Institute of Biochemistry, ETH Zurich, Otto-Stern-Weg 3, 8093 Zurich, Switzerland; Wissenschaftskolleg zu Berlin, Institute for Advanced Study, Wallotstrasse 19, 14193 Berlin, Germany.
Institute of Biochemistry, ETH Zurich, Otto-Stern-Weg 3, 8093 Zurich, Switzerland; Randall Division of Cell and Molecular Biophysics, King's College London, London SE1 1UL, UK.
Curr Biol. 2017 Mar 20;27(6):773-783. doi: 10.1016/j.cub.2017.01.069. Epub 2017 Mar 2.
In order to produce rejuvenated daughters, dividing budding yeast cells confine aging factors, including protein aggregates, to the aging mother cell. The asymmetric inheritance of these protein deposits is mediated by organelle and cytoskeletal attachment and by cell geometry. Yet it remains unclear how deposit formation is restricted to the aging lineage. Here, we show that selective membrane anchoring and the compartmentalization of the endoplasmic reticulum (ER) membrane confine protein deposit formation to aging cells during division. Supporting the idea that the age-dependent deposit forms through coalescence of smaller aggregates, two deposits rapidly merged when placed in the same cell by cell-cell fusion. The deposits localized to the ER membrane, primarily to the nuclear envelope (NE). Strikingly, weakening the diffusion barriers that separate the ER membrane into mother and bud compartments caused premature formation of deposits in the daughter cells. Detachment of the Hsp40 protein Ydj1 from the ER membrane elicited a similar phenotype, suggesting that the diffusion barriers and farnesylated Ydj1 functioned together to confine protein deposit formation to mother cells during division. Accordingly, fluorescence correlation spectroscopy measurements in dividing cells indicated that a slow-diffusing, possibly client-bound Ydj1 fraction was asymmetrically enriched in the mother compartment. This asymmetric distribution depended on Ydj1 farnesylation and intact diffusion barriers. Taking these findings together, we propose that ER-anchored Ydj1 binds deposit precursors and prevents them from spreading into daughter cells during division by subjecting them to the ER diffusion barriers. This ensures that the coalescence of precursors into a single deposit is restricted to the aging lineage.
为了产生年轻的女儿细胞，酵母细胞的有丝分裂将衰老因子（包括蛋白质聚集体）限制在衰老的母细胞中。这些蛋白质沉积物的不对称遗传是通过细胞器和细胞骨架的附着以及细胞形状来介导的。然而，沉积物的形成如何被限制在衰老谱系中仍然不清楚。在这里，我们表明选择性的膜锚定和内质网（ER）膜的区室化将蛋白质沉积物的形成限制在有丝分裂过程中的衰老细胞中。支持这样一种观点，即年龄依赖性沉积物是通过较小聚集体的融合形成的，两个沉积物在通过细胞融合放置在同一细胞中时迅速融合。沉积物定位于 ER 膜，主要位于核膜（NE）。引人注目的是，削弱将 ER 膜分隔成母细胞和芽细胞隔室的扩散屏障会导致子细胞中过早形成沉积物。Hsp40 蛋白 Ydj1 与 ER 膜的分离引起了类似的表型，这表明扩散屏障和法尼基化的 Ydj1 共同作用将蛋白质沉积物的形成限制在有丝分裂过程中的母细胞中。因此，在有丝分裂细胞中的荧光相关光谱测量表明，一种扩散缓慢的、可能与客户结合的 Ydj1 部分在母细胞隔室中不对称地富集。这种不对称分布依赖于 Ydj1 的法尼基化和完整的扩散屏障。综合这些发现，我们提出 ER 锚定的 Ydj1 结合沉积物前体，并通过将其置于 ER 扩散屏障中来防止它们在有丝分裂过程中扩散到子细胞中。这确保了前体的融合成一个单一的沉积物被限制在衰老的谱系中。
