Key Points We have inserted a FRed reporter cassette into the mouse Csf1r locus. Expression of CSF1R-FRed is restricted to cells of the mononuclear phagocyte lineage. CSF1R-FRed is absent from lineage-negative stem cell populations in bone marrow. The proliferation, differentiation, and survival of cells of the mononuclear phagocyte system (MPS; progenitors, monocytes, macrophages, and classical dendritic cells) are controlled by signals from the M-CSF receptor (CSF1R). Cells of the MPS lineage have been identified using numerous surface markers and transgenic reporters, but none is both universal and lineage restricted. In this article, we report the development and characterization of a CSF1R reporter mouse. A FusionRed (FRed) cassette was inserted in-frame with the C terminus of CSF1R, separated by a T2A-cleavable linker. The insertion had no effect of CSF1R expression or function. CSF1R-FRed was expressed in monocytes and macrophages and absent from granulocytes and lymphocytes. In bone marrow, CSF1R-FRed was absent in lineage-negative hematopoietic stem cells, arguing against a direct role for CSF1R in myeloid lineage commitment. It was highly expressed in marrow monocytes and common myeloid progenitors but significantly lower in granulocyte-macrophage progenitors. In sections of bone marrow, CSF1R-FRed was also detected in osteoclasts, CD169+ resident macrophages, and, consistent with previous mRNA analysis, in megakaryocytes. In lymphoid tissues, CSF1R-FRed highlighted diverse MPS populations, including classical dendritic cells. Whole mount imaging of nonlymphoid tissues in mice with combined CSF1R-FRed/Csf1r-EGFP confirmed the restriction of CSF1R expression to MPS cells. The two markers highlight the remarkable abundance and regular distribution of tissue MPS cells, including novel macrophage populations within tendon and skeletal muscle and underlying the mesothelial/serosal/capsular surfaces of every major organ. The CSF1R-FRed mouse provides a novel reporter with exquisite specificity for cells of the MPS.

中文翻译：

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一种报告 CSF1R 蛋白表达的转基因品系为小鼠单核吞噬细胞系统提供了明确的标志物

关键点 我们已将 FRed 报告基因盒插入小鼠 Csf1r 基因座中。CSF1R-FRed 的表达仅限于单核吞噬细胞谱系的细胞。骨髓中的谱系阴性干细胞群中不存在 CSF1R-FRed。单核吞噬细胞系统（MPS；祖细胞、单核细胞、巨噬细胞和经典树突细胞）的增殖、分化和存活受来自 M-CSF 受体 (CSF1R) 的信号控制。已经使用多种表面标记和转基因报告基因鉴定了 MPS 谱系的细胞，但没有一个是通用的且谱系受限的。在本文中，我们报告了 CSF1R 报告小鼠的开发和表征。FusionRed (FRed) 盒与 CSF1R 的 C 端框内插入，由 T2A 可切割接头隔开。插入对 CSF1R 表达或功能没有影响。CSF1R-FRed 在单核细胞和巨噬细胞中表达，在粒细胞和淋巴细胞中不存在。在骨髓中，谱系阴性造血干细胞中不存在 CSF1R-FRed，反对 CSF1R 在骨髓谱系定型中的直接作用。它在骨髓单核细胞和常见髓系祖细胞中高度表达，但在粒细胞 - 巨噬细胞祖细胞中显着降低。在骨髓切片中，还在破骨细胞、CD169+ 常驻巨噬细胞中检测到 CSF1R-FRed，并且与之前的 mRNA 分析一致，在巨核细胞中也检测到了。在淋巴组织中，CSF1R-FRed 突出了不同的 MPS 群体，包括经典的树突细胞。CSF1R-FRed/Csf1r-EGFP 组合小鼠非淋巴组织的整体成像证实了 CSF1R 表达对 MPS 细胞的限制。这两个标记突出了组织 MPS 细胞的显着丰度和规律分布，包括肌腱和骨骼肌内以及每个主要器官的间皮/浆膜/囊表面下方的新型巨噬细胞群。CSF1R-FRed 小鼠为 MPS 细胞提供了一种具有精致特异性的新型报告基因。