Widely Used Mutants of eiger, Encoding the Drosophila Tumor Necrosis Factor, Carry Additional Mutations in the NimrodC1 Phagocytosis Receptor

The process of apoptosis in epithelia involves activation of caspases, delamination of cells, and degradation of cellular components. Corpses and cellular debris are then rapidly cleared from the tissue by phagocytic blood cells. In studies of the Drosophila TNF, Eiger (Egr) and cell death in wing imaginal discs, the epithelial primordia of fly wings, we noticed that dying cells appeared to transiently accumulate in egr(3) mutant wing discs, raising the possibility that their phagocytic engulfment by hemocytes was impaired. Further investigation revealed that lymph glands and circulating hemocytes from egr(3) mutant larvae were completely devoid of NimC1 staining, a marker of phagocytic hemocytes. Genome sequencing uncovered mutations in the NimC1 coding region that are predicted to truncate the NimC1 protein before its transmembrane domain, and provide an explanation for the lack of NimC staining. The work that we report here demonstrates the presence of these NimC1 mutations in the widely used egr(3) mutant, its sister allele, egr(1), and its parental strain, Regg1(GS9830). As the egr(3) and egr(1) alleles have been used in numerous studies of immunity and cell death, it may be advisable to re-evaluate their associated phenotypes.