(A) Representative low magnification fluorescence image of 3-month-old Adipoq/Td/Col1-GFP mouse distal femur reveals many bone marrow Td⁺ cells. Scale bar: 200 μm. (B–F) At a high magnification, Td does not label chondrocytes in articular cartilage (AC) (B) and growth plate (GP) (C), osteoblasts, nor osteocytes (D, E, F). White and yellow arrows point to Td⁺GFP^– cells and Td⁺GFP⁺ cells at the bone surface, respectively. BM, bone marrow; CB, cortical bone. Scale bars: 200 μm (B, C) and 50 μm (D–F). (G) Quantification of Td⁺ cells in trabecular osteoblasts (OB) and osteocytes (Ocy) within trabecular (Trab.) and cortical (Cort.) bone (n = 3 mice/group). More than 1000 cells were counted per mouse. (H) Td labels pericytes (arrowheads) in bone marrow. Emcn, endomucin for vessel staining. (I) In Adipoq/Td mice, Td does not label CD45⁺ hematopoietic cells. (J) In vivo EdU injection reveals that bone marrow Td⁺ cells do not proliferate. (K) All Perilipin⁺ adipocytes (arrowheads) are Td⁺ as well. Scale bar: 20 μm (H–K). (L) CFU-F assay of bone marrow cells from Adipoq/Td mice shows that all CFU-F colonies are made of Td^– cells (left image). Some Td⁺ cells did attach to the dish and form a small cluster within a Td^– CFU-F colony (right image). Scale bar: 100 μm. (M) In vitro adipogenic differentiation of Td^– mesenchymal progenitors reveals that Td signal is turned on first followed by lipid accumulation. The same area was imaged daily by inverted fluorescence microcopy. Scale bar: 100 μm. (N) In vitro osteogenic differentiation of Td^– mesenchymal progenitors reveals that Td signal remains off when a bony nodule forms. The same area was imaged daily by inverted fluorescence microcopy. Arrowheads point to a boney nodule. Scale bar: 100 μm.