Published in:
Journal of Cell Science, 108 (1995) 7, Seite 2693-2703
Language:
English
DOI:
10.1242/jcs.108.7.2693
ISSN:
0021-9533;
1477-9137
Origination:
Footnote:
Description:
<jats:title>ABSTRACT</jats:title>
<jats:p>Feedback mechanisms preventing M phase occurrence before S phase completion are assumed to depend on inhi bition of cyclin B-cdc2 kinase activation by unreplicated DNA. In sea urchin, fertilization stimulates protein synthesis and releases eggs from G1 arrest. We found that in the one-cell sea urchin embryo cyclin B-cdc2 kinase undergoes partial activation before S phase, reaching in S phase a level that is sufficient for G2-M phase transition. S phase entry is not inhibited by this level of cyclin B-dependent kinase activity. Inhibition of DNA replication by aphidicolin suppresses nuclear envelope breakdown, yet it does not prevent the microtubule array from being converted from its interphasic to its mitotic state. Moreover, mitotic cytoplasmic events occur at the same time in control and aphidicolin-treated embryos. Thus unreplicated DNA only prevents mitotic nuclear, not cyto plasmic, events from occurring prematurely. These results together show that the inhibition of cyclin B-cdc2 kinase activation is probably not the only mechanism that prevents mitotic nuclear events from occurring as long as DNA replication has not been completed. In contrast, cyto plasmic mitotic events seem to be controlled by a timing mechanism independent of DNA replication, set up at fer tilization, that prevents premature opening of a window for mitotic events.</jats:p>