Characterization of FSP1.GFP transgenic mice. (a) Plasmid map of the FSP1.GFP transgene injected into B6D2 zygotes for the production of transgenic mice. Ex 1, exon 1; In 1, intron 1. (b) Adult FSP1.GFP transgenic mice express GFP protein in all tissue fibroblasts. In adult FSP1.GFP mice, the eyes are demonstrably green under a Woods light compared with the wild-type because the GFP⁺ fibroblasts in the cornea cast a green tint. (c) RT-PCR screen of normal, whole-organ tissues for mRNA encoding GFP from GFP⁺ (+) or GFP^– (–) littermates: skin, lungs, liver, kidney, heart/pericardium, thymus, and brain. (d) Green GFP⁺ fibroblasts from normal FSP1.GFP kidneys, liver, lung, and heart that costained with anti-FSP1 antibody (red) in their cytoplasm were occasionally observed in interstitial organ spaces; between tubules in kidney. ×630. (e) FACScan of FSP1.GFP bone marrow shows that 5–6% of FSP1⁺ marrow cells are GFP⁺ and that 95% of these FSP1⁺, GFP⁺ fibroblasts costain with anti-FSP1 antibody labeled with phycoerythrin (PE). Approximately 95% of GFP⁺ fibroblasts were also CD34^–. (f) Decalcified bones from FSP1.GFP and GFP^– wild-type mice were costained with propidium iodide, and GFP⁺ cells were identified in two locations by confocal microscopy, either scattered throughout the abluminal marrow as FSP1⁺, MSCs tethered to the sinusoidal network, or as FSP1⁺, GFP⁺ endosteal lining cells (BMLCs) adjacent to decalcified osteoid (B). ×630.