CLONING OF A B-TYPE CYCLIN HOMOLOG FROM BOMBYX-MORI AND THE PROFILES OF ITS MESSENGER-RNA LEVEL IN NONDIAPAUSE AND DIAPAUSE EGGS

To understand the molecular mechanism of G(2)-arrest of cell division in embryonic diapause of the silkworm, Bombyx mori, we have cloned a c DNA encoding a Bombyx homolog of B-type cyclin. Levels of Bm cyclin-B mRNA were examined during diapause stage and early embryogenesis. The results showed that this G(2)-arrest did not always correspond to lowe red transcriptional levels of cyclin-B, and that the mRNA accumulated in oocytes began to be degraded during the first hour after ovipositio n, i.e. the first meiosis, suggesting that the penetration of sperm tr iggered the degradation of maternal cyclin-B mRNA.