In vitro development of OPU‐derived bovine embryos cultured either individually or in groups with the silk protein sericin and the viability of frozen‐thawed embryos after transfer

Abstract

The optimization of single-embryo culture conditions is very important, particularly in the in vitro production of bovine embryos using the ovum pick-up (OPU) procedure. The purpose of this study was to examine the development of embryos derived from oocytes obtained by OPU that were cultured either individually or in groups in medium supplemented with or without sericin and to investigate the viability of the frozen-thawed embryos after a direct transfer. When two-cell-stage embryos were cultured either individually or in groups for 7 days in CR1aa medium supplemented with or without 0.5% sericin, the rates of development to blastocysts and freezable blastocysts were significantly lower for the embryos cultured individually without sericin than for the embryos cultured in groups with or without sericin. Moreover, the rate of development to freezable blastocysts of the embryos cultured individually with sericin was significantly higher than that of the embryos cultured without sericin. When the frozen-thawed embryos were transferred directly to recipients, the rates of pregnancy, abortion, stillbirth and normal calving in the recipients were similar among the groups, irrespective of the culture conditions and sericin supplementation. Our findings indicate that supplementation with sericin during embryo culture improves the quality of the embryos cultured individually but not the viability of the frozen-thawed embryos after transfer to recipients.

Combined effects of individual culture and atmospheric oxygen on preimplantation mouse embryos in vitro

“…We would suggest that the embryotrophic effect of group culture may not necessarily be embryo-specific, but neighbouring embryos may substitute for the lack of paracrine signals from the reproductive tract. This is supported by the observation that embryos from bovine, which is a monovulatory species, also benefit from group culture (Carolan et al, 1996;Doherty et al, 1997;Donnay et al, 1997;Ferry et al, 1994;Fujita et al, 2006;Ikeda et al, 2000;Isobe et al, 2015;Keefer et al, 1994;Larson and Kubisch, 1999;Nagao et al, 2008;Senatore et al, 2010). Interestingly, this effect also occurs between species; mouse embryos can stimulate the development of both cat and cow embryos (Spindler et al, 2006;Stilley et al, 2003).…”

“…As metabolites also act as signalling molecules, oxygen has the potential to alter paracrine signalling through regulating metabolism. Addition of antioxidants (Truong et al, 2016) or ROS-reducing protein (Isobe et al, 2015) during culture has been demonstrated to improve single embryo development more than when embryos are cultured in groups, indicating that culturing embryos in groups may reduce oxidative stress.…”

“…Nonetheless, blastocyst development rates and cell numbers in vitro are improved by group culture with other embryos (Gardner et al, 1994;Keefer et al, 1994;Lane and Gardner, 1992;Moessner and Dodson, 1995;Paria and Dey, 1990). Recent studies, including those with human embryos, demonstrate that advances in culture systems have not yet replicated the benefits of embryo group culture (Ebner et al, 2010;Isobe et al, 2015;Sun et al, 2014;Vutyavanich et al, 2011). In addition to negative effects on blastocyst development, cell numbers and allocation, individual culture has also been reported to increase apoptosis (Brison and Schultz, 1997), and affect the embryo secretome (Contramaestre et al, 2008;Larson and Kubisch, 1999).…”

“…It remains unclear whether pregnancy rate in humans is affected by individual culture (Almagor et al, 1996;Ebner et al, 2010;Spyropoulou et al, 1999), and there have been no reports on birth weights or other pregnancy outcomes. The few animal studies that have investigated post-implantation outcomes following individual embryo culture have observed only a trend for decreased implantation rates or live birth rates (Isobe et al, 2015;Kato and Tsunoda, 1994;Lane and Gardner, 1992), and the long term development and health of such offspring has not been monitored.…”

In vitro culture of individual mouse preimplantation embryos: the role of embryo density, microwells, oxygen, timing and conditioned media

“…Individual culture of in vitro fertilised embryos has become standard practice in many clinics, and will likely become more common with the application of new technologies for embryo monitoring and selection, such as time-lapse microscopy (Conaghan et al, 2013;Kirkegaard et al, 2014;Rubio et al, 2014). Compared with embryos cultured in groups, individual culture in multiple species results in slower cleavage divisions, fewer embryos developing to the blastocyst stage, blastocysts with reduced cell number and altered cell allocation, and increased levels of apoptosis (Brison and Schultz, 1997;Gardner et al, 1994;Isobe et al, 2015;Keefer et al, 1994;Kelley and Gardner, 2016;Lane and Gardner, 1992;Paria and Dey, 1990). Studies in humans have also reported lower cell numbers, blastocyst rates and pregnancy rates after single culture (Almagor et al, 1996;Ebner et al, 2010;Moessner and Dodson, 1995;Rebollar-Lazaro and Matson, 2010), although some studies have found that single and group culture produce the same results (Rijnders and Jansen, 1999;Spyropoulou et al, 1999).…”