Breakdown of cytoskeletal proteins during meiosis of starfish oocytes and proteolysis induced by calpain

Meiosis reinitiation in sta(r)fish oocytes is characterized by Ca2+ transie nts in the cytosol and in the nucleus and is accompanied by the disassembly of the nuclear envelope, a process which is likely to be mediated by the c leavage of selected proteins. We have used mass spectrometry analysis (mass profile finger-printing) on 2D polyacrylamide gels of extracts of oocytes in which meiosis resumption was induced by 1-methyladenine and have identif ied five proteins that were specifically degraded: alpha-tubulin, lamin B, dynamin, and two kinds of actin. They are all components of the cytoskeleto n or associated with it. We then investigated whether calpain, which is act ivated by the increase in cell Ca2+, could cleave the same proteins that be came degraded under the influence of 1-methyladenine and thus be involved i n nuclear membrane breakdown. The investigation was prompted by the finding that microinjection of calpain into the nuclei of prophase arrested oocyte s induced meiosis in the absence of 1-methyladenine. Incubation of prophase arrested (disrupted) oocytes with calpain produced a 2D gel protein patter n in which some of the degradation products coincided with those seen in oo cytes challenged with 1-methyladenine. (C) 2000 Academic Press.