Osteoblast depletion leads to early loss of B lymphopoiesis in bone marrow. Col2.3Δ-TK transgenic mice were treated with vehicle (□) or GCV (▪) for 8 days (n = 5). (A) Osteocalcin staining of bone tissue section at day 0 and day 8 after GCV treatment (left-hand panel), as well as day-8 BM (femurs and tibiae) and spleen cellularities of vehicle- or GCV-treated mice (right-hand panel). (B) Flow cytometric analyses of B-lymphocyte precursors recovered from the BM of vehicle- or GCV-treated mice, with the percent of each subpopulation within the mononuclear bone marrow fractions noted (left-hand panel); absolute numbers of different B-lymphocyte precursor populations within BM after treatment (means ± SD, n = 5) (left-hand panel). (C) Absolute numbers of Gr-1^loc-Kit⁺⁺ myeloid progenitors, Gr-1⁺⁺Mac-1⁺⁺ granulocytes, and Gr-1⁺Mac-1⁺⁺ monocytes within the BM of vehicle- or GCV-treated mice (means ± SD, n = 5). (D) Detection of Lin⁻Sca⁺Kit⁺ BM cells in vehicle- and GCV-treated mice by flow cytometry, with percent LSK cells noted (left-hand panel), and absolute numbers (right-hand panel) of LSK cells detected in total BM, as determined by multiplying percent LSK cells × total cellularity/femurs + tibias (means ± SD).