Differential scaling of gene expression with cell size may explain size control in budding yeast.

Yeast cells must grow to a critical size before committing to division. It is unknown how size is measured. We find that as cells grow, mRNAs for some cell cycle activators scale faster than size, increasing in concentration, while mRNAs for some inhibitors scale slower than size, decreasing in concentration. Size-scaled gene expression could cause an increasing ratio of activators to inhibitors with size, triggering cell cycle entry. Consistent with this, expression of the CLN2 activator from the promoter of the WHI5 inhibitor, or vice versa, interfered with cell size homeostasis, yielding a broader distribution of cell sizes. We suggest that size homeostasis comes from differential scaling of gene expression with size. Such regulation of gene expression as a function of cell size could affect many cellular processes.酵母细胞在启动分裂前，必须生长至临界体积。目前学界尚未明确细胞如何感知自身体积。我们发现，随着细胞生长，部分细胞周期激活因子的信使RNA（mRNA）的丰度增长速率快于细胞体积增长，其浓度随之升高；而部分细胞周期抑制因子的信使RNA的丰度增长速率慢于细胞体积增长，其浓度随之降低。这种随细胞体积缩放的基因表达模式，可能会使激活因子与抑制因子的比例随体积增大而上升，进而触发细胞周期启动。与此假说一致的是，若将细胞周期激活因子CLN2的编码序列置于抑制因子WHI5的启动子下调控表达，或反之操作，会干扰细胞体积稳态，导致细胞体积分布范围变宽。我们据此提出，细胞体积稳态源于基因表达随细胞体积产生的差异性缩放。这种以细胞体积为调控依据的基因表达模式，可能会对诸多细胞生理过程产生影响。