The objective of this proposal is to determine what molecular signals are required to initiate the onset of tooth eruption. Because the dental follicle is required for eruption to occur and because molecules such as epidermal growth factor (EGF) and colony-stimulating factor-1 (CSF-1 accelerate eruption when injected into rats early postnatally, experiments will be conducted to determine if the genes for these and other putative tooth eruption molecules, as well as molecules that regulate transcription of them, are expressed in the dental follicle at the early postnatal times. In situ hybridization will be employed to detect gene expression in vivo in mandibular molars by detecting the mRNAs of EGF, CSF-1, IL- 1alpha, TGF-beta/1 and EGF-receptor. Immunolocalization will then be conducted to determine if the mRNAs for a given molecule also are being translated. After it has been determined which genes are transcribed and translated at the appropriate time and in the appropriate tissue, experiments will be done in which either CSF-1, IL-1alpha, TGF-beta/1 or EGF is injected and its effect on gene expression determined by in situ hybridization and quantitated by reverse transcription polymerase chain reaction techniques. This will test the hypothesis that in vivo a cascade of signals is required to initiate eruption, a hypothesis that is based in part on in vitro results demonstrating specific effects of these molecules on gene expression in either cultured dental follicle cells or stellate reticulum cells. Once a probable sequence of molecular signals to initiate tooth eruption is established, experiments will be conducted to determine if a given molecule is indeed required for eruption; e.i., is it physiologically significant. To answer this, specific antisense deoxyoligonucleotides will be injected to prevent the translation of specific putative tooth eruption molecules and the effect of this on eruption time will be examined. These studies to determine the molecular basis of tooth eruption are of clinical significance because knowing what molecules initiate eruption would eventually lead to methods by which impacted teeth could be induced to erupt, perhaps by injection of the molecules into the dental follicle area. Similarly, orthodontics could benefit from the knowledge of which molecules either accelerate or inhibit eruption by also using such molecules to modify eruption rates to prevent malocclusion of the teeth.
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