Regulation of preimplantation development of bovine embryos by interleukin-1β

Abstract

Experiments were performed to determine the actions of recombinant bovine interleukin-1β (IL-1β) on the growth of preimplantation embryos. In the first series of studies, IL-1β was added at 8-10 h after insemination, and the percentage of oocytes developing to the blastocyst stage was evaluated. IL-1β increased development to the blastocyst stage when embryos were cultured at high density (~25-30 embryos/drop) but decreased or had no effect on development when cultured at low density (~10 embryos/drop). Thus, the positive effect of IL-1β depends upon some other embryo-derived product. The effect of IL-1β on embryonic development was maintained in completely denuded embryos, indicating that cumulus cells do not mediate the actions of IL-1β. Maximum development of embryos cultured at ~25-30/drop occurred at 0.1-1 ng/ml; 10 ng/ml was less effective. Addition of IL-1β to groups of ~25-30 embryos/drop at 8-10 h after insemination also increased embryo cell number at Day 5 postinsemination by increasing the proportion of embryos that reached the 9- to 16-cell stage. However, IL-1β had no effect on the proportion of blastocysts when added at Day 5 postinsemination. Thus, IL-1β probably acts to increase blastocyst numbers by exerting actions on embryo growth before Day 5. In contrast to its effect on embryos, addition of IL- 1β during oocyte maturation did not affect cumulus expansion, cleavage rate of oocytes, or subsequent development to the blastocyst stage. In conclusion, IL-1β can modulate growth of bovine embryos at early stages of development in a manner dependent upon embryo density.