Mouse and bovine models for human IVF

In vitro systems for intercepting early embryo-maternal cross-talk in the bovine oviduct

A comprehensive understanding of the complex embryo-maternal interactions during the preimplantation period requires the analysis of very early stages of pregnancy. These are difficult to assess in vivo due to the small size of the embryo exerting local paracrine effects. Specifically designed experiments and holistic transcriptome and proteome analyses to address the early embryo-maternal cross-talk in the oviduct require sufficient numbers of well-defined cells in a standardized experimental environment. The pronounced estrous cycle-dependent changes in gene expression and morphology of bovine oviduct epithelial cells (BOECs) clearly show that a precise definition of the stage of estrous cycle is essential for obtaining a well-defined homogenous population of functional cells. The number of intact cells isolated from individual ampullae by solely mechanical means was 10-fold higher than previously reported cell yields after enzymatic treatment, and the purity was comparable. Bovine oviduct epithelial cells have been cultured as monolayers or in suspension. Proliferating cells grown in monolayers dedifferentiated, with a concomitant loss of important morphologic characteristics. After several days in culture, BOECs in monolayers are less likely to mimic the oviduct environment in vivo than BOEC vesicles formed of epithelial sheets in short-term suspension culture. A 24-h culture system for BOECs isolated on Day 3.5 of the estrous cycle showed excellent preservation of morphologic criteria, marker gene expression, and hormone responsiveness. The short-term BOEC culture system provides well-defined and functional BOECs in sufficient quantities for studies of early embryo-maternal interactions in experiments that mimic the environment in the oviduct in vivo.

Effect of PVP on sperm capacitation status and embryonic development in cattle

The objective of this study was to investigate the effects of polyvinylpyrrolidone (PVP) on sperm capacitation status and embryonic development in cattle (Bos taurus). Acrosome-reacted sperm (chlortetracycline stain) and the fertilization rate after intracytoplasmic sperm injection (ICSI) were enhanced (P<0.05) when sperm were cultured in a medium containing 10% PVP. However, injection of bovine in vitro-produced (IVP) embryos with medium containing 10% PVP suppressed development of these embryos to the 2-cell, morula, and blastocyst stages and cell number at the blastocyst stage (P<0.01) but did not affect chromosomal integrity (P>0.05). Embryo developmental capacity differed (P<0.01) among PVP from three suppliers, but there were no significant differences among three solvent media. The PVP remained localized in 40.9% of PVP-injected IVP embryos. In conclusion, PVP affected the acrosome reaction and enhanced the fertilization rate after ICSI. However, PVP remained detectable in IVP embryos and suppressed their developmental capacity.

The role of IGF1 in the in vivo production of bovine embryos from superovulated donors

IGF1 plays an important role in bovine follicular growth, acquisition of oocyte competence and embryo viability. Current data also indicate a critical role for IGF1 in both the ovarian response and the embryo yield following the superovulatory treatments. IGF1 can have either positive or negative effects on embryo viability which is related to the concentration of IGF1 induced by superovulation treatment. These effects impact either on oocyte competence or directly on the embryo. Concentrations in the physiological range appear to result in the production of higher quality embryos, mainly due to the mitogenic and the anti-apoptotic activities of IGF1. However, high superovulatory responses are associated with decreased embryo viability and a concomitant increase in apoptosis. Studies in mice suggest that this increase in apoptosis is related to the downregulation of the IGF1 receptor in the embryo associated with high IGF1 concentrations. Strategies capable of controlling the IGF1 concentrations could be one approach to improve superovulation responses. A range of possible approaches for research within the IGF system in gonadotrophin-stimulated cattle is discussed in this review, including the possible use of superovulated female cattle as an alternative animal experimental model for research on reproductive disorders in humans associated with abnormal IGF1 concentrations.

Comparison of the efficacy of two commercially available media for culturing one-cell embryos in the in vitro fertilization mouse model

OBJECTIVE

To examine the effects of two commercial media on the development of mouse ova fertilized in vitro to the blastocyst stage.

DESIGN

Animal model.

SETTING

Academic institution.

ANIMAL(S)

Eight-week old, superovulated mice.

INTERVENTION(S)

One-cell embryos cultured in vitro up to the blastocyst stage in potassium-enriched simplex optimized medium (KSOM) or G1/G2 medium.

MAIN OUTCOME MEASURE(S)

Blastocyst and hatching rates, total cell number count, and proportion of allocation of cells to the inner cell mass (ICM) and trophectoderm (TE).

RESULT(S)

The percentage of zygotes that developed to the blastocyst stage 96 and 120 hours after insemination was statistically significantly higher in the KSOM group. The percentage of blastocysts that partially or completely hatched by day 5 of culture was 84% and 71% for the KSOM and G1/G2 groups, respectively, showing a statistically significant difference between the groups. The mean number of ICM cells was 11.7 +/- 4.0 and 9.2 +/- 5.2 for the zygotes cultured in KSOM and G1/G2 media, respectively, revealing a statistically significantly higher cell number in the ICM of blastocysts derived from culture in KSOM medium. The ICM/TE ratio in the blastocysts cultured in KSOM or G1/G2 media was similar in both groups.

CONCLUSION(S)

Commercially available KSOM medium is superior to sequential G1/G2 media for culturing one-cell embryos up to the blastocyst stage in the mouse IVF model.

Virtues and limitations of the preimplantation mouse embryo as a model system

The mouse is the most widely used model of preimplantation embryo development, but is it a good model? Its small size, prolificacy and ease of handling make the mouse a relatively low cost, readily available and attractive alternative when embryos from other species are difficult or expensive to obtain. However, the real power of the mouse as a model lies in mouse genetics. The development of inbred mouse strains facilitated gene discovery as well as our understanding of gene function and regulation while the development of tools to introduce precise genetic modifications uniquely positioned the mouse as a powerful model system for uncovering gene function. However, all models have limitations; the small size of the mouse limits tissue availability and manipulations that can be performed and differences in physiology among species may make it inappropriate to extrapolate from the mouse to other species. Thus, rather than extrapolating directly from the mouse to other species, it may be more useful to use the mouse as a model system for developing and refining hypotheses to be tested directly in species of interest. In this brief review, the value of the preimplantation mouse embryo as a model is considered, both as a model for other species and as a model for the mouse, as understanding the virtues and limitations of the mouse as a model system is essential to its appropriate use.

Somatic cell nuclear transfer: Past, present and future perspectives

It is now over a decade since the birth, in 1996, of Dolly the first animal to be produced by nuclear transfer using an adult derived somatic cell as nuclear donor. Since this time similar techniques have been successfully applied to a range of species producing live offspring and allowing the development of transgenic technologies for agricultural, biotechnological and medical uses. However, though applicable to a range of species, overall, the efficiencies of development of healthy offspring remain low. The low frequency of successful development has been attributed to incomplete or inappropriate reprogramming of the transferred nuclear genome. Many studies have demonstrated that such reprogramming occurs by epigenetic mechanisms not involving alterations in DNA sequence, however, at present the molecular mechanisms underlying reprogramming are poorly defined. Since the birth of Dolly many studies have attempted to improve the frequency of development, this review will discuss the process of animal production by nuclear transfer and in particular changes in the methodology which have increased development and survival, simplified or increased robustness of the technique. Although much of the discussion is applicable across species, for simplicity we will concentrate primarily on published data for cattle, sheep, pigs and mice.

Embryo culture medium: which is the best?

With the growing move in in-vitro fertilization (IVF) clinics to transfer fewer embryos to women, there is an increasing reliance on the IVF laboratory to maximize embryo viability. Subsequently, there is justified scrutiny on the culture system and the media used to sustain the human embryo in vitro. The transfer of fewer embryos to patients also creates an increased dependence on the ability to cryopreserve embryos successfully. Therefore, in addition to the ability of a culture system to produce a single top-quality embryo for transfer, it is also necessary to enhance the cryotolerance of sibling embryos so that they can survive freezing or vitrification. Therefore, when examining which culture media is the best, it is prudent to not only examine the ability of a culture system to produce a pregnancy with the one or two highest-grade embryos, but also to determine how many embryos from the entire cohort (both fresh and frozen embryos) are capable of producing a live birth. Additionally, research on animal models has demonstrated that stress, and the resultant adaptation to conditions during pre-implantation stages, can affect pregnancy loss and fetal growth. It is therefore important to understand the role of each medium component and to identify possible sources of cellular stress to the embryo that will ultimately affect the function and viability of the conceptus.

Use of a novel washing method combining multiple density gradients and trypsin for removing human immunodeficiency virus-1 and hepatitis C virus from semen

OBJECTIVE

To determine the effectiveness of a novel treatment designed to remove human immunodeficiency virus (HIV) -1 and hepatitis C virus (HCV) from spiked semen and to evaluate sperm motility and viability after treatment.

DESIGN

A prospective clinical laboratory-based study.

SETTING

The human studies were conducted in academic and national research environments. The bovine study was conducted in an accredited research facility.

PATIENT(S)

Healthy volunteers provided the semen samples used in the human studies; abattoir-derived material was used for the bovine embryo production study.

INTERVENTIONS(S)

None.

MAIN OUTCOME MEASURE(S)

Cytopathic, reverse transcriptase-polymerase chain reaction, and branched DNA assays were used to test the efficacy of the procedure for inactivating or removing viruses from spiked semen; standard semen evaluation criteria were used to assess the effects of the procedures on sperm motility and viability.

RESULT(S)

Trypsin exposure significantly reduced the infectivity of HIV-1. The triple density gradient treatment, with or without trypsin, had no detrimental affect on fresh or cryopreserved/thawed sperm 2-48 hours after treatment. The treatment of semen spiked with HIV-1 or HCV indicated that the procedure was effective for reducing viral copies to undetectable levels or below levels of clinical relevance.

CONCLUSION(S)

The procedure was effective for significantly inactivating or reducing HIV-1 and HCV in spiked semen without adversely affecting sperm quality.

Cloning: Eight Years After Dolly

It is now 8 years since the birth of Dolly, the first animal produced by nuclear transfer using a donor cell population established from an adult animal. During this time, the technique of nuclear transfer has been successfully applied to a range of mammalian species for the production of offspring using a plethora of donor cell types derived from both foetal and adult tissues. In addition, when coupled with genetic manipulation of the donor cells, transgenic offspring have been produced with a range of genetic modifications including gene knockouts and gene knockings. Despite the apparent successes of the technology, the efficiency of development to live offspring has remained low and developmental abnormalities still occur. The objectives of this paper are to review some of the successes and failures of the nuclear transfer procedure since the production of Dolly. In particular, we will review the major steps in the procedure and discuss studies from our laboratory and others which have modified the procedure in ways which may impact on development.