Wagner M, Briza P, Pierce M, Winter E
Department of Biochemistry and Molecular Pharmacology, Thomas Jefferson University, Philadelphia, Pennsylvania 19107, USA.
Genetics. 1999 Apr;151(4):1327-40. doi: 10.1093/genetics/151.4.1327.
The SMK1 mitogen-activated protein kinase is required for spore morphogenesis in Saccharomyces cerevisiae. In contrast to the multiple aberrant spore wall assembly patterns seen even within a single smk1 null ascus, different smk1 missense mutants block in a coordinated fashion at intermediate stages. One smk1 mutant forms asci in which the four spores are surrounded only by prospore wall-like structures, while another smk1 mutant forms asci in which the spores are surrounded by inner but not outer spore wall layers. Stepwise increases in gene dosage of a hypomorphic smk1 allele allow for the completion of progressively later morphological and biochemical events and for the acquisition of distinct spore-resistance phenotypes. Furthermore, smk1 allelic spore phenotypes can be recapitulated by reducing wild-type SMK1 expression. The data demonstrate that SMK1 is required for the execution of multiple steps in spore morphogenesis that require increasing thresholds of SMK1 activity. These results suggest that quantitative changes in mitogen-activated protein kinase signaling play a role in coordinating multiple events of a single cellular differentiation program.
SMK1丝裂原活化蛋白激酶是酿酒酵母孢子形态发生所必需的。与在单个smk1缺失的子囊中甚至可见的多种异常孢子壁组装模式不同，不同的smk1错义突变体在中间阶段以协调的方式受阻。一种smk1突变体形成的子囊中，四个孢子仅被前孢子壁样结构包围，而另一种smk1突变体形成的子囊中，孢子被内孢子壁层而非外孢子壁层包围。低表达smk1等位基因的基因剂量逐步增加，使得越来越晚的形态学和生物化学事件得以完成，并获得不同的孢子抗性表型。此外，通过降低野生型SMK1的表达，可以重现smk1等位基因的孢子表型。数据表明，SMK1是孢子形态发生中多个步骤执行所必需的，这些步骤需要不断增加的SMK1活性阈值。这些结果表明，丝裂原活化蛋白激酶信号传导的定量变化在协调单个细胞分化程序的多个事件中起作用。
