PgmNr Z6254: Committed stem cells derived from the somites supply the osteoblasts during adult bone homeostasis and regeneration.

Authors:
K. Ando 1 ; E. Shibata 1 ; A. Kudo 1 ; G. Abe 2 ; K. Kawakami 2 ; S. Hans 3 ; M. Brand 3 ; A. kawakami 1


Institutes
1) Tokyo Institute of Technology, Yokohama, JP; 2) National Institute of Genetics, Mishima, JP; 3) DFG-Center for Regenerative Therapies Dresden, Germany.


Abstract:

Calcified bone is a characteristic feature of vertebrates that is indispensable for maintaining their terrestrial lives. Since the bone matrix needs to be actively renewed and repaired throughout the animal life, a constant supply of osteoblasts is essential. It is thought that the progenitor cells of osteoblast, the osteoprogenitor cells (OPCs), which are derived from the mesenchymal stem cells (MSCs) in the bone marrow in the case of mammals, produce the osteoblasts in post-developmental stages; however, the identity, function and developmental origin of OPCs in adult vertebrates are unclear.

Here, from the analysis of transgenic (Tg) zebrafish of matrix metalloproteinase 9 (mmp9), we identified a stem cell that produces the osteoblasts during adult zebrafish fin regeneration. In the mmp9 BAC Tg, the EGFP localization was associated with bony tissues, and in particular a strong fluorescence was seen in the joints of adult fin. The Cre-loxP-mediated cell lineage tracing showed that mmp9-positive cells migrate from the nearby joints after fin amputation and produce the osteoblasts and new mmp9-positive joint cells as well, indicating that mmp9-positive cells are the committed stem cells, osteoblast stem cells (OSCs). The genetic ablation of mmp9-positive cells by nitroredutase and prodrug exhibited a significant decrease of the number of regenerating osteoblasts and the regenerating bone, indicating that the OSCs indeed play a role in bone regeneration, although they are not an only source of osteoblasts during fin regeneration.

To investigate the developmental origin of OSCs, we conducted the somite transplantation analysis. Donor somites from the Tg(mmp9:eGFP; beta-actin:DsRed2), which ubiquitously expresses DsRed2, not only produced the osteoblasts in the caudal fin, but also gave rise to the mmp9-expressing OSCs, indicating that the OSCs were originated from the somites. However, the early OSCs labelled by the Cre-loxP recombination at 4 weeks post fertilization neither produced osteoblasts nor new OSCs in the fin, suggesting that mmp9-negative precursors produce the BSCs and osteoblasts during infant stage. On the other hand, at later stages after 3 months, the OSCs at the fin joints gave rise to the fin ray osteoblasts by the homeostatic cell turnover. These observations suggest that the OSCs are a reserved population of stem cells that are dedicated to the homeostasis and regeneration of calcified bones.



ZFIN Genetics Index
1. mmp9