Opn plays a key role in the TMM and lodgment of HSCs in the endosteal marrow region and hematopoietic reconstitution. (A) Compared with transplants of HSCs into a wt microenvironment (▦), there was no evidence of TMM toward the endosteal region in an Opn^–/– microenvironment (▪). Conversely, there was evidence of significant TMM toward the central region (P < .005), which resulted in significantly fewer cells lodging in the endosteal region 15 hours after transplantation compared with wt controls (P < .01). Data are the mean ± SEM of between 5 and 6 individual mice. (B) Comparison of hematopoietic regeneration and survival out to 3 weeks following myeloablation in wt and Opn^–/– mice that received transplants with limiting numbers of wt LSK BM cells (solid bar and ▪ versus open bar and ▴, respectively). Data are the mean of between 12 and 19 recipients from 3 individual experiments.