Abstract
Eater and NimC1 are transmembrane receptors of the Drosophila Nimrod family, specifically expressed in haemocytes, the insect blood cells. Previous ex vivo and in vivo RNAi studies have pointed to their role in the phagocytosis of bacteria. Here, we have created a novel NimC1 null mutant to re‐evaluate the role of NimC1, alone or in combination with Eater, in the cellular immune response. We show that NimC1 functions as an adhesion molecule ex vivo, but in contrast to Eater it is not required for haemocyte sessility in vivo. Ex vivo phagocytosis assays and electron microscopy experiments confirmed that Eater is the main phagocytic receptor for Gram‐positive, but not Gram‐negative bacteria, and contributes to microbe tethering to haemocytes. Surprisingly, NimC1 deletion did not impair phagocytosis of bacteria, nor their adhesion to the haemocytes. However, phagocytosis of both types of bacteria was almost abolished in NimC1 1 ;eater 1 haemocytes. This indicates that both receptors contribute synergistically to the phagocytosis of bacteria, but that Eater can bypass the requirement for NimC1. Finally, we uncovered that NimC1, but not Eater, is essential for uptake of latex beads and zymosan particles. We conclude that Eater and NimC1 are the two main receptors for phagocytosis of bacteria in Drosophila, and that each receptor likely plays distinct roles in microbial uptake.
Highlights
Phagocytosis is an ancient and evolutionarily conserved process, generally defined as the cellular uptake of particles bigger than 0.5 lm
As Nimrod C1 (NimC1) is expressed in haemocytes and has been implicated in phagocytosis, we combined the NimC1 mutation with the previously described eater1 null mutant [16], generating a double mutant NimC11;eater1 (Fig. 1)
We characterized the function of NimC1 focussing on haemocytes of third instar larvae
Summary
Phagocytosis is an ancient and evolutionarily conserved process, generally defined as the cellular uptake of particles bigger than 0.5 lm. Phagocytosis is an important feeding mechanism in primitive and unicellular organisms, such as amoeba [1]. Phagocytosis is performed by dedicated cells (phagocytes) and is used as a powerful process to internalize and eliminate pathogens, as well as to trigger host inflammation [2]. Phagocytosis is a complex membrane-driven process guided by the actin cytoskeleton of the host phagocytic cell. It involves the recognition and subsequent binding of the microbe by surface receptors. These interactions are essential to activate intracellular signalling pathways that culminate in the formation of the phagosome [4]. Several studies have highlighted similarities between the phagocytic machinery of Drosophila and mammals, such as the Abbreviations DAPI, 40,6- diamidino-2-phenylindole; EdU, 5-ethynyl-20-deoxyuridine; Hml, Hemolectin; Nim, Nimrod; PTU, phenylthiourea; SEM, scanning electron microscopy; TEM, transmission electron microscopy
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