Female meiosis II and pronuclear fusion require Bicaudal-D

Drosophila Clathrin heavy chain (Chc) is transported by the dynein/dynactin microtubule motor through its interaction with the adaptor protein Bicaudal-D (BicD). Here we show that Drosophila BicD and Chc localize to centrosomes and spindles during mitosis and to the tandem spindles during female meiosis II. Reducing the activity of BicD::GFP specifically in freshly laid eggs revealed that BicD is essential for the production of normal female meiosis II products and for pronuclear fusion. Chc interacts with BicD and D-TACC, and BicD is needed to correctly localize the microtubule-stabilizing factors D-TACC, clathrin, and Msps to the meiosis II spindles, suggesting that BicD acts by localizing these proteins. In unfertilized eggs, reduced BicD levels cause the female meiotic products to re-enter the cell cycle. As BicD is required to localize the spindle assembly checkpoint (SAC) components Mad2 and BubR1 to the female meiotic products, it appears that BicD functions to localize them to control metaphase arrest of polar bodies. Finally, Drosophila and C. elegans orthologs of BicD and tacc are also needed for pronuclear fusion.