For over a decade, the primary function of hemocytes, the blood cells of invertebrates, has been attributed to their immune roles in clearing harmful microorganisms and controlling the microbiota during development. It was thought they had otherwise dispensable functions, as the reduced eclosion rates seen in hemocyte-ablated Drosophila pupae could be rescued by growth with antibiotics or under germ-free conditions. However, these studies only produced 60–75% reduction in larval hemocyte numbers. In this Issue, Alf Herzig and colleagues showcase a new hemocyte-specific driver line which specifically and almost completely ablates hemocytes in Drosophila larvae. As in previous studies, this is lethal to early pupae but, contrastingly, cannot be rescued by growth under axenic conditions. The authors also perform RNA-sequencing to assess gene expression changes before pupal lethality, finding that hemocyte ablation leads to dysregulation of midgut-expressed genes. Concurrently, larval gut lengths in these flies were significantly reduced, suggesting hemocytes may function in early midgut development. Together, these data highlight a previously unreported and crucial role of hemocytes beyond immune regulation during Drosophila development and demonstrate an effective hemocyte ablation tool that will be useful for further studies into hemocyte functions.
