OB/P Cx43 expression is required for progenitor-dependent radioprotection and serial transplantation engraftment of WT HSCs. (A) Survival curve of secondary recipients of WT hematopoiesis from WT (dashed line) or OB/P Cx43-deficient primary recipients (solid line), which had been transplanted with 1 × 10⁶ WT BM cells (high dose). BM from primary recipient mice were pooled and transplanted into secondary recipients and analyzed. The remaining secondary recipient mice were killed on day 71 after transplantation and the experiment was terminated (arrow). (B) Representative micrographs (original magnification ×10; bar = 0.25 mm) of longitudinal femoral sections (H&E staining) of WT in WT secondary recipients and WT in OB/P Cx43-deficient secondary recipients. Migrographs were obtained with an Olympus CKX41, objectives ×10, ×40, and ×100. The images were acquired with a motican 2500 color camera (5.0 MPixel, USB2.0), Motich China Group Co Ltd, and processed using Motic Images Plus 2.0 software. (C-E) PB counts of control and WT hematopoiesis in OB/P Cx43-deficient secondary recipients on day 71 after transplantation. Empty bars represent data from WT controls; solid bars represent data from secondary recipients of WT hematopoiesis into OB/P Cx43-deficient hematopoiesis in primary recipients. (F-H) Quantification of BM cell populations from secondary recipients receiving WT chimeric BM from a primary recipient HM that was either WT (empty bar) or OB/P Cx43-deficient HM (solid bar). (F) Total CD45.1⁺ BM cellularity. (G) CD45.1⁺ Lin⁻/c-kit⁺ BM cells. (H) CD45.1⁺ LSK BM cells. Values shown are mean ± SEM n ≥ 5 mice per group (**P < .01).