West C M, Erdos G W
Dept. of Anatomy and Cell Biology, University of Florida College of Medicine, Gainesville 32610.
Dev Genet. 1990;11(5-6):492-506. doi: 10.1002/dvg.1020110526.
The spore coat forms as a rigid extracellular wall around each spore cell during culmination. Coats purified from germinated spores contain multiple protein species and an approximately equal mass of polysaccharide, consisting mostly of cellulose and a galactose/N-acetylgalactosamine polysaccharide (GPS). All but the cellulose are prepackaged during prespore cell differentiation in a regulated secretory compartment, the prespore vesicle. The morphology of this compartment resembles an anastomosing, tubular network rather than a spherical vesicle. The molecules of the prespore vesicles are not uniformly mixed but are segregated into partially overlapping domains. Although lysosomal enzymes have been found in the prespore vesicle, this compartment does not function as a lysosome because it is not acidic, and a common antigen associated with acid hydrolases is found in another, acidic vesicle population. All the prespore vesicle profiles disappear at the time of appearance of their contents outside of the cell; this constitutes an early stage in spore coat formation, which can be detected both by microscopy and flow cytometry. As an electron-dense layer, the future outer layer of the coat, condenses, cellulose can be found and is located immediately beneath this outer layer. Certain proteins and the GPS become associated with either the outer or inner layers surrounding this middle cellulose layer. Assembly of the inner and outer layers occurs in part from a pool of glycoproteins that is shared between spores, and unincorporated molecules loosely reside in the interspore matrix, a location from which they can be easily washed away. When the glycosylation of several major protein species is disrupted by mutation, the coat is assembled, but differences are found in its porosity and the extractibility of certain proteins. In addition, the retention or loss of proteolytic fragments in the mutants indicates regions of spore coat proteins that are required for association with the coat. Comparative examination of the macrocyst demonstrates that patterns of molecular distributions are not conserved between the macrocyst and spore coats. Thus spore coat assembly is characterized by highly specific intermolecular interactions, leading to saturable associations of individual glycoproteins with specific layers and the exclusion of excess copies to the interspore space.
在发育成熟过程中，孢子外壁在每个孢子细胞周围形成一层坚硬的胞外壁。从萌发孢子中纯化得到的外壁含有多种蛋白质以及质量大致相等的多糖，多糖主要由纤维素和一种半乳糖/N - 乙酰半乳糖胺多糖（GPS）组成。除纤维素外，所有成分在芽孢前体细胞分化过程中，在一个受调控的分泌区室——芽孢前体小泡中预先包装。这个区室的形态类似于一个相互连接的管状网络，而不是球形小泡。芽孢前体小泡中的分子并非均匀混合，而是被分隔到部分重叠的区域。尽管在芽孢前体小泡中发现了溶酶体酶，但这个区室并不发挥溶酶体的功能，因为它不是酸性的，并且与酸性水解酶相关的一种常见抗原存在于另一群酸性小泡中。所有芽孢前体小泡的轮廓在其内容物出现在细胞外时消失；这构成了孢子外壁形成的早期阶段，可通过显微镜检查和流式细胞术检测到。随着作为外壁未来外层的电子致密层凝聚，可以发现纤维素并位于该外层之下。某些蛋白质和GPS与围绕中间纤维素层的外层或内层相关联。内层和外层的组装部分源于孢子间共享的一组糖蛋白，未结合的分子松散地存在于孢子间基质中，它们很容易从这个位置被冲走。当几种主要蛋白质的糖基化因突变而被破坏时，外壁仍能组装，但在其孔隙率和某些蛋白质的可提取性方面存在差异。此外，突变体中蛋白水解片段的保留或丢失表明了孢子外壁蛋白质与外壁结合所需的区域。对大囊泡的比较研究表明，大囊泡和孢子外壁之间的分子分布模式并不保守。因此，孢子外壁的组装具有高度特异性的分子间相互作用的特征，导致单个糖蛋白与特定层的饱和结合，并将多余的拷贝排除到孢子间空间。
