Disassembly of the nuclear envelope of spisula oocytes in a cell-free system

Nuclei isolated from oocytes of the surf clam Spisula solidissima are disassembled when exposed to extracts from maturing oocytes. In the course of this process the nuclear lamina undergoes a marked reduction in size and the nuclear membrane appears to be fragmented into vesicles. These events are accompanied by extensive phosphorylation of the oocyte 67-kDa lamin and its solubilization. The changes observed are similar to those which occur in vivo in activated Spisula oocytes. Nuclear envelope breakdown in vitro requires ATP and Mg²⁺, but not Ca²⁺. It is not affected by protease inhibitors and is inhibited by alkaline phosphatase.