Chondrocytes-osteoblast transition in endochondral ossification
The concern of chondrocyte-osteoblast transition in skeleton development has continued for more than one century. Even though many morphological and in vitro data clearly indicated osteoblast differentiation as an alternative fate choice of chondrocytes besides of undergoing apoptosis, absence of the solid in vivo observation led to this chondrocyte-osteoblast transition concept stagnant. Fortunately, the development of gene-manipulated strategy in biology assisted to resolve the century-problem by in vivo lineage tracing and the concept of chondrocyte-osteoblast transition was finally accepted until 2014, when three elegant studies published. These works done by three individual groups reached out similar conclusion about chondrocyte-osteoblast transdifferentiation in the process of endochondral bone formation. The acceptance of this concept shed light on skeletal biology and the endochondral ossification (EO) chapter of text book will be re-written with this finding. However, the different origins and the proposed functional discrepancy of skeletal osteoblasts also bring us to re-explain and think of previous data again. More in-depth studies will implement more curiosity on the underlying molecular mechanism of chondrocyte-osteoblast differentiation and the physiological function of chondrocyte-derived osteogenic cells in both skeleton homeostasis and bone marrow environment.