title: Inducible transgenes under the control of the hCD68 promoter identifies mouse macrophages with a distribution that differs from the F4/80 - and CSF-1R-expressing populations.
abstract: OBJECTIVE
  Macrophages are critical components of diverse microenvironments (ME) in adulthood, as well as during embryogenesis. Their role in development precludes the use of gene-targeting and knockout approaches for studying their function. Hence, we proposed to create a macrophage-specific inducible transgenic mouse where genes can be turned on or off at will.
  
  
  METHODS
  A transgenic mouse in which the reverse tetracycline activator (rtTA-M2) is expressed under the hCD68 promoter for macrophage-specific gene induction was developed and crossed with a second transgenic reporter mouse strain in which the gene for green fluorescent protein (GFP) is under the control of tetracycline responsive element promoter. After doxycycline induction of the double transgenic animals (designated CD68-rtTA-tet-GFP), inducible expression of GFP was characterized by multicolor flow cytometric analysis of blood, marrow, and spleen cells and by demonstration of GFP expression in fresh-frozen sections in diverse tissues.
  
  
  RESULTS
  In bone marrow, inducible GFP expression was not confined to, or inclusive of, all cells expressing the classical macrophage markers, such as F4/80. However, GFP-expressing cells in thioglycollate-elicited peritoneal macrophages were also positive for F4/80 and monocyte-macrophage-specific 2 antigen. Interestingly, flow analysis also indicated little overlap between the F4/80 and CSF-1R-positive populations. Fresh-frozen samples of tissues known to contain macrophages revealed GFP-expressing cells with variable morphologies.
  
  
  CONCLUSIONS
  Our results show that the hCD68 promoter directs gene expression in a macrophage population distinct from that defined by classical monocyte-macrophage markers or promoters. Whether this population is functionally distinct remains to be established.
authors.affiliation: Clinical Research Division, Fred Hutchinson Cancer Research Center, Seattle, Washington, USA. Manoj.Pillai@UCDenver.edu
authors.forename: Manoj M
authors.initials: MM
authors.lastname: Pillai
authors.forename: Brian
authors.initials: B
authors.lastname: Hayes
authors.forename: Beverly
authors.initials: B
authors.lastname: Torok-Storb
mesh_terms: D000818:Animals; D015703:Antigens, CD / Q000235:genetics*; D000943:Antigens, Differentiation / Q000378:metabolism*; D015214:Antigens, Differentiation, Myelomonocytic / Q000235:genetics*; D005260:Female; D005434:Flow Cytometry; D049452:Green Fluorescent Proteins / Q000235:genetics / Q000378:metabolism; D006801:Humans; D017737:Macrophages, Peritoneal / Q000166:cytology / Q000378:metabolism*; D008297:Male; D051379:Mice; D008822:Mice, Transgenic; D008856:Microscopy, Fluorescence; D010920:Placenta / Q000378:metabolism; D011247:Pregnancy; D011401:Promoter Regions, Genetic / Q000235:genetics*; D016186:Receptor, Macrophage Colony-Stimulating Factor / Q000378:metabolism*; D015533:Transcriptional Activation; D019076:Transgenes / Q000235:genetics*; D000097382:CD68 Molecule
chemical_list: D015703:Antigens, CD; D000943:Antigens, Differentiation; D015214:Antigens, Differentiation, Myelomonocytic; D049452:Green Fluorescent Proteins; D016186:Receptor, Macrophage Colony-Stimulating Factor; C067980:CD68 antigen, human; D000097382:CD68 Molecule; C036763:monocyte-macrophage differentiation antigen