Cloning of a B-type cyclin homolog from Bombyx mori and the profiles of its mRNA level in non-diapause and diapause eggs

Abstract

To understand the molecular mechanism of G2-arrest of cell division in embryonic diapause of the silkworm, Bombyx mori, we have cloned a cDNA 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 G2-arrest did not always correspond to lowered transcriptional levels of cyclin-B, and that the mRNA accumulated in oocytes began to be degraded during the first hour after oviposition, i.e. the first meiosis, suggesting that the penetration of sperm triggered the degradation of maternal cyclin-B mRNA.

The 20-hydroxyecdysone-induced cellular arrest in G2 phase is preceded by an inhibition of cyclin expression

“…We have cloned two partial cDNAs, PcycB and PcycA, encoding Plodia cyclins A and B, respectively. The PcycA and PcycB probes revealed two transcripts whose sizes, 3 and 2.5 kb, were close to those of cyclin A and B mRNAs of Drosophila melanogaster (Lehner and O'Farrell, 1989;Lehner and O'Farrell, 1990) and to that of cyclin B mRNA of Bombyx mori (Takahashi et al, 1996).…”

“…The 333 amino acid region of PcycB presented 67.7% identity with Bombyx mori cyclin B (Takahashi et al, 1996), 24.8% with Drosophila melanogaster cyclin B (Whitfield et al, 1990) and only 18% with Drosophila melanogaster cyclin A (Lehner and O'Farrell, 1990) and 20% with PcycA (Fig. 4).…”

Identifying potential maternal genes of Bombyx mori using digital gene expression profiling

“…In this study, the expression levels of most OMGs decreased along points-in-time, such as Clusters 1 and 3. BGIBMGA003747, one of the OMDEGs, is the homologous gene of Dmcyclin B (the maternal gene) in Drosophila melanogaster and has been previously cloned from silkworm eggs [ 25 ]. The accumulation and degradation of cyclin B played a critical role in mitosis and karyokinesis [ 26 – 29 ].…”

BmCyclin B and BmCyclin B3 are required for cell cycle progression in the silkworm, Bombyx mori

“…BmCyclin B3 genes PCR primers for BmCyclin B were designed based on the coding sequences of the BmCyclin B genes [13]. The sequences of the primers were as follows: forward primer (5′-GGAGACAACAACAGCCCTT-3′) and reverse primer (5′-AAACAAAATCGCCAACATC-3′).…”

“…This domain can combine with CDKI to form complexes, which, when activated by CDK-activating kinase, drives cells from the G2 phase limit point to the M phase. The Cyclin B gene has previously been cloned from silkworm eggs [13]. The expression of Cyclin B was reduced in silkworm ovarian BmN cells, 24 h after infection by nucleopolyhedrovirus (BmNPV), and the cells then arrested in G2/M phase [14].…”