Department of Molecular Biology, Princeton University, Princeton, NJ 08544, USA.
Mol Biol Cell. 2012 Apr;23(7):1208-18. doi: 10.1091/mbc.E11-08-0723. Epub 2012 Feb 9.
Cell fusion is the key event of fertilization that gives rise to the diploid zygote and is a nearly universal aspect of eukaryotic biology. In the yeast Saccharomyces cerevisiae, several mutants have been identified that are defective for cell fusion, and yet the molecular mechanism of this process remains obscure. One obstacle has been that genetic screens have mainly focused on mating-specific factors, whereas the process likely involves housekeeping proteins as well. Here we implicate Cdc42p, an essential protein with roles in multiple aspects of morphogenesis, as a core component of the yeast cell fusion pathway. We identify a point mutant in the Rho-insert domain of CDC42, called cdc42-138, which is specifically defective in cell fusion. The cell fusion defect is not a secondary consequence of ineffective signaling or polarization. Genetic and morphological data show that Cdc42p acts at a late stage in cell fusion in concert with a key cell fusion regulator, Fus2p, which contains a Dbl-homology domain. We find that Fus2p binds specifically with activated Cdc42p, and binding is blocked by the cdc42-138 mutation. Thus, in addition to signaling and morphogenetic roles in mating, Cdc42p plays a role late in cell fusion via activation of Fus2p.
细胞融合是受精的关键事件，它产生了二倍体合子，是真核生物生物学的一个几乎普遍的方面。在酵母酿酒酵母中，已经鉴定出几种突变体，它们在细胞融合方面有缺陷，但这个过程的分子机制仍然不清楚。一个障碍是遗传筛选主要集中在交配特异性因素上，而这个过程可能还涉及管家蛋白。在这里，我们将参与形态发生的多个方面的必需蛋白 Cdc42p 牵连为酵母细胞融合途径的核心组成部分。我们鉴定出 Rho-插入结构域的 CDC42 中的一个点突变体，称为 cdc42-138，它在细胞融合中特异性缺陷。细胞融合缺陷不是信号转导或极化无效的次要后果。遗传和形态学数据表明，Cdc42p 与关键的细胞融合调节剂 Fus2p 一起在细胞融合的晚期发挥作用，后者包含一个 Dbl 同源结构域。我们发现 Fus2p 特异性地与激活的 Cdc42p 结合，而 cdc42-138 突变会阻断结合。因此，除了在交配中具有信号转导和形态发生作用外，Cdc42p 通过激活 Fus2p 在细胞融合的晚期发挥作用。
