The meiotic LINC complex component KASH5 is an activating adaptor for cytoplasmic dynein

Area of Science:

• Cell Biology
• Molecular Biology
• Genetics

Background:

• Cytoplasmic dynein is vital for chromosome movement during mammalian meiotic prophase I, enabling synapsis and genetic exchange.
• Dynein links to chromosome telomeres through KASH5 and SUN proteins, which traverse the nuclear envelope.

Purpose of the Study:

• To investigate the role of KASH5 in regulating cytoplasmic dynein activity and its interaction with dynein components.
• To elucidate the mechanism by which KASH5 facilitates dynein recruitment and complex assembly at the nuclear envelope.

Main Methods:

• In vitro assays to assess KASH5's effect on dynein motility.
• Biochemical analyses to identify KASH5 interaction domains with dynein light intermediate chains (DYNC1LI1/DYNC1LI2).
• Mutagenesis studies to examine the role of KASH5's EF-hands and calcium-binding residues.
• Investigating the recruitment of dynein, dynactin, and LIS1 to KASH5 at the nuclear envelope.

Main Results:

• KASH5 enhances dynein motility in vitro and its cytosolic form inhibits interphase dynein functions.
• KASH5 directly interacts with dynein light intermediate chains via a conserved C-terminal helix, essential for dynein recruitment.
• KASH5's N-terminal EF-hands are critical for dynein interaction, independent of cellular calcium levels.
• Dynein recruitment to KASH5 is independent of dynactin, but LIS1 is required for dynactin incorporation.

Conclusions:

• The transmembrane protein KASH5 functions as an activating adaptor for cytoplasmic dynein.
• This study clarifies the hierarchical assembly of KASH5-dynein-dynactin complexes at the nuclear envelope.