transfer of embryos with lower IFN-tau production prior to transfer resulted in higher pregnancy rates (p = 0.047). These results demonstrate that IFN-tau secretion may be a useful tool to predict pregnancy outcome, but only within certain developmental stages.

Identification of bovine and novel interferon-? alleles in the American plains bison (bison bison) by analysis of hybrid cattle x bison blastocysts

The objective of this study was to generate bison x cattle hybrid embryos by in vitro fertilization, to assess their developmental potential, to determine the pattern of secretion of the embryonic signaling molecule interferon-tau (IFN-tau), and to identify novel IFN-tau mRNA polymorphism in the American plains bison. A total of 600 bovine oocytes were inseminated with frozen-thawed bison semen. Of these, 40.7% cleaved and 14.8% proceeded to the blastocyst stage. Individual blastocysts were cultured on a basement membrane (Matrigel) and their ability to attach and form outgrowths was monitored. A total of 36 blastocysts were cultured of which 22 formed outgrowths. During individual culture, medium samples were collected and their IFN-tau concentration was measured. On day 6 after onset of individual culture, attached outgrowths produced significantly more IFN-tau than unattached viable or degenerate blastocysts. At this time, female conceptuses also produced significantly more IFN-tau than their male cohorts. However, by day 12 this difference had disappeared. Total mRNA was extracted from three individual outgrowths and analyzed by RT-PCR. Subsequent sequencing of 28 clones showed several known bovine IFN-tau sequences as well as two novel sequences termed bisIFN-tau1 and 2. To determine the origin of these, DNA was extracted from bison semen and analyzed by PCR. One bovine IFN-tau sequence (bovIFN-tau1d) as well as bisIFN-tau2 and a third novel sequence bisIFN-tau3 were detected. This study demonstrates the feasibility of using hybrid embryos for the analysis of developmentally regulated gene expression in species where embryos may not be available.

Effects of oxidative stress and inhibitors of the pentose phosphate pathway on sexually dimorphic production of IFN-? by bovine blastocysts

Bovine interferon-tau (IFN-tau), the anti-luteolytic factor secreted by conceptuses of pecoran ruminants, is a product of autosomal genes, yet in vitro produced (IVP) female expanded blastocysts (EB) secrete about twice as much IFN-tau as males. Two possible explanations have been tested here. One is that embryos of one sex are differentially susceptible to oxidative stress. The second is that female EB produce more IFN-tau because pentose-phosphate pathway (PPP) activity is elevated as a result of delayed X-chromosome inactivation. IVP bovine zygotes were cultured to the 8-cell stage and placed under conditions designed either to promote oxidative stress (+/-H2O2; 20 vs. 5% O2), or to inhibit glucose 6-phosphate dehydrogenase (G6PDH) activity (addition of dehydroepiandrosterone, DHEA or 6-aminonicotinamide, 6-AN to the medium). At day 8, blastocysts were cultured individually for a further 48 hr to assess IFN-tau production, and embryo sex determined retrospectively. Blastocyst numbers were reduced (P < 0.05) and their continued development impaired (P < 0.05) in presence of H2O2 (200 microM) and 20% O2, but neither IFN-tau production nor sexually dimorphic expression of IFN-tau were affected. IFN-tau production was reduced, particularly in females (P < 0.05), and sexual dimorphic differences in production were lost in the presence of both DHEA (100 microM) and 6-AN (1 microM). In the case of 6-AN, these effects were achieved without a significant decline in blastocyst developmental progression, quality, or cell number. The data suggest that the higher production of IFN-tau by female EB is an indirect outcome of the increased activity of the oxidative arm of the PPP pathway.

Temporal divergence in the pattern of messenger RNA expression in bovine embryos cultured from the zygote to blastocyst stage in vitro or in vivo

The objective of this study was to examine the time during the postfertilization period that gene expression patterns in in vitro-cultured bovine embryos diverge from those of their in vivo-cultured counterparts. Presumptive bovine zygotes were produced by in vitro maturation and fertilization of immature oocytes collected from the ovaries of slaughtered animals. Approximately 20 h post insemination (hpi), zygotes were denuded and randomly divided into two groups for culture either in vitro, in synthetic oviduct fluid medium, or in vivo, in the ewe oviduct. Embryos were recovered from both systems at approximately 30 hpi (2-cell), 2 (4-cell), 3 (8-cell), 4 (16-cell), 5 (early morula), 6 (compact morula), or 7 (blastocyst) days post insemination. On recovery, they were examined for stage of development and snap frozen in liquid nitrogen for the analysis of transcript abundance using real-time polymerase chain reaction. The transcripts studied were glucose transporter 5, sarcosine oxidase, mitochondrial Mn-superoxide dismutase, connexin 43, interferon tau, insulin-like growth factor II, apoptosis regulator box-alpha and insulin-like growth factor-I receptor, most of which are known from our previous work to differ in terms of transcript abundance in blastocysts derived from culture in vitro or in vivo. The results demonstrate that the relative abundance of the transcripts studied varies throughout the preimplantation period and is strongly influenced by the culture environment. In addition, the data demonstrate that changes in transcript abundance in blastocyst stage embryos are in many cases a consequence of perturbed transcription earlier in development. Depending on the transcript, these differences may be evident by as little as 10 h of initiation of culture. Such information has implications not only for basic biology but also for human assisted reproduction in which there is a move toward culturing embryos to the blastocyst stage, necessitating prolonged culture in vitro under potentially deleterious conditions.

A novel role of luteinizing hormone in the embryo development in cocultures

Bovine oviductal epithelium contains LH receptors, which function in the increase of synthesis of oviductal glycoprotein (OGP). As with cocultures of embryos with oviductal epithelial cells, OGP is thought to promote early embryonic growth and development. These findings led us to test the hypothesis that LH treatment of cocultures further increases embryo development through OGP mediation. Coculture of > or=10 two-cell bovine embryos with bovine oviductal epithelial cells increased the development of the embryos into blastocysts. Treatment of these cocultures with hCG, used as a surrogate for LH because of its stability and purity, further increased embryo development. The hCG effect is dose dependent and hormone specific and requires the dimer conformation and the presence of LH receptors in oviductal epithelial cells. The inhibition of OGP synthesis and prevention of protein kinase A activation blocked the hCG effect in cocultures. Reverse transcription polymerase chain reaction and indirect immunofluorescence with laser scanning confocal microscopy demonstrated the presence of LH receptors in bovine oocytes, embryos, and blastocysts. However, embryo LH receptors may not have played any role in the beneficial hCG effects in cocultures. These findings suggest that elevated periovulatory LH levels may promote preimplantation embryo development in oviducts. These results have important implications for assisted reproductive technologies in which cocultures are used to improve pregnancy rates.

Possible Role of Interferon-.TAU. on In Vitro Development of Bovine Embryos

The effect of interferon-tau on in vitro development of bovine embryos was investigated. After in vitro fertilization, embryos developed to the morula stage were cultured for 3 days in TCM-199 or CR1 medium containing BSA or FCS supplemented with or without recombinant IFN-tau produced by a baculovirus expression system. Addition of baculovirus-expressed IFN-tau (100 ng/ml) significantly promoted development to the blastocyst stage in both culture media. Addition of E. coli expressed IFN-tau (2 microg/ml) also significantly promoted the embryonic development. Supplementation of BSA or FCS did not affect the growth-promoting effect of IFN-tau. To determine whether the growth-promoting effect of IFN-tau is related to the interferon type I receptors that bind to type I interferon such as IFN-alpha, embryos were cultured with IFN-alpha. Although IFN-alpha significantly promoted the development, a much higher concentration (25 microg/ml) was required than IFN-tau. A reverse transcription polymerase chain reaction analysis revealed the expression of mRNA encoded type-I IFN receptor subunit from morula to blastocyst stage embryos. The overall results suggest a novel function for IFNs in promoting embryonic development and the effect may be related to type-I IFN receptor expressed in the early stages of preimplantation embryos.

Bovine embryo culture in the presence or absence of serum: implications for blastocyst development, cryotolerance, and messenger RNA expression

We have previously shown that, while the intrinsic quality of the oocyte is the main factor affecting blastocyst yield during bovine embryo development in vitro, the main factor affecting the quality of the blastocyst is the postfertilization culture conditions. Therefore, any improvement in the quality of blastocysts produced in vitro is likely to derive from the modification of the postfertilization culture conditions. The objective of this study was to examine the effect of the presence or absence of serum and the concentration of BSA during the period of embryo culture in vitro on 1) cleavage rate, 2) the kinetics of embryo development, 3) blastocyst yield, and 4) blastocyst quality, as assessed by cryotolerance and gene expression patterns. The quantification of all gene transcripts was carried out by real-time quantitative reverse transcription-polymerase chain reaction. Bovine blastocysts from four sources were used: 1) in vitro culture in synthetic oviduct fluid (SOF) supplemented with 3 mg/ml BSA and 10% fetal calf serum (FCS), 2) in vitro culture in SOF + 3 mg/ml BSA in the absence of serum, 3) in vitro culture in SOF + 16 mg/ml BSA in the absence of serum, and 4) in vivo blastocysts. There was no difference in overall blastocyst yield at Day 9 between the groups. However, significantly more blastocysts were present by Day 6 in the presence of 10% serum (20.0%) compared with 3 mg/ml BSA (4.6%, P < 0.001) or 16 mg/ml BSA (11.6%, P < 0.01). By Day 7, however, this difference had disappeared. Following vitrification, there was no difference in survival between blastocysts produced in the presence of 16 mg/ml BSA or those produced in the presence of 10% FCS; the survival of both groups was significantly lower than the in vivo controls at all time points and in terms of hatching rate. In contrast, survival of blastocysts produced in SOF + 3 mg/ml BSA in the absence of serum was intermediate, with no difference remaining at 72 h when compared with in vivo embryos. Differences in relative mRNA abundance among the two groups of blastocysts analyzed were found for genes related to apoptosis (Bax), oxidative stress (MnSOD, CuZnSOD, and SOX), communication through gap junctions (Cx31 and Cx43), maternal recognition of pregnancy (IFN-tau), and differentiation and implantation (LIF and LR-beta). The presence of serum during the culture period resulted in a significant increase in the level of expression of MnSOD, SOX, Bax, LIF, and LR-beta. The level of expression of Cx31 and Cu/ZnSOD also tended to be increased, although the difference was not significant. In contrast, the level of expression of Cx43 and IFN-tau was decreased in the presence of serum. In conclusion, using a combination of measures of developmental competence (cleavage and blastocyst rates) and qualitative measures such as cryotolerance and relative mRNA abundance to give a more complete picture of the consequences of modifying medium composition on the embryo, we have shown that conditions of postfertilization culture, in particular, the presence of serum in the medium, can affect the speed of embryo development and the quality of the resulting blastocysts. The reduced cryotolerance of blastocysts generated in the presence of serum is accompanied by deviations in the relative abundance of developmentally important gene transcripts. Omission of serum during the postfertilization culture period can significantly improve the cryotolerance of the blastocysts to a level intermediate between serum-generated blastocysts and those derived in vivo. The challenge now is to try and bridge this gap.

Interferon-tau in bovine blastocysts following parthenogenetic activation of oocytes: pattern of secretion and polymorphism in expressed mRNA sequences

A series of experiments were conducted to examine the pattern of production and secretion of interferon-tau (IFN-tau) by blastocysts following parthenogenetic activation of bovine oocytes. In the first experiment, 36.8, 24.1, and 33.2% of IVF-derived and parthenogenetically activated oocytes cultured in the presence or absence of a monolayer of buffalo rat liver cells, respectively, reached the blastocyst stage. Following individual culture of blastocysts, IFN-tau concentration in medium droplets was similar among the three groups, although IVF-derived blastocysts contained significantly more cells. In the second experiment, 156 IVF-derived blastocysts were sexed by PCR with 75 and 81, respectively, being male and female. IFN-tau secretion of these was compared to that of 70 parthenogenetic blastocysts. Female and parthenogenetic blastocysts produced significantly more IFN-tau than their male counterparts. In the third experiment, the ability of hatched blastocysts to form outgrowths and the pattern of their IFN-tau secretion were examined. Of the 48 IVF-derived blastocysts, 44 formed outgrowths compared to 41 of the 42 hatched parthenotes. Parthenogenetic outgrowths were significantly larger after 7 days, but this difference had disappeared after 14 days. IFN-tau secretion did not differ between the two groups. Lastly, sequence analyses of expressed mRNA from individual parthenogenetic blastocyst outgrowths showed four different transcript types which, based on their predicted amino acid sequence, belong to two subgroups, IFN-tau1 and IFN-tau3. In addition, one new transcript sequence was identified, encoding a new protein isoform.

Sexual dimorphism among bovine embryos in their ability to make the transition to expanded blastocyst and in the expression of the signaling molecule IFN-tau

IFN-tau is a secretory product of trophectoderm of cattle, sheep, and their relatives and is expressed for a few days in early pregnancy after the blastocyst first forms. It serves to alert the mother that she is pregnant. A delayed or less than robust IFN-tau signal is a likely cause of embryonic loss. Here we have determined whether blastocyst production of IFN-tau, which is encoded by a cluster of genes on chromosome 9, differs between the sexes in cattle, as assessed by culture of in vitro-derived embryos on two different media, one complex (tissue culture medium 199 supplemented with serum) with coculture support, the other relatively simple (synthetic oviductal fluid plus albumin). With both media, female blastocysts produced approximately double the amount of IFN-tau as males, regardless of such variables as oocyte batch, blastocyst quality, hatching, and length of time in culture. However, in either tissue culture medium 199, which contains 5.5 mM d-glucose, or in synthetic oviductal fluid, in the presence but not in the absence of added glucose, significantly fewer female than male embryos were able to progress from the morula/early blastocyst stage to more advanced stages of development. It is possible that the differences between male and female embryos both in their production of IFN-tau and in their ability to progress in development in glucose-rich media are manifestations of phenomena that occur in vivo and provide plasticity in embryo selection during early pregnancy.

The effect of Ureaplasma diversum activated mononuclear leukocytes on the development and interferon-tau production by bovine IVF-derived embryos

Ureaplasma diversum is an opportunistic pathogen of the bovine genital tract causing herd outbreaks of granular vulvitis, abortion and infertility. Early embryonic death probably contributes to reduction of the reproductive performance in cows, however, pathogenesis of the disease remains obscure. The aim of the study was to examine whether activation of mononuclear leukocytes by U. diversum may affect embryo development and IFN-tau production. Bovine peripheral blood mononuclear leukocytes were cultured with U.diversum antigen for 24 h. The levels of IL-1, TNF-alpha, NO and GM-CSF in the cell culture supernatants were measured. IVF-derived embryos were cultured in the presence of supernatants from activated leukocytes. The development of embryos until day 6 postinsemination and the rate of morulae/blastocysts were determined. IFN-tau production in supernatants of cultured embryos was examined by inhibition of a virally-induced cytopathic effect. The results showed that U. diversum stimulated mononuclear leukocyte production of IL-1, TNF-alpha and NO. Supernatants from U. diversum-activated cells did not impair the rates of the embryo development and blastocyst formation. The products of activated leukocytes increased the IFN-tau production by cultured blastocysts. This suggest that U. diversum infection provides leukocyte-mediated signals for developing embryos for generation of additional production of cytokine - an important component of innate immunity.