The FHA domain determines Drosophila Chk2/Mnk localization to key mitotic structures and is essential for early...

Area of Science:

• Cell Biology
• Molecular Biology
• Genetics

Background:

• DNA damage responses are vital for maintaining genome integrity.
• In syncytial Drosophila embryos, these responses include mitotic centrosome inactivation, cell-cycle delay, and nuclear dropping.
• The conserved signaling kinase Chk2, known as Mnk/Loki, is essential for these DNA damage responses.

Purpose of the Study:

• To investigate the domain functions of Mnk in vivo.
• To elucidate the role of the forkhead-associated (FHA) domain in Mnk localization and DNA damage response.
• To understand the mechanisms of Mnk activation and recruitment during embryonic development.

Main Methods:

• Expression of functional EGFP-Mnk and its variants in Drosophila embryos.
• Analysis of Mnk localization using fluorescence microscopy.
• Site-directed mutagenesis to disrupt FHA and SQ/TQ-cluster domains (SCD).
• Assessment of Mnk transphosphorylation and autophosphorylation.
• Identification of a nuclear localization signal (NLS) at the C-terminus.

Main Results:

• Functional EGFP-Mnk localized to the nucleus, centrosomes, centromeres, midbody, and pseudocleavage furrows.
• Upon DNA damage, Mnk formed foci on mitotic chromosomes.
• A triple mutation in the FHA domain's phosphopeptide-binding site disrupted localization and foci formation.
• FHA mutations and SCD deletion abolished Mnk transphosphorylations and autophosphorylations.
• A C-terminal NLS was identified as essential for normal Mnk function.

Conclusions:

• The FHA domain of Mnk plays dual roles in DNA damage response: activating Mnk in the nucleus and recruiting it to subcellular structures.
• Mnk activation upon DNA damage involves transphosphorylation and autophosphorylation.
• The C-terminal NLS is critical for Mnk's overall function in embryonic DNA damage responses.