Abstract
To investigate the origin and postnatal changes
of mouse mandibular angular cartilage, in situ
hybridization for cartilaginous marker proteins,
histochemistry for alkaline phosphatase (ALP)
and tartrate-resistant acid phosphatase (TRAP),
and bromodeoxyuridine (BrDU) analyses were
performed. Chondrocytes of the mandibular angular
cartilage were derived from ALP-positive progenitor
cells and first detected at embryonic day (E)
15.5. Newly formed chondrocytes rapidly differentiated
into hypertrophic chondrocytes and hypertrophic
cell zone rapidly extended in subsequent a
few days. During this period, bone sialoprotein
mRNA was more widely expressed than osteopontin
mRNA in cartilage. Endochondral bone formation
started at E 17.5 with the resorption of the
bone collar by osteoclasts. These characteristics
were consistent with those of the condylar cartilage,
although developmental process was 0.5-1.5
day delayed relative to the condylar cartilage.
During the postnatal period, contrast to the
condylar cartilage, the angular cartilage constantly
decreased in volume with advancing age.
Reduction of proliferating activity estimated by
BrDU incorporation accounts for this phenomenon.
We demonstrate new structural features of the
mandibular angular cartilage that may contribute to
a coming research for the secondary cartilage.
