Importin α and vNEBD Control Meiotic Spindle Disassembly in Fission Yeast

Abstract

Summary: In metazoans, the nuclear envelope (NE) breakdown (NEBD) occurs during “open” mitosis and meiosis. In the fission yeast Schizosaccharomyces pombe, the mitosis and the first meiotic division (MI) are “closed,” during which the NE is maintained. Intriguingly, during the second meiotic division (MII), the NE is also maintained, but nuclear and cytoplasmic molecules are mixed similarly to open mitosis, a phenomenon of unknown biological significance called “virtual” NEBD (vNEBD). Here, we show that importin-α-dependent nucleocytoplasmic transport regulates spindle disassembly late in anaphase B at MI, as previously reported for mitosis. At MII, however, spindle dissolution is triggered by vNEBD early in anaphase B, a mechanism that short-circuits the nucleocytoplasmic transport system. We demonstrate that the sequential action of these two spindle disassembly systems regulates the spatiotemporal order and ploidy of the meiotic products. : vNEBD is a phenomenon described in the fission yeast second meiotic division (MII), which resembles the nuclear envelope breakdown that characterizes the mitotic phase in eukaryotes. Flor-Parra et al. describe a biological role of vNEBD in spindle disassembly. Keywords: spindle disassembly, meiosis, nuclear envelope, vNEBD, Imp1, nucleocytoplasmic transport, fission yeast, Schizosaccharomyces pombe