Developmental Phases of Individual Mouse Preimplantation Embryos Characterized by Lipid Signatures using Desorption Electrospray Ionization Mass Spectrometry

Knowledge of the lipids present in individual preimplantation embryos is of interest in fundamental studies of embryology, in attempts to understand cellular pluripotency and in optimization of in vitro culture conditions necessary for the application and development of biotechnologies such as in vitro fertilization and transgenesis. In this work, the profiles of fatty acids and phospholipids (PL) in individual mouse preimplantation embryos and oocytes were acquired using an analytical strategy based on desorption electrospray ionization mass spectrometry (DESI-MS). The methodology avoids sample preparation and provides information on the lipids present in these microscopic structures. Differences in the lipid profiles observed for unfertilized oocytes, two- and four-cell embryos, and blastocysts were characterized. For a representative set of embryos (N = 114) using multivariate analysis (specifically principal component analysis) unfertilized oocytes showed a narrower range of PL species than did blastocysts. Two- and four-cell embryos showed a wide range of PLs compared with unfertilized oocytes and high abundances of fatty acids, indicating pronounced synthetic activity. The data suggest that the lipid changes observed in mouse preimplantation development reflect acquisition of a degree of cellular membrane functional and structural specialization by the blastocyst stage. It is also noteworthy that embryos cultured in vitro from the two-cell through the blastocyst stage have a more homogeneous lipid profile as compared with their in vivo-derived counterparts, which is ascribed to the restricted diversity of nutrients present in synthetic culture media. The DESI-MS data are interpreted from lipid biochemistry and previous reports on gene expression of diverse lipids known to be vital to early embryonic development.