Dynein light intermediate chain 1 is required for progress through the spindle assembly checkpoint

Area of Science:

• Cell Biology
• Molecular Biology
• Genetics

Background:

• The spindle assembly checkpoint (SAC) ensures accurate chromosome segregation during cell division.
• Cytoplasmic dynein is implicated in SAC function by removing proteins from kinetochores.
• The specific dynein subunit involved in this process remained unidentified.

Purpose of the Study:

• To identify the dynein subunit responsible for regulating SAC component localization at kinetochores.
• To elucidate the role of dynein light intermediate chain 1 (LIC1) in SAC silencing.

Main Methods:

• Depletion of dynein light intermediate chain 1 (LIC1) in human cells using siRNA.
• Analysis of kinetochore-microtubule attachments and tension.
• Immunofluorescence microscopy to assess localization of checkpoint proteins (Mad1/2, Zw10, BubR1).
• Complementation assays with wild-type and mutant LIC1.

Main Results:

• LIC1 depletion caused metaphase delay and increased interkinetochore distances, indicating SAC activation.
• Mad1/2 and Zw10 localized to kinetochores under tension in LIC1-depleted cells, while BubR1 levels decreased.
• These phenotypes were rescued by depleting SAC components or re-expressing specific LIC1 forms.
• A Cdk1-phosphorylated form of LIC1, but not a non-phosphorylatable mutant, rescued the observed defects.

Conclusions:

• A Cdk1-phosphorylated form of LIC1 is essential for the removal of Mad1/2 and Zw10 from kinetochores during SAC silencing.
• LIC1's function in SAC silencing is independent of BubR1 localization.
• This study identifies LIC1 as a key regulator of SAC component dynamics at kinetochores.