Cell size is fundamental to cell physiology. For example, cell size determines the spatial scale of organelles and intracellular transport and thereby affects biosynthesis. Although some genes that affect mammalian cell size have been identified, the molecular mechanisms through which cell growth drives cell division have remained elusive. We show that cell growth during the G₁ phase of the cell division cycle dilutes the cell cycle inhibitor Retinoblastoma protein (Rb) to trigger division in human cells. RB overexpression increased cell size and G₁ duration, whereas RB deletion decreased cell size and removed the inverse correlation between cell size at birth and the duration of the G₁ phase. Thus, Rb dilution through cell growth in G₁ provides one of the long-sought molecular mechanisms that promotes cell size homeostasis.

细胞大小是细胞生理学的基础。例如，细胞大小决定了细胞器和细胞内运输的空间尺度，从而影响生物合成。尽管已经确定了一些影响哺乳动物细胞大小的基因，但细胞生长驱动细胞分裂的分子机制仍然难以捉摸。我们发现，细胞分裂周期 G ₁期的细胞生长会稀释细胞周期抑制剂视网膜母细胞瘤蛋白 (Rb)，从而触发人体细胞分裂。 RB过表达增加了细胞大小和 G ₁持续时间，而RB缺失则减少了细胞大小并消除了出生时细胞大小与 G ₁期持续时间之间的负相关性。因此，通过 G ₁细胞生长进行 Rb 稀释提供了人们长期寻找的促进细胞大小稳态的分子机制之一。