Zheng Xin-De, Wang Yan-Ming, Wang Yue
Microbial Collection and Screening Laboratory, Institute of Molecular and Cell Biology, Singapore 117609.
Mol Microbiol. 2003 Sep;49(5):1391-405. doi: 10.1046/j.1365-2958.2003.03646.x.
Saccharomyces cerevisiae Spa2p is a component of polarisome that controls cell polarity. Here, we have characterized the role of its homologue, CaSpa2p, in the polarized growth in Candida albicans. During yeast growth, GFP-tagged CaSpa2p localized to distinct growth sites in a cell cycle-dependent manner, while during hyphal growth it persistently localized to hyphal tips throughout the cell cycle. Persistent tip localization of the protein was also observed in Catup1Delta and Canrg1Delta, mutants constitutive for filamentous growth. Caspa2Delta exhibited defects in polarity establishment and maintenance, such as random budding and failure to confine growth to a small surface area leading to round cells with wide, elongated bud necks and markedly thicker hyphae. It was also defective in nuclear positioning, presumably a result of defective interactions between cytoplasmic microtubules with certain polarity determinants. The highly conserved SHD-I and SHD-V domains were found to be important and responsible for different aspects of CaSpa2p function. Caspa2Delta exhibited no virulence in the mouse systemic candidiasis model. Because of the existence of distinct growth forms and the easy control of the switch between them in vitro, C. albicans may serve as a useful model in cell polarity research.
酿酒酵母Spa2p是控制细胞极性的极化体的一个组成部分。在此，我们已阐明其同源物CaSpa2p在白色念珠菌极性生长中的作用。在酵母生长期间，绿色荧光蛋白标记的CaSpa2p以细胞周期依赖性方式定位于不同的生长位点，而在菌丝生长期间，它在整个细胞周期中持续定位于菌丝尖端。在丝状生长组成型突变体Catup1Delta和Canrg1Delta中也观察到该蛋白持续定位于尖端。CaSpa2Delta在极性建立和维持方面表现出缺陷，如随机出芽以及无法将生长限制在小表面积上，导致细胞呈圆形，芽颈宽且拉长，菌丝明显变粗。它在核定位方面也存在缺陷，推测这是细胞质微管与某些极性决定因素之间相互作用缺陷的结果。发现高度保守的SHD-I和SHD-V结构域很重要，并负责CaSpa2p功能的不同方面。CaSpa2Delta在小鼠系统性念珠菌病模型中无致病性。由于存在不同的生长形式且在体外易于控制它们之间的转换，白色念珠菌可能是细胞极性研究中的一个有用模型。
