The function of the conserved regulatory element within the second intron of the mammalian Csf1r locus

Gene regulatory network analysis predicts cooperating transcription factor regulons required for FLT3-ITD+ AML growth

Acute myeloid leukemia (AML) is a heterogeneous disease caused by different mutations. Previously, we showed that each mutational subtype develops its specific gene regulatory network (GRN) with transcription factors interacting within multiple gene modules, many of which are transcription factor genes themselves. Here, we hypothesize that highly connected nodes within such networks comprise crucial regulators of AML maintenance. We test this hypothesis using FLT3-ITD-mutated AML as a model and conduct an shRNA drop-out screen informed by this analysis. We show that AML-specific GRNs predict crucial regulatory modules required for AML growth. Furthermore, our work shows that all modules are highly connected and regulate each other. The careful multi-omic analysis of the role of one (RUNX1) module by shRNA and chemical inhibition shows that this transcription factor and its target genes stabilize the GRN of FLT3-ITD+ AML and that its removal leads to GRN collapse and cell death.

Gene regulatory network analysis predicts cooperating transcription factor regulons required for FLT3-ITD+ AML growth

AML is a heterogenous disease caused by different mutations. We have previously shown that each mutational sub-type develops its specific gene regulatory network (GRN) with transcription factors interacting with multiple gene modules, many of which are transcription factor genes themselves. Here we hypothesized that highly connected nodes within such networks comprise crucial regulators of AML maintenance. We tested this hypothesis using FLT3-ITD mutated AML as a model and conducted an shRNA drop-out screen informed by this analysis. We show that AML-specific GRNs predict identifying crucial regulatory modules required for AML but not normal cellular growth. Furthermore, our work shows that all modules are highly connected and regulate each other. The careful multi-omic analysis of the role of one (RUNX1) module by shRNA and chemical inhibition shows that this transcription factor and its target genes stabilize the GRN of FLT3-ITD AML and that its removal leads to GRN collapse and cell death.

CNS Border-Associated Macrophages: Ontogeny and Potential Implication in Disease

Being immune privileged, the central nervous system (CNS) is constituted by unique parenchymal and non-parenchymal tissue-resident macrophages, namely, microglia and border-associated macrophages (BAMs), respectively. BAMs are found in the choroid plexus, meningeal and perivascular spaces, playing critical roles in maintaining CNS homeostasis while being phenotypically and functionally distinct from microglial cells. Although the ontogeny of microglia has been largely determined, BAMs need comparable scrutiny as they have been recently discovered and have not been thoroughly explored. Newly developed techniques have transformed our understanding of BAMs, revealing their cellular heterogeneity and diversity. Recent data showed that BAMs also originate from yolk sac progenitors instead of bone marrow-derived monocytes, highlighting the absolute need to further investigate their repopulation pattern in adult CNS. Shedding light on the molecular cues and drivers orchestrating BAM generation is essential for delineating their cellular identity. BAMs are receiving more attention since they are gradually incorporated into neurodegenerative and neuroinflammatory disease evaluations. The present review provides insights towards the current understanding regarding the ontogeny of BAMs and their involvement in CNS diseases, paving their way into targeted therapeutic strategies and precision medicine.

Epigenetics and tissue immunity-Translating environmental cues into functional adaptations

There is an increasing appreciation that many innate and adaptive immune cell subsets permanently reside within non-lymphoid organs, playing a critical role in tissue homeostasis and defense. The best characterized are macrophages and tissue-resident T lymphocytes that work in concert with organ structural cells to generate appropriate immune responses and are functionally shaped by organ-specific environmental cues. The interaction of tissue epithelial, endothelial and stromal cells is also required to attract, differentiate, polarize and maintain organ immune cells in their tissue niche. All of these processes require dynamic regulation of cellular transcriptional programmes, with epigenetic mechanisms playing a critical role, including DNA methylation and post-translational histone modifications. A failure to appropriately regulate immune cell transcription inevitably results in inadequate or inappropriate immune responses and organ pathology. Here, with a focus on the mammalian kidney, an organ which generates differing regional environmental cues (including hypersalinity and hypoxia) due to its physiological functions, we will review the basic concepts of tissue immunity, discuss the technologies available to profile epigenetic modifications in tissue immune cells, including those that enable single-cell profiling, and consider how these mechanisms influence the development, phenotype, activation and function of different tissue immune cell subsets, as well as the immunological function of structural cells.

A single-cell atlas of mouse olfactory bulb chromatin accessibility

Olfaction, the sense of smell, is a fundamental trait crucial to many species. The olfactory bulb (OB) plays pivotal roles in processing and transmitting odor information from the environment to the brain. The cellular heterogeneity of the mouse OB has been studied using single-cell RNA sequencing. However, the epigenetic landscape of the mOB remains mostly unexplored. Herein, we apply single-cell assay for transposase-accessible chromatin sequencing to profile the genome-wide chromatin accessibility of 9,549 single cells from the mOB. Based on single-cell epigenetic signatures, mOB cells are classified into 21 clusters corresponding to 11 cell types. We identify distinct sets of putative regulatory elements specific to each cell cluster from which putative target genes and enriched potential functions are inferred. In addition, the transcription factor motifs enriched in each cell cluster are determined to indicate the developmental fate of each cell lineage. Our study provides a valuable epigenetic data set for the mOB at single-cell resolution, and the results can enhance our understanding of regulatory circuits and the therapeutic capacity of the OB at the single-cell level.

CNS macrophages differentially rely on an intronic Csf1r enhancer for their development

The central nervous system hosts parenchymal macrophages, known as microglia, and non-parenchymal macrophages, collectively termed border-associated macrophages (BAMs). Microglia, but not BAMs, were reported to be absent in mice lacking a conserved Csf1r enhancer: the fms-intronic regulatory element (FIRE). However, it is unknown whether FIRE deficiency also impacts BAM arrival and/or maintenance. Here, we show that macrophages in the ventricular system of the brain, including Kolmer's epiplexus macrophages, are absent in Csf1r^{ΔFIRE/ΔFIRE} mice. Stromal choroid plexus BAMs are also considerably reduced. During normal development, we demonstrate that intracerebroventricular macrophages arrive from embryonic day 10.5, and can traverse ventricular walls in embryonic slice cultures. In Csf1r^{ΔFIRE/ΔFIRE} embryos, the arrival of both primitive microglia and intracerebroventricular macrophages was eliminated, whereas the arrival of cephalic mesenchyme and stromal choroid plexus BAMs was only partially restricted. Our results provide new insights into the development and regulation of different CNS macrophage populations.

Summary: Deletion of the fms-intronic regulatory element of Csf1r in mouse disrupts the engraftment and maintenance of central nervous system macrophages in a compartment-specific manner.

The M-CSF receptor in osteoclasts and beyond

Colony-stimulating factor 1 receptor (CSF1R, also known as c-FMS) is a receptor tyrosine kinase. Macrophage colony-stimulating factor (M-CSF) and IL-34 are ligands of CSF1R. CSF1R-mediated signaling is crucial for the survival, function, proliferation, and differentiation of myeloid lineage cells, including osteoclasts, monocytes/macrophages, microglia, Langerhans cells in the skin, and Paneth cells in the intestine. CSF1R also plays an important role in oocytes and trophoblastic cells in the female reproductive tract and in the maintenance and maturation of neural progenitor cells. Given that CSF1R is expressed in a wide range of myeloid cells, altered CSF1R signaling is implicated in inflammatory, neoplastic, and neurodegenerative diseases. Inhibiting CSF1R signaling through an inhibitory anti-CSF1R antibody or small molecule inhibitors that target the kinase activity of CSF1R has thus been a promising therapeutic strategy for those diseases. In this review, we cover the recent progress in our understanding of the various roles of CSF1R in osteoclasts and other myeloid cells, highlighting the therapeutic applications of CSF1R inhibitors in disease conditions.

Drugs directed at a key signaling receptor involved in breaking down bone tissue could help treat diseases marked by pathological bone loss and destruction. In a review article, Kyung-Hyun Park-Min and colleagues from the Hospital for Special Surgery in New York, USA, discuss the essential roles played by the colony-stimulating factor 1 receptor (CSF1R) protein in the survival, function, proliferation and differentiation of myeloid lineage stem cells in the bone marrow, including bone-resorbing osteoclasts. They explore the links between the CSF1R-mediated signaling pathway and diseases such as cancer and neurodegeneration. The authors largely focus on bone conditions, highlighting mouse studies in which CSF1R-blocking drugs were shown to ameliorate bone loss and inflammatory symptoms in models of arthritis, osteoporosis and metastatic cancer. Clinical trials are ongoing to test therapeutic applications.

Polymorphisms of CSF1R and WISP1 genes are associated with severity of familial adenomatous polyposis in APC1311 pigs

Hereditary familial adenomatous polyposis (FAP) in humans significantly increases the risk of development of colorectal cancer (CRC). Germline mutations in the APC (adenomatous polyposis coli) gene are responsible for FAP. Despite having the same causative mutation, the severity of the disease differs from patient to patient. The porcine FAP model carrying a truncating APC¹³¹¹ mutation, orthologous to the dominant human mutation that leads to severe form of the disease (APC¹³⁰⁹), mirrors the severity of polyposis. Earlier RNAseq studies have revealed the differential expression of WISP1 and CSF1R in samples derived from low-grade (LG-IEN) and more advanced high-grade (HG-IEN) colon polyps of APC^1311/+ pigs. The grade of dysplasia was correlated with the severity of polyposis in APC^1311/+ pigs characterized by a low (LP) and high (HP) numbers of polyps. The goal of this work was to find DNA variants that regulate the expression of CSF1R and WISP1 in LP and HP pigs. In total, 32 and 36 polymorphisms in CSF1R and WISP1 were found, respectively. Of these, the genotype frequency of four silent SNPs in the coding region of WISP1 differed significantly between LP and HP lines. In silico analysis revealed an elevated minimum free energy (MFE) for three of these SNPs, suggesting their role in mRNA structure stability. Furthermore, four polymorphisms in the promoter region of CSF1R, cosegregating as a common haplotype, were associated with polyp number in APC^1311/+ pigs. A secreted alkaline phosphatase (SEAP) assay showed, however, that these variants have no direct effect on the activity of the CSF1R promoter. Concluding, our study identified polymorphisms in CSF1R and WISP1 that are potentially associated with the severity of polyposis in APC^1311/+ pigs.

Deletion of a Csf1r enhancer selectively impacts CSF1R expression and development of tissue macrophage populations

The proliferation, differentiation and survival of mononuclear phagocytes depend on signals from the receptor for macrophage colony-stimulating factor, CSF1R. The mammalian Csf1r locus contains a highly conserved super-enhancer, the fms-intronic regulatory element (FIRE). Here we show that genomic deletion of FIRE in mice selectively impacts CSF1R expression and tissue macrophage development in specific tissues. Deletion of FIRE ablates macrophage development from murine embryonic stem cells. Csf1rΔFIRE/ΔFIRE mice lack macrophages in the embryo, brain microglia and resident macrophages in the skin, kidney, heart and peritoneum. The homeostasis of other macrophage populations and monocytes is unaffected, but monocytes and their progenitors in bone marrow lack surface CSF1R. Finally, Csf1rΔFIRE/ΔFIRE mice are healthy and fertile without the growth, neurological or developmental abnormalities reported in Csf1r-/- rodents. Csf1rΔFIRE/ΔFIRE mice thus provide a model to explore the homeostatic, physiological and immunological functions of tissue-specific macrophage populations in adult animals.

mTOR masters monocyte development in bone marrow by decreasing the inhibition of STAT5 on IRF8

Monocytes and macrophages play a key role in defending pathogens, removing the dead cells or cell debris, and wound healing. The mammalian target of rapamycin (mTOR) inhibitor rapamycin (RPM) is widely used in clinics to treat patients with organ transplantation or tumors. The role of mTOR in monocyte/macrophage development remains to be clarified. Here we found that mTOR intrinsically controls monocyte/macrophage development, as evidenced by the decreased percentages and cell numbers of CD11b⁺F4/80⁺ cells resulting from mTOR inhibition in SCID mice, mTOR-deficient mice, and mixed chimera mice, and the in vitro colony formation and monocyte/macrophage induction assays. However, Lyzs-mTOR knockout mice displayed normal levels of monocytes/macrophages, indicating that mTOR is not essential for the survival and maturation of monocytes/macrophages. Further studies showed that mTOR deficiency significantly reduced macrophage colony-stimulating factor receptor CD115 expression at the transcriptional and translational levels. The molecular mechanism studies indicate that the impaired monocyte/macrophage development caused by mTOR deficiency is mainly a result of the overactivated STAT5 and subsequent downregulation of IRF8, but not the altered cell metabolism and autophagy. Therefore, our work identifies that mTOR is an intrinsic master for monocyte/macrophage development at the early stages through regulating STAT5-IRF8-dependent CD115-expressing pathway. Long-term usage of RPM may cause a defect of myeloid progenitors in bone marrow.

The evolution of the macrophage-specific enhancer (Fms intronic regulatory element) within the CSF1R locus of vertebrates

The Csf1r locus encodes the receptor for macrophage colony-stimulating factor, which controls the proliferation, differentiation and survival of macrophages. The 300 bp Fms intronic regulatory element (FIRE), within the second intron of Csf1r, is necessary and sufficient to direct macrophage-specific transcription. We have analysed the conservation and divergence of the FIRE DNA sequence in vertebrates. FIRE is present in the same location in the Csf1r locus in reptile, avian and mammalian genomes. Nearest neighbor analysis based upon this element alone largely recapitulates phylogenies inferred from much larger genomic sequence datasets. One core element, containing binding sites for AP1 family and the macrophage-specific transcription factor, PU.1, is conserved from lizards to humans. Around this element, the FIRE sequence is conserved within clades with the most conserved elements containing motifs for known myeloid-expressed transcription factors. Conversely, there is little alignment between clades outside the AP1/PU.1 element. The analysis favours a hybrid between “enhanceosome” and “smorgasbord” models of enhancer function, in which elements cooperate to bind components of the available transcription factor milieu.

Transcriptional mechanisms that control expression of the macrophage colony-stimulating factor receptor locus

The proliferation, differentiation, and survival of cells of the macrophage lineage depends upon signals from the macrophage colony-stimulating factor (CSF) receptor (CSF1R). CSF1R is expressed by embryonic macrophages and induced early in adult hematopoiesis, upon commitment of multipotent progenitors to the myeloid lineage. Transcriptional activation of CSF1R requires interaction between members of the E26 transformation-specific family of transcription factors (Ets) (notably PU.1), C/EBP, RUNX, AP-1/ATF, interferon regulatory factor (IRF), STAT, KLF, REL, FUS/TLS (fused in sarcoma/ranslocated in liposarcoma) families, and conserved regulatory elements within the mouse and human CSF1R locus. One element, the Fms-intronic regulatory element (FIRE), within intron 2, is conserved functionally across all the amniotes. Lineage commitment in multipotent progenitors also requires down-regulation of specific transcription factors such as MYB, FLI1, basic leucine zipper transcriptional factor ATF-like (BATF3), GATA-1, and PAX5 that contribute to differentiation of alternative lineages and repress CSF1R transcription. Many of these transcription factors regulate each other, interact at the protein level, and are themselves downstream targets of CSF1R signaling. Control of CSF1R transcription involves feed–forward and feedback signaling in which CSF1R is both a target and a participant; and dysregulation of CSF1R expression and/or function is associated with numerous pathological conditions. In this review, we describe the regulatory network behind CSF1R expression during differentiation and development of cells of the mononuclear phagocyte system.

Transcriptional Regulation and Macrophage Differentiation

Monocytes and macrophages are professional phagocytes that occupy specific niches in every tissue of the body. Their survival, proliferation, and differentiation are controlled by signals from the macrophage colony-stimulating factor receptor (CSF-1R) and its two ligands, CSF-1 and interleukin-34. In this review, we address the developmental and transcriptional relationships between hematopoietic progenitor cells, blood monocytes, and tissue macrophages as well as the distinctions from dendritic cells. A huge repertoire of receptors allows monocytes, tissue-resident macrophages, or pathology-associated macrophages to adapt to specific microenvironments. These processes create a broad spectrum of macrophages with different functions and individual effector capacities. The production of large transcriptomic data sets in mouse, human, and other species provides new insights into the mechanisms that underlie macrophage functional plasticity.

Chromatin programming by developmentally regulated transcription factors: lessons from the study of haematopoietic stem cell specification and differentiation

Although the body plan of individuals is encoded in their genomes, each cell type expresses a different gene expression programme and therefore has access to only a subset of this information. Alterations to gene expression programmes are the underlying basis for the differentiation of multiple cell types and are driven by tissue-specific transcription factors (TFs) that interact with the epigenetic regulatory machinery to programme the chromatin landscape into transcriptionally active and inactive states. The haematopoietic system has long served as a paradigm for studying the molecular principles that regulate gene expression in development. In this review article, we summarize the current knowledge on the mechanism of action of TFs regulating haematopoietic stem cell specification and differentiation, and place this information into the context of general principles governing development.

A Csf1r-EGFP Transgene Provides a Novel Marker for Monocyte Subsets in Sheep

Expression of Csf1r in adults is restricted to cells of the macrophage lineage. Transgenic reporters based upon the Csf1r locus require inclusion of the highly conserved Fms-intronic regulatory element for expression. We have created Csf1r-EGFP transgenic sheep via lentiviral transgenesis of a construct containing elements of the mouse Fms-intronic regulatory element and Csf1r promoter. Committed bone marrow macrophage precursors and blood monocytes express EGFP in these animals. Sheep monocytes were divided into three populations, similar to classical, intermediate, and nonclassical monocytes in humans, based upon CD14 and CD16 expression. All expressed EGFP, with increased levels in the nonclassical subset. Because Csf1r expression coincides with the earliest commitment to the macrophage lineage, Csf1r-EGFP bone marrow provides a tool for studying the earliest events in myelopoiesis using the sheep as a model.

RUNX1 positively regulates a cell adhesion and migration program in murine hemogenic endothelium prior to blood emergence

During ontogeny, the transcription factor RUNX1 governs the emergence of definitive hematopoietic cells from specialized endothelial cells called hemogenic endothelium (HE). The ultimate consequence of this endothelial-to-hematopoietic transition is the concomitant activation of the hematopoietic program and downregulation of the endothelial program. However, due to the rare and transient nature of the HE, little is known about the initial role of RUNX1 within this population. We, therefore, developed and implemented a highly sensitive DNA adenine methyltransferase identification-based methodology, including a novel data analysis pipeline, to map early RUNX1 transcriptional targets in HE cells. This novel transcription factor binding site identification protocol should be widely applicable to other low abundance cell types and factors. Integration of the RUNX1 binding profile with gene expression data revealed an unexpected early role for RUNX1 as a positive regulator of cell adhesion- and migration-associated genes within the HE. This suggests that RUNX1 orchestrates HE cell positioning and integration prior to the release of hematopoietic cells. Overall, our genome-wide analysis of the RUNX1 binding and transcriptional profile in the HE provides a novel comprehensive resource of target genes that will facilitate the precise dissection of the role of RUNX1 in early blood development.

The MacBlue binary transgene (csf1r-gal4VP16/UAS-ECFP) provides a novel marker for visualisation of subsets of monocytes, macrophages and dendritic cells and responsiveness to CSF1 administration

The MacBlue transgenic mouse uses the Csf1r promoter and first intron to drive expression of gal4-VP16, which in turn drives a cointegrated gal4-responsive UAS-ECFP cassette. The Csf1r promoter region used contains a deletion of a 150 bp conserved region covering trophoblast and osteoclast-specific transcription start sites. In this study, we examined expression of the transgene in embryos and adult mice. In embryos, ECFP was expressed in the large majority of macrophages derived from the yolk sac, and as the liver became a major site of monocytopoiesis. In adults, ECFP was detected at high levels in both Ly6C+ and Ly6C- monocytes and distinguished them from Ly6C+, F4/80+, CSF1R+ immature myeloid cells in peripheral blood. ECFP was also detected in the large majority of microglia and Langerhans cells. However, expression was lost from the majority of tissue macrophages, including Kupffer cells in the liver and F4/80+ macrophages of the lung, kidney, spleen and intestine. The small numbers of positive cells isolated from the liver resembled blood monocytes. In the gut, ECFP+ cells were identified primarily as classical dendritic cells or blood monocytes in disaggregated cell preparations. Immunohistochemistry showed large numbers of ECFP+ cells in the Peyer's patch and isolated lymphoid follicles. The MacBlue transgene was used to investigate the effect of treatment with CSF1-Fc, a form of the growth factor with longer half-life and efficacy. CSF1-Fc massively expanded both the immature myeloid cell (ECFP-) and Ly6C+ monocyte populations, but had a smaller effect on Ly6C- monocytes. There were proportional increases in ECFP+ cells detected in lung and liver, consistent with monocyte infiltration, but no generation of ECFP+ Kupffer cells. In the gut, there was selective infiltration of large numbers of cells into the lamina propria and Peyer's patches. We discuss the use of the MacBlue transgene as a marker of monocyte/macrophage/dendritic cell differentiation.

Visualisation of chicken macrophages using transgenic reporter genes: insights into the development of the avian macrophage lineage

We have generated the first transgenic chickens in which reporter genes are expressed in a specific immune cell lineage, based upon control elements of the colony stimulating factor 1 receptor (CSF1R) locus. The Fms intronic regulatory element (FIRE) within CSF1R is shown to be highly conserved in amniotes and absolutely required for myeloid-restricted expression of fluorescent reporter genes. As in mammals, CSF1R-reporter genes were specifically expressed at high levels in cells of the macrophage lineage and at a much lower level in granulocytes. The cell lineage specificity of reporter gene expression was confirmed by demonstration of coincident expression with the endogenous CSF1R protein. In transgenic birds, expression of the reporter gene provided a defined marker for macrophage-lineage cells, identifying the earliest stages in the yolk sac, throughout embryonic development and in all adult tissues. The reporter genes permit detailed and dynamic visualisation of embryonic chicken macrophages. Chicken embryonic macrophages are not recruited to incisional wounds, but are able to recognise and phagocytose microbial antigens.

Conservation in first introns is positively associated with the number of exons within genes and the presence of regulatory epigenetic signals

Background

Genomes of higher eukaryotes have surprisingly long first introns and in some cases, the first introns have been shown to have higher conservation relative to other introns. However, the functional relevance of conserved regions in the first introns is poorly understood. Leveraging the recent ENCODE data, here we assess potential regulatory roles of conserved regions in the first intron of human genes.

Results

We first show that relative to other downstream introns, the first introns are enriched for blocks of highly conserved sequences. We also found that the first introns are enriched for several chromatin marks indicative of active regulatory regions and this enrichment of regulatory marks is correlated with enrichment of conserved blocks in the first intron; the enrichments of conservation and regulatory marks in first intron are not entirely explained by a general, albeit variable, bias for certain marks toward the 5’ end of introns. Interestingly, conservation as well as proportions of active regulatory chromatin marks in the first intron of a gene correlates positively with the numbers of exons in the gene but the correlation is significantly weakened in second introns and negligible beyond the second intron. The first intron conservation is also positively correlated with the gene’s expression level in several human tissues. Finally, a gene-wise analysis shows significant enrichments of active chromatin marks in conserved regions of first introns, relative to the conserved regions in other introns of the same gene.

Conclusions

Taken together, our analyses strongly suggest that first introns are enriched for active transcriptional regulatory signals under purifying selection.

Electronic supplementary material

The online version of this article (doi:10.1186/1471-2164-15-526) contains supplementary material, which is available to authorized users.

CSF-1 receptor signaling in myeloid cells

The CSF-1 receptor (CSF-1R) is activated by the homodimeric growth factors colony-stimulating factor-1 (CSF-1) and interleukin-34 (IL-34). It plays important roles in development and in innate immunity by regulating the development of most tissue macrophages and osteoclasts, of Langerhans cells of the skin, of Paneth cells of the small intestine, and of brain microglia. It also regulates the differentiation of neural progenitor cells and controls functions of oocytes and trophoblastic cells in the female reproductive tract. Owing to this broad tissue expression pattern, it plays a central role in neoplastic, inflammatory, and neurological diseases. In this review we summarize the evolution, structure, and regulation of expression of the CSF-1R gene. We discuss the structures of CSF-1, IL-34, and the CSF-1R and the mechanism of ligand binding to and activation of the receptor. We further describe the pathways regulating macrophage survival, proliferation, differentiation, and chemotaxis downstream from the CSF-1R.

Transcription and enhancer profiling in human monocyte subsets

In-depth regulome analysis of human monocyte subsets, including transcription and enhancer profiling. Description of metabolomic differences in human monocyte subsets.

Lentiviral vectors containing mouse Csf1r control elements direct macrophage-restricted expression in multiple species of birds and mammals

The development of macrophages requires signaling through the lineage-restricted receptor Csf1r. Macrophage-restricted expression of transgenic reporters based upon Csf1r requires the highly conserved Fms-intronic regulatory element (FIRE). We have created a lentiviral construct containing mouse FIRE and promoter. The lentivirus is capable of directing macrophage-restricted reporter gene expression in mouse, rat, human, pig, cow, sheep, and even chicken. Rat bone marrow cells transduced with the lentivirus were capable of differentiating into macrophages expressing the reporter gene in vitro. Macrophage-restricted expression may be desirable for immunization or immune response modulation, and for gene therapy for lysosomal storage diseases and some immunodeficiencies. The small size of the Csf1r transcription control elements will allow the insertion of large "cargo" for applications in gene therapy and vaccine delivery.