f neuronal IFs transported by Dynein and Kinesin. In each of these biological processes, Ndel1 not only plays a key role in maintaining 9349566 structural integrity but also appears to position organelles and traffic order Nutlin3 membranes via MTs and molecular motors. For instance, Ndel1 participates in the positioning of Golgi membranes through the MTs/Lis1/Dynein pathway. Whether Ndel1 contributes to membrane trafficking per se through other mechanisms such as by regulating proteins that shape membranes structure, remains however undefined. Dynamin is a large cytosolic GTPase that was first isolated from the brain as a microtubule-binding protein, although little evidence points to a role for Dyn in MTs remodelling. However, a recent study indicates that Dyn2 is involved in dynamic instability of MTs. Dyns are most well characterized for their action on membranes. Dyn associates with membranes and through oligomerization into ring-like structures, wraps around the neck of budding vesicles. Following hydrolysis of GTP, Dyn changes its conformation to constrict and January 2011 | Volume 6 | Issue 1 | e14583 Ndel1 Regulates Dyn2 Activity pinch membranes. A longitudinal tension appears to be required to pull apart the membranes and allow membrane fission during membrane trafficking in yeast, vertebrate and mammalian cells. There are three isoforms of Dynamin: Dyn1, Dyn2 and Dyn3. Whereas Dyn1 and Dyn3 are expressed in a tissue-specific manner, Dyn2 is ubiquitously expressed. Dyn2 is enriched in clathrin-coated pits at the plasma membrane. A very minor fraction of Dyn2 is presumably found at the trans-Golgi network . Dyns have also been linked to actin dynamics and implicated in calveolae internalization, vesicles recycling at the synapse, lamellipodia formation, cell migration and 
invasion. In a yeast two-hybrid screen, we recovered Dyn2 as a Ndel1binding partner. We verified this interaction biochemically and molecularly. We also found that Ndel1, like Dyn2, impacts the intracellular distribution of the a-amino-3-hydroxyl-5-methyl-4isoxazole-propionate receptor GluR1, possibly through regulation of Dyn2 GTPase activity. but not the PRD of Dyn2 interacted with His-Ndel1. The F5 construct containing all three binding sites bound less to Ndel1 than the individual F1-F3 constructs suggesting possible conformational changes in Dyn2 and/or competition between multiple binding sites. To map the interaction domain on Ndel1, Nterminus, C-terminus or full length Flag-Ndel1 constructs were transfected in HeLa cells and co-immunoprecipitation experiments were performed with Flag antibody. The C-terminus and full length Ndel1, but not the Nterminus, interacted with endogenous Dyn2. This Ndel1 tail/Dyn2 direct interaction was confirmed by yeast two-hybrid assays. Together, these results indicate that the Cterminus of Ndel1 is sufficient for direct interaction with Dyn2, possibly with all domains excluding the PRD. Ndel1 enhances Dynamin 2 GTPase activity in vitro The above findings showing that Ndel1 binds to Dyn2 through its regulatory domains including the GTPase domain raised the question as to whether Ndel1 regulates Dyn2 GTPase activity. To test whether Ndel1 modulates Dyn2 activity, we performed two different in vitro GTPase assays. Previous studies have shown 9373158 that Dyn2 activity is stimulated by oligomerization of the enzyme. Based on these reports, we reconstituted Dyn2 oligomers in vitro under low salt conditions and measured the GTPase activity upon addition of