A Hedgehog- and Antennapedia-dependent niche maintains Drosophila haematopoietic precursors

Abstract

This week, two papers from separate groups define a signalling centre in the Drosophila lymph gland that controls maintenance of blood cell precursors. Signals generated in the posterior signalling centre of the lymph gland control the balance of progenitors and differentiating blood cells through JAK/STAT and Notch signalling pathways. Mandal et al. also show that the signalling centre is specified early in embryonic development by the homeotic gene Antennapedia. And Krzemień et al. show that Notch signalling controls Collier, the Drosophila equivalent of mammalian early B cell factor. This work suggests that the Drosophila model for blood development could be an important tool for genetic manipulation. One of two papers that define the region of the posterior signalling centre (PSC) in the Drosophila melanogaster lymph gland that controls maintenance of blood cell precursors. This paper also showed that the PSC is specified early in embryonic development by the homeotic gene Antennapedia. The Drosophila melanogaster lymph gland is a haematopoietic organ1,2,3 in which pluripotent blood cell progenitors proliferate and mature into differentiated haemocytes. Previous work4 has defined three domains, the medullary zone, the cortical zone and the posterior signalling centre (PSC), within the developing third-instar lymph gland. The medullary zone is populated by a core of undifferentiated, slowly cycling progenitor cells, whereas mature haemocytes comprising plasmatocytes, crystal cells and lamellocytes are peripherally located in the cortical zone. The PSC comprises a third region that was first defined as a small group of cells expressing the Notch ligand Serrate5. Here we show that the PSC is specified early in the embryo by the homeotic gene Antennapedia (Antp) and expresses the signalling molecule Hedgehog. In the absence of the PSC or the Hedgehog signal, the precursor population of the medullary zone is lost because cells differentiate prematurely. We conclude that the PSC functions as a haematopoietic niche that is essential for the maintenance of blood cell precursors in Drosophila. Identification of this system allows the opportunity for genetic manipulation and direct in vivo imaging of a haematopoietic niche interacting with blood precursors.