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

Abstract

Cyclin B is an important regulator of the cell cycle G2 to M phase transition. The silkworm genomic database shows that there are two Cyclin B genes in the silkworm (Bombyx mori), BmCyclin B and BmCyclin B3. Using silkworm EST data, the cyclin B3 (EU074796) gene was cloned. Its complete cDNA was 1665 bp with an ORF of 1536 bp derived from seven exons and six introns. The BmCyclin B3 gene encodes 511 amino acids, and the predicted molecular weight is 57.8 kD with an isoelectric point of 9.18. The protein contains one protein damage box and two cyclin boxes. RNA interference-mediated reduction of BmCyclin B and BmCyclin B3 expression induced cell cycle arrest in G2 or M phase in BmN-SWU1 cells, thus inhibiting cell proliferation. These results suggest that BmCyclin B and BmCyclin B3 are necessary for completing the cell cycle in silkworm cells. Cyclin B is a mitotic cyclin protein. It is expressed and gradually accumulates from the G1 late phase, reaches a maximum level at the G2 late phase, continues to be maintained to the middle of metaphase, and is then immediately degraded. The accumulation and degradation of cyclin B plays a critical role in mitosis and karyokinesis [1][2][3]. A cyclin box and conserved cdk-binding domains are present in all cyclins. A-and B-type cyclins possess a destruction box, a motif containing ~nine amino acids required to target cyclins to ubiquitin-dependent degradation during mitosis [46]. Cyclin B genes can be placed in two evolutionary branches, the B-type and B3-type cyclin families [7]. B-type cyclins are present in both yeast and higher eukaryotes. Although a single Cyclin B gene has been found in invertebrate species, a pair of very closely related B-type cyclins is present in vertebrates. These vertebrate cyclin B1 and B2 proteins differ in their subcellular localization [8,9]. The Cyclin B3-type family is conserved in metazoans and has a similarity of 39%-46% in the cyclin protein box [1012].Both cyclin B and cyclin B3 have a conserved amino acid sequence, which is known as the cell cyclin box. 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].The silkworm undergoes complete metamorphosis, and is a good model organism of Lepidoptera. A full understanding of its cell-cycle regulation mechanism would improve

Genome-Wide Identification, Expression Profiling, and Characterization of Cyclin-like Genes Reveal Their Role in the Fertility of the Diamondback Moth

“…RT-qPCR was performed to confirm transcriptomic expression profilings of cyclin-like genes at different stages and tissues. Based on previous reports in B. mori and D. melanogaster [ 12 , 15 , 16 , 19 ], six ( PxCyc D3 , PxCyc B1 , PxCyc G1 , PxCyc A2 , PxCyc B3 , PxCyc D , PxCyc C2 ) genes were selected. PxCyc D3 and PxCyc G1 exhibited significantly high relative expressions in adult females, followed by adult males and eggs.…”

“…Furthermore, the DmCyc G negatively regulates the cell growth and development process since overproduction of DmCyc G results in a limited number of cells, while a lack of DmCyc G results in a large number of cells [ 18 ]. In Bombyx mori , the suppression of BmCyclin B and BmCyclin B3 expression through RNAi causes cell cycle detention at the G2 and M phases in the BmN cell line, reducing cell proliferation, which indicates that BmCyclin B and BmCyclin B3 are required for completion of the cell cycle in the BmN cell line [ 19 ]. Previous reports in D. melanogaster and B. mori suggest that cyclin-like genes are not only involved in cell cycle regulations but play significant roles in growth, development, and reproduction.…”

Morphological characterization and molecular mapping of an irradiation‐induced Speckled mutant in the silkworm, Bombyx mori

“…melanogaster , PEX1 mutants are lethal at different developmental stages (Deak et al ., ; Mast et al ., ). BGIBMGA003777 , another candidate gene, BmCyclin B3 (BmCycB3) , is required for cell cycle progression in the silkworm (Pan et al ., ). The identification of CycB3 in chicken ( Gallus gallus ), the nematode Caenorhabditis elegans and D .…”

“…In D. melanogaster, PEX1 mutants are lethal at different developmental stages (Deak et al, 1997;Mast et al, 2011). BGIBMGA003777, another candidate gene, BmCyclin B3 (BmCycB3), is required for cell cycle progression in the silkworm (Pan et al, 2013). The identification of CycB3 in chicken (Gallus gallus), the nematode Caenorhabditis elegans and D. melanogaster revealed that CycB3 is conserved during the evolution of higher eukaryotes (Gallant & Nigg, 1994;Kreutzer et al, 1995;Sigrist et al, 1995).…”

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

“…The BmCyclin B was necessary to complete the cell cycle in BmN cells and had revealed mitotic cell divisions function in silk gland development of embryogenesis in B . mori [ 30 , 31 ]. The Bmcyclin B mRNA, abundant in matured eggs, began to degrade sharply just after oviposition, which suggested that the penetration of sperm triggered the degradation of maternal Bmcyclin B mRNA in the first meiosis [ 25 ].…”