ALTERNATIVE SPLICING OF THE MOUSE AMELOGENIN PRIMARY RNA TRANSCRIPT

A heterogeneous mixture of amelogenins can be extracted from developin g tooth enamel matrix. In an attempt to discover the extent to which a lternative splicing of the amelogenin primary RNA transcript can gener ate unique isoforms, we have conducted a thorough search for cDNAs amp lified by reverse transcription-polymerase chain reaction (RT-PCR). Ov er 2400 colonies were screened by colony hybridization. Seven differen t alternatively spliced amelogenin mRNAs were isolated. The predicted translation products of the messages are 194, 180, 156, 141, 74, 59, a nd 44 amino acids in length. RT-PCR amplification products not predict ed by these seven amelogenin cDNAs were characterized. The intron sepa rating exons 5 and 6 was cloned and sequenced. Using rapid amplificati on of cDNA ends (RACE) techniques, the 5' ends of the amelogenin mRNAs were cloned and characterized. The finding that the same exon 1 is co mmon to all of the cloned mRNAs indicates that mouse amelogenin is tra nscribed from a single promoter. The mouse amelogenin transcription an d translation initiation sites, the 5' untranslated leader, and the se gment encoding the signal peptide were determined. The distinctly nona melogenin-like exon 4, first observed in human amelogenin cDNAs, has a lso been found in mice. Antibodies were raised to synthetic exon 4-enc oded polypeptides and used to immunostain Western transfers and histol ogic tooth sections.