Morishita Masayo, Engebrecht Joanne
Section of Molecular and Cellular Biology, University of California, Davis, California 95616, USA.
Genetics. 2005 Aug;170(4):1561-74. doi: 10.1534/genetics.105.041459. Epub 2005 Jun 8.
During sporulation in Saccharomyces cerevisiae, vesicles transported to the vicinity of spindle pole bodies are fused to each other to generate bilayered prospore membranes (PSMs). PSMs encapsulate the haploid nuclei that arise from the meiotic divisions and serve as platforms for spore wall deposition. Membrane trafficking plays an important role in supplying vesicles for these processes. The endocytosis-deficient mutant, end3Delta, sporulated poorly and the spores produced lost resistance to ether vapor, suggesting that END3-mediated endocytosis is important for sporulation. End3p-GFP localized to cell and spore peripheries in vegetative and sporulating cells and colocalized with actin structures. Correspondingly, the actin cytoskeleton appeared aberrant during sporulation in end3Delta. Analysis of meiosis in end3Delta mutants revealed that the meiotic divisions occurred with wild-type kinetics. Furthermore, PSMs were assembled normally. However, the levels of proteins required for spore wall synthesis and components of the spore wall layers at spores were reduced, indicating that end3Delta mutants are defective in spore wall synthesis. Thus, END3-mediated endocytosis is important for spore wall formation. Additionally, cytological analyses suggest that trafficking between the plasma membrane and PSMs is important earlier during sporulation.
在酿酒酵母的孢子形成过程中，运输到纺锤极体附近的囊泡相互融合，形成双层的前孢子膜（PSM）。PSM包裹减数分裂产生的单倍体细胞核，并作为孢子壁沉积的平台。膜运输在为这些过程提供囊泡方面发挥着重要作用。内吞作用缺陷型突变体end3Δ孢子形成能力差，产生的孢子对乙醚蒸汽失去抗性，这表明END3介导的内吞作用对孢子形成很重要。End3p-GFP定位于营养细胞和孢子形成细胞的细胞及孢子周边，并与肌动蛋白结构共定位。相应地，在end3Δ的孢子形成过程中，肌动蛋白细胞骨架出现异常。对end3Δ突变体减数分裂的分析表明，减数分裂以野生型动力学进行。此外，PSM正常组装。然而，孢子壁合成所需蛋白质的水平以及孢子壁层的成分在孢子处减少，表明end3Δ突变体在孢子壁合成方面存在缺陷。因此，END3介导的内吞作用对孢子壁形成很重要。此外，细胞学分析表明，质膜和PSM之间的运输在孢子形成早期更为重要。
