Figure 4. Sustained elevation of intracellular zinc availability following egg activation leads to reestablishment of metaphase arrest.

Eggs were activated with strontium chloride (SrCl₂) then treated with zinc pyrithione (ZnPT) 1.5 hours later (a). At 6 h post-activation, control eggs form pronuclei (b, arrowheads) whereas the majority of eggs treated with ZnPT do not (c). When visualized by fluorescence, control eggs display decondensed DNA organized within a defined nucleus (d). F-actin is homogeneous around the egg’s cortex (e) and α-tubulin remains organized as a spindle midbody remnant (f), which is visible between the egg and the second polar body (g, merged image). In contrast, ZnPT-treated eggs display condensed chromosomes (h) adjacent to an area of concentrated, cortical F-actin (i). α-tubulin is organized in a metaphase-like configuration (j) around the chromosomes (k, merged image). This layout mirrors the subcellular arrangement in unfertilized eggs (l-o), which also display condensed chromosomes (l) overlaid with an actin cap (m), surrounded by a metaphase spindle (n). Scale bar = 80 μm (b, c) or 25 μm (d-o).