The zebrafish: A fintastic model for hematopoietic development and disease

Journal of Leukocyte Biology

Gomez

lyer

et al. 2020

The mononuclear phagocytic system consists of many cells, in particular macrophages, scattered throughout the body. However, there is increasing evidence for the heterogeneity of tissue‐resident macrophages, leading to a pressing need for new tools to discriminate mononuclear phagocytic system subsets from other hematopoietic lineages. Macrophage‐expressed gene (Mpeg)1.1 is an evolutionary conserved gene encoding perforin‐2, a pore‐forming protein associated with host defense against pathogens. Zebrafish mpeg1.1:GFP and mpeg1.1:mCherry reporters were originally established to specifically label macrophages. Since then more than 100 peer‐reviewed publications have made use of mpeg1.1‐driven transgenics for in vivo studies, providing new insights into key aspects of macrophage ontogeny, activation, and function. Whereas the macrophage‐specific expression pattern of the mpeg1.1 promoter has been firmly established in the zebrafish embryo, it is currently not known whether this specificity is maintained through adulthood. Here we report direct evidence that beside macrophages, a subpopulation of B‐lymphocytes is marked by mpeg1.1 reporters in most adult zebrafish organs. These mpeg1.1+ lymphoid cells endogenously express mpeg1.1 and can be separated from mpeg1.1+ macrophages by virtue of their light‐scatter characteristics using FACS. Remarkably, our analyses also revealed that B‐lymphocytes, rather than mononuclear phagocytes, constitute the main mpeg1.1‐positive population in irf8null myeloid‐defective mutants, which were previously reported to recover tissue‐resident macrophages in adulthood. One notable exception is skin macrophages, whose development and maintenance appear to be independent from irf8, similar to mammals. Collectively, our findings demonstrate that irf8 functions in myelopoiesis are evolutionary conserved and highlight the need for alternative macrophage‐specific markers to study the mononuclear phagocytic system in adult zebrafish.

Section: Introductionmentioning

confidence: 99%

Themacrophage-expressed gene(mpeg)1identifies a subpopulation of B cells in the adult zebrafish

Journal of Leukocyte Biology

Gomez

lyer

et al. 2020

“…Zebrafish are particularly suitable to study immune cell development in vivo as they develop ex utero, are genetically tractable, and are transparent during early development (Ellett and Lieschke, 2010; Gore et al, 2018). We used our previously generated zebrafish line that is deficient for both csf1ra and csf1rb paralogs ( csf1r DM ), since the phenotypes of these fish, such as osteopetrosis and a lack of microglia, resemble those observed in mice, rats and humans (Caetano-Lopes et al, 2020; Chatani et al, 2011; Dai et al, 2002; Guo et al, 2019; Meireles et al, 2014; Oosterhof et al, 2019b; Oosterhof et al, 2018b; Pridans et al, 2018).…”

Section: Introductionmentioning

confidence: 99%

Zebrafish macrophage developmental arrest underlies depletion of microglia and reveals Csf1r-independent metaphocytes

Kuil

Oosterhof

et al. 2020

Preprint

20Macrophages derive from multiple sources of hematopoietic progenitors. Most macrophages 21 require colony-stimulating factor 1 receptor (CSF1R), but some macrophages persist in the 22 absence of CSF1R. Here, we analyzed mpeg1:GFP-expressing macrophages in csf1r-23 deficient zebrafish and report that embryonic macrophages emerge followed by their 24 developmental arrest. In larvae, mpeg1+ cell numbers then increased showing two distinct 25 types in the skin: branched, putative Langerhans cells, and amoeboid cells. In contrast, 26 although numbers also increased in csf1r-mutants, exclusively amoeboid mpeg1+ cells were 27 present, which we showed by genetic lineage tracing to have a non-hematopoietic origin. 28They expressed macrophage-associated genes, but also showed decreased phagocytic 29 gene expression and increased epithelial-associated gene expression, characteristic of 30 metaphocytes, recently discovered ectoderm-derived cells. We further demonstrated that 31 juvenile csf1r-deficient zebrafish exhibit systemic macrophage depletion. Thus, Csf1r 32 deficiency disrupts embryonic to adult macrophage development. Csf1r-deficient zebrafish 33 are viable and permit analyzing the consequences of macrophage loss throughout life. 34 35 36 106 fate mapping and gene expression profiling, we identified csf1r DM mpeg1+ cells as 107 metaphocytes, a population of ectoderm-derived macrophage-like cells recently reported in 108 zebrafish (Alemany et al., 2018a; Lin et al., 2019). Extending our analyses, we further 109 demonstrated that adult csf1r DM fish exhibit a global defect in macrophage generation. In 110 5 conclusion, our study highlights distinct requirements for Csf1r during macrophage 111 generation and metaphocyte ontogeny, resolving part of the presumed macrophage 112 heterogeneity and their sensitivity to loss of Csf1r. 113 Results 114Zebrafish embryonic macrophages are formed independently of csf1r but display 115 migration and proliferation defects 207 both csf1r DM primitive macrophages and early microglia. 208Next, we assessed the presence of macrophages in developing csf1r DM animals by in 209 vivo fluorescence imaging of one lateral side of entire, individual larvae on 4 consecutive 210 days, starting at 5 dpf. We visualized ~450 macrophages in control animals, whereas csf1r DM 211 animals contained > 4-fold fewer (~100) ( Figure 3D). Over the next 4 days, macrophage 212 numbers in both groups remained stable ( Figure 3D). This suggests that, at this stage, there 213 is neither proliferative expansion of embryonic macrophages nor supply of macrophages 214 from an alternative source, causing macrophage numbers in csf1r DM larvae to remain much 215 lower than those in controls up to 9 dpf. Together these data indicate that, onwards from the 216 initiation of embryonic tissue colonization, proliferative expansion of macrophages remains 217 halted in csf1r DM animals.218 219 csf1r DM skin lacks highly branched putative Langerhans cells 220 8Given that macrophages are produced by consecutive waves of primiti...

“…Over the last decades, the zebrafish has become a powerful model to study biological processes conserved with mammals 1,2 . In the fields of hematopoiesis and immunology, zebrafish has provided a new level of precision in understanding key aspects of developmental immunity and disease 3,4 , some of which are currently being tested in the clinic 5 . Consequently, many efforts have been engaged to thoroughly characterize the zebrafish immune system.…”

Section: Introductionmentioning

confidence: 99%

Themacrophage-expressed gene(mpeg)1identifies a subpopulation of B cells in the adult zebrafish

Gomez

Iyer

et al. 2019

Preprint

SENTENCEMpeg1 is not a restricted macrophage marker, but also labels B cells in the adult zebrafish. Therefore, previously identified irf8-independent macrophages likely consist of B lymphocytes. 2 ABSTRACTThe mononuclear phagocytic system (MPS) consists of many cells, in particular macrophages, scattered throughout the body. However, there is increasing evidence for the heterogeneity of tissue-resident macrophages, leading to a pressing need for new tools to discriminate MPS subsets from other hematopoietic lineages. Mpeg1.1 is an evolutionary conserved gene encoding perforin-2, a pore-forming protein associated with host defense against pathogens. Zebrafish mpeg1.1:GFP and mpeg1.1:mCherry reporters were originally established to specifically label macrophages. Since, more than 100 peer-reviewed publications have made use of mpeg1.1-driven transgenics for in vivo studies, providing new insights into key aspects of macrophage ontogeny, activation and function. However, while the macrophagespecific expression pattern of the mpeg1.1 promoter has been firmly established in the zebrafish embryo, it is currently not known whether this specificity is maintained through adulthood. Here we report direct evidence that beside macrophages, a subpopulation of B-lymphocytes is marked by mpeg1.1 reporters in most adult zebrafish organs. These mpeg1.1 + lymphoid cells endogenously express mpeg1.1 and can be separated from mpeg1.1 + macrophages by virtue of their light-scatter characteristics using FACS. Remarkably, our analyses also revealed that Blymphocytes, rather than mononuclear phagocytes, constitute the main mpeg1.1positive population in irf8 null myeloid-defective mutants, which were previously reported to recover tissue-resident macrophages in adulthood. One notable exception are skin macrophages, whose development and maintenance appear to be independent from irf8, similar to mammals. Collectively, our findings demonstrate that irf8 functions in myelopoiesis are evolutionary conserved and highlight the need for alternative macrophage-specific markers to study the MPS in adult zebrafish.