Methods: Bone marrow was removed from the ulna, femur, tibia, humerus and ribs of five rats (100-110 grams), and plated separately into 25cm2 culture flasks. After initial plating the non-adherent cells were removed and cells cultured until they were 90% confluent. Cultures were then lysed and total RNA extracted. Gene expression was assessed by RT-PCR (Taqman) to investigate levels of Hoxa1, Hoxa2, Hoxa4, Hoxa5, Hoxa7, Hoxa10, Hoxa13, ALP, Osteocalcin, and Tgfbi.
Results: Hox genes were expressed by all cultures. Expression of the Hox genes in the rib was distinct from other sites, with highest expression of Hoxa4 and 5 and low levels of Hoxa7. Patterns of expression of marrow from the femur, tibia and humerus were similar, with highest expression of Hoxa7 and lower levels of Hoxa10. Expression of Hoxa13 was restricted to the ulna. Levels of Hoxa1 and Hoxa2 were uniformly low throughout.
Conclusion: The analysis confirms that there are significant differences in the pattern of genes expressed in cultured marrow populations. These findings raise the possibility that bone marrow may be positionally linked to the bone where it is located. Testing the plasticity of bone marrow will show if it can integrate with all parts of the skeleton. This work was supported in part by a scholarship of the Royal Thai Government to S. Prajaneh.