Nuclear Export of Cyclin B Mediated by the Nup62 Complex is Required for Meiotic Initiation in Drosophila Males

Background: The central channel of the nuclear pore complex (NPC) plays an important role in the selective transport of proteins between the nucleus and cytoplasm. Previous studies have demonstrated that depletion of the Nup62 complex, constructing the nuclear pore channel in premeiotic Drosophila cells, resulted in absence of meiotic cells. We attempted understanding the mechanism underlying the cell cycle arrest before meiosis. Methods: We induced dsRNAs against the nucleoporin mRNAs using the Gal4/UAS system in Drosophila. Results: The cell cycle of the Nup62-depleted cells was arrested before meiosis without CDK1 activation. Ectopic over-expression of CycB, but not constitutively active CDK1, resulted in partial rescue from the arrest. CycB accumulated precociously in the nuclei of Nup62-depleted cells and cells depleted of exportin (encoded by emb). Protein complexes containing CycB, Emb, and Nup62 complex components were observed in premeiotic spermatocytes. CycB, which had precociously migrated into the nucleus, was associated with Emb, and the complex was transported back to the cytoplasm through the central channel, interacting with the Nup62 complex. Conclusion: We proposed that CycB is exported with Emb through the channel interacting with the Nup62 complex before initiation of meiosis. The nuclear export ensures production of active CycB-CDK1 in the cytoplasm.