Neutrophils are the most abundant type of leukocyte in the body, and are an important component of the rapid non-specific innate immune response. Our results demonstrate that mpx expression is controlled differently in the ALPM and PLPM regions and describe novel roles for etv2 and gata1 during primitive neutropoiesis. Intriguingly, initiation of mpx expression in the PLPM is dependent on gata1 but not etv2 function. Additionally, we demonstrate that mpx expression within the PLPM overlaps with gata1 expression, potentially marking the cells with a dual myelo-erythroid potential. We further show that Scl functions downstream of Etv2 in anterior neutropoiesis. Our results argue that ALPM-derived neutrophils originate from etv2-expressing cells which downregulate etv2 during neutropoiesis. Here we demonstrate using zebrafish embryos that Etv2 has a specific cell-autonomous function during primitive neutropoiesis in the anterior lateral plate mesoderm (ALPM) but has little effect on erythropoiesis or the posterior lateral plate mesoderm (PLPM) expression of neutrophil marker myeloperoxidase mpo/ mpx. However, its role during neutrophil development is not well understood. An ETS-family transcription factor Etsrp/Etv2/ER71 has been implicated in vasculogenesis and hematopoiesis in multiple vertebrates. In zebrafish embryos, it has been suggested that primitive neutrophils may originate in two distinct sites, the anterior (ALPM) and posterior lateral plate mesoderm (PLPM). In vertebrates the first neutrophils are thought to originate during primitive hematopoiesis, which precedes hematopoietic stem cell formation. Neutrophilic granulocytes are the most abundant type of myeloid cells and form an essential part of the innate immune system.
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