DROSOPHILA IMMUNITY - ANALYSIS OF LARVAL HEMOCYTES BY P-ELEMENT-MEDIATED ENHANCER TRAP

Our aim was to identify new genes involved in the cellular aspects of defense mechanisms of Drosophila, as well as in melanotic tumor format ion processes that are linked to blood cell disregulation. We have scr eened 1341 enhancer detector fly lines for expression of the lacZ repo rter gene in larval hemocytes at the end of the third instar. We have selected 21 lines in which we observed a reproducible lacZ expression in blood cells. These lines were classified according to the subsets o f hemocytes in which lacZ was expressed, and we identified five lines that can be used as lamellocyte markers. Three lines were selected for further analysis. The first exhibited strong lacZ expression in all l amellocytes. The second expressed lacZ in plasmatocytes and lamellocyt es, and exhibited a melanotic tumor phenotype in larvae homozygous for the insertion. A third Line showed a striking insertion-linked phenot ype of melanized lymph glands (the hematopoietic organ), which resulte d in the total absence of circulating hemocytes in the mutant larvae. We anticipate that this mutation, which we named domino, will prove a useful tool in the analysis of the role of hemocytes during the variou s aspects of immune response and melanotic tumor formation.