Spindle assembly in animal cells requires nuclear envelope breakdown (NEBD). NEBD is a multistep process, which begins when Cdk1/cyclinB phosphorylates multiple components of the nuclear envelope. Given below are some components that are directly phosphorylated by Cdk1/cyclinB:

A. Nuclear Pore Complexes
B. Nuclear lamina
C. Greatwall kinase
D. Histone H3

Choose the option with correct Cdk1/cyclinB substrate/s that are directly associated with NEBD.

Correct option is C

Sol.

• Nuclear Pore Complexes (A) and Nuclear lamina (B) are key structural components of the nuclear envelope and are directly phosphorylated by Cdk1/cyclinB to trigger nuclear envelope breakdown.

• Greatwall kinase (C) is involved in mitotic entry regulation but not directly phosphorylated by Cdk1/cyclinB during NEBD.

• Histone H3 (D) phosphorylation occurs during mitosis but is not directly linked to NEBD; it’s mainly mediated by Aurora kinases and other mitotic kinases.

Information Booster:

• NEBD is essential for mitotic spindle assembly as it allows microtubules to access chromosomes.

• Phosphorylation of nuclear pore complexes and nuclear lamins disrupts nuclear envelope integrity, leading to its breakdown.

• Greatwall kinase regulates mitotic progression through inhibition of phosphatases but is not a direct substrate of Cdk1 in NEBD.

• Histone H3 phosphorylation is a mitotic marker but unrelated to nuclear envelope disassembly.