Live imaging analysis of the growth plate in a murine long bone explanted culture system.

Skeletal growth in mammals, which owes the growth of an individual, occurs at the growth plate and to observe and analyze its dynamic growth is of high interest. Here we performed live imaging analysis of the growth plate of a fetal murine long bone organ culture using two-photon excitation microscopy. We could observe a dynamic growth of the growth plate of explanted fetal murine ulna, as well as the resultant linear elongation of the explants. As for the factors contributing to the elongation of the growth plate, the displacement length of each chondrocyte was larger in the prehypertrophic or hypertrophic zone than in the proliferative zone. The segmented area and its extracellular component were increased in both the proliferative and prehypertrophic-hypertrophic zones, whereas an increase in cellular components was only seen in the prehypertrophic-hypertrophic zone. C-type natriuretic peptide, a known positive stimulator of endochondral bone growth mainly targeting prehypertrophic-hypertrophic zone, augmented all of the factors affecting growth plate elongation, whereas it had little effect on the proliferation of chondrocytes. Collectively, the axial trajectory of each chondrocyte mainly owes cellular or extracellular expansion especially in prehypertrophic-hypertrophic zone and results in growth plate elongation, which might finally result in endochondral bone elongation.