Is direct cell-to-cell contact needed to improve embryonic development in co-culture?

Coculture of porcine cumulus–oocyte complexes with porcine luteal cells during IVM: effect on oocyte maturation and embryo development

Coculture with somatic cells is an alternative to improve suboptimal invitro culture conditions. In pigs, IVF is related to poor male pronuclear formation and high rates of polyspermy. The aim of this study was to assess the effect of a coculture system with porcine luteal cells (PLCs) on the IVM of porcine cumulus–oocyte complexes (COCs). Abattoir-derived ovaries were used to obtain PLCs and COCs. COCs were matured invitro in TCM-199 with or without the addition of human menopausal gonadotrophin (hMG; C+hMG and C-hMG respectively), in coculture with PLCs from passage 1 (PLC-1) and in PLC-1 conditioned medium (CM). In the coculture system, nuclear maturation rates were significantly higher than in the C-hMG and CM groups, but similar to rates in the C+hMG group. In cumulus cells, PLC-1 coculture decreased viability, early apoptosis and necrosis, and increased late apoptosis compared with C+hMG. PLC-1 coculture also decreased reactive oxygen species levels in cumulus cells. After IVF, monospermic penetration and IVF efficiency increased in the PLC-1 group compared with the C+hMG group. After invitro culture, higher blastocysts rates were observed in the PLC-1 group. This is the first report of a coculture system of COCs with PLCs. Our model could be an alternative for the conventional maturation medium plus gonadotrophins because of its lower rates of polyspermic penetration and higher blastocysts rates, key issues in porcine invitro embryo production.

Mammalian embryo co-culture: Trials and tribulations of a misunderstood method

Embryo-somatic cell co-culture was devised over 40 years ago in an attempt to improve the development and viability of mammalian preimplantation embryos generated and cultured in vitro. While initial endeavours were successful in this respect, other studies soon highlighted a number of significant long-term detrimental impacts of this approach. Surprisingly little is known about the mechanisms underlying the beneficial effects of co-culture, although the production of embryotrophic compounds, modulation of nutrient profile, protection against culture-induced stress and/or toxin clearance are all contenders. The extent to which the inadvertent exposure of embryos to serum accounts for many of these effects remains open to question. Although the popularity of somatic cell co-culture has recently declined in favour of the use of sequential media due to concerns associated with its risk of disease transmission and long-term sequelae, we argue that complete dismissal of this technique is ill advised, given that our limited understanding of basic somatic cell interactions has prevented us from fully exploiting its potential. In this respect, there is some merit in focussing future research strategies based on reconstructed maternal tract tissue. Although the use of co-culture in clinical practice is unacceptable and its implementation in domestic species for commercial purposes should be viewed with diffidence, this technique can still provide a wealth of information on the development of novel, more physiological embryo in vitro culture systems. The proviso for acquiring such information is to gain a fuller understanding of the culture requirements/biochemistry of somatic cells and their interaction with the early conceptus.

Human blastocyst culture and derivation of embryonic stem cell lines

Human embryonic stem cell (hESC) biology is expected to revolutionize the future of medicine by the provision of cell-based therapies for the treatment of a variety of deliberatig diseases. The tremendous versatility of hESCs has reinforced this hope. To understand the biology of these mysterious cells and attempt to differentiate them into desirable tissues, bona fide hESCs that maintain their stability with time are required for research and clinical application. This review discusses the various protocols to derive and propagate hESCs from high quality embryos. The nature and properties of hESCs are also described together with unanswered questions that need to be addressed if this science is to be taken to the bedside.

Effects of species and cellular activity of oviductal epithelial cells on their dialogue with co-cultured mouse embryos

An efficient co-culture system, especially with oviductal or uterine epithelial cells, is important not only for the production of high quality embryos, but also for the study of the molecular dialogue between embryos and their maternal environment. Although mouse embryos have been co-cultured successfully with oviductal epithelial cells (OECs) from several species, studies on the effects of species and functionality of OECs are few. Reports concerning the necessity of direct contact between the embryo and OECs and about the culture of mouse embryos in medium conditioned with heterologous OECs have been controversial. In this study, pronuclear embryos from Kunming mice, characterized by an obvious two-cell block in vitro, were co-cultured with mouse, goat, and chick OECs. The functionality of OECs was determined by analyzing the cell cycle, apoptosis, the numbers of mitochondria and cilia, and the ability both to support embryonic development and to remove hypoxanthine from the culture medium. The necessity of direct contact between OECs and embryos was studied by repeated renewal of culture medium with fresh conditioned medium, the culture of embryos in plastic wells connected by tunnels to wells with OEC monolayers, and the co-culture of embryos separated from OECs by a filter. Both goat and chick OECs supported mouse embryonic development, but their embryotrophic lifespan was shorter than that of the mouse OECs. Whereas media conditioned with mouse OECs supported mouse embryonic development satisfactorily, medium conditioned with goat OECs supported little development. Immediate dialogue between heterologous OECs and embryos was essential for efficient co-culture, whereas direct contact between the two cell types was not; neither dialogue nor contact was needed between isologous OECs and embryos. Embryotrophic activity and the ability to remove hypoxanthine from conditioned medium declined with time after confluence and number of passages of OECs, mainly because of apoptosis and dedifferentiation. Thus, the species and functionality of OECs have profound effects on their molecular dialogue with co-cultured embryos, and efficient co-culture depends upon both positive and negative conditioning.

Improved development of very-poor-quality human preembryos by coculture with human fallopian ampullary cells

PURPOSE

To determine whether a confluent culture of fallopian ampullary epithelial cells, taken from women at the end of their reproductive life, is capable of rescuing very-poor-quality preembryos from cleavage arrest and/or degeneration.

METHODS

Human preembryos. rejected for transfer or freezing because of very poor quality, and arrested within 24 h of cleavage, were cultured for 5 days in medium alone or over a confluent culture of fallopian ampullary epithelia] cells. Morphological criteria were utilized to assess preembryo degeneration and stage of development.

RESULTS

The described coculture rescued preembryos from degeneration, enhancing development to the blastocyst stage 2.2-fold, compared with cultures in medium alone. Furthermore, fully expanded and hatching blastocysts were observed only under coculture conditions.

CONCLUSIONS

Very-poor-quality human preembryos may be rescued from degeneration, and their growth and development dramatically improved, when cocultured with a confluent culture of fallopian ampullary epithelial cells.

The mechanism of action of coculture on embryo development in the mouse model: direct embryo-to-cell contact and the removal of deleterious components

OBJECTIVE

To elucidate the mechanism for the mode of action of coculture by the use of a coculture system for mouse one-cell embryos with human oviductal epithelial cells.

DESIGN

Prospective, controlled in vitro experimental study.

SETTING

Academic research laboratory.

ANIMAL(S)

Female ICR strain mice aged between 6 and 8 weeks.

INTERVENTION(S)

Flushed one-cell embryos were cultured in human tubal fluid medium alone (control), in coculture system with human oviductal cells, in five kinds of conditioned media, and in a contactless coculture system using a cell-culture insert.

MAIN OUTCOME MEASURE(S)

The percentage of the embryos developed to hatching blastocyst stage and the level of superoxide anion in the supernatant from each culture condition.

RESULT(S)

The rates of embryo development to the hatching blastocyst stage were significantly higher in the coculture group (43%) than in the control group (none) (P <.05). The embryo development rate in the control group was similar to that of the embryos in the five kinds of conditioned media. The effects of coculture on embryo development disappeared in the contactless coculture group. The level of superoxide anion was significantly reduced in the coculture group compared to the control group.

CONCLUSION(S)

The present coculture system overcomes the two-cell block in vitro and improves the embryo development. The beneficial effect may be a result of direct cell-to-cell contact between the embryo and helper cells and the removal of deleterious components from medium, rather than a result of embryotrophic factors.

A simplified coculture system using homologous, attached cumulus tissue results in improved human embryo morphology and pregnancy rates during in vitro fertilization

PURPOSE

This study was undertaken to evaluate simplified methods of human embryo coculture using either attached or nonattached autologous cumulus tissue.

METHODS

Eight hundred one zygotes were cultured for 48 hr in a prospective, randomized trial comparing culture of embryos either with intact cumulus tissue, with cumulus tissue added to the droplet of culture medium, or without any cumulus tissue. In a follow-up study, embryo quality, pregnancy rates, and implantation rates were compared in 120 consecutive patients undergoing in vitro fertilization with a coculture system using cumulus tissue compared to a cohort of 127 patients undergoing IVF immediately preceding the institution of the coculture protocol.

RESULTS

Embryo morphology was significantly improved (P < 0.05) following culture with attached cumulus tissue (5.61 +/- 0.29) and culture with added cumulus tissue (4.72 +/- 0.31) compared to that of embryos grown in culture medium without cumulus tissue (3.95 +/- 0.26). The clinical pregnancy rate improved from 39.4% (50/127) to 49.2% (59/120) following institution of a system of coculture with attached cumulus tissue.

CONCLUSIONS

These data indicate that a simple coculture system using autologous cumulus tissue can result in improved embryo morphology, implantation rates, and clinical pregnancy rates during in vitro fertilization. This coculture system is simple, is non-labor intensive, and eliminates many of the risks which may be present in other embryo coculture systems.