Changing profiles of mRNA levels of Cdc2 and a novel Cdc2-related kinase (Bcdrk) in relation to ovarian development and embryonic diapause of Bombyx mori

To reveal the regulatory mechanism of G₂-arrest of cell division in embryos at the diapause stage of the silkworm, Bombyx mori, the profiles for mRNA levels of a Bombyx homologue of Cdc2 and a novel Bombyx Cdc2-related kinase (Bcdrk) were examined during ovarian development, early embryogenesis and diapause stage, using a reverse transcription/polymerase chain reaction system. Although levels of mRNAs for Cdc2 and Bcdrk were higher in paired ovaries during the early pupal stage, the levels decreased at the middle stage. Both mRNAs became abundant in oocytes toward the maturation. From oviposition up to the stage just before cellular blastoderm, high levels of both mRNAs were maintained, and thereafter the levels declined. In diapausing eggs kept at 25°C, mRNA levels remained lower, whilst in diapause eggs exposed to 5°C from 2 days after oviposition, in order to break diapause, relatively higher levels of mRNAs were found. In eggs treated with HCl to avert the entry into diapause, mRNA levels per egg for Cdc2 and Bcdrk increased 2 days after treatment, although these increases were not observed in terms of mRNA levels per actin mRNA. These results were discussed in relation to the activities of nuclear/cellular division in ovaries and eggs. In addition, Bcdrk was suggested to play a role similar to that in Bombyx Cdc2 kinase, because the changing profile for levels of Bcdrk mRNA resembled that for cdc2 mRNA.