Endoscopic approaches to manage in vitro and in vivo embryo development: Use of the bovine oviduct

Specificity protein 1 (SP1) plays an essential role in early bovine embryo development

A previous RNA-Seq study revealed that the transcript abundance of specificity protein 1 (SP1) was significantly higher in Day 7 bovine blastocysts compared to conceptuses on Days 10, 13, 16, and 19, suggesting a stage-specific role in early bovine embryo development. The present study aimed to characterize the mRNA expression of SP1 and associated candidate genes (ACSS1, C1QBP, ATF3, MAT2A, and POLD1) during early bovine embryo development from the 2-cell to blastocyst stage. Further, the effects of SP1 inhibition on embryo development were evaluated by culturing embryos with the SP1 inhibitor, mithramycin A (MT) at varying concentrations (0, 25, 50, 100, and 1000 nM). As further validation, we examined expression of SP1 and associated genes by interrogating transcriptomic data from Day 4 (16-cell stage) embryos cultured in vitro or in vivo in the oviducts of lactating or nonlactating dairy cows. The relative abundance of SP1 peaked at the time of embryonic genome activation, being higher (P < 0.05) in 8- and 16-cell embryos compared to the 2-cell stage, and decreasing thereafter (at the morula and blastocyst stages). Similarly, transcript abundance for most of the selected candidate genes involved in the SP1 network were upregulated (P < 0.05) at the 8- and 16-cell stage, but not at other stages investigated. Inhibition of SP1 with MT did not affect embryo development up to the 8-cell stage but reduced (P < 0.05) the proportion of embryos reaching the 16-cell and blastocyst stages in a dose-dependent manner. Moreover, blastocysts produced in the presence of MT contained fewer (P < 0.05) cells than blastocysts developed without MT. Expression of SP1 and associated genes in 16-cell stage (Day 4) embryos produced either in vitro or in vivo was higher (P < 0.05) compared to in vitro-produced 2- to 4- cell stage (Day 2) embryos. These findings suggest an essential role of SP1 during early embryo development, particularly around the time of embryonic genomic activation.

The potential effect of melatonin on in vitro oocyte maturation and embryo development in animals

Melatonin is a hormone mainly secreted by the pineal gland during the circadian cycle, with low levels during the daytime and prominent levels during the night. It is involved in numerous physiological functions including the immune system, circadian rhythm, reproduction, fertilization, and embryo development. In addition, melatonin exerts anti-inflammatory and antioxidant effects inside the body by scavenging reactive oxygen and reactive nitrogen species, increasing antioxidant defenses, and blocking the transcription factors of pro-inflammatory cytokines. Its protective activity has been reported to be effective in various reproductive biotechnological processes, including in vitro maturation (IVM), embryo development, and survival rates. In this comprehensive review, our objective is to summarize and debate the potential mechanism and impact of melatonin on oocyte maturation and embryo development through various developmental routes in different mammalian species.

In vivo dynamics of pro-inflammatory factors, mucins, and polymorph nuclear neutrophils in the bovine oviduct during the follicular and luteal phase

Dynamic functional changes in the oviductal microenvironment are the prerequisite for the establishment of pregnancy. The objective of this study was to gain the first insights into oestrous cycle-dependent dynamics of polymorph nuclear neutrophils (PMN) and the mRNA abundance of selected genes and their correlations in the oviduct of living cows. Mini-cytobrush samples were taken from the oviducts of healthy heifers (n = 6) and cows (n = 7) during the follicular (FOL) and luteal phase (LUT) by transvaginal endoscopy. Total RNA was isolated from the samples and subjected to reverse transcription-quantitative PCR for selected pro-inflammatory factors, glycoproteins, and a metabolic marker. The percentage of PMN was determined by cytological examination. The mean PMN percentage was 2.8-fold greater during LUT than FOL. During LUT, significantly greater mRNA abundance of the pro-inflammatory factors IL1B, CXCL1, CXCL3, and CXCL8 was observed. The OVGP1 mRNA abundance was twice as high during FOL than in LUT. Pearson correlation, principal component analysis and heatmap analyses indicated characteristic functional patterns with strong correlations among investigated factors. Using this novel approach, we illustrate complex physiological dynamics and interactions of the mRNA expression of pro-inflammatory factors, mucins, OVGP1, and PMN in the oviduct during the oestrous cycle.

The interaction between the environment and embryo development in assisted reproduction

It can be assumed that the natural processes of selection and developmental condition in the animal provide the best prerequisites for embryogenesis resulting in pregnancy and subsequent birth of a healthy neonate. In contrast, circumventing the natural selection mechanisms and all developmental conditions in a healthy animal harbors the risk of counteracting, preventing or reducing the formation of embryos or substantially restricting their genesis. Considering these facts, it seems to be obvious that assisted reproductive techniques focusing on early embryonic stages serve an expanded and unselected germ cell pool of oocytes and sperm cells, and include the culture of embryos outside their natural habitat during and after fertilization for manipulation and diagnostic purposes, and for storage. A significant influence on the early embryonic development is seen in the extracorporeal culture of bovine embryos (in vitro) or stress on the animal organism (in vivo). The in vitro production per se and metabolic as well as endocrine changes in the natural environment of embryos represent adequate models and serve for a better understanding. The purpose of this review is to give a brief presentation of recent techniques aimed at focusing more on the complex processes in the Fallopian tube to contrast in vivo and in vitro prerequisites and abnormalities in early embryonic development and serve to identify potential new ways to make the use of ARTs more feasible.

Asynchrony between the early embryo and the reproductive tract affects subsequent embryo development in cattle

The aim of this study was to determine the effect of maternal-embryonic asynchrony in the reproductive tract (oviduct and uterus) on subsequent embryo development in cattle. Fifty Day 1invitro-produced zygotes were transferred endoscopically into the oviduct ipsilateral to the corpus luteum of heifers (n=40) that were either synchronous with the embryos (Day 1 after ovulation) or asynchronous and ahead of the embryo (Day 3 after ovulation). A subset of heifers was killed in a commercial abattoir 3, 6 or 14 days after embryo transfer. Location within the reproductive tract, developmental stage and the quality of embryos were recorded. Transfer of embryos to an advanced (asynchronous) oviduct resulted, on Day 4, in fewer embryos at the expected location (oviduct), and a greater number of degenerated and retarded embryos with a lower total cell number than for embryos in the synchronous group. Similarly, on Day 7, asynchrony led to a greater number of degenerated and retarded embryos compared with the synchronous group. Total embryo cell number was similar among groups. Although Day 15 conceptuses were longer following asynchronous transfer, only 50% of the asynchronous heifers yielded conceptuses, compared with 100% in the synchronous group. In conclusion, asynchrony between the developing embryo and the reproductive tract has a negative effect on embryo development.

[Bovine uterine diseases: Aspects of microbiology, molecular biology, and immunology]

Postpartum uterine diseases, such as puerperal metritis and clinical endometritis may affect over 40 % of cows in dairy farms. Regardless of their severity, these diseases are one of the main reasons for impaired fertility, causing declines in dairy cow productivity and hence, resulting in economic losses. Although uterine diseases have been the topic of scientific discussion for many years, until now it was not possible to agree on uniform definitions for the different kinds of manifestation. By including technical innovations and testing procedures, enormous scientific progress and a deeper knowledge of the physiology as well as the pathologic mechanisms have been achieved. Bovine metritis and endometritis may be regarded as multifactorial diseases caused by a combination of microbial infection, the dysregulation of the immune system, and additional risk factors. These interactions have been analyzed on microbial and molecular biological levels as well as by the use of bioinformatics and molecular genetics. As a result, new species of bacteria and inflammatory mediators possibly contributing to the development of uterine diseases have recently been described. Additionally, metabolic and genetic risk factors and their roles in leading to fertility impairment have been evaluated. In conclusion, it was possible to identify new approaches for possible therapeutic and preventive methods, a subset of which may already be implemented into daily practical routine. This article provides an overview of recent scientific results concerning bovine metritis and endometritis with a focus on microbial, microbiological and immunological studies.

Review: Environmental impact on early embryonic development in the bovine species

Assisted reproduction techniques (ARTs) provide access to early stage embryos whose analysis and assessment deliver valuable information. The handling of embryos, including the in vitro production of bovine embryos, is a rapidly evolving area which nonetheless exposes the embryos to unnatural conditions for a period of time. The Fallopian tube provides innumerable quantitative and qualitative factors, all of which guarantee the successful development of the embryo. It is well known that the Fallopian tube can be bypassed, using embryo transfer, resulting in successful implantation in the target recipient animal and the birth of calves. However, the question arises as to whether such circumvention has a negative impact on the embryo during this sensitive development period. First crosstalk between the embryo and its environment confirms mutual recognition activities and indicate bilateral effects. Nowadays, in vitro production of bovine embryos is a well-established technology. However, it is still evident that in vitro generated embryos are not qualitatively comparable to embryos obtained ex vivo. To counteract these differences, comparative studies between in vitro and ex vivo embryos are advantageous, as embryos grown in their physiological environment can provide a blueprint or gold standard against which to compare embryos produced in vitro. Attempts to harness the bovine oviduct were sometimes very invasive and did not result in wide acceptance and routine use. Long-term development and refinement of transvaginal endoscopy for accessing the bovine oviduct has meanwhile been routinely applied for research as well as in practice. Comparative studies combining in vitro development with development in the cattle oviduct revealed that the environmental conditions to which the embryo is exposed before activation of the embryonic genome can have detrimental and lasting effects on its further development. These effects are manifested as deviations in gene expression profiles and methylation signatures as well as frequency of whole chromosomal or segmental aberrations. Furthermore, it was shown that hormonal superstimulation (multiple ovulation and embryo transfer), varying progesterone concentrations as well as metabolic disorders caused by high milk production, markedly affected embryo development in the postpartum period. Assisted reproductive techniques that allow the production and handling of extra numbers of generated embryos promise to have a very high impact on scientific and practical application. Any influence on the early embryonic life, both in animals and in vitro, is accompanied by a sensitive change in embryonic activity and should be assessed in vivo on the basis of physiological conditions before being used for ART.

Intrafollicular oocyte transfer in cattle – a technical report

The aim of the study was to develop and evaluate the functionality of a new equipment for intrafollicular oocyte transfer (IFOT) in dairy cattle. The new system for IFOT is composed of the applicator, the aspirator, and the injector. After aspiration of oocytes, the IFOT set is inserted into the working tube of the ultrasound transducer holder, the content of the applicator can be injected into the preovulatory follicle via transvaginal ultrasonography by one operator. The function of instruments used for IFOT was firstly verified in laboratory conditions. Slaughterhouse oocytes filled into the instruments were injected into Petri dishes. The highest recovery rates in vitro (97.5%) were achieved when the applicator was stored with the needle in a downward position. Synchronized Holstein heifers were used for in vivo test. Intrafollicular injection of saline (n = 9) was performed to find whether ovulation is affected by the injection. Then IFOTs of phosphate buffered saline with 20 oocytes (n = 21) were performed into the preovulatory follicles followed by 7-day-old embryo collection. Total ovulation rates were 86.7% (26/30). Total recovery rates (oocytes + embryos) were 23.1%, embryo recovery rates were 10.1%. The new instrument allows for the loading of oocytes and easy transportation to recipients, and also allows IFOT to be performed by one person in field conditions. The method does, however, need further investigation.

Proteomics Analysis Reveals that Warburg Effect along with Modification in Lipid Metabolism Improves In Vitro Embryo Development under Low Oxygen

The molecular mechanism regulating embryo development under reduced oxygen tension remains elusive. This study aimed to identify the molecular mechanism impacting embryo development under low oxygen conditions. Buffalo embryos were cultured under 5% or 20% oxygen and were evaluated according to their morphological parameters related to embryo development. The protein profiles of these embryos were compared using iTRAQ-based quantitative proteomics. Physiological O2 (5%) significantly promoted blastocyst yield, hatching rate, embryo quality and cell count as compared to atmospheric O2 (20%). The embryos in the 5% O2 group had an improved hatching rate of cryopreserved blastocysts post-warming (p < 0.05). Comparative proteome profiles of hatched blastocysts cultured under 5% vs. 20% O2 levels identified 43 differentially expressed proteins (DEPs). Functional analysis indicated that DEPs were mainly associated with glycolysis, fatty acid degradation, inositol phosphate metabolism and terpenoid backbone synthesis. Our results suggest that embryos under physiological oxygen had greater developmental potential due to the pronounced Warburg Effect (aerobic glycolysis). Moreover, our proteomic data suggested that higher lipid degradation, an elevated cholesterol level and a higher unsaturated to saturated fatty acid ratio might be involved in the better cryo-survival ability reported in embryos cultured under low oxygen. These data provide new information on the early embryo protein repertoire and general molecular mechanisms of embryo development under varying oxygen levels.

In vivo genome editing targeted towards the female reproductive system

The discovery of sequence specific nucleases such as ZFNs, TALENs, and CRISPR/Cas9 has revolutionized genome editing. The CRISPR/Cas9 system has particularly emerged as a highly simple and efficient approach towards generating genome-edited animal models of most of the experimental species. The limitation of these novel genome editing tools is that, till date, they depend on traditional pronuclear injection (PI)-based transgenic technologies developed over the last three decades. PI requires expensive micromanipulator systems and the equipment operators must possess a high level of skill. Therefore, since the establishment of PI-based transgenesis, various research groups worldwide have attempted to develop alternative and simple gene delivery methods. However, owing to the failure of chromosomal integration of the transgene, none of these methods gained the level of confidence as that by the PI method in order to be adapted as a routine approach. The recently developed genome editing systems do not require complicated techniques. Therefore, presently, attention is being focused on non-PI-based gene delivery into germ cells for simple and rapid production of genetically engineered animals. For example, a few reports during the previous 1-2 years demonstrated the use of electroporation (EP) in isolated zygotes that helped to overcome the absolute dependency on PI techniques. Recently, another breakthrough technology called genome editing via oviductal nucleic acids delivery (GONAD) that directly delivers nucleic acids into zygotes within the oviducts in situ was developed. This technology completely relieves the bottlenecks of animal transgenesis as it does not require PI and ex vivo handling of embryos. This review discusses in detail the in vivo gene delivery methods targeted towards female reproductive tissues as these methods that have been developed over the past 2-3 decades can now be re-evaluated for their suitability to deliver the CRISPR/Cas9 components to produce transgenic animals. This review also provides an overview of the latest advances in CRISPR-enabled delivery technologies that have caused paradigm shifts in animal transgenesis methodologies.

Impact of maternal malnutrition during the periconceptional period on mammalian preimplantation embryo development

During episodes of undernutrition and overnutrition the mammalian preimplantation embryo undergoes molecular and metabolic adaptations to cope with nutrient deficits or excesses. Maternal adaptations also take place to keep a nutritional microenvironment favorable for oocyte development and embryo formation. This maternal-embryo communication takes place via several nutritional mediators. Although adaptive responses to malnutrition by both the mother and the embryo may ensure blastocyst formation, the resultant quality of the embryo can be compromised, leading to early pregnancy failure. Still, studies have shown that, although early embryonic mortality can be induced during malnutrition, the preimplantation embryo possesses an enormous plasticity that allows it to implant and achieve a full-term pregnancy under nutritional stress, even in extreme cases of malnutrition. This developmental strategy, however, may come with a price, as shown by the adverse developmental programming induced by even subtle nutritional challenges exerted exclusively during folliculogenesis and the preimplantation period, resulting in offspring with a higher risk of developing deleterious phenotypes in adulthood. Overall, current evidence indicates that malnutrition during the periconceptional period can induce cellular and molecular alterations in preimplantation embryos with repercussions for fertility and postnatal health.

Biomedical applications of ovarian transvaginal ultrasonography in cattle

Ovarian transvaginal ultrasonography (OTU) has been used world-wide for commercial ovum pick-up programs for in vitro embryo production in elite herds, providing an excellent model for the elucidation of factors controlling bovine oocyte developmental competence. Noninvasive sampling and treatment of ovarian structures is easily accomplished with bovine OTU techniques providing a promising system for in vivo delivery of transgenes directly into the ovary. The current review summarizes existing bovine OTU models and provides prospective applications of bovine OTU to undertake research in reproductive topics of biomedical relevance, with special emphasis on the development of in vivo gene transfer strategies.

The ART of studying early embryo development: progress and challenges in ruminant embryo culture

The study of preimplantation mammalian embryo development is challenging due to difficulties in accessing in vivo-derived embryos in large numbers at the early stages and the inability to culture embryos in vitro much beyond the blastocyst stage. Nonetheless, embryos exhibit an amazing plasticity and tolerance when it comes to adapting to the environment in which they are cultured. They are capable of developing in media ranging in composition from simple balanced salt solutions to complex systems involving serum and somatic cells. At least a proportion of the blastocysts that develop in culture are developmentally competent as evidenced by the fact that live offspring have resulted following transfer. However, several studies using animal models have shown that such embryos are sensitive to environmental conditions that can affect future pre- and post-natal growth and developmental potential. This review summarises some key aspects of early embryo development and the approaches taken to study this important window in early life.

Live birth from slow-frozen rabbit oocytes after in vivo fertilisation

In vivo fertilisation techniques such as intraoviductal oocyte transfer have been considered as alternatives to bypass the inadequacy of conventional in vitro fertilisation in rabbit. There is only one study in the literature, published in 1989, that reports live offspring from cryopreserved rabbit oocytes. The aim of the present study was to establish the in vivo fertilisation procedure to generate live offspring with frozen oocytes. First, the effect of two recipient models (i) ovariectomised or (ii) oviduct ligated immediately after transfer on the ability of fresh oocytes to fertilise were compared. Second, generation of live offspring from slow-frozen oocytes was carried out using the ligated oviduct recipient model. Throughout the experiment, recipients were artificially inseminated 9 hours prior to oocyte transfer. In the first experiment, two days after unilateral transfer of fresh oocytes, oviducts and uterine horns were flushed to assess embryo recovery rates. The embryo recovery rates were low compared to control in both ovariectomised and ligated oviduct groups. However, ligated oviduct recipient showed significantly (P<0.05) higher embryo recovery rates compared to ovariectomised and control-transferred. In the second experiment, using bilateral oviduct ligation model, all females that received slow-frozen oocytes became pregnant and delivered a total of 4 live young naturally. Thus, in vivo fertilisation is an effective technique to generate live offspring using slow-frozen oocytes in rabbits.

Novel aspects of endometrial function: a biological sensor of embryo quality and driver of pregnancy success

Successful pregnancy depends on complex biological processes that are regulated temporally and spatially throughout gestation. The molecular basis of these processes have been examined in relation to gamete quality, early blastocyst development and placental function, and data have been generated showing perturbations of these developmental stages by environmental insults or embryo biotechnologies. The developmental period falling between the entry of the blastocyst into the uterine cavity to implantation has also been examined in terms of the biological function of the endometrium. Indeed several mechanisms underlying uterine receptivity, controlled by maternal factors, and the maternal recognition of pregnancy, requiring conceptus-produced signals, have been clarified. Nevertheless, recent data based on experimental perturbations have unveiled unexpected biological properties of the endometrium (sensor/driver) that make this tissue a dynamic and reactive entity. Persistent or transient modifications in organisation and functionality of the endometrium can dramatically affect pre-implantation embryo trajectory through epigenetic alterations with lasting consequences on later stages of pregnancy, including placentation, fetal development, pregnancy outcome and post-natal health. Developing diagnostic and prognostic tools based on endometrial factors may enable the assessment of maternal reproductive capacity and/or the developmental potential of the embryo, particularly when assisted reproductive technologies are applied.