Molecular characterization of Lava Lamp, a novel Golgin required for cellularization. O. Papoulas¹, Y. Wang¹, T. Hays², J. Sisson¹. 1) The Section of MCD Biology, The University of Texas, Austin, TX; 2) The Department of Genetics, Cell Biology, and Development, The University of Minnesota, MN.

   Mounting evidence suggests that cytokinesis in many animal cells depends on polarized membrane secretion and actomyosin-based contraction. In cleavage stage Drosophila embryos the formation of cellularization furrows, which are special cytokinesis furrows, depends on Golgi-derived membrane secretion and the activity of a novel Golgin named Lava Lamp (Lva). Golgins comprise a family of Golgi-associated proteins implicated in membrane trafficking and in several human autoimmune diseases. Initial models proposed that Golgins function as a structural membrane scaffold or to tether specific membrane vesicles prior to fusion with the Golgi. However, recently the mammalian Golgin BicD has been implicated in recruitment of cytoplasmic dynein to Golgi, suggesting a broader range of molecular tethering functions for Golgins. Consistent with this view, our results suggest that Lva functions in Drosophila to recruit cytoplasmic dynein to Golgi or regulate its function on Golgi. Lva-associated Golgi compartments undergo microtubule-dependent movements that require cytoplasmic dynein. Furthermore, a combination of immunofluorescence and biochemical co-fractionation suggests cytoplasmic dynein associates with a Lva/-Spectrin complex on the surface of Golgi. In order to explore these protein interactions in more depth we are mapping the Lva domains that mediate its associations with -Spectrin and dynein. We are using a contiguous set of Lva fragments as GST fusions for pull-down assays and affinity chromatography with native extracts to test for direct and indirect protein interactions. These in vitro studies will be complemented by overexpression studies in S2 cells to assay cellular phenotypes. These combined approaches will provide a clearer picture of Lva function and a better overall understanding of the role of Golgins in membrane-trafficking.