Drosophila macrophages require integrins for effective migration but not for phagocytosis. S. Huelsmann¹, M.D. Martin-Bermudo^{2, 3}, R. Reuter¹. 1) Div. Animal Genetics, Institute for Cellbiology, University of Tuebingen, Germany; 2) Department of Anatomy, Cambridge University, UK; 3) present address: IPB "Lopez-Neyra", CSIC, Granada, Spain.

   Macrophages in the Drosophila embryo migrate from the cephalic mesoderm along several invariant migratory paths through the interstitial space of the whole embryo. In many systems the integrin heterodimers are involved in the regulation of migration and related processes like cell adhesion, cytoskeleton organization and assembly of extracellular matrix.
   We demonstrate that myospheroid (mys), encoding the Drosophila integrin beta subunit PS, is necessary for the proper migration of macrophages: in mys germ line clones the migration is severely disrupted, e.g. the migration along the ventral midline. By means of gfp time lapse movies we show that integrins are essential for the proper adhesion of cellular protrusions during the process of migration but not for the formation of such structures. These phenotypes are consequences of the lack of integrins in the macrophages themselves as the expression of an adhesion deficient form of mys in the macrophages leads to a migration phenotype similar to the one of mys germ line clones. Furthermore, the expression of wild-type mys in the macrophages, but not in other tissues is sufficient to rescue the macrophage migration in mys germ line clones. The examination of embryos mutant for various PS subunits suggests that PS3 and PS4 act with PS in the migration of embryonic macrophages. Other developmental processes which could have required integrin function in macrophages - e.g. cell maturation, cell survival or phagocytosis - are not affected in mys germline clones.