Lipid droplet utilization by the mouse embryo

High numbers of lipid droplets (LDs) in mammalian eggs are stored and maintained throughout embryo development without marked signs of their utilization. It was previously demonstrated in large domestic mammals that removing lipids from the zygote does not influence post-implantation development in terms of the rate of delivered offspring. Previously studied pig and cow eggs contain considerable amounts of LDs, while mice have a very low level of ooplasmic lipids, which allows to more precisely analyze any effect of lipid removal on developmental dynamics in vitro . We wanted to know if lipid fraction removal would influence the dynamics of preimplantation development of mouse embryos. To do this, mouse zygotes were mechanically delipidated and their progression to the blastocyst stage was evaluated in vitro . Part of blastocysts were transferred to pseudopregnant females for development to term, and then offspring health parameters were evaluated. Our experiments showed no effects of lipid removal on the rate and timing of mouse embryo development. Furthermore, there were no differences in post-natal characteristics of offspring developed from delipidated and non-delipidated embryos. In conclusion, normal developmental progression of dilapidated embryos indicates that LDs are largely unutilized during preimplantation stages. The apparent dispensability of the LDs fraction throughout preimplantation development prompts questions about their so far uncovered role in mammalian embryo. Based on our preliminary observation of the ultrastructure of diapaused blastocysts from mouse and sheep, we speculate that LDs are utilized by the embryo during delayed implantation, i.e., while waiting for the maternal receptivity signal before implantation.