Abstract
Consideration of embryo-derived growth factors, such as IGF1, is important when culturing an embryo in an in vitro fertilization (IVF) setting, or when studying the effect of growth factors on embryo development in vitro. Addition of IGF1 to the culture medium has been reported to cause a range of developmental responses in preimplantation mouse embryos. This variability may be due to culture of embryos in suboptimal culture media and at different culture densities/volumes. This study examined the role of exogenous and autocrine IGF1 on mouse preimplantation development in vitro, by treatment of embryos with an IGF1R neutralising antibody (IGF1R nAb) under low density (1 embryo/100 microl) or high density (1 embryo/1 microl) culture conditions. At low density, IGF1R nAb reduced development to the blastocyst stage, hatching, and total cell numbers in blastocysts and increased the number of apoptotic cells in blastocysts, suggesting that autocrine IGF1 signalling is occurring, even at low density. This signalling is independent of IGF1 present in the zona pellucida, since culturing embryos in the absence of their zona pellucida had no effect on blastocyst development. Addition of 10 ng/ml IGF1 increased blastocyst development at low density, but decreased hatching at high density. Similarly, high levels of exogenous IGF1 at low density decreased hatching. IGF1 appears to play a role in cell survival and treatment of blastocysts with IGF1 increased Akt phosphorylation. The IGF1R antagonist picropodophyllin was also used in this study, but was found to have non-specific effects on the mitotic spindle. In conclusion, IGF1 is an important growth factor for the improvement of preimplantation development; however, for optimal development the total amount of IGF1 present must be tightly controlled.