Abstract
ABSTRACTIn higher eukaryotes, nuclear envelope (NE) disassembly allows chromatin to condense and spindle microtubules to access kinetochores. The nuclear lamina, which strengthens the NE, is composed of a polymer meshwork made of A- and B-type lamins. We found that the B-type lamin (Lam) is not fully disassembled and continues to localize along the spindle envelope structure during Drosophila male meiosis I, while the A-type lamin (LamC) is completely dispersed throughout the cytoplasm. Among the nuclear pore complex proteins, Nup107 co-localized with Lam during this meiotic division. Surprisingly, Lam depletion resulted in a higher frequency of cytokinesis failure in male meiosis. We also observed the similar meiotic phenotype in Nup107-depleted cells. Abnormal localization of Lam was found in the Nup-depleted cells at premeiotic and meiotic stages. The central spindle microtubules became abnormal and recruitment of a contractile ring component to the cleavage sites was disrupted in Lam-depleted cells and Nup107-depleted cells. Therefore, we speculate that both proteins are required for a reinforcement of the spindle envelope, which supports the formation of central spindle microtubules essential for cytokinesis in Drosophila male meiosis.
Highlights
The nuclear envelope (NE) is a characteristic structure of eukaryotic cells and consists of two closely juxtaposed membranes, termed the outer and inner nuclear membranes (D’Angelo and Hetzer, 2008; Hetzer, 2010; Hetzer et al, 2005; Tran and Wente, 2006)
Lam depletion abolishes formation of central spindle microtubules To understand why the depletion of Lam eventually resulted in a failure of cytokinesis in male meiosis, we examined whether the microtubule structure constructed at later stages of meiotic divisions was affected in Lam-depleted cells
We investigated whether a B-type lamin (Lam), an A-type lamin (LamC) and nuclear pore complex components play a certain role in Drosophila male meiotic divisions
Summary
The nuclear envelope (NE) is a characteristic structure of eukaryotic cells and consists of two closely juxtaposed membranes, termed the outer and inner nuclear membranes (D’Angelo and Hetzer, 2008; Hetzer, 2010; Hetzer et al, 2005; Tran and Wente, 2006). We compared this with the MLC distribution in abnormal cells contained in a telophase I cyst depleted of Lam. The MLC ring failed to be constructed at a proper position in one such telophase I-like cell possessing fewer amounts of central spindle microtubules, the chromosomes had fully segregated (Fig. 5B). We obtained evidences that Lam is localized on the spindle envelope in meiosis I and that its depletion affects construction of this envelope structure, the formation of central spindle microtubules and the contractile ring formation
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