Figure 4.

(A) Zinc fluxes in invertebrates have significant parallels to those seen in mammals. Both C. elegans and mouse oocytes accrue large quantities of total zinc during early stages of meiotic progression and achieve the maximum concentration at Metaphase II; total zinc then drops as the final phases of meiosis come to completion in both species. The timing of fertilization in both species is denoted by the presence of a blue sperm; in worm, fertilization occurs at the end of Prophase I, whereas in mouse, fertilization occurs at Metaphase II. Pronounced fluxes in labile zinc begin upon fertilization, which is restricted to different stages in the meiotic cycle, i.e., Prophase I in worm and Metaphase II arrest in mouse. (B) TPEN-induced zinc insufficiency in isolated, developing embryos experience polar body retention or retraction during Meiosis II, resulting in hyperploidy, spindle defects, and cell cycle arrest. (C) Labile zinc (pink) is acquired during the early stages of Meiosis I, when the embryo is permeable. Influx continuously occurs until Anaphase II, and then zinc is expelled from the cytoplasm over 30 min. Finally, labile zinc accumulates in the general eggshell region.