Sequential PKC- and Cdc2-mediated phosphorylation events elicit zebrafish nuclear envelope disassembly

Area of Science:

• Cell Biology
• Molecular Biology
• Biochemistry

Background:

• The nuclear envelope disassembles during meiosis and mitosis, but the precise molecular mechanisms remain incompletely understood.
• Key proteins of the inner nuclear membrane and nuclear lamina play critical roles in nuclear envelope dynamics.

Purpose of the Study:

• To investigate the molecular regulation of nuclear envelope disassembly in zebrafish.
• To identify the specific kinases and phosphorylation events involved in this process.

Main Methods:

• Identification and partial characterization of zebrafish nuclear envelope proteins NEP55 and L68.
• Inhibition studies using specific kinase inhibitors (PKC, Cdc2) in vivo and in vitro.
• Phosphorylation assays using meiotic cytosol and in vitro systems.
• Immunological and functional comparisons with human homologs (LAP2beta, lamin B).

Main Results:

• Zebrafish NEP55 and L68 are functionally and immunologically related to human LAP2beta and lamin B.
• Nuclear envelope disassembly is dependent on sequential phosphorylation of NEP55 and L68 by PKC and Cdc2 kinase.
• PKC-mediated phosphorylation of L68 prior to Cdc2-mediated phosphorylation of L68 and NEP55 is essential for nuclear envelope breakdown.
• Inhibition of either PKC or Cdc2, or disruption of the sequential phosphorylation order, prevents nuclear envelope disassembly.

Conclusions:

• Sequential phosphorylation by PKC, followed by Cdc2, is required for zebrafish nuclear envelope disassembly.
• Phosphorylation of inner nuclear membrane proteins alone is insufficient to trigger nuclear envelope breakdown.
• The findings suggest a multi-layered regulatory mechanism governing nuclear envelope component disassembly during cell division.