Mol. Cells 2020; 43(2): 114-120
Published online January 29, 2020
https://doi.org/10.14348/molcells.2019.0249
© The Korean Society for Molecular and Cellular Biology
Correspondence to : *Correspondence: jshim@hanyang.ac.kr
This is an open-access article distributed under the terms of the Creative Commons Attribution-NonCommercial-ShareAlike 3.0 Unported License. To view a copy of this license, visit http://creativecommons.org/licenses/by-nc-sa/3.0/.
Drosophila hematopoiesis is comparable to mammalian differentiation of myeloid lineages, and therefore, has been a useful model organism in illustrating the molecular and genetic basis for hematopoiesis. Multiple novel regulators and signals have been uncovered using the tools of Drosophila genetics. A Runt domain protein, lozenge, is one of the first players recognized and closely studied in the hematopoietic lineage specification. Here, we explore the role of lozenge in determination of prohemocytes into a special class of hemocyte, namely the crystal cell, and discuss molecules and signals controlling the lozenge function and its implication in immunity and stress response. Given the highly conserved nature of Runt domain in both invertebrates and vertebrates, studies in Drosophila will enlighten our perspectives on Runx-mediated development and pathologies.
Keywords crystal cells, Drosophila melanogaster, hematopoiesis, lozenge, lymph gland, melanization, prophenoloxidase, RUNX
The fruit fly is a holometabolous insect which undergoes four distinct phases in its development with each stage emphatically different in both anatomy and physiology (Fig. 1A) (Snodgrass, 1954). In brief, the adult female produces fertilized eggs after copulation, which then undergoes stages of internal rearrangements to form an embryo. Upon hatching, a larva goes through two more molts while consistently feeding before turning into a pupa. Active feeding at this stage ceases, allowing internal and external structures to be generated or reorganized within the pupal case (Ashburner and Novitski, 1976). A winged fly emerges after four to five days from the point of pupa formation, but the whole cycle takes about ten days under normal conditions. The emergent fly can fly and feed after a couple of hours and generally lives up to fifty days, within which the cycle is repeated several times (Linford et al., 2013; Robertson, 1936; Stocker and Gallant, 2008).
Hematopoiesis in the fruit fly, though very multifaceted, is mainly classified into two waves: primitive and definitive hematopoiesis (Evans et al., 2003). In the first wave or primitive hematopoiesis, hemocytes are derived from the embryonic head mesoderm from which point they migrate to designated areas and facilitate organogenesis and immune responses (Holz et al., 2003; Moreira et al., 2010; Olofsson and Page, 2005; Tepass et al., 1994; Wood et al., 2006). Upon hatching, hemocytes are released either into circulation or to specialized sites including the hematopoietic pockets. During larval stages, these hemocytes perform diverse functions including phagocytosis of debris, immune responses, and metabolic regulation (Agaisse et al., 2003; Elrod-Erickson et al., 2000; Lanot et al., 2001; Lebestky et al., 2000; Makhijani et al., 2011; Márkus et al., 2009; Tepass et al., 1994).
The second wave or definitive hematopoiesis occurs in a specific organ called the lymph gland (Rugendorff et al., 1994). The lymph gland originates from the cardiogenic mesoderm, distinctive from the embryonic lineage, which later differentiates into hemangioblast-like cells that give rise to the posterior signaling center (PSC) and pre-prohemocytes (Crozatier et al., 2004; Krzemień et al., 2007; Mandal et al., 2004; 2007; Rugendorff et al., 1994). Pre-prohemocytes turn into prohemocytes which produces three types of mature hemocytes: plasmatocytes, crystal cells, and lamellocytes (Jung et al., 2005; Krzemien et al., 2010; Lebestky et al., 2000; Shrestha and Gateff, 1982). The late-third-instar larval lymph gland is comprised of four pairs of lobes of which the biggest—the primary lobe—is further divided into four areas: the PSC, the medullary zone (MZ), the cortical zone (CZ), and the intermediate zone (IZ) (Fig. 1B) (Ferguson and Martinez-Agosto, 2014b; Krzemień et al., 2007; Krzemien et al., 2010; Mandal et al., 2007). The posterior lobes express similar markers as the primary lobe, yet, their detailed functions remain uncharacterized (Grigorian et al., 2011; Jung et al., 2005). The PSC, located at the medio-posterior region of the lymph gland, serves as a signaling center for the maintenance of prohemocytes (Crozatier et al., 2004; Krzemień et al., 2007; Lebestky et al., 2003; Mandal et al., 2004). Recent studies have suggested that the dorsal vessel plays additional signaling roles for the regulation of prohemocytes (Morin-Poulard et al., 2016). Closest to the PSC and the dorsal vessel is the MZ, possessing potentials to generate mature hemocytes of the lymph gland (Jung et al., 2005). The MZ is connected to the CZ via the IZ (Blanco-Obregon et al., 2019). The IZ is identified by reactive oxygen species (ROS),
During normal development, both circulation and the lymph gland maintain constant ratios of mature hemocytes. Plasmatocytes generally make up approximately 95% of the total hemocytes whereas crystal cells cover 5% (Bangs et al., 2000; De Gregorio et al., 2002; Holz et al., 2003; Lanot et al., 2001; Ramet et al., 2002; Rizki, 1957; Shrestha and Gateff, 1982; Tepass et al., 1994). Another group of hemocytes, which are seen under severe immune responses, is lamellocytes (Brehelin, 1982; Lanot et al., 2001; Rizki, 1957). Lamellocytes encapsulate eggs deposited by parasitic wasps into the larva and neutralize them as an active defense mechanism (Carton et al., 2008; Keebaugh and Schlenke, 2013; Russo et al., 1996).
Runt is a DNA-binding domain first identified in
In
Similarly, in the second instar larval lymph gland,
In addition to GATA and Zinc finger transcription factors,
Crystal cells are responsible for a significant part of the
Extensive and thorough studies on
This work was supported by National Research Foundation (NRF) grant funded by the Ministry of Science and ICT, Republic of Korea (NRF-2019R1A2C2006848) to J.S.
The authors thank members of the Shim lab for helpful discussions, and Bumsik Cho for Figure illustrations.
The authors have no potential conflicts of interest to disclose.
Mol. Cells 2020; 43(2): 114-120
Published online February 29, 2020 https://doi.org/10.14348/molcells.2019.0249
Copyright © The Korean Society for Molecular and Cellular Biology.
Ferdinand Koranteng1,4 , Nuri Cha1,4
, Mingyu Shin1,4
, and Jiwon Shim1,2,3,*
1Department of Life Science, Hanyang University, Seoul 04763, Korea, 2Research Institute for Natural Science, Hanyang University, Seoul 04763, Korea, 3Research Institute for Convergence of Basic Sciences, Hanyang University, Seoul 04763, Korea, 4These authors contributed equally to this work.
Correspondence to:*Correspondence: jshim@hanyang.ac.kr
This is an open-access article distributed under the terms of the Creative Commons Attribution-NonCommercial-ShareAlike 3.0 Unported License. To view a copy of this license, visit http://creativecommons.org/licenses/by-nc-sa/3.0/.
Drosophila hematopoiesis is comparable to mammalian differentiation of myeloid lineages, and therefore, has been a useful model organism in illustrating the molecular and genetic basis for hematopoiesis. Multiple novel regulators and signals have been uncovered using the tools of Drosophila genetics. A Runt domain protein, lozenge, is one of the first players recognized and closely studied in the hematopoietic lineage specification. Here, we explore the role of lozenge in determination of prohemocytes into a special class of hemocyte, namely the crystal cell, and discuss molecules and signals controlling the lozenge function and its implication in immunity and stress response. Given the highly conserved nature of Runt domain in both invertebrates and vertebrates, studies in Drosophila will enlighten our perspectives on Runx-mediated development and pathologies.
Keywords: crystal cells, Drosophila melanogaster, hematopoiesis, lozenge, lymph gland, melanization, prophenoloxidase, RUNX
The fruit fly is a holometabolous insect which undergoes four distinct phases in its development with each stage emphatically different in both anatomy and physiology (Fig. 1A) (Snodgrass, 1954). In brief, the adult female produces fertilized eggs after copulation, which then undergoes stages of internal rearrangements to form an embryo. Upon hatching, a larva goes through two more molts while consistently feeding before turning into a pupa. Active feeding at this stage ceases, allowing internal and external structures to be generated or reorganized within the pupal case (Ashburner and Novitski, 1976). A winged fly emerges after four to five days from the point of pupa formation, but the whole cycle takes about ten days under normal conditions. The emergent fly can fly and feed after a couple of hours and generally lives up to fifty days, within which the cycle is repeated several times (Linford et al., 2013; Robertson, 1936; Stocker and Gallant, 2008).
Hematopoiesis in the fruit fly, though very multifaceted, is mainly classified into two waves: primitive and definitive hematopoiesis (Evans et al., 2003). In the first wave or primitive hematopoiesis, hemocytes are derived from the embryonic head mesoderm from which point they migrate to designated areas and facilitate organogenesis and immune responses (Holz et al., 2003; Moreira et al., 2010; Olofsson and Page, 2005; Tepass et al., 1994; Wood et al., 2006). Upon hatching, hemocytes are released either into circulation or to specialized sites including the hematopoietic pockets. During larval stages, these hemocytes perform diverse functions including phagocytosis of debris, immune responses, and metabolic regulation (Agaisse et al., 2003; Elrod-Erickson et al., 2000; Lanot et al., 2001; Lebestky et al., 2000; Makhijani et al., 2011; Márkus et al., 2009; Tepass et al., 1994).
The second wave or definitive hematopoiesis occurs in a specific organ called the lymph gland (Rugendorff et al., 1994). The lymph gland originates from the cardiogenic mesoderm, distinctive from the embryonic lineage, which later differentiates into hemangioblast-like cells that give rise to the posterior signaling center (PSC) and pre-prohemocytes (Crozatier et al., 2004; Krzemień et al., 2007; Mandal et al., 2004; 2007; Rugendorff et al., 1994). Pre-prohemocytes turn into prohemocytes which produces three types of mature hemocytes: plasmatocytes, crystal cells, and lamellocytes (Jung et al., 2005; Krzemien et al., 2010; Lebestky et al., 2000; Shrestha and Gateff, 1982). The late-third-instar larval lymph gland is comprised of four pairs of lobes of which the biggest—the primary lobe—is further divided into four areas: the PSC, the medullary zone (MZ), the cortical zone (CZ), and the intermediate zone (IZ) (Fig. 1B) (Ferguson and Martinez-Agosto, 2014b; Krzemień et al., 2007; Krzemien et al., 2010; Mandal et al., 2007). The posterior lobes express similar markers as the primary lobe, yet, their detailed functions remain uncharacterized (Grigorian et al., 2011; Jung et al., 2005). The PSC, located at the medio-posterior region of the lymph gland, serves as a signaling center for the maintenance of prohemocytes (Crozatier et al., 2004; Krzemień et al., 2007; Lebestky et al., 2003; Mandal et al., 2004). Recent studies have suggested that the dorsal vessel plays additional signaling roles for the regulation of prohemocytes (Morin-Poulard et al., 2016). Closest to the PSC and the dorsal vessel is the MZ, possessing potentials to generate mature hemocytes of the lymph gland (Jung et al., 2005). The MZ is connected to the CZ via the IZ (Blanco-Obregon et al., 2019). The IZ is identified by reactive oxygen species (ROS),
During normal development, both circulation and the lymph gland maintain constant ratios of mature hemocytes. Plasmatocytes generally make up approximately 95% of the total hemocytes whereas crystal cells cover 5% (Bangs et al., 2000; De Gregorio et al., 2002; Holz et al., 2003; Lanot et al., 2001; Ramet et al., 2002; Rizki, 1957; Shrestha and Gateff, 1982; Tepass et al., 1994). Another group of hemocytes, which are seen under severe immune responses, is lamellocytes (Brehelin, 1982; Lanot et al., 2001; Rizki, 1957). Lamellocytes encapsulate eggs deposited by parasitic wasps into the larva and neutralize them as an active defense mechanism (Carton et al., 2008; Keebaugh and Schlenke, 2013; Russo et al., 1996).
Runt is a DNA-binding domain first identified in
In
Similarly, in the second instar larval lymph gland,
In addition to GATA and Zinc finger transcription factors,
Crystal cells are responsible for a significant part of the
Extensive and thorough studies on
This work was supported by National Research Foundation (NRF) grant funded by the Ministry of Science and ICT, Republic of Korea (NRF-2019R1A2C2006848) to J.S.
The authors thank members of the Shim lab for helpful discussions, and Bumsik Cho for Figure illustrations.
The authors have no potential conflicts of interest to disclose.
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