Nuclear envelope disassembly and nuclear lamina depolymerization during germinal vesicle breakdown in starfish

Abstract

During germinal vesicle breakdown (GVBD) 2 2 Abbreviations used: 1-MA, 1-methyladenine; ASW, artificial seawater; CaFSW, calcium-free seawater; DIC, differential interference contrast; GV, germinal vesicle; GVBD, germinal vesicle breakdown; HVEM, high voltage electron microscopy; MPF, maturation-promoting factor; SEM, scanning electron microscopy. in starfish, the nuclear envelope disassembles before the nuclear lamina completely depolymerizes, judging from correlative ultrastructural, immunolabeling, and light microscopic analyses. At 13°C, prophase-arrested oocytes of Pisaster ochraceus begin GVBD and rapidly undergo nuclear envelope disassembly about 50 min after addition of the maturation-inducing hormone 1-methyladenine (1-MA). The nuclear lamina of these oocytes, however, remains present for 10–20 min following the vesiculation of the nuclear envelope. Completion of GVBD, as evidenced by a blending of the nuclear contents with the surrounding cytoplasm, occurs within about 15 min after the nuclear lamina has fully depolymerized. Immunofluorescence studies also indicate that a marked increase in the phosphorylations of nuclear proteins precedes the structural reorganizations of the nuclear envelope and nuclear lamina during GVBD.