Cbfa1/Runx2 gene expression in articular chondrocytes of the mice temporomandibular and knee joints in vivo

Healthy articular cartilage is thought to be maintained by the modulation of Cbfa1 expression, although little is currently known about Cbfa1 expression in such tissues. Therefore, we examined in vivo Cbfa1 transcript levels in the temporomandibular (TM) and knee joints of 3- and 10-week-old male ICR mice (weighing 50-70 g). A digoxigenin-11-UTP-labeled single-stranded RNA probe (0.6 kbp PstI-HindIII fragment of the 3′ of untranslated region in exon 8 of mouse Cbfa1 cDNA) was prepared and in situ hybridization was performed on paraffin-embedded TM and knee joint sections. The antisense probe detected Cbfa1 transcripts in prehypertrophic chondrocytes, but not in the articular surface layer chondrocytes of 3- and 10-week-old mice TMJs. Despite the intense Cbfa1 expression in prehypertrophic chondrocytes, articular surface layer chondrocytes of the knee joints expressed low and undetectable level of Cbfa1 in the 3- and 10-week-old mice, respectively. These results indicate that Cbfa1 are highly expressed in the prehypertrophic chondrocytes presumably for articular tissue remodeling during the entire lifespan of the mouse, whereas Cbfa1 expression is suppressed in the articular surface chondrocytes in the adult mouse TM and knee joints to obtain the permanent cartilage phenotype.