Spatial Organisation of the Drosophila Actin Cytoskeleton. B. Baum ¹, Z. Wills ², D. VanVactor ², N. Perrimon ¹. 1) Dept Genetics, HHMI, Harvard Medical Sch, Boston, MA; 2) Dept Cell Biology, Harvard Medical Sch, Boston, MA.

   The Drosophilafollicular epithelium has a simple polarised arrangement of actin filaments and so provides a useful model system with which to study the spatial organisation of the actin cytoskeleton. In capmutant follicle cells, actin filaments form specifically at the apical cell surface. This demonstrates that actin dynamics can be independently modified at opposite poles of an epithelium. We show that Ena is a key regulator of actin polymerisation in Drosophilaand is found concentrated with F-actin at apical junctions in the WT, where actin filaments first accumulate in the capmutant. Furthermore, Ena protein colocalises with F-actin aggregates in capmutant follicle cells and is required for their formation. So, in the WT, CAP may regulate the distribution of actin filaments by inhibiting Ena. Abl, an Ena antagonist, also controls polarity and F-actin organisation in follicle cells. Moreover, we show that CAP, Ena and Abl physically interact in Drosophilacells. Therefore we propose that CAP, Ena and Abl act together in Drosophilato control the spatial organisation of F-actin. Since CAP limits the ability of Ena to promote actin filament formation, cells may alter the cellular distribution of actin filaments by varying CAP activity or Ena localisation, perhaps in response to cues from the cell surface acting through Abl. Analogous signals are thought to regulate actin dynamics within the growth cones of migrating neurons. Therefore CAP, Ena and Abl may be elements in a common pathway that controls the spatial organisation of F-actin within many types of polarised cell.