Induction of amelogenin and ameloblastin by insulin and insulin-like growth factors (IGF-I and IGF-II) during embryonic mouse tooth development in vitro

Insulin and insulin-like growth factors (IGF-I and IGF-II) are considered p leiotropic, acting as both mitogen and differentiation factors. Several inv estigators have demonstrated the expression of insulin, IGFs, their cognate receptors and IGF binding proteins during tooth morphogenesis, Previous wo rk done in our laboratory indicated that exogenous insulin and IGFs induce the accumulation of enamel extracellular matrix on mouse mandibular molars cultured in a serumless, chemically defined medium. In order to determine t he level of control of these factors in the induction of enamel biominerali zation, we designed experiments to quantitate mRNAs for enamel specific-gen e products. Mandibular first molars (M1) obtained from E15 Swiss Webster mi ce were placed in organ culture in the presence of insulin (1000 ng/ml), IG F-I (100 ng/ml) or IGF-II (100 ng/ml) for 6, 12 and 18-days. At termination date, the RNA was extracted and the concentration of mRNAs for amelogenin, tuftelin and ameloblastin were determined using a quantitative competitive reverse transcription-polymerase chain reaction (RT-PCR) technique (PCR mi mic), Our results showed that after 6-days in culture; treatment with insul in, IGF-I and IGF-II increased the synthesis of amelogenin and ameloblastin . In contrast, the expression of tuftelin mRNA was not affected by either f actor. In conclusion, our studies showed that the increase in enamel matrix formation by overexpression of IGFs is the result of transcriptional regul ation of enamel specific proteins like amelogenin and ameloblastin but not tuftelin, These studies also suggest that the regulatory mechanisms control ling tuftelin gene expression are different than the mechanisms regulating ameloblastin and amelogenin transcription.