Nudel Functions In Membrane Traffic And Mitosis

Cytoplasmic dynein, a microtubule (MT)-based and minus-end-directed motor, exertsmultiple functions, such as membrane transport, mitosis, neuronal migration. Nudel and Lis1appear to regulate cytoplasmic dynein in neuronal migration and mitosis through directinteractions. Whether they regulate other functions of dynein, however, remainselusive.Herein, in part one, overexpression of Nudel mutant defective in association witheither Lis1 or dynein heavy chain is shown to cause dispersions of membranousorganelles whose trafficking depends on dynein. In contrast, the wild-type Nudel andthe double mutant which binds to neither proteins are much less effective. Time-lapsemicroscopy for lysosomes reveals significant reduction in both frequencies andvelocities of their minus end-directed motions in cells expressing thedynein-binding-defective mutant, while the plus end-directed motility is considerablyaltered. Moreover, silencing Nudel expression by RNA interference results in Golgiapparatus fragmentation. Taking together, it is concluded that Nudel is critical fordynein motor activity in membrane transport through interactions with both Lis1 anddynein heavy chain.In part two, we discover that Nudel is an outer component of kinetochore protein,as well as with Lis1 and dynein. Depletion of Nudel by RNAi causes multiple mitoticdefects including prometaphase arrest, kinetochore-microtubule misattachments, andmultipolar spindle with scattered chromosome. Time-lapse imaging reveals Nudel isessential for both establishment and maintenance of stable kinetochore-microtubuleattachement. Furthermore, kinetochore Nudel is required for targeting dynein, Lis1 andCLIP-170 to kinetochores, partially depends on ZW10. Meanwhile, Overexpression ofC36, a Nudel mutant, lacking interaction with dynein, also causes similar phenotypesto Nudel RNAi. All the results indicate that Nudel is essential forkinetochore-microtubule attachment and mitotic spindle regulation.Therefore, in interphase, Nudel fuctions in the membrane traffic throughinteraction with Lis1;in mitosis, Nudel is the upstream regulator of dynein function atkintetochore, and is essential for kinetochore-microtubule attachment and mitoticspindle regulation. So it is concluded that Nudel functions in the dynein-mediatedprogress as a regulator of dynein acivity .