Abstract
Hematopoiesis is a necessary process for development and immune defense in Drosophila from the embryonic period to adulthood. There are two main stages in this process: the first stage occurs in the head mesoderm during the embryonic stage, and the second occurs in a specialized hematopoietic organ along the dorsal vessel, the lymph gland, during the larval stage. The lymph gland consists of paired lobes, each of which has distinct regions: the cortical zone (CZ), which contains mature hemocytes; the medullary zone (MZ), which contains hematopoietic progenitors; and the posterior signaling center (PSC), which specifically expresses the early B-cell factor (EBF) transcription factor Collier (Col) and the HOX factor Antennapedia (Antp) to form a microenvironment similar to that of the mammalian bone marrow hematopoietic stem cell niche. The PSC plays a key role in regulating hematopoietic progenitor differentiation. Moreover, the PSC contributes to the cellular immune response to wasp parasitism triggered by elevated ROS levels. Two recent studies have revealed that hematopoietic progenitor maintenance is directly regulated by Col expressed in the MZ and is independent of the PSC, challenging the traditional model. In this review, we summarize the regulatory networks of PSC cell proliferation, the controversy regarding PSC-mediated regulation of hematopoietic progenitor differentiation, and the wasp egg infection response. In addition, we discuss why the PSC is an ideal model for investigating mammalian hematopoietic stem cell niches and leukemia.
Highlights
Hematopoiesis in Drosophila and vertebrates is highly conserved, and there are significant similarities in the molecular mechanisms between the cardiogenic mesoderm in Drosophila and the aorta-gonadal-mesonephros mesoderm in mammals (Medvinsky and Dzierzak, 1996; Mandal et al, 2004)
These findings suggest that the epidermal growth factor receptor (EGFR) and Toll/nuclear factor κB (NFκB) pathways may act in parallel in response to wasp infection in posterior signaling center (PSC) cells to regulate lamellocyte differentiation
The Drosophila lymph gland is a powerful model for studying hematopoiesis, and the PSC has become an ideal model for studying niche interactions with hematopoietic stem cells (HSCs)
Summary
Hematopoiesis in Drosophila and vertebrates is highly conserved, and there are significant similarities in the molecular mechanisms between the cardiogenic mesoderm in Drosophila and the aorta-gonadal-mesonephros mesoderm in mammals (Medvinsky and Dzierzak, 1996; Mandal et al, 2004). The cardiogenic mesoderm of the embryo subsequently becomes a specialized organ, the lymph gland, and another hematopoietic pool is created in the larval stage (Shrestha and Gateff, 1982; Jung et al, 2005). In the third larval stage, the Drosophila lymph gland matures and can be separated into three distinct zones: the cortical zone (CZ), the medullary zone (MZ) and the posterior signaling center (PSC) (Jung et al, 2005). The CZ consists of mature hemocytes, including plasmatocytes and crystal cells, whereas the MZ, located in the inner region of each lymph gland lobe, contains hematopoietic progenitors that can differentiate into mature hemocytes. Immune Response to Parasitic Wasp Infection”) (Crozatier et al, 2004; Sinenko et al, 2012; Louradour et al, 2017)
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