Fig 5. Growth of nucleus surface and volume assembly.

(A) Modelling the growth of nucleus, coupled to the dynamics of the astral microtubule structure. Building blocks for nuclear envelope (NE) are actively transported by dynein motors along the astral microtubules surrounding the nucleus. Filaments in the aster grow by incorporating tubulins from the cytoplasmic pool. (B) Dynamics of nucleus size (normalised radius R_n) and single microtubule length (normalised). (Inset) Nucleus size decreases with increasing nuclei number in a given volume, in agreement with in vitro data [48]. (C) Effect of the size of confinement, R_sys, on nucleus size R_n, where R_n increases with increasing R_sys, eventually saturating for large R_sys. Solid line is model fit, and black triangles represent experimental data [48]. The confinement radius was increased while keeping the confinement volume constant, as in experiments [48]. (D) Scaling of nucleus volume, V_n, with cell volume V_cell. Theory predicts that size scaling is quadratic if V_n is controlled by the growth of NE, but the scaling is linear if V_n is regulated by NP assembly. The linear scaling fits quantitatively with the nucleus-to-cell size scaling measured in an eukaryotic cell [10]. Parameters: NE subunit concentration = 8.0 μm⁻³, α = 0, β = 1, NE subunit size (δA) = 0.215 μm², k⁺(NE) = 5 × 10⁻³ μm³min⁻¹, k⁻(NE) = 10⁻¹min⁻¹, NP subunit concentration = 0.75 μm⁻³, NP subunit size (δV) = 0.1 μm³, k⁺(NP) = 2.0 μm³min⁻¹, k⁻(NP) = 10⁻³ min⁻¹, MT subunit concentration ≃ 0.67 μM, MT subunit size (δL) = 5 nm, $k_m^{+}=2.0$ μm³min⁻¹, $k_m^{-}={10}^{-2}$ min⁻¹.