Mud binds the kinesin-14 Ncd in Drosophila

Area of Science:

• Cell Biology
• Molecular Biology
• Genetics

Background:

• Proper mitotic spindle structure is crucial for accurate chromosome segregation during cell division.
• Kinesin motors, like Non-claret dysjunctional (Ncd), are essential for spindle assembly, geometry, and bipolarity.
• Regulatory mechanisms controlling Ncd activity during mitosis remain largely uncharacterized.

Purpose of the Study:

• To identify and characterize novel regulators of the kinesin-14 motor protein Ncd in *Drosophila*.
• To investigate the interaction between Ncd and its binding partner, Mushroom body defect (Mud).
• To elucidate the functional consequences of the Mud-Ncd interaction on Ncd activity and spindle organization.

Main Methods:

• Co-immunoprecipitation assays to confirm direct binding between Mud and Ncd.
• In vitro biochemical assays to map interaction domains (Mud^CC and Ncd^nMBD, Ncd^CTm and Ncd^nMBD).
• Microtubule binding assays to assess the effect of Mud on Ncd's interaction with microtubules.

Main Results:

• Mushroom body defect (Mud), the *Drosophila* ortholog of human NuMA, was identified as a direct binding partner of Ncd.
• The interaction involves Mud's coiled-coil domain (Mud^CC) binding Ncd's N-terminal microtubule-binding domain (Ncd^nMBD).
• Mud binding disrupts Ncd self-association (Ncd^CTm-Ncd^nMBD interaction) and enhances Ncd^nMBD microtubule binding.

Conclusions:

• A novel interaction between spindle-associated proteins Mud and Ncd has been characterized.
• Mud acts as a regulator of Ncd, modulating its self-association and microtubule binding properties.
• This study suggests a new mechanism for regulating minus-end directed motor protein activity at mitotic spindle poles.