EARLY DETERMINATION AND PERMISSIVE EXPRESSION OF AMELOGENIN TRANSCRIPTION DURING MOUSE MANDIBULAR FIRST MOLAR DEVELOPMENT

The expression of tissue-specific enamel matrix genes is believed to r equire both instructive and permissive interactions of enamel organ ep ithelium with dental papilla mesenchyme and/or extracellular matrix du ring a restricted period of development. Biosynthesis of amelogenin ge ne products has been found to be associated with the terminal differen tiation of inner enamel organ epithelium. The developing mouse first m andibular molar was used for a detailed examination of the temporal in itiation and developmental pattern of amelogenin transcription. These studies define temporally instructive versus permissive influences on amelogenin transcription. During in vivo development, amelogenin trans cripts were detected in late cap (15 days in utero; E15) through bell stage (E16 through E19) mouse molar tooth formation utilizing reverse transcription coupled to polymerase chain reaction amplification. Alte rnatively spliced amelogenin transcripts were detected in late bell st age (E18) molars. Amelogenin transcripts were also detected in isolate d late cap stage (E15) enamel organ epithelium dissected free of denta l papilla mesenchyme and cultured within a substitute basement membran e gel, but not in identical cap stage enamel organ epithelium cultured on plastic or a laminin-coated filter. Amelogenin transcripts were al so found in early cap stage (E14) isolated enamel organ epithelium cul tured within a basement membrane gel, but were not detected in enamel organ epithelium isolated from earlier stages of odontogenesis and cul tured within a basement membrane gel. The results of these experiments indicate that a basement membrane gel is a useful extracellular subst rate which provides permissive interactions required for the expressio n of amelogenin transcripts by enamel organ epithelium and that instru ctive interactions which determine enamel organ epithelium to become c ommitted to amelogenin transcription occur prior to the early cap stag e (E14) of odontogenesis. The results also suggest that continued inte ractions of enamel organ epithelium with dental papilla mesenchyme ser ve to regulate amelogenin transcription and post-transcriptional amelo genin RNA splicing in a complex manner during odontogenesis. (C) 1994 Academic Press, Inc.