Fig. 6.

Proposed function and regulation of Num1 clustering. (A) Differential functions of small and large Num1 clusters. Small Num1 clusters mediate dynein anchoring and cortical spindle-pulling function (1). Mdm36 and mitochondria cooperatively mediate formation of large Num1 clusters (2) for mitochondrial-tethering function (3). Enhancing the number of Num1 molecules in the patch reduces cortical dynein targeting (4), probably because Mdm36 and mitochondria both bind to the same CC domain of Num1 as dynein. As proposed previously (Kraft and Lackner, 2017), mitochondria in turn promotes large cluster formation and stabilization (5). (B) Model for Mdm36- and mitochondria-dependent enhancement of Num1 clustering. Diagram illustrates scenarios in WT and Mdm36^OX cells. In both cases, two morphologically and functionally distinct populations of Num1 clusters (i.e. small and large clusters) mediate spindle pulling and mitochondrial-tethering functions at the cell cortex.