Hohmann Stefan
Department of Cell and Molecular Biology/Microbiology, Göteborg University, S-405 30 Göteborg, Sweden.
Microbiol Mol Biol Rev. 2002 Jun;66(2):300-72. doi: 10.1128/MMBR.66.2.300-372.2002.
The ability to adapt to altered availability of free water is a fundamental property of living cells. The principles underlying osmoadaptation are well conserved. The yeast Saccharomyces cerevisiae is an excellent model system with which to study the molecular biology and physiology of osmoadaptation. Upon a shift to high osmolarity, yeast cells rapidly stimulate a mitogen-activated protein (MAP) kinase cascade, the high-osmolarity glycerol (HOG) pathway, which orchestrates part of the transcriptional response. The dynamic operation of the HOG pathway has been well studied, and similar osmosensing pathways exist in other eukaryotes. Protein kinase A, which seems to mediate a response to diverse stress conditions, is also involved in the transcriptional response program. Expression changes after a shift to high osmolarity aim at adjusting metabolism and the production of cellular protectants. Accumulation of the osmolyte glycerol, which is also controlled by altering transmembrane glycerol transport, is of central importance. Upon a shift from high to low osmolarity, yeast cells stimulate a different MAP kinase cascade, the cell integrity pathway. The transcriptional program upon hypo-osmotic shock seems to aim at adjusting cell surface properties. Rapid export of glycerol is an important event in adaptation to low osmolarity. Osmoadaptation, adjustment of cell surface properties, and the control of cell morphogenesis, growth, and proliferation are highly coordinated processes. The Skn7p response regulator may be involved in coordinating these events. An integrated understanding of osmoadaptation requires not only knowledge of the function of many uncharacterized genes but also further insight into the time line of events, their interdependence, their dynamics, and their spatial organization as well as the importance of subtle effects.
适应游离水可利用量变化的能力是活细胞的一项基本特性。渗透适应背后的原理高度保守。酿酒酵母是研究渗透适应分子生物学和生理学的极佳模型系统。当转移至高渗环境时，酵母细胞会迅速激活有丝分裂原激活蛋白（MAP）激酶级联反应，即高渗甘油（HOG）途径，该途径协调部分转录反应。HOG途径的动态运作已得到充分研究，其他真核生物中也存在类似的渗透感应途径。蛋白激酶A似乎介导对多种应激条件的反应，也参与转录反应程序。转移至高渗环境后的表达变化旨在调节代谢和细胞保护剂的产生。渗透溶质甘油的积累也受跨膜甘油转运改变的控制，这至关重要。当从高渗转变为低渗时，酵母细胞会激活不同的MAP激酶级联反应，即细胞完整性途径。低渗休克后的转录程序似乎旨在调节细胞表面特性。甘油的快速输出是适应低渗的重要事件。渗透适应、细胞表面特性的调节以及细胞形态发生、生长和增殖的控制是高度协调的过程。Skn7p反应调节因子可能参与协调这些事件。对渗透适应的全面理解不仅需要了解许多未表征基因的功能，还需要进一步深入了解事件的时间线、它们的相互依赖性、动态性和空间组织以及细微效应的重要性。
