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

Abstract

The Drosophila melanogaster lymph gland is a haematopoietic organ1 -3 in which pluripotent blood cell progenitors proliferate and mature into differentiated haemocytes. Previous work 4 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 Serrate 5 . 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.The Drosophila lymph gland primordium is formed by the coalescence of three paired clusters of cells that express Odd-skipped (Odd) and arise within segments T1-T3 (Fig. 1a) of the embryonic cardiogenic mesoderm 6 . At developmental stages 11-12, mesodermal expression of Antp is restricted to the T3 segment (Fig. 1b, c). A fraction of these Antp-expressing cells will contribute to the formation of the dorsal vessel 7,8 , whereas the remainder, which also express Odd, give rise to the PSC (Fig. 1d, e). By stages 13-16, the clusters coalesce and Antp is observed in 5-6 cells at the posterior boundary of the lymph gland (Fig. 1d, e). The expression of Antp is subsequently maintained in the PSC through the third larval instar (see Fig. 2a). The embryonic stage 16 PSC can also be distinguished by Fasciclin III expression (Fig. 1f, g) and at stage 17 these are the only cells in the lymph gland that incorporate BrdU (Fig. 1h).Previous studies have identified the transcription factor Collier (Col) as an essential component regulating PSC function 9 . The gene for this protein is initially expressed in the entire embryonicCorrespondence and requests for materials should be addressed to U.B. (banerjee@mbi.ucla.edu). Author Information Reprints and permissions information is available at www.nature.com/reprints. The authors declare no competing financial interests. NIH Public Access Author ManuscriptNature. Author manuscript; available in PMC 2010 January 17. (Fig. 1i). In contrast, col expression is absent in the PSC of Antp mutant embryos (Fig. 1j, k), establishing that Antp functions genetically upstream of Col in the PSC.In imaginal discs, the expression of Antp is related to that of the homeodomain cofactor Homothorax (Hth) 10 . In the embryonic l...

ARF1–GTP regulates Asrij to provide endocytic control of Drosophila blood cell homeostasis

“…The niche is specified by the homeobox transcription factor Antp (29) and maintained by the early B-cell factor ortholog Collier and the endocytic protein Asrij (6,30). Collier activates JAK/STAT signaling to maintain prohemocytes.…”

Cell lineage tracing reveals the plasticity of the hemocyte lineages and of the hematopoietic compartments in Drosophila melanogaster

“…The primary lobes are separated into three functional areas: the medullary zone comprises prohemocytes, the cortical zone built up by plasmatocytes and crystal cells, and the posterior signaling center (PSC), formed by a few cells on the posterior tip of the primary lobes. The PSC halts the differentiation of the prohemocytes in the medullary zone (Mandal et al, 2007;Krzemień et al, 2007). The sessile population of hemocytes is located underneath the larval cuticle (Goto et al, 2003;Lanot et al, 2001;Zettervall et al, 2004), serving as a precursor pool for effector cells, plasmatocytes and lamellocytes in the course of the cell mediated immune response (Zettervall et al, 2004;Márkus et al, 2009).…”

Elimination of plasmatocytes by targeted apoptosis reveals their role in multiple aspects of the Drosophila immune response

“…The second wave of hematopoiesis occurs at the larval stage in the lymph gland. The precursors of the lymph gland derive from the dorsal thoracic mesoderm and subsequently grow during the first and second larval instars (12)(13)(14)(15). At the third-instar larval stage, the lymph gland is the main site of hemocyte production.…”