The assessment of cell cycle genes in the rat mandibular condyle.

Objectives: We aimed to investigate the expression profile of cell cycle genes in the mandibular condyle on mechanical strain and natural growth, and quantify their expression intensity.

Methods: Three hundred and fifty 35 days old Sprague-Dawley rats were randomly divided into experimental groups fitted with bite-jumping appliances and control groups. Groups were sacrificed at days 1, 3, 7, 9, 14, 30, and 33. Then, condyles were dissected and total RNA was extracted for microarray analysis.

Results: Thirty-nine known cell cycle genes were present in the condyle, where Cyclin D1, PCNA, and Wnt5a were differentially expressed. Reverse transcriptase-PCR confirmed that Wnt5a showed a 2-fold increase on experimental day 1, Cyclin D1 showed a 2-fold increase on experimental day 1 and a 3-fold increase on experimental day 14, while PCNA shows 2.2-fold increase both on experimental days 9 and 30. PCNA, Cyclin D1, and Wnt5a were all expressed by cells in both the proliferative layer and erosive zone.

Conclusion: Mandibular advancement leads to the expression of Cyclin D1 that accelerates entry to the S phase. The increased level of PCNA indicates increased DNA replication of MSC. Then, elevated level of Wnt5a indicates the commitment of MSC to the chondrogenic lineage.