Mammalian cell size homeostasis

A small newly divided cell can wait longer before it starts copying its DNA, giving it time to grow. Cells of the same type tend toward a characteristic size. What specifies that target, and how does it change between cell types and conditions?[1] [2]

In mouse skin, smaller newly born stem cells tend to spend longer growing before DNA copying begins. This corrects differences between cells, but what chooses the size they approach? The growth period before DNA copying is G1; copying begins in S phase. A 2025 study found that this transition depends on the RB family of proteins, which helps restrain cell-cycle entry. Removing two family members disrupted the relationship between birth size and time spent in G1.[2]

Size can control division. What sets and changes the target remains incomplete.[1] [2]

The checkpoint shows size-dependent progression in this tissue. It does not identify every cell type’s target or prove that dilution of RB proteins is the in vivo size sensor; that proposed mechanism needs further direct tests.[1] [2]

Size affects the proportions of components inside cells and how cells fit into tissues. This question connects the timing of division to the kind of cell being built.[1]

Larger animal cells do not simply contain scaled-up copies of every component: protein groups can change in relative abundance. Size regulation therefore belongs to the question of how a cell maintains its internal working conditions while a tissue keeps renewing itself.[1]