SPATIAL AND TEMPORAL DISTRIBUTION OF SONIC-HEDGEHOG MESSENGER-RNA IN THE EMBRYONIC MOUSE MANDIBLE BY REVERSE TRANSCRIPTION POLYMERASE CHAIN-REACTION AND IN-SITU HYBRIDIZATION ANALYSIS

Hedgehog genes have recently been implicated in the control of pattern formation in many developing organ systems. Vertebrate homologues of the Drosophila hedgehog have been identified in mouse and rat embryos. The temporal regulation of sonic hedgehog (mouse homologue) has previ ously been studied by Northern analysis of whole embryos with varying results. Sonic hedgehog transcript expression in the mouse mandibular process was now characterized using polymerase chain reaction (PCR) an d in situ hybridization techniques. PCR analysis revealed transcripts at gestational days 10 and 11, before the formation of the dental lami na, but not at days 12-14, after tooth buds have formed. Transcripts w ere localized to, primarily, the epithelium in the presumptive incisor region of the mandibular midline at gestational day 10. No mRNA was d etected by in situ hybridization techniques in the presumptive molar r egions of odontogenic epithelium. Sonic hedgehog expression may be inv olved in the regulation of pattern formation through establishment of an incisor-molar axis of polarity.