Endochondral ossification of the mouse nasal septum

Endochondral ossification at the caudal junctions of the cartilaginous nasal septum, in combination with interstitial expansion of the septum, is thought to displace the facial skeleton away from the neurocranium. However, the rate of endochondral ossification has not been measured or related to rates of septal enlargement. This study examined endochondral ossification at these junctions in mice from postnatal days 0-15, in the context of known cranial growth sites, the synchondroses. BrdU labeling was used to compare cell division at the septoethmoidal and septopresphenoidal junctions with cell division at the synchondroses, and double-fluorochrome labeling was used to measure mineralization rate. The results showed that the septoethmoidal and septopresphenoidal junctions develop the characteristic morphology of growth plates postnatally, and that the pattern of cell division is similar to that of synchondroses. Mineralization at these junctions occurred at rates that were not statistically different from those of the synchondroses. However, the cartilaginous septum increased in length much more rapidly than could be explained by caudal growth, implying that interstitial expansion is the more important contributor to septal growth.