Importance of oil overlay for production of porcine embryos in vitro

Abstract

Technologies to edit the zygote genome have revolutionized biomedical research not only for the creation of animal models for the study of human disease but also for the generation of functional human cells and tissues through interspecies blastocyst complementation technology. The pig is the ideal species for these purposes due to its great similarity in anatomy and physiology to humans. Emerging biotechnologies require the use of oocytes and/or embryos of good quality, which might be obtained using in vitro production (IVP) techniques. However, the current porcine embryo IVP systems are still suboptimal and result in low monospermic fertilization and blastocyst formation rates and poor embryo quality. During recent years, intensive investigations have been performed to evaluate the influence of specific compounds on gametes and embryos and to avoid the use of undefined supplements (serum and serum derivate) in the incubation media. However, little consideration has been given to the use of the mineral oil (MO) to overlay incubation droplets, which, albeit being a routine component of the IVP systems, is a totally undefined and thus problematic product for the safety of gametes and embryos. In this review, we provide an overview on the advantages and disadvantages of using MO to cover the incubation media. We also review one important concern in IVP laboratories: the use of oils containing undetected contamination. Finally, we discuss the effects of different types of oils on the in vitro embryo production outcomes and the transfer of compounds from oil into the culture media.

Evaluation of a small volume oil‐free in vitro production system for bovine embryos

“…To beware an oil overlay and avoid evaporation of medium, large volumes of medium will be usually used. Conversely, with large volumes, important compounds such as paracrine and autocrine factors for embryo interaction can be diluted (Canseco et al, 1992;Martinez et al, 2018;Nagao et al, 2008). Gasperin et al (2010) showed that an increase in the osmolality in 400 µl medium can be avoided by adding water in the central hole of a four well plate.…”

“…The presence or absence of oil per se did not alter the output of an IVP system. If oil is used, however, the type of oil (Martinez et al., 2018; Van Soom et al., 2001) and a potential treatment of the used oil (Tae et al., 2006) have an impact on embryo development and quality. Also, the batch of the oil, especially for silicon oil ((Van Soom et al., 2001); own observations) and the storage (light and temperature; (Otsuki et al., 2009)), affect the results.…”

“…Furthermore, the used oil can contain toxic compounds able to transfer to the medium as reviewed by Martinez et al (2018).…”

“…Furthermore, the used oil can contain toxic compounds able to transfer to the medium as reviewed by Martinez et al. (2018). Added chelating agents (EDTA or BSA) as well as haemoglobin (nitric oxide scavenger) and co‐culture systems are partially able to resolve toxic effects (Lee et al., 2004; Tae et al., 2006; Van Soom et al., 2001).…”

“…The most commonly used system is a microdrop culture method, where drops of medium are covered with an oil overlay, because of the simple assessment of cumulus–oocytes complexes (COCs) and embryos (Tae et al., 2006). Furthermore, protection from bacterial contamination, absorption of lipophilic toxic compounds, avoidance from evaporation of the medium, maintenance of osmotic pressure and pH value (Martinez et al., 2018) are usually quoted as beneficial impacts of the drop system. Three different types of oil are used for covering the drops, silicone oil, mineral oil and paraffin oil.…”