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Contents

  1. Top of page
  2. Contents
  3. Introduction
  4. What Happens in the Oviduct
  5. Morphological Properties to Access and Use the Bovine Oviduct for Embryo Development
  6. What is Different in Embryos Developing In Vivo vs In Vitro
  7. Effect of Hormonal Modifications
  8. Effect of Hormonal Super-Stimulation on Embryo Development
  9. Conclusion
  10. Conflicts of interest
  11. References

This review highlights the role of the oviduct in early embryo development, which has to fulfil many aligned and well-tuned tasks during early embryogenesis. The oviductal lining is subjected to dynamic changes to timely accomplish gamete transport, fertilization and embryo development and to deliver a competent and healthy conceptus to the endometrium which can implant and develop to term. Although knowledge about the role of the oviduct is limited, we know that embryos are very sensitive to the environment in which they develop. The success of in vitro embryo production techniques demonstrates that it is possible to bypass the oviduct during early development and, to a certain extent, replicate the conditions in vitro. However, comparative studies show that embryos developed in vivo are superior to their in vitro produced counterparts, underlining our relatively poor knowledge of the biology of the oviduct. Oviduct activity is orchestrated by various factors, depending on cyclic dynamics, which crucially affect the success of tubal transfer and/or (re-)collection of embryos in embryo transfer studies. This paper reviews data which demonstrate that in vivo culture of embryos in the bovine oviduct is a useful tool for the assessment of embryos developed under various conditions (e.g. superovulation vs single ovulation, lactating dairy cows vs non-lactating cows). It is concluded that more work in the field of early embryo development within the oviduct would contribute to improved ART protocols leading to healthy pregnancies and offspring.


Introduction

  1. Top of page
  2. Contents
  3. Introduction
  4. What Happens in the Oviduct
  5. Morphological Properties to Access and Use the Bovine Oviduct for Embryo Development
  6. What is Different in Embryos Developing In Vivo vs In Vitro
  7. Effect of Hormonal Modifications
  8. Effect of Hormonal Super-Stimulation on Embryo Development
  9. Conclusion
  10. Conflicts of interest
  11. References

The oviduct plays a pivotal function in early reproductive events. Over the past few decades, there has been a steady increase in our elementary knowledge of oviduct biology (Leese et al. 2008). Undoubtedly, there are many routes to manage and direct early embryo development with and without oviductal guidance. For example, endocrine stimulation (superovulation) leads to additional numbers of day 7 blastocysts suitable for transfer; techniques like in vitro production of embryos (IVP) allow the bypassing of tubal support and form the basis for more sophisticated technologies such as somatic cell nuclear transfer. All these techniques are capable of providing sufficient numbers of embryos for different scientific as well practical purposes, but overall they do not adequately replace or mimic the plethora of development-specific steps for which the oviduct has evolved a unique and dynamic microenvironment (Kenngott and Sinowatz 2007).

Recently, more attention has been paid to the early embryo and the maternal environment in terms of long-term consequences for maternal recognition, implantation, maintenance of gestation, birth and adult phenotype (Fazeli 2008). Moreover, in the context of infertility, especially in high-producing dairy cows, the majority of embryonic losses occur prior to maternal recognition of pregnancy (approximately day 16) (Thatcher et al. 2001; Diskin and Morris 2008; Berg et al. 2010). The following review aims to highlight the role of the oviduct in supporting the development of a healthy embryo by focusing on and emphasizing studies carried out in cattle.

What Happens in the Oviduct

  1. Top of page
  2. Contents
  3. Introduction
  4. What Happens in the Oviduct
  5. Morphological Properties to Access and Use the Bovine Oviduct for Embryo Development
  6. What is Different in Embryos Developing In Vivo vs In Vitro
  7. Effect of Hormonal Modifications
  8. Effect of Hormonal Super-Stimulation on Embryo Development
  9. Conclusion
  10. Conflicts of interest
  11. References

The oviduct is a small tube responsible for the transient hosting of gametes and embryos. Although it seems to be an unimposing organ, the oviduct orchestrates a series of complex actions, all of which need to be precisely initiated and completed. The oocyte and spermatozoa enter the oviduct from opposite ends, meet each other via a counter-current transport system and fuse to form an embryo which represents the primal form of completeness from the genetic point of view. To meet all these demands, the oviduct features a subtle anatomy represented by the infundibulum, ampulla and isthmus, which are equipped with longitudinal and circular aligned muscle layers, endothelial ciliated and non-ciliated cells. The segments are characterized by polymorphic folds and ridges varying in amplitude and variably furrowing longitudinally, diverging or converging, or forming irregular net-like structures encircling formations such as grooves, pockets and crypts (Yániz et al. 2000; Kenngott and Sinowatz 2007). Overall, these structures provide all the prerequisites for a selective sperm entry into the oviduct by sperm trapping and binding including the concurrent capacitation, hyperactivation and release from the epithelium to successfully fertilize the matured and ovulated cumulus–oocyte complex in the ampulla (Hunter and Rodriguez-Martinez 2004; Talevi and Gualtieri 2010; Koelle et al. 2010; Killian 2011).

The presence of gametes and embryos initiate and modulate local mechanisms at the molecular level, which represent the first exchange of signals with the maternal environment (Georgiou et al. 2007; Koelle et al. 2010; Holt and Fazeli 2010). The oviduct exhibits an extraordinary flexibility that is hormonally driven and exactly timed according to the embryonic stage and site where it directly contacts the epithelium (Spilman et al. 1978; Abe and Hoshi 2008; Nakahari et al. 2011). In 1975, Ruckebusch and Bayard impressively demonstrated that during di-oestrus, there is a barely detectable sporadic weak tubal motility whereas during pro-oestrus, oestrus and metoestrus progressively increasing waves of muscular activity have been measured, originating from the uterotubal junction and spreading to the distal and middle part of the oviduct. The infundibular region does not appear to be involved in the appearance of muscular activities (Ruckebusch and Bayard 1975). In synchrony with the muscular activity, the epithelial cells simultaneously multitask steps preparing and providing the optimal environment for perception and micro-movement of the oocyte, spermatozoa and the embryo, as well as the production of nutrients and factors necessary for stimulating embryo growth (Aguilar and Reyley 2005). To address this task, the epithelium displays ciliated and non-ciliated cells that undergo cycle-dependent regional fluctuations. In general, the infundibular and ampullar regions have more ciliated cells than the isthmic part. However, close to the time of ovulation there are many more elongated ciliated cells and secretory cells having a maximum height than in di-oestrus (Yániz et al. 2000; Abe and Hoshi 2008; Ulbrich et al. 2010; Nakahari et al. 2011). In the rat, ciliary motility in the ampulla is solely capable of transporting the ova without the need for muscular help (Halbert et al. 1989). Koelle et al. (2009) studied the cilia beat frequency (CBF) and reported that ciliary activity differs among the proximal, medial and distal regions of the oviduct. It was emphasized that CBF seems to be independent of the cycle stage and pregnancy status, but the vital importance of this study was that a local recognition system initiated by the presence of the embryo modulates CBF, vascularization and the formation of secretory cells in close vicinity to the maternal environment. Trapping of the cumulus–oocyte complexes, the anchorage to and detachment of the epithelium of the ampulla, the release of sperm and the continuation of migration are strictly controlled by the oviduct (Koelle et al. 2009).

The secretory cells of the epithelium have a noticeable amount of intracytoplasmic granules that are thought to be released by an exocytosis-like mechanism. These granules are distinctly diminished in the ampullar cells during the luteal period. In the cytoplasm of the isthmic cells, many granules were observed throughout the ovarian cycle, but the luteal phase was also characterized by a reduction in the number of granules (Abe and Hoshi 2007). The formation of epithelial cells that line the lumen of the oviduct mainly determines the composition of the fluid in the oviduct, which is thought to make a major contribution to embryo survival. Besides peritoneal as well as follicular fluid, which enters the oviduct mainly during the peri-ovulation period, the main components of oviduct fluid passively find their way into the oviduct via the blood and lymphatic vessels by transudation and actively by de novo synthesis. The most relevant tubal components are amino acids and proteins, lipids, ions, energy substrates, hormones and growth factors, which are dissolved in the tubal fluid (Henault and Killian 1993; Buhi 2002; Kenny et al. 2002; Hugentobler et al. 2007, 2008; Goncalves et al. 2008). All of these components, as well as the volume of tubal fluid, are subjected to cyclic changes (Bauersachs et al. 2003), which finally determine the functional (Aguilar and Reyley 2005; Hugentobler et al. 2010; Avilés et al. 2010) and physical (Nichol et al. 1997; Hunter et al. 2011) characteristics of the fluid. Even the presence of granulosa and cumulus cells close to an oocyte or embryo assumes the function as a paracrine tissue (Gabler et al. 2008). Overall, the oviductal fluid in which the embryos are swayed back and forth juggled on the crown of the kinocilia and maintained constantly in motion underlies a permanent reconstruction and adaption ensuring proper development.

Generally, there are two options to study the patho-physiology of early embryo development. To date, attempts to replace the oviductal environment result in significant drops in efficiency (Aguilar and Reyley 2005) and lead to long-term consequences for the health of foetuses and adult animals (Fazeli 2008). This scenario, however, would be not only time-consuming, expensive but also technically challenging. In contrast, access to the oviduct in vivo eliminates the need for further extensive and expensive in vitro scenarios and provides insight into in situ embryo development. For 20 years, we have developed and established techniques that facilitate access to oviduct for different purposes. For this reason, this review will focus on the bovine oviduct and its role in early embryo development.

Morphological Properties to Access and Use the Bovine Oviduct for Embryo Development

  1. Top of page
  2. Contents
  3. Introduction
  4. What Happens in the Oviduct
  5. Morphological Properties to Access and Use the Bovine Oviduct for Embryo Development
  6. What is Different in Embryos Developing In Vivo vs In Vitro
  7. Effect of Hormonal Modifications
  8. Effect of Hormonal Super-Stimulation on Embryo Development
  9. Conclusion
  10. Conflicts of interest
  11. References

Tremendous efforts including increasing laboratory experience and expertise undoubtedly led to significant improvements in embryo production; however, these achievements were also associated with marked deviations from in vivo-developed embryos, low predictability and reproducibility. Moreover, the culture period up to the blastocyst stage actually does not allow to fully reveal immediate effects on embryo development. Improvements of in vitro techniques should be evaluated using sophisticated microscopic and holistic molecular analyses by short term as well as long-term approaches. Among all tested in vivo systems, only the ovine oviduct has been routinely used for the culture of bovine embryos in large numbers for scientific as well as practical purposes. This system has reached a high degree of optimization, which allows the production of high-quality embryos from in vitro matured and fertilized oocytes (Lazzari et al. 2010). Nonetheless, it is unanimously accepted that the period of early embryo development during which most embryo loss occurs is poorly understood. Although the use of heterologous embryo culture can support early development, some limitations and barriers such as local subinflammatory alterations caused by ligation, endocrine heterogeneity, additional production and deposition of foreign substance such as a mucin coat in the case of the rabbit and inappropriate extended culture in the uterine horns may cause disturbance of normal physiology and generate deleterious and undesired side effects (Talbot et al. 2000; Joung et al. 2004; Leese et al. 2008; Velazquez et al. 2010). Hence, the bovine oviduct may represent a means of increasing knowledge in the field of reproduction.

Access to the oviducts was traditionally performed using longstanding laparotomy techniques. Oocytes and embryos were transferred surgically into the oviduct whereas embryo recovery was accomplished at slaughter or by non-invasive collection of advanced embryonic stages from the uterine horns. Generally, access was achieved via the lumbar or midventral route; occasionally, ovariohysterectomy per vaginam was used for embryo collection via in vitro flushing of oviducts (Hartman et al. 1931; Roschlau et al. 1989; Trounson et al.1976; Willadsen and Polge 1981; Leibfried-Rutledge et al. 1987; Eyestone and First 1986). However, laparotomy is a costly and time-consuming invasive procedure that relegates its use as a scientific tool. Compromise solutions aimed at long-term cannulation of the oviducts for in vivo culture or final transfer resulted in the recovery of a few developed embryos and the birth of one calf (Jillella et al. 1977; Schmidt et al. 1997).

The development of endoscopy was a breakthrough in the field of reproduction (Liess 1936). In contrast to surgical procedures for which lumbar entry is used, endoscopy avoids extensive manipulation such as relocation and exteriorization of the reproductive organs. Briefly, the positioning of the instruments in front of the reproductive organs via a punctiform entry allows minimally invasive in situ visualization and manipulation. Besides observations of cyclic activities (Laurincik et al. 1991) and ovum pickup for oocyte collection via the flanks (Sirard and Lambert 1985; Lambert et al. 1986; Schellander et al. 1989; Fayrer-Hosken and Caudle 1991) or the vagina (Reichenbach et al. 1994), Fayrer-Hosken and his team successfully achieved endoscopic transfer of embryos into the oviduct of cows. Trocars for the endoscope as well as the Semm’s grasping forceps were placed in the paralumbar fossa. The forceps were used to grasp the infundibulum distal to the oviductal opening. Oocytes and two- to four-cell stage embryos were loaded into a catheter that was passed through the operating channel of a bronchoscope and deposited in the ipsilateral oviduct. The transfers resulted in multiple embryo recovery and a normal term pregnancy (Fayrer-Hosken et al. 1989; Fayrer-Hosken and Caudle 1991). In 1998, we described an endoscopic method to routinely access the oviduct for embryo transfer. Although the preliminary results were based on a small number of transfers, we obtained evidence that the bovine oviduct has a potential effect on embryo development; for example, the first two transfers of two embryos each led to two twin pregnancies leading to the birth of a pair of twins and a single calf, whereas after a prolonged in vitro culture the transfer of a morula resulted in a large calf, which had to be delivered by caesarean section (Besenfelder and Brem 1998). This study also described the first experience with regard to the manipulation of the small and active tubal organ transiently hosting embryos but exerting an intrinsic effect on the receipt, migration and development of embryos.

Physiologically, expanded cumulus–oocyte complexes (COCs) are released by the Graafian follicle, trapped by the fimbria of the infundibulum and transported into the lumen of the ampulla. Consequently, the transfer of oocytes and embryos into the proximal part of the oviduct should reflect these features. We followed these morphological properties, transferred oocytes and embryos into the oviducts of synchronized animals and found that the re-collection rate increased with the size of the solid matrix (denuded zygotes, zygotes with cumulus cells, gamete transfer, alginate-embedded embryos) around the embryo (Wetscher et al. 2005a). Moreover, and depending on the stage of transferred oocytes and embryos to synchronous recipient animals, it was demonstrated that the transfer of more advanced embryonic stages into the oviduct resulted in significantly more blastocysts compared to COCs transfer into recipients which had been inseminated or to transfer of both gametes (GIFT) (Wetscher et al. 2005b). Finally, we observed that tubal transfer was associated with a delayed migration of embryos into the uterine horns, which was confirmed by separately flushing of uterine horns followed by the flushing both cohesively, oviduct and uterine horn (Havlicek et al. 2005). Taken together, the success of transfer of oocytes and early stage embryos into the oviduct is under clear control of cyclic activities mainly reflected by the oviduct motility (Ruckebusch and Bayard 1975) ciliary beat frequency (Nishimura et al. 2010; Nakahari et al. 2011; Halbert et al. 1989) and amount of secreted oviductal fluid (Roberts et al. 1975; Aguilar and Reyley 2005). These first studies let us to conclude that (i) during the peri-ovulatory period, the oviduct has a hyper-dynamic activity that might negatively influence the continuance of oocyte and embryo development in the oviduct, (ii) oocytes and zygotes seem to respond more sensitively to in vitro manipulation compared to more advanced developmental stages, and (iii) in vitro matured oocytes are not suitable for being fertilized in vivo.

What is Different in Embryos Developing In Vivo vs In Vitro

  1. Top of page
  2. Contents
  3. Introduction
  4. What Happens in the Oviduct
  5. Morphological Properties to Access and Use the Bovine Oviduct for Embryo Development
  6. What is Different in Embryos Developing In Vivo vs In Vitro
  7. Effect of Hormonal Modifications
  8. Effect of Hormonal Super-Stimulation on Embryo Development
  9. Conclusion
  10. Conflicts of interest
  11. References

Recently, Killian (2011) referred to the use of reproductive techniques including cell and tissue culture techniques as a ‘treasure trove’ of information and techniques towards a better understanding of how the oviduct manages gamete and embryo development. Meanwhile, numerous parameters and standards have been assessed to characterize morphological as well as molecular features of embryos developed under different culture conditions. Comparative studies dealing with embryos produced in vivo, partially and completely cultured in vitro may have the potential to highlight the role of oviduct for production of vital embryos as a prerequisite for health pregnancies and offspring (Lonergan et al. 2003; Gad et al. 2012).

It is unanimously accepted that in vivo-developed embryos are of superior quality than those produced in vitro in terms of cryoresistance (Fair et al. 2001; Rizos et al. 2002a), ultrastructure (number of desmosomal junctions, microvilli, lipid droplets) (Crosier et al. 2001; Fair et al. 2001; Rizos et al. 2002b), gene expression (Lazzari et al. 2002; Rizos et al. 2002c; Tesfaye et al. 2004; Smith et al. 2009), chromosome abnormalities (Viuff et al. 1999) and foetal and peripartal development (Lazzari et al. 2002; Farin et al. 2010).

Other designs made use of embryo validation by slaughtering the animals or performing surgery at different time points. Knijn et al. (2005) use a selective set of gene transcripts involved in metabolism and apoptosis in bovine embryos that had been collected in vitro or ex vivo at different time intervals and cultured to the blastocyst stage. However, the findings did not reveal a critical effect of embryo culture on maternal embryo transition. In addition, Smith et al. (2009) surgically recovered embryos 24 h post-insemination, which were cultured in vitro until the blastocyst stage. These blastocysts were compared to blastocysts produced in vitro or collected at day 7 by analysing expression profiles including approximately 6300 unique genes. The results of the study demonstrated that even in vitro culture alone has a dramatic impact on gene expression (Smith et al. 2009). This finding was confirmed by Viuff et al. (2001) who performed a MOET program to obtain embryos at precisely defined times after ovulation (four-cell stage embryos, eight-cell stage embryos, 16–32-cell stage embryos and morula). It was clearly demonstrated that in vivo embryos show a lower frequency of mixoploidy and polyploidy (Viuff et al. 2001), and some chromosomal defects are in vitro-specific and do not occur in vivo.

Merton et al. (2003) gave a comprehensive overview of embryo production according to the origin of the oocyte, followed by maturation, fertilization and early development with special regard to the stepwise transition from in vivo to in vitro development. A successive decrease in embryo development was noted the more development was shifted towards in vitro. However, the origin of the oocyte was seen as the main reason responsible for the blastocyst outcome (Merton et al. 2003).

To provide more detailed information, extensive studies have been carried out based upon the temporary culture of IVP-derived bovine embryos in the sheep oviduct. To date, this technology has been very effective for the production of large numbers of embryos for commercial purposes (Galli et al. 2003). In addition, it was shown that in vivo culture in the ovine oviduct is superior to IVP that was implicated in the deviation in early embryo development leading to large offspring syndrome (Farin and Farin 1995; Lazzari et al. 2002). In another study, in vitro oocyte maturation (IVM), fertilization (IVF) and embryo culture (IVC) were accomplished by successively replacing each in vitro step by in vivo, or IVM/IVF embryos were cultured in the ovine oviduct. It was clearly demonstrated that blastocyst yield is determined by the origin of the oocyte, that is, oocytes from the same source (either in vitro or in vivo) are expected to yield a similar blastocyst development irrespective of the culture environment. In contrast, the quality of the blastocysts mainly depends on the post-fertilization culture period, which is believed to have a crucial effect on embryo metabolism (Rizos et al. 2002c).

For approximately two decades, minimally invasive techniques have been developed at our institute to access the oviducts of different species for a better understanding of early embryo development as it occurs in vivo. There were several reasons that prompted us to concentrate on early embryogenesis in cattle:

In our first experiments, we confirmed that culture of in vitro-derived bovine embryos in the homologous oviduct resulted in improved developmental rates. For instance, in vivo culture conditions affected the quantity of blastocyst nuclear material and actin cytoskeleton, even when embryos were cultured for a short time in vivo (Kuzmany et al. 2011). These microstructural changes were reflected in improved cryoresistance of in vivo cultured embryos; the longer the embryos were kept under in vivo conditions, the better the post-thaw survival (Havlicek et al. 2006, 2007, 2010). In addition, the zona pellucida (ZP) plays a major physical part within the application of in vivo transfer techniques. Actually, the ZP represents the barrier that separates the embryo from the oviductal epithelium on the one hand and on the other hand acts as a biological filter. In accordance with cyclic and developmental changes of the epithelium, gametes and embryos, the ZP is also exposed to permanent adaptations. These adaptations are mainly induced by oviductal secretions that are associated with the timely fulfilment of physiological events (from fertilization to hatching) as well as to the prevention of viral infections (Van Soom et al. 2010). Recently, it was demonstrated that physical evaluation of the ZP using polarized light can be a successful predictor of the developmental potential of embryos (Held et al. 2012). The ZP plays a major physical part within the application of in vivo transfer techniques. Using electron microscopy, we could observe that in vivo morulae and blastocysts have a thicker ZP mainly caused by an increase in the reticular part. The pores of the ZP were smaller-sized and totally covered by secreted granules. Up to 50% of the in vitro embryos exhibited partly degenerated outer layers of the ZP (Mertens et al. 2007). This deviation becomes also obvious when the ZP hardness is measured (Itoi et al. 2007). Altogether, these investigations indicate that in vitro and in vivo ZPs are significantly different reflecting a negative influence of exposure to in vitro culture conditions.

It becomes clear that the embryo and its surrounding epithelial cells represent a very sensitive system that responds, howsoever small, to each signal. The in vivo system also illustrates that the term embryo plasticity encompasses a very broad spectrum of factors which can be hardly associated with the categories of being beneficial, compensable or detrimental for the growing of embryo. Consequently, holistic gene expression studies become the focus our interest. The endoscopic access to the bovine oviduct was used to determine the transcriptomes of bovine oocytes and early stage of in vivo embryos up to the blastocyst. Some hundred genes were transcribed well before the 8–16-cell stage. It is noteworthy that embryos at the two-cell, four-cell, eight-cell, morula and blastocyst stages had stage-specific expression patterns, suggesting dynamic changes in the embryonic expression profile even in the groups of transiently active genes. The genome-wide expression profiling revealed significant differences in vivo and in vitro matured oocytes, emphasizing the advantage of the use of both in vivo-derived oocytes and embryos (Kues et al. 2008).

Currently, this endoscopic-mediated design was used for a large-scale transcriptome profile of early bovine embryos in correlation with the cultural environment to identify molecular mechanisms and pathways. For these studies, embryos of all stages (from oocytes up to blastocysts) and origin (IVP, MOET, successive in vitro vs in vivo culture) were analysed using a unique custom microarray (42 242 oligo probes, Agilent, Santa Clara, CA, USA). The experiments identified clusters of pathways and mechanisms that were affected by changing culture conditions. It is suggested that the results of the analysis will launch future strategies to perform a time-related optimization of embryo culture (Gad et al. 2012).

Effect of Hormonal Modifications

  1. Top of page
  2. Contents
  3. Introduction
  4. What Happens in the Oviduct
  5. Morphological Properties to Access and Use the Bovine Oviduct for Embryo Development
  6. What is Different in Embryos Developing In Vivo vs In Vitro
  7. Effect of Hormonal Modifications
  8. Effect of Hormonal Super-Stimulation on Embryo Development
  9. Conclusion
  10. Conflicts of interest
  11. References

The high embryonic loss is generally assumed to be a result of insufficient communication between the conceptus and the maternal environment (Wolf et al. 2003; Fazeli 2008). Consequently, the embryo by its presence in the oviduct has a co-determining capability to influence its immediate fate. Following the question whether the embryo or the maternal environment is more important, 1800 in vitro-derived bovine embryos were endoscopically transferred to the oviducts of synchronized post-partum dairy cows and nulliparous heifers to support the development of early embryos to the blastocyst stage. The day 7 progesterone concentrations in the heifers were 2.2-fold higher compared to the cows. Approximately 80% of the transferred embryos into the heifers could be re-collected, whereas in cows, only 57% remained in the reproductive tract until flushing. Of the recovered embryos, twice as many embryos developed to the blastocysts in heifers compared to cows (Rizos et al. 2010). This experiment was repeated using cows that were either dried off immediately after calving or entered the milking herd. Again, in the non-lactating cows, significantly more embryos developed to blastocysts compared to lactating cows (Maillo et al. 2012). These data provide clear evidence that the oviducts and uterus of post-partum lactating dairy cows suffer from the incapability to support early embryo growth, shown by either the total loss of embryos or reduced development.

Effect of Hormonal Super-Stimulation on Embryo Development

  1. Top of page
  2. Contents
  3. Introduction
  4. What Happens in the Oviduct
  5. Morphological Properties to Access and Use the Bovine Oviduct for Embryo Development
  6. What is Different in Embryos Developing In Vivo vs In Vitro
  7. Effect of Hormonal Modifications
  8. Effect of Hormonal Super-Stimulation on Embryo Development
  9. Conclusion
  10. Conflicts of interest
  11. References

It has to be asked whether ex vivo-derived embryos out of superovulation programmes are ‘normal’ or whether new scientific approaches provide novel clues for optimization of superstimulation protocols. Merton et al. (2003) reviewed oocyte quality and quantity with regard to commercial use of embryo technologies in the cattle breeding industry. Summarizing the highlights of the last decades, it was concluded that no real breakthroughs have been made in MOET. In 2001, Greve and Callesen described embryo development in the oviduct as a long and meticulously well-tuned process, which may be perturbed by superovulatory treatment. Moreover, they pointed out that aberrant endocrine patterns following superovulatory treatments could have an adverse impact on the oviductal milieu, thus lowering fertility (Greve and Callesen 2005). The proportion of mixoploid embryos in vivo increases during the preimplantation period. Data on chromosome analysis at day 5 displayed 31% of mixoploid embryos from superovulated donor animals (Viuff et al. 2001). Studies using superovulation protocols in mice showed deviations in embryo developmental kinetics, impaired implantation and increased post-implantation losses (Ertzeid and Storeng 2001). The high incidence of pregnancy loss and abnormal phenotypes have been associated with aberrant DNA methylation in these early developing embryos (Shi and Haaf 2002). To date, long-term consequences have not been examined. Recently, we have studied environmental effects on embryo development in the first seven days post ovulation. Superovulated heifers were flushed on day 2, and embryos were immediately transferred into oviducts of synchronized, single-ovulating recipients using endoscopy. At day 7, embryos were re-collected and compared to embryos that were flushed contemporaneously from superovulated donors. A lower percentage of embryos reached the blastocyst stage, which were obtained from day 7 superovulated heifers compared to single-ovulating heifers. Blastocysts that were left in the superstimulated heifers for 7 days under the abnormal endocrine conditions exhibited higher cellular and metabolic activities. Genes involved in the oxidative phosphorylation pathway, different metabolic processes and translation and transcription processes, and genes expressed in response to stress, were more highly expressed than in control embryos from non-superstimulated animals (Gad et al. 2011). Overall, these results are consistent with other studies in many species showing that the application of assisted reproductive technologies is associated with aberrant mechanisms in DNA methylation, mitosis and apoptosis in early embryos leading to pregnancy failure and abnormal phenotypes (Gardner and Lane 2005; Velazquez et al. 2009)

Conclusion

  1. Top of page
  2. Contents
  3. Introduction
  4. What Happens in the Oviduct
  5. Morphological Properties to Access and Use the Bovine Oviduct for Embryo Development
  6. What is Different in Embryos Developing In Vivo vs In Vitro
  7. Effect of Hormonal Modifications
  8. Effect of Hormonal Super-Stimulation on Embryo Development
  9. Conclusion
  10. Conflicts of interest
  11. References

Many studies have been conducted in which a multiplicity of fertility parameters has been assessed through elaborate experimental designs. All these studies agree that any manipulation of early embryo development acts as stressor which negatively impacts its fate (Leese et al. 2008). The oviduct undoubtedly has to accomplish a complex role in hosting gametes and matching the optimal environment within a short but very important transitional period before the embryo reaches the uterus. During this critical time, the embryo can draw strength from tubal support, which is required for implantation, pre- and post-natal survival. However, it is hypothesized that the tubal plasticity is mainly exhausted by oviduct-specific tasks that do not allow the compensation of additional disturbance factors. Hence, it would be desirable to perform future holistic studies aimed at evaluating the epigenetic status of healthy early stage embryos acting as suitable model for a better understanding of reproduction and associated disorders mirrored in pre- and postnatal survival including phenotypic characteristics.

References

  1. Top of page
  2. Contents
  3. Introduction
  4. What Happens in the Oviduct
  5. Morphological Properties to Access and Use the Bovine Oviduct for Embryo Development
  6. What is Different in Embryos Developing In Vivo vs In Vitro
  7. Effect of Hormonal Modifications
  8. Effect of Hormonal Super-Stimulation on Embryo Development
  9. Conclusion
  10. Conflicts of interest
  11. References
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