RELEASE OF METAPHASE ARREST BY PARTIAL INHIBITION OF PROTEIN-SYNTHESIS IN BLUE MUSSEL OOCYTES

In the blue mussel Mytilus edulis, shed oocytes are arrested at metaphase I of meiosis until fertilization. In this study, the mechanisms involved for maintaining the oocytes in metaphase were investigated. Analysis of 35‐methionine‐labelled proteins separated by 1D SDS‐PAGE reveals that two protein bands of apparent MW of 50 and 54 kDa periodically appear and disappear during meiotic and mitotic cycles. Moreover, the 50 kDa protein band, clearly detected in unfertilized oocytes, is seen to disappear within 15 min after fertilization. Unfertilized or fertilized oocytes treated with emetine have a protein synthesis rate reduced to less than half the normal rate observed in the untreated cells. Addition of this protein synthesis inhibitor at various times after fertilization inhibits the normal progression through the cell cycles. However, emetine added to unfertilized oocytes induces the completion of first meiotic maturation, polar body extrusion, and the decondensation of chromosomes which form one or two large pronuclei. This process is accompanied by DNA synthesis, and is preceded by the early disappearance of the 50 kDa protein band, seen to cycle after fertilization. These results indicate that metaphase arrest, in mussel oocytes, requires the continuous synthesis of short‐lived proteins, the destruction of which is sufficient to induce meiosis resumption followed by DNA synthesis. Copyright © 1990 Wiley‐Liss, Inc., A Wiley Company