Interorganelle interactions and inheritance patterns of nuclei and vacuoles in budding yeast meiosis

Many of the mechanisms by which organelles are inherited by spores during meiosis are not well understood. Dramatic chromosome motion and bouquet formation are evolutionarily conserved characteristics of meiotic chromosomes. The budding yeast bouquet genes (NDJ1, MPS3, CSM4) mediate these movements via telomere attachment to the nuclear envelope (NE). Here, we report that during meiosis the NE is in direct contact with vacuoles via nucleus-vacuole junctions (NVJs). We show that in meiosis NVJs are assembled through the interaction of the outer NE-protein Nvj1 and the vacuolar membrane protein Vac8. Notably, NVJs function as diffusion barriers that exclude the nuclear pore complexes, the bouquet protein Mps3 and NE-tethered telomeres from the outer nuclear membrane and nuclear ER, resulting in distorted NEs during early meiosis. An increase in NVJ area resulting from Nvj1-GFP overexpression produced a moderate bouquet mutant-like phenotype in wild-type cells. NVJs, as the vacuolar contact sites of the nucleus, were found to undergo scission alongside the NE during meiotic nuclear division. The zygotic NE and NVJs were partly segregated into 4 spores. Lastly, new NVJs were also revealed to be synthesized de novo to rejoin the zygotic NE with the newly synthesized vacuoles in the mature spores. In conclusion, our results revealed that budding yeast nuclei and vacuoles exhibit dynamic interorganelle interactions and different inheritance patterns in meiosis, and also suggested that nvj1Δ mutant cells may be useful to resolve the technical challenges pertaining to the isolation of intact nuclei for the biochemical study of meiotic nuclear proteins.减数分裂过程中细胞器经孢子传递的诸多机制目前仍未被充分阐明。染色体剧烈运动与花束形成是减数分裂染色体在进化上保守的特征。出芽酵母的花束相关基因（NDJ1、MPS3、CSM4）通过端粒锚定至核被膜（NE）介导上述过程。本研究发现，减数分裂期间核被膜可通过核-液泡连接（NVJs）与液泡直接接触。我们证实，减数分裂中NVJs的组装依赖于核被膜外膜蛋白Nvj1与液泡膜蛋白Vac8的相互作用。值得注意的是，NVJs可作为扩散屏障，将核孔复合物、花束蛋白Mps3以及锚定在核被膜的端粒排除在外，使其无法进入核外膜与核内质网（ER），进而导致减数分裂早期核被膜形态畸变。过表达Nvj1-GFP以增加NVJ面积，可在野生型细胞中诱导出中等程度的花束突变体表型。作为细胞核与液泡的接触位点，NVJs可在减数分裂核分裂过程中伴随核被膜发生断裂分离。合子核被膜与NVJs可部分分离进入4个孢子中。最后，我们还发现新的NVJs可从头合成，将合子核被膜与成熟孢子中新生成的液泡重新连接。综上，本研究结果揭示出芽酵母的细胞核与液泡在减数分裂过程中存在动态的细胞器间相互作用，并呈现不同的遗传模式；同时提示nvj1Δ突变体细胞可用于解决减数分裂核蛋白生化研究中分离完整细胞核的技术难题。