Jones Laura A, Sudbery Peter E
Department of Molecular Biology and Biotechnology, University of Sheffield, Western Bank, United Kingdom.
Eukaryot Cell. 2010 Oct;9(10):1455-65. doi: 10.1128/EC.00109-10. Epub 2010 Aug 6.
During the extreme polarized growth of fungal hyphae, secretory vesicles are thought to accumulate in a subapical region called the Spitzenkörper. The human fungal pathogen Candida albicans can grow in a budding yeast or hyphal form. When it grows as hyphae, Mlc1 accumulates in a subapical spot suggestive of a Spitzenkörper-like structure, while the polarisome components Spa2 and Bud6 localize to a surface crescent. Here we show that the vesicle-associated protein Sec4 also localizes to a spot, confirming that secretory vesicles accumulate in the putative C. albicans Spitzenkörper. In contrast, exocyst components localize to a surface crescent. Using a combination of fluorescence recovery after photobleaching (FRAP) and fluorescence loss in photobleaching (FLIP) experiments and cytochalasin A to disrupt actin cables, we showed that Spitzenkörper-located proteins are highly dynamic. In contrast, exocyst and polarisome components are stably located at the cell surface. It is thought that in Saccharomyces cerevisiae exocyst components are transported to the cell surface on secretory vesicles along actin cables. If each vesicle carried its own complement of exocyst components, then it would be expected that exocyst components would be as dynamic as Sec4 and would have the same pattern of localization. This is not what we observe in C. albicans. We propose a model in which a stream of vesicles arrives at the tip and accumulates in the Spitzenkörper before onward delivery to the plasma membrane mediated by exocyst and polarisome components that are more stable residents of the cell surface.
在真菌菌丝的极端极性生长过程中，分泌囊泡被认为会在一个称为“Spitzenkörper”的亚顶端区域积累。人类真菌病原体白色念珠菌可以以出芽酵母或菌丝形式生长。当它以菌丝形式生长时，Mlc1会在一个亚顶端斑点积累，提示存在类似Spitzenkörper的结构，而极化体成分Spa2和Bud6则定位于表面新月形区域。在这里我们表明，囊泡相关蛋白Sec4也定位于一个斑点，证实分泌囊泡在假定的白色念珠菌Spitzenkörper中积累。相比之下，外泌体成分定位于表面新月形区域。通过结合光漂白后荧光恢复（FRAP）和光漂白荧光损失（FLIP）实验以及细胞松弛素A破坏肌动蛋白电缆，我们表明位于Spitzenkörper的蛋白具有高度动态性。相比之下，外泌体和极化体成分稳定地位于细胞表面。据认为，在酿酒酵母中，外泌体成分沿着肌动蛋白电缆通过分泌囊泡运输到细胞表面。如果每个囊泡都携带自己的外泌体成分补充，那么可以预期外泌体成分会像Sec4一样动态，并具有相同的定位模式。但这并不是我们在白色念珠菌中观察到的情况。我们提出了一个模型，即囊泡流到达顶端并在Spitzenkörper中积累，然后由更稳定地驻留在细胞表面的外泌体和极化体成分介导向前递送至质膜。
