Zinc physiology and biochemistry in oocytes and embryos

Abstract

The essential role of zinc in embryogenesis was identified through studies of its presence in eggs and embryos, the effects of its deficiency and its role in metallo proteins required for organ development and formation. The Xenopus laevis oocyte zinc content varies during oogenesis. It increases from 3 to 70 ng zinc/oocyte as it progresses from stage I to VI. The oocyte zinc is derived from the maternal liver as part of a metallo-complex with vitellogenin. The latter transports the metal in plasma and into the oocyte. Once internalized, most of the zinc is stored within yolk platelets bound to lipovitellin, one of the processed products of vitellogenin. About 90% of the total zinc is associated with the yolk platelet lipovitellin while the remaining I 0% is in a compartment associated with hitherto unknown molecule(s) or organelle(s) of the cytoplasm. The bi-compartmental distribution remains constant throughout embryogenesis since the embryo behaves as a closed system for zinc after fertilization. The yolk platelet zinc is used after the tadpole is hatched while we proposed that the I 0% of the zinc in the non-yolk platelet pool is the one used for embryogenesis. It provides zinc to newly synthesized molecules responsible for the development of zinc-dependent organ genesis. Interference with the availability of this zinc by the chelating agent I, I 0-phenanthroline results in the development of embryos that lack dorsal organs, including brain, eyes and spinal cord. The extensive teratology is proposed to be due to altered or absent zinc distribution between the cytosolic pool and zinc-transcription factors. The data identify the components of a zinc transport, storage and distribution system in a vertebrate organism.

Maternal transfer of trace elements in leatherback turtles (Dermochelys coriacea) of French Guiana

“…In fishes and amphibians, binding of elements such as Cd or Zn to vitellogenin is an important mechanism for ovarian uptake of the metals (Ghosh and Thomas, 1995;Falchuk and Montorzi, 2001). In reptiles, the copper transporter protein (CRT) has been suggested to function in Cu acquisition and transport into growing oocytes and eggs (Riggio et al, 2002) and a study by Unrine et al (2006) showed that Se was also incorporated in the lipovitellin, another egg protein (Unrine et al, 2006).…”

A vitellogenin chain containing a superoxide dismutase-like domain is the major component of yolk proteins in cladoceran crustacean Daphnia magna

“…They serve as storage proteins providing amino acids, carbohydrates, lipids and phosphates to the developing embryo (Byrne et al, 1989). They also serve as trace mineral-transporting proteins (Falchuk and Montorzi, 2001). Accumulation of VTG or VTN in oocytes is one of the key events in the process of ovarian maturation.…”

Affinity isolation and mass spectral analysis of 1,10-phenanthroline (OP)-stimulated UV-damaged-DNA binding proteins expressed in zebrafish (Danio rerio) embryos

“…Analysis of UV damage DNA-binding activity in fractionated zebrafish extracts showed that proteins interacting preferentially with 6-4PPs were effectively separated from nonspecific binding proteins due to In oviparous vertebrates, Vgs are produced in the liver in response to estrogen stimulation. After secretion to the blood, these metalloproteins are taken up from the plasma by developing oocytes via receptormediated endocytosis and are cleaved into three portions-lipovitellin I (Lv1), phosvitin (PV), and lipovitellin II (Lv2) (Woods and Roth 1984;Montorzi et al 1995;Falchuk and Montorzi 2001). As a metalloprotein, the 220-kDa Vg of the frog Xenopus laevis was shown to carry different metals at varied levels.…”