Expression of IGF Family in Developing Mouse Mandibular Condylar Cartilage

Methods: ICR mice, E13 – 18.5 were used. The heads of each mouse were fixed with paraformaldehyde and routinely embedded in paraffin. Five µm sections were cut longitudinally to the mandibular condylar process. Messenger RNA for IGF-I, IGF-II, IGF receptor and IGFBP-2, 3, 4, 5, 6, and -7 was detected by in situ hybridization using 35SUTP-labeled RNA probes.

Results: At E 14 the anlage of mandibular condylar process (termed the condylar anlage) consisted of mesenchymal cell condensation. IFG-I and IGF-II mRNA was expressed in the peripheral region of it. Alternatively IGF receptor mRNA was detected in the interior region of the condylar anlage. At E15 cartilage tissue was first detected within the condylar anlage, and newly formed condylar cartilage remarkably extended in length at E16. During these periods, IFG-I and IGF-II mRNA was expressed in the peripheral region of the cartilage (regarded as the perichondrium), and IGF receptor mRNA was expressed in the upper layer of the cartilage. Furthermore, IGFBP-4 mRNA was expressed in the outer layer of the perichondrium, while IGFBP-5 was expressed in the inner layer of it at E15. At E16, mesenchymal cell condensation of future articular disc was distinctively identified, and IGFBP-4 mRNA was expressed in this condensation and in the outer layer of the pericondrium, while IGFBP-5 mRNA was continuously expressed in the inner layer of it. IGFBP-2 mRNA was restrictedly expressed in the mesenchymal cell condensation of future articular disc.

Conclusion: IGF family are involved not only in the condylar cartilage formation and growth, but also articular disc formation.