Inorganic profiles of preimplantation embryos reveal a role for zinc in blastocyst development.

Elements such as iron, copper and zinc play essential roles in the mammalian oocyte, egg, and embryo, however among these metals, zinc plays unique regulatory roles. Temporal fluctuations in zinc concentrations drive reproductive milestones such as meiotic resumption, egg activation, and initiation of the mitotic cell cycle. Roles for zinc in late preimplantation embryo development, have not been well characterized. Using a quantitative element approach we report the inorganic profiles of mouse embryos progressing through the late blastocyst stage. We find that blastocysts, like oocytes and eggs, and distinct to somatic cells, maintain higher levels of zinc than copper and iron. All three of these essential metals are more abundant in the inner cell mass, which contains the population of pluripotent stem cells that give rise to the fetus, relative to the trophectoderm which gives rise to the placenta and extraembryonic tissues. To test whether zinc abundance was associated with mitotic progress and cell fate lineage, we perturbed zinc homeostasis during blastocyst formation by artificially raising intracellular zinc concentrations with zinc pyrithione. This treatment during the morula-to-blastocyst transition when cell fate lineages emerge resulted in an elevation of zinc in the ICM. This treatment did not impact cell number, but did increase expression of the pluripotency and epiblast marker, Nanog, and decreased expression of the primitive endoderm marker, Gata4. These results demonstrate that the inorganic profiles of the late preimplantation embryo retain elemental hallmarks of earlier developmental stages and perturbation of zinc levels alters pluripotency gene expression in the blastocyst.