Drosophilahematopoiesis under normal conditions and in response to immune stress

Abstract

The emergence of hematopoietic progenitors and their differentiation into various highly specialized blood cell types constitute a finely tuned process. Unveiling the genetic cascades that control blood cell progenitor fate and understanding how they are modulated in response to environmental changes are two major challenges in the field of hematopoiesis. In the last 20 years, many studies have established important functional analogies between blood cell development in vertebrates and in the fruit fly, Drosophila melanogaster. Thereby, Drosophila has emerged as a powerful genetic model for studying mechanisms that control hematopoiesis during normal development or in pathological situations. Moreover, recent advances in Drosophila have highlighted how intricate cell communication networks and microenvironmental cues regulate blood cell homeostasis. They have also revealed the striking plasticity of Drosophila mature blood cells and the presence of different sites of hematopoiesis in the larva. This review provides an overview of Drosophila hematopoiesis during development and summarizes our current knowledge on the molecular processes controlling larval hematopoiesis, both under normal conditions and in response to an immune challenge, such as wasp parasitism.

Innate and intrinsic antiviral immunity in Drosophila

“…Proteolytic cascades involving sequential activation of serine proteases participate in the activation of the Toll pathway, and in the clotting and melanization responses to wounding [7, 8]. Cellular responses involving both circulating and sessile hemocytes also participate in antimicrobial host defense in flies, in particular via phagocytosis of bacteria by macrophage-like plasmatocytes and encapsulation of parasitic wasp eggs in larvae by lamellocytes [9–11]. …”

Control of RUNX-induced repression of Notch signaling by MLF and its partner DnaJ-1 during Drosophila hematopoiesis

“…Indeed, a number of proteins regulating blood cell development in human, such as RUNX and Notch, also control Drosophila blood cell development [27]. In Drosophila , the RUNX factor Lozenge (Lz) is specifically expressed in crystal cells and it is absolutely required for the development of this blood cell lineage [28].…”

“…In Drosophila , the RUNX factor Lozenge (Lz) is specifically expressed in crystal cells and it is absolutely required for the development of this blood cell lineage [28]. Crystal cells account for ±4% of the circulating larval blood cells; they are implicated in melanization, a defense response related to clotting, and they release their enzymatic content in the hemolymph by bursting [27]. The Notch pathway also controls the development of this lineage: it is required for the induction of Lz expression and it contributes to Lz + cell differentiation as well as to their survival by preventing their rupture [28–31].…”

The matrix protein Tiggrin regulates plasmatocyte maturation inDrosophilalarva

“…In addition, a small group of cells termed the posterior signaling center (PSC) controls differentiation and specification of hemocytes in the CZ (Benmimoun et al, 2015;Oyallon et al, 2016). Although much remains to be understood, the fly LG has developed into a powerful model for hematopoiesis and stem cell/progenitor regulation (Crozatier and Meister, 2007;Crozatier and Vincent, 2011;Letourneau et al, 2016;Martinez-Agosto et al, 2007;MorinPoulard et al, 2013;Shim et al, 2013). …”

“…Plasmatocytes contribute about 95% of all mature hemocytes in healthy animals (Crozatier and Meister, 2007;Letourneau et al, 2016). These cells are the equivalent of mammalian macrophages, which are able to clean both apoptotic debris and foreign materials (Gold and Brückner, 2015).…”