Stage Specific Effects of Zn

The treatment of sea urchin embryos by Zn2+ followed by culture with Zn2+ -specific chelators such as ethylenediamine-N, N'-diacetic acid and N-hydroxyethylethylenediamine-N, N', N'-triacetic acid, was performed at various developmental stages to find out specific stages for Zn2+ to induce abnormal differentiation. The treatment with 1 mM ZnSO4 at 20°C during a period including two spans of development between 0 and 8 hr and between 14 and 16 hr post fertilization yielded permanent blastulae. Zn2+ -treatment during the former span produced abnormal prisms and plutei with small archenteron. The treatment for a period including only the latter span failed to produce abnormal ones. Zn2+ -treatment during a period including the gastrula stage also produced abnormal spherical embryos. Without the culture with these chelators, abnormal embryos were produced by Zn2+ -treatment performed at any stages before gastrulation. A high zinc amount in the embryos just after the treatment became as low as in normal embryos soon after the culture with these chelators and was maintained during the culture without them. These results indicate that zinc retention occurs in the Zn2+ -treated embryos and causes abnormal differentiation when the treated embryos develop in normal sea water through the Zn2+ -specific periods of development.