Purification and characterization of a low molecular weight zinc binding protein from human placenta

Role of zinc in female reproduction

Zinc is a critical component in a number of conserved processes that regulate female germ cell growth, fertility, and pregnancy. During follicle development, a sufficient intracellular concentration of zinc in the oocyte maintains meiotic arrest at prophase I until the germ cell is ready to undergo maturation. An adequate supply of zinc is necessary for the oocyte to form a fertilization-competent egg as dietary zinc deficiency or chelation of zinc disrupts maturation and reduces the oocyte quality. Following sperm fusion to the egg to initiate the acrosomal reaction, a quick release of zinc, known as the zinc spark, induces egg activation in addition to facilitating zona pellucida hardening and reducing sperm motility to prevent polyspermy. Symmetric division, proliferation, and differentiation of the preimplantation embryo rely on zinc availability, both during the oocyte development and post-fertilization. Further, the fetal contribution to the placenta, fetal limb growth, and neural tube development are hindered in females challenged with zinc deficiency during pregnancy. In this review, we discuss the role of zinc in germ cell development, fertilization, and pregnancy with a focus on recent studies in mammalian females. We further detail the fundamental zinc-mediated reproductive processes that have only been explored in non-mammalian species and speculate on the role of zinc in similar mechanisms of female mammals. The evidence collected over the last decade highlights the necessity of zinc for normal fertility and healthy pregnancy outcomes, which suggests zinc supplementation should be considered for reproductive age women at risk of zinc deficiency.

Ultrastructural Demonstration of Mercury Granules in the Placenta of Metallothionein-Null Pregnant Mice after Exposure to Mercury Vapor

The placenta plays an important role in the regulation of maternal to fetal transfer of toxic substances, including nonessential metals. Metallothioneins (MTs), which are known to have protective effects against heavy metal toxicity, exist in the placenta, but the exact localization of placental MTs (both MT-I and MT-III) and their physiological role in the placenta exposed to mercury are unclear. The present study was performed to examine the localization of MTs and mercury granules in the placenta of mice exposed to mercury vapor. On gestational day 16, MT-I & II-null and wild-type mice were exposed to mercury vapor at 4.9 to 5.9 mg/m3 for 2 hours. At 24 and 48 hours after exposure, the placentas were examined for mercury distribution (autometallography), MT immunoreactivity, and MT mRNA expression (in situ hybridization). No histological changes were observed in the placentas of either MT-null or wild-type mice. Mercury deposition was demonstrated along the boundary between the junctional zone and the labyrinth zone, as well as in the yolk sac, maternal decidual cells, and labyrinth trophoblasts of both MT-null and wild-type mice. MT-I & -II immunoreactivity, which was confined to wild-type mice, was demonstrated in the yolk sac and decidual cells; mercury was also shown in both structures, suggesting that mercury granules were bound to MTs. MT-III mRNA expression was observed in the yolk sac, decidual cells, and spongiotrophoblasts in both MT-null and wild-type mice. There was, however, no evidence of MT at the boundary between the junctional and labyrinth zones, where substantial mercury deposits were demonstrated. These results suggest that placental MTs and the other unknown molecules may be related to the barrier to the placental transfer of mercury.