Abstract
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.
Highlights
The skeleton is crucial for retaining the shape of an individual organism and several modes of skeletogenesis have developed in the process of evolution[1]
As a positive intervention, we examined the effect of C-type natriuretic peptide (CNP), a known potent stimulator of endochondral bone growth on this system[5,6], in order to extract the factors which contribute to stimulating the longitudinal growth of the growth plate cartilage
To observe the time-dependent growth of the growth plate of mammalian long bone, we established a dynamic imaging system of a fetal murine ulnar explanted culture using two-photon excitation microscopy
Summary
The skeleton is crucial for retaining the shape of an individual organism and several modes of skeletogenesis have developed in the process of evolution[1]. Mammals have adopted a process called endochondral bone formation, in which a cartilaginous anlage is formed first and replaced by calcified bone tissue. Endochondral bone formation is a precisely controlled dynamic process through which bones are formed and elongate longitudinally[2]. In this process, chondrocytes in the cartilaginous anlage undergo dramatic changes in their morphometric and biological properties. Sequential changes in cell size, shape, and orientation define distinct zones, i.e., resting, proliferative, and hypertrophic zones[3]. We adopted fetal murine ulnar explants to this live-imaging system and investigated the behavior and morphometric changes of chondrocytes in each zone of the growth plate. As a positive intervention, we examined the effect of C-type natriuretic peptide (CNP), a known potent stimulator of endochondral bone growth on this system[5,6], in order to extract the factors which contribute to stimulating the longitudinal growth of the growth plate cartilage
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