Coculture of in vitro fertilized bovine embryos with oviductal epithelial cells originating from different stages of the estrous cycle

The embryo non-invasive pre-implantation diagnosis era: how far are we?

Advancements in assisted reproduction (AR) methodologies have allowed significant improvements in live birth rates of women who otherwise would not be able to conceive. One of the tools that allowed this improvement is the possibility of embryo selection based on genetic status, performed via preimplantation genetic testing (PGT). Even though the widespread use of PGT from TE biopsy helped to decrease the interval from the beginning of the AR intervention to pregnancy, especially in older patients, in AR, there are still many concerns about the application of this invasive methodology in all cycles. Therefore, recently, researchers started to study the use of cell free DNA (cfDNA) released by the blastocyst in its culture medium to perform PGT, in a method called non-invasive PGT (niPGT). The development of a niPGT would bring the diagnostics power of conventional PGT, but with the advantage of being potentially less harmful to the embryo. Its implementation in clinical practice, however, is under heavy discussion since there are many unknowns about the technique, such as the origin of the cfDNA or if this genetic material is a true representative of the actual ploidy status of the embryo. Available data indicates that there is high correspondence between results observed in TE biopsies and the ones observed from cfDNA, but these results are still contradictory and highly debatable. In the present review, the advantages and disadvantages of niPGT are presented and discussed in relation to tradition TE biopsy-based PGT. Furthermore, there are also presented some other possible non-invasive tools that could be applied in the selection of the best embryo, such as quantification of other molecules as quality biomarkers, or the use artificial intelligence (AI) to identify the best embryos based on morphological and/or morphokitetic parameters.

Early embryo-maternal communication in the oviduct: A review

An intact embryo-maternal communication is critical for the establishment of a successful pregnancy. To date, a huge number of studies have been performed describing the complex process of embryo-maternal signaling within the uterus. However, recent studies indicate that the early embryo communicates with the oviductal cells shortly after fertilizationand that this is important for the successful establishment of pregnancy. Only if the early embryo is capable to signal the mother within a precise timeframe and to garner a response, will the embryo be able to survive and reach the uterus. This review will give an overview of all the experimental designs which have investigated embryo-maternal interaction in the oviduct. In addition to that, it will provide a comprehensive analysis of the findings to date elucidating the morphological and molecular changes in the oviduct which are induced by the presence of the early embryo highlighting how the tubal responses affect embryo development and survival.

[Use of an in vitro model in bovine to evidence a functional and molecular dialogue between preimplantation embryo and oviduct epithelial cells]

Beyond being a pipe between ovary and uterus, the oviduct is an active player in different aspects of early reproductive processes, in particular in the transport of embryos to the site of implantation and the regulation of its early development. Different studies evidenced a communication between oviduct and early embryo at the molecular and functional levels. Since the study of these interactions is difficult in vivo, different in vitro systems have been developed to mimic the maternal milieu during early development. These systems allowed to confirm the action of the cells on the quality of early development (blastocyst rate and viability). In turn, the embryos are producing signals that are able to modify and adapt the activity of maternal cells.

Culture systems: embryo co-culture

During the 1970s, domestic animal biotechnology, i.e., embryo transfer in farm animals, was confronted with the problem of embryonic developmental arrest observed in vitro, especially during the cycle in which maternal to zygotic transition (MZT) cycle takes place. In farm animals, obtaining blastocysts is mandatory, as transfer at earlier stages results in expulsion of the embryo from the vagina. In humans, the first attempts to obtain blastocysts with classical culture media were disappointing, and the use of a coculture strategy was naturally tempting: the first significant results of successful blastocyst development were obtained in the early 1980s, using trophoblastic tissue as a feeder layer in order to mimic an autocrine embryotrophic system. The next supporting cell systems were based on oviduct epithelial cells and uterine cells in order to achieve a paracrine effect. Non-hormone dependence was then demonstrated with the use of prepubertal cells, and finally with the use of established cell lines of nongenital origin (African Green Monkey Kidney, Vero cells). The embryotrophic properties are linked to features of "transport epithelia." Vero cells have been extensively used in human ART, and most of our knowledge about the human blastocyst was gathered with the use of this technology. Coculture is still in current use, but with systems that employ autologous uterine cells. Results following the use of this technology in human ART are superior to those observed with the use of sequential media. The benefit is linked to the release of free radical scavengers and growth factors by the feeder cells. In animal biotechnology, an important part of the "precious embryos," i.e., those resulting from cloning technology, involves coculture with buffalo rat liver (BRL) cells or Vero cells.

Review: role of tubal environment in preimplantation embryogenesis: application to co-culture assays

The culture of early preimplantation stage embryo is still delicate and the metabolic pathways of embryos are not completely understood. Embryo needs are evolutionary during the preimplantation development, consequently it is difficult to meet embryo needs in vitro. Culture conditions have to respect several physical and chemical equilibria: such as redox potential, pH, osmotic pressure, metabolic flux of energetic compounds, endogenous pools of amino acids and transcripts, etc. Embryo culture media are generally supplemented with amino acids, glucose, other energetic metabolites and antioxidant compounds, vitamin, and growth factors etc. Furthermore autocrine and paracrine regulation of embryo development probably exist. In fact embryo culture conditions have to be as non-toxic as possible. Various types of co-culture systems have been devised to overcome these problems. Complex interrelations exist between embryos and co-cultured cells. The beneficial effects of co-cultured cells may be due to continuous modifications of the culture medium, i.e. the elimination of toxic compounds and/or the supply of embryotrophic factors.

Embryos and culture cells: a model for studying the effect of progesterone

A positive association between P4 concentration and initial bovine embryo survival has been reported. The objective of this study was to establish two coculture systems as a model to study the influence of progesterone on the initial bovine embryo development. Granulosa cells (GC) or bovine oviduct epithelial cells (BOECs) were used at the base of embryo culture medium microdroplets (TCM199 and 10% of superovulated oestrus cow serum, (SOCS)) supplemented or not with progesterone (P4, 33.4 ng mL(-1)) and/or a progesterone receptor antagonist (onapristone, OP, 2.2x10(-5)M). Presumptive zygotes were transferred to monolayers after in vitro maturation and fertilization of bovine oocytes with thawed swim-up selected sperm. Embryo development was carried out according to the following groups: experiment 1, BOEC (n=378) and BOEC plus OP (n=325); experiment 2, GC (n=514); GC plus OP (n=509); BOEC (n=490); BOEC plus P4 (n=500); BOEC plus P4 and OP (n=502). Embryos were checked for cleavage at day 2 and for stage development between days 8 and 12 of culture. In experiment 1, no differences (P>0.05) were identified between BOEC and BOECOP groups for embryo rates of development, quality or developmental stages. Also in experiment 2, no differences were found in embryo rates of development, quality or developmental stages between embryos cultured under the two coculture systems when no supplementation was added. Embryo development rates were not affected by OP presence in GCOP group. However, P4 negatively affected Day 8 (D8) embryo development rates in BOEC system (BOECP4=16.8+/-2.6% vs. BOEC=23.7+/-1.7%, P=0.02). This negative effect was abolished when P4 antagonist (OP) was added to the culture medium. BOEC supplementation with P4 also induced a delay on embryo development at D8 as confirmed by a lower development score (BOECP4=3.0+/-1.4 vs. GC=3.4+/-0.1, GCOP=3.5+/-0.1, BOEC=3.4+/-0.1 and BOECP4OP=3.5+/-0.1; P<0.05). These results demonstrate that OP supplementation had no harmful effect on embryo development either in granulosa, where P4 is naturally synthesised, or in BOEC coculture systems. Also we can not confirm a direct association between high P4 concentrations and embryo survival during early stages, although P4 may influence early embryo development through different mechanisms mediated by the type of cells present.

Effect of embryo developmental stage and culture conditions on number and quality of ovine in vitro produced blastocysts

This study evaluated the final output and quality of in vitro produced blastocysts derived from in vivo recovered sheep embryos cultured at various early developmental stages to blastocyst. A total of 270 embryos were recovered from the oviduct, at different days of the early luteal phase, and were classified into three different developmental stages: 2- to 4-cell (n = 93); 5- to 8-cell (n = 92) and 9- to 12-cell (n = 85). The effect of culture conditions was studied, at the same time, by randomly allocating the embryos to one of four groups: three groups of culture with fresh oviduct monolayers (2, 4 and 5 days old) and a fourth group with 2-day monolayers derived from frozen-thawed oviduct cells. Two control groups were established: first, embryos cultured in semi-defined medium (n = 29) and, second, blastocysts obtained in vivo and cryopreserved (n = 43). Influence on blastocyst yield of embryo developmental stage at the start of culture was statistically significant (p < 0.001). Two- to four-cell embryos showed a significantly lower developmental rate (67.7%) than the 5- to 8-cell (83.6%; p < 0.001) and 9- to 12-cell groups (90.5%; p < 0.0001) and lower quality in terms of blastocyst cryotolerance (56.0 vs. 83.7%; p < 0.005). There were no detected effects relating to the age or handling of the monolayer on the embryo developmental rate, but the day of blastocyst appearance was different between embryos cultured on monolayers derived from fresh or frozen-thawed cells (p < 0.0001); the main influence was on the group of 9- to 12-cell embryos (p < 0.0001). Current results confirm the temporal sensitivities of sheep embryos to in vitro culture, regardless of the culture conditions.

Blastocyst Formation Rates In Vivo and In Vitro of In Vitro-Matured Equine Oocytes Fertilized by Intracytoplasmic Sperm Injection1

This study was conducted to evaluate in vivo and in vitro development of in vitro-matured equine oocytes fertilized by intracytoplasmic sperm injection. Oocytes were collected from slaughterhouse-derived ovaries, matured in vitro, and injected with frozen-thawed stallion sperm. In vivo development was assessed after transfer of injected oocytes to the oviducts of recipient mares. Mares were killed 7.5-8.5 days after transfer and the uterus and oviducts flushed for embryo recovery. Of 132 injected oocytes transferred, 69 (52%) were recovered; of these, 25 (36%) were blastocysts with a blastocoele and capsule. In vitro development was assessed in three culture systems. Culture of zygotes in modified Chatot, Ziomek, Bavister medium with BSA containing either 5.5 mM glucose for 7.5 days or 0.55 mM glucose for 3 days, followed by 3 mM glucose for 2 days, then 4.3 mM glucose for 2.5 days, did not result in blastocyst formation. Culture of zygotes in Dulbecco modified Eagle medium (DMEM)/F-12 with 10% fetal bovine serum with and without coculture with equine oviductal epithelial explants yielded 16% and 15% blastocyst development, respectively. Development to blastocyst was significantly lower in G1.3/2.3/BSA than in DMEM/F-12/BSA or in either medium with 10% added serum (2% vs. 18%, 18% or 20%; P < 0.05), suggesting that requirements for equine embryo development differ from those for other species. These results indicate that in vitro-matured equine oocytes are sufficiently competent to form 36% blastocysts in an optimal environment (in vivo). While we identified an in vitro culture system that provided repeatable blastocyst development without coculture, this yielded only half the rate of development achieved in vivo.

Embryo-maternal communication in bovine - strategies for deciphering a complex cross-talk

Early embryonic development, implantation and maintenance of a pregnancy are critically dependent on an intact embryo-maternal communication. So far, only few signals involved in this dialogue have been identified. In bovine and other ruminants, interferon tau is the predominant embryonic pregnancy recognition signal, exhibiting antiluteolytic activity. However, this is just one aspect of the complex process of embryo-maternal signalling, and a number of other systems are more likely to be involved. To gain a more comprehensive understanding of these important mechanisms, integrated projects involving specialists in embryology, reproductive biotechnology and functional genome research are necessary to perform a systematic analysis of interactions between pre-implantation stage embryos and oviduct or uterine epithelial cells, respectively. State-of-the-art transcriptomic and proteomic technologies will identify reciprocal signals between embryos and their maternal environment and the respective downstream reaction cascades. For in vivo studies, the use of monozygotic twins as recipient animals provides elegant model systems, thus eliminating genetic variability as a cause of differential gene expression. In addition, suitable systems for the co-culture of oviduct epithelial or endometrium cells with the respective embryonic stages need to be established for functional validation of candidate genes potentially involved in the dialogue between embryos and their maternal environment. The knowledge of these mechanisms should help to increase the pregnancy rate following embryo transfer and to avoid embryonic losses. Candidate genes involved in embryo-maternal communication will also be used to define new quality criteria for the selection of embryos for transfer to recipients. Another application is the supplementation of embryotrophic factors or components of embryo-maternal signalling in optimized formulations, such as bioartificial matrices. As a long-term goal, signalling mechanisms identified in bovine will also be functionally evaluated in other species, including the human.

Development of in vitro matured and fertilized bovine embryos cocultured with bovine oviductal epithelial cells obtained from oviducts ipsilateral to cystic follicles

The present experiment was conducted to clarify the effect of bovine oviductal epithelial cells (BOEC) collected from oviducts ipsilateral to cystic follicles (CFs) using an in vitro coculture system on the development of in vitro matured/fertilized (IVM/IVF) bovine embryos. In the first comparison, the effect of the presence of CF on the development of the embryos cocultured with BOEC derived from the cows with CF (n = 18) and corpus hemorrhagicum (CH, n = 10) was examined. In the second comparison, the effect of the type of cyst [progesterone (P4)-dominant; n = 9, estradiol-17beta (E2)-dominant; n = 5] on the development of the embryos cocultured with BOEC derived from the cystic cows was examined. No difference was observed between CF and CH (control) groups in the mean developmental rates of embryos developed to > or =2-cell (86.3% vs. 86.4%), 8-16 cells (53.0% vs. 56.2%), blastocyst (24.2% vs. 24.8%) and hatched blastocyst (12.0% vs. 14.6%). However, the blastocyst production rate was significantly different (P<0.05) between the P4-dominant (19.8%) and E2-dominant (32.6%) groups. The rate of development from cleavage stage embryo to blastocyst was significantly different between P4-dominant (22.9%) and E2-dominant (37.9%) groups. Moreover, the blastocyst rate from 8-16 cells of E2-dominant group (61.6%) was significantly higher than that of P4-dominant one (39.5%). These results indicate that the effects of BOEC collected from oviduct ipsilateral to CFs on embryo development are variable, and the variability is closely associated with the steroid hormone profiles of the follicular fluid.

Correlations between chemical parameters, mitogenic activity and embryotrophic activity of bovine oviduct-conditioned medium

To establish parameters predicting the quality of bovine oviduct epithelial cell-conditioned media, we compared media conditioned by oviduct cells from cows at Day 2 (n = 3) and Day 15 (n = 3) of the estrous cycle. In addition, we tested the influence of time of conditioning. Media were evaluated for their embryotrophic activity using a cumulus cell co-culture system as a control. The same media were tested for their mitogenic activity on NIH 3T3 cells and for chemical parameters, including total protein, and de novo synthesized protein as well as for concentrations of glucose, lactate and ammonium. Analysis of variance did not reveal a significant effect by stage of the estrous cycle on the embryotrophic activity of conditioned media. However, there was a significant effect by time of conditioning on the proportion of 5- to 8-cell embryos (P < 0.01) and of blastocysts and hatched blastocysts (P < 0.05). None of the conditioned media (19 to 31% blastocysts) was superior to the cumulus cell co-culture system (32% blastocysts). In the conditioned media, the proportion of 5- to 8-cell embryos correlated positively with mitogenic activity on 3T3 cells (r = 0.64; P < 0.05), whereas the proportion of blastocysts was not significantly correlated with this parameter. In summary, our results provide evidence for an effect of time of conditioning on embryotrophic activity of oviduct epithelial cell-conditioned media. The fact that mitogens for NIH 3T3 cells affect the proportion of 5- to 8-cell embryos but not of blastocysts suggests different culture requirements for early and late preimplantation stage development of bovine embryos.

Persistence of the developmental block of in vitro fertilized domestic cat embryos to temporal variations in culture conditions

A series of studies examined the influence and temporal interaction of energy substrate, media complexity, and tissue co-culture on the development of in vitro fertilized cat embryos and the persistence of the morula-to-blastocyst developmental block. In study I, oocytes were fertilized and cultured for 144 hr in a simple culture medium (modified Krebs Ringer bicarbonate; mKrb), containing either glucose or glutamine, or cultured in mKrb w/ glutamine for the initial 72 hr with transfer to mKrb w/ glucose for the final 72 hr. Fertilization rate, percent development to morulae, and cell number per embryo were similar (P > 0.05) between treatments and blastocyst formation was universally low (< 10%). In Study II, oocytes were fertilized and cultured in either mKrb (w/glucose or glutamine) or in a complex medium, Ham's F10 (w/ 10% fetal bovine serum [FBS]). After 72 hr of initial culture, embryos in mKrb were transferred into Ham's F10. Fertilization rate was lower (P < 0.01) in Ham's F10 but embryo development to the morulae stage and cell number per embryo were comparable (P > 0.05) for all treatments. A higher percentage of blastocysts and morulae becoming blastocysts were observed after initial culture in mKrb w/ glutamine than after initial culture in mKrb w/ glucose. In Study III, oocytes were fertilized and cultured initially in mKrb (w/ glutamine), and then switched to either Ham's F10 or cat oviductal cell monolayers (in Ham's F10). Additional embryos were cultured exclusively in Ham's F10 or on cat oviductal cell monolayers. Fertilization rates were lower (P < 0.05) on oviductal cells but cell number per embryo was similar (P > 0.05) in all treatments. Blastocyst formation was lower (P < 0.05) on oviductal cells than in mKrb-Ham's F10 treatment and was < 20% in all treatments. In summary, while in vitro fertilization-derived cat embryos develop to morulae under a variety of culture conditions, the morula-to-blastocyst developmental block was minimally responsive to alterations in energy substrate and medium complexity or fluctuations in their temporal availability. In addition, oviductal cell culture, alone or in combination with other culture variations, was ineffective in overcoming the developmental block.

Culture of bovine oviduct epithelial cells (BOEC)

BACKGROUND

Bovine oviduct epithelial cells are widely used in co-culture experiments to improve early embryonic development and in vitro fertilization in embryo transfer programmes for domestic animals.

METHODS

The present study compares different methods for harvesting and culture of bovine oviduct epithelial cells in order to optimize handling. Bovine oviduct epithelial cells were mechanically or enzymatically isolated and cultured on glass, on permeable membranes, or in suspension. Growth of the cells and their state of differentiation was examined by means of classical staining methods, immunohistochemistry and electron microscopy.

RESULTS

Initial cell suspensions contained sheets of ciliated and nonciliated (secretory) cells; 24 h after seeding, free floating epithelial cells formed vesicles with cilia on their external surface. First adhesion of cells was seen 72 h after seeding. Later on, cells grew continuously and confluent monolayers were formed after 7 days. Results were identical after mechanical or enzymatical cell harvesting and were identical on both substrata tested, i.e., on glass and on permeable membranes. Light and electron microscopy proved the monolayers to resemble a polarized, simple, cuboidal to columnar epithelial membrane with intact junctional complexes and numerous apical microvilli. Their epithelial nature was established by immunostaining for cytokeratins. Cilia were missing and secretory granules were scarce. A layer of acidic glycoprotein material was demonstrated on the apical surface. Monolayers of bovine oviduct epithelial cells stored lipid droplets and large quantities of glycogen. About 50% of the seeded cells did not adhere but survived in the culture medium as free floating cells. These suspended cells maintained morphological criteria of differentiation (cilia and secretory granules) until day 12 of culture. Proliferation rates of cultivated cells were determined by counting mitoses and by immunostaining with MIB1 antibody. Results showed coincidence of rapid proliferation and morphological dedifferentiation of monolayers. Suspended cells, by contrast, did not proliferate but retained cellular differentiation under identical culture conditions.

CONCLUSIONS

The results strongly suggest that monolayers of bovine oviduct epithelial cells will not fully substitute for original oviduct epithelium when used in co-culture experiments after in vitro fertilization.

Co-culture of the early human embryo: factors affecting human blastocyst formation in vitro

Co-culture systems have been designed to overcome the embryonic developmental arrest observed in vitro in conventional culture media. Oviduct and uterine epithelial cells can sustain embryonic development, as can trophoblastic tissue and transport epithelia of non-genital origin. Its benefits involve neither hormone dependency nor histo-specificity. Fibroblasts do not overcome the developmental arrest in most mammalian species, but whether they do in humans is still unsure. In all systems, the quality of the feeder cells and the co-culture medium are very important. Using the Vero cell line, 60% of human IVF embryos reach the blastocyst stage. The quality of the sperm seems to affect results. We have observed: For 10% of the patients with unexplained fertility, blastocyst stage is not attained; this probably involves a maternal (ovarian) problem. When at least one blastocyst is transferred, the pregnancy rate per transfer is 31%. The implantation rate in pregnant women is higher than after transfer at day 2. After repeated failures of transfer at early stages (2-6 cells), transfer at the blastocyst stage gives high pregnancy rates (40%). This indicates an in vitro selection. There is a strong paternal effect on blastocyst formation: poor quality sperm give lower rates of blastocyst. Co-culture helps to understand treatment failures related to male factors. Around 60% of the patients having spare embryos have had blastocysts frozen. Transfers of frozen-thawed blastocysts give a 20% pregnancy rate and an implantation rate per embryo of 11%. Co-culture is a new tool which has to be carefully evaluated in human IVF programs. It does not impair "a minima" embryo viability and it allows in vitro selection.(ABSTRACT TRUNCATED AT 250 WORDS)