All cells establish and maintain an axis of polarity that is critical for cell shape and progression through the cell cycle. A well-studied example of polarity establishment is bud emergence in the yeast Saccharomyces cerevisiae, which is controlled by the Rho GTPase Cdc42p. The prevailing view of bud emergence does not account for regulation by extrinsic cues. Here, we show that the filamentous growth mitogen activated protein kinase (fMAPK) pathway regulates bud emergence under nutrient-limiting conditions. The fMAPK pathway regulated the expression of polarity targets including the gene encoding a direct effector of Cdc42p, Gic2p. The fMAPK pathway also stimulated GTP-Cdc42p levels, which is a critical determinant of polarity establishment. The fMAPK pathway activity was spatially restricted to bud sites and active during the period of the cell cycle leading up to bud emergence. Time-lapse fluorescence microscopy showed that the fMAPK pathway stimulated the rate of bud emergence during filamentous growth. Unregulated activation of the fMAPK pathway induced multiple rounds of symmetry breaking inside the growing bud. Collectively, our findings identify a new regulatory aspect of bud emergence that sensitizes this essential cellular process to external cues.

中文翻译：

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酿酒酵母中分化型 MAPK 途径对内在极性建立的调节。

所有细胞都建立并维持极性轴，这对于细胞形状和细胞周期的进展至关重要。极性建立的一个经过充分研究的例子是酿酒酵母中的芽出现，它由 Rho GTPase Cdc42p 控制。关于芽出现的普遍观点并没有考虑到外在因素的调节。在这里，我们证明丝状生长丝裂原激活蛋白激酶（fMAPK）途径在营养限制条件下调节芽的出现。fMAPK 通路调节极性靶标的表达，包括编码 Cdc42p 直接效应子 Gic2p 的基因。fMAPK 通路还刺激 GTP-Cdc42p 水平，这是极性建立的关键决定因素。fMAPK 途径活性在空间上仅限于芽位点，并在导致芽出现的细胞周期期间活跃。延时荧光显微镜显示，fMAPK 途径刺激了丝状生长过程中的芽出现率。fMAPK 通路不受调控的激活导致生长芽内发生多轮对称性破坏。总的来说，我们的研究结果确定了芽出现的一个新的调控方面，该方面使这一重要的细胞过程对外部线索敏感。