We investigated the immunohistochemical localisation of types II
and
X collagen as well as the cytochemical
localisation of alkaline phosphatase in the developing condylar cartilage
of
the fetal mouse mandible on
d 14–16 of pregnancy. On d 14 of pregnancy, although no immunostaining
for types II and X collagen was
observed, alkaline phosphatase activity was detected in all cells in the
anlage
of the future condylar process.
On d 15 of pregnancy, immunostaining for both collagen types was simultaneously
detected in the primarily
formed condylar cartilage. Alkaline phosphatase activity was also detected
in chondrocytes at this stage.
By d 16 of pregnancy, the hypertrophic cell zone rapidly increased in size.
These findings strongly support a
periosteal origin for the condylar cartilage of the fetal mouse mandible,
and
show that progenitor cells for
condylar cartilage rapidly or directly differentiate into hypertrophic
chondrocytes.