Figure 1.

Nuclear volume and the number of nuclear pore complexes (NPCs) almost double during interphase in dividing cells. NPC formation, but not nuclear growth, is governed by cyclin-dependent kinases (Cdks) from G₁ (left) to G₂ (right) phase. The nuclear size and NPC density of quiescent G₀ nuclei in normal human fibroblasts was similar to those of G₁ nuclei.⁹,²⁸ The Mek1 inhibitor, PD98059, blocked NPC formation during interphase. Ras/Erk signaling occurs upstream of Cdks in the regulation of NPC formation.