The role and regulation of Ndel1 during assembly of the mitotic spindle

Assembly of the mitotic spindle is a highly regulated process, which requires cooperation between multiple motors and microtubule associated proteins. The cytoplasmic dynein is the major end directed microtubule motor in the cell, involved in numerous aspects of spindle formation. Due to its multifunctional nature, dynein is tightly regulated by proteins such as dynactin, LIS1 and two paralogues Nde1 and Ndel1. LIS1 and Nde1/Ndel1 were initially characterized as regulators of dynein-dependent neuronal migration in the fungus Aspergillus nidulans, but until recently their role remained elusive. My graduate research aimed at understanding how Ndel1 facilitates its function as a dynein regulator at the molecular level and how Ndel1 itself is regulated. Using structure-function analysis in mitotically arrested Xenopus egg extracts, I characterized the minimal functional domain within the coiled-coil of Ndel1 which brings together LIS1 and the dynein intermediate chain to lower concentration of LIS1 required for proper dynein function. This activity of Ndel1 is controled by multiple phosphorylation sites within its unstructured C-terminal tail. A novel phosphorylation site was identified by mass spectrometry on serine 285, which is a target of the centrosomal kinase Aurora A. Subsequently, I found that Ndel1 interacts with dynein along astral and spindle microtubules, and serine 285 phosphorylations inhibits this interaction to facilitate pole formation. Together, my findings have significantly contributed to the current understanding of Ndel1 as a scaffold that is spatially and temporarily regulated to modulate dynein function.

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